IPsec Fault Tolerance

IPsec Fault Tolerance

 

IPsec Fault Tolerance

 

IPsec Fault Tolerance

In today’s interconnected world, network security is of utmost importance. Organizations rely heavily on secure communication channels to safeguard sensitive information from unauthorized access. One such technology that plays a vital role in ensuring secure data transmission is IPsec (Internet Protocol Security). However, even the most robust security measures are not immune to failures. That’s where IPsec fault tolerance comes into play. In this blog post, we will explore the concept of IPsec fault tolerance and the measures organizations can take to ensure uninterrupted network security.

IPsec fault tolerance refers to the ability of a network or system to continue functioning effectively in the event of a failure or disruption in IPsec services. It involves implementing redundancy and failover mechanisms to maintain continuous secure communication, even during adverse conditions.

Highlights: IPsec Fault Tolerance

  • Highlighting IPsec

IPsec is a secure network protocol used to encrypt and authenticate data over the internet. It is a critical part of any organization’s secure network infrastructure, and it is essential to ensure fault tolerance. Optimum end-to-end IPsec networks require IPsec fault tolerance in several areas for ingress and egress traffic flows. Key considerations must include asymmetric routing, where a packet traverses from a source to a destination in one path and takes a different path when it returns to the source.

  • Reverse Route Injection

Potential options include Reverse Route Injection (RRI), which can inject static routes automatically inserted into the routing process for those networks and hosts protected by a remote tunnel endpoint. The diagram below displays components susceptible to failure to achieve an IPsec fault tolerance. Design each element with redundancy in mind. Failure components include the Backbone network, Access links, and IPsec gateway.

 

For additional pre-information, you may find the following helpful

  1. SD WAN SASE
  2. VPNOverview
  3. Dead Peer Detection
  4. What Is Generic Routing Encapsulation
  5. Routing Convergence

 

Back to basics with IPsec Fault tolerance

Concept of IPsec

Internet Protocol Security (IPsec) is a set of protocols to secure communications over an IP network. It provides authentication, integrity, and confidentiality of data transmitted over an IP network. IPsec establishes a secure tunnel between two endpoints, allowing data to be transmitted securely over the Internet. In addition, IPsec provides security by authenticating and encrypting each packet of data that is sent over the tunnel.

IPsec is typically used in Virtual Private Network (VPN) connections to ensure secure data sent over the Internet. It can also be used for tunneling to connect two remote networks securely. IPsec is an integral part of ensuring the security of data sent over the Internet and is often used in conjunction with other security measures such as firewalls and encryption.

IPsec VPN
Diagram: IPsec VPN. Source Wikimedia.

 

IPsec session

There are Several components exist used to create and maintain an IPsec session. By integrating these components, we get the required security services that protect the traffic for unauthorized observers. IPsec establishes tunnels between endpoints; these can also be described as peers. The tunnel can be protected by various means, such as integrity and confidentiality.

IPsec provides security services using two protocols, the Authentication Header and Encapsulating Security Payload. Both protocols use cryptographic algorithms for authenticated integrity services; Encapsulation Security Payload provides encryption services in combination with authenticated integrity.

 

  • A key point: Lab on IPsec between two ASAs. Site to Site IKEv1

In this lab, we will look at site-to-site IKEv1. Site-to-site IPsec VPNs are used to “bridge” two distant LANs together over the Internet.  So we want IP reachability for R1 and R2, which are in the INSIDE interfaces of their respective ASAs. Generally, on the LAN, we use private addresses, so the two LANs cannot communicate without tunneling.

This lesson will teach you how to configure IKEv1 IPsec between two Cisco ASA firewalls to bridge two LANs. In the diagram below, you will see we have two ASAs. ASA1 and ASA2 are connected using their G0/1 interfaces. This is to simulate the outside connection. In the real world, this would be the WAN.

This is also set to the “OUTSIDE” security zone, so imagine this is their Internet connection. Each ASA has a G0/0 interface connected to the “INSIDE” security zone. R1 is on the network 192.168.1.0 /24 while R2 is in 192.168.2.0 /24. The goal of this lesson is to ensure that R1 and R2 can communicate with each other through the IPsec tunnel.

 

Site to Site VPN

 

IPsec and DMVPN

DMVPN builds tunnels between locations as needed, unlike IPsec VPN tunnels that are hard coded. As with SD-WAN, it uses standard routers without additional features. However, unlike hub-and-spoke networks, DMVPN tunnels are mesh networks. Organizations can choose from three basic DMVPN topologies when implementing a DMVPN network.

The first topology is the Hub and Spoke topology. The second topology is the Fully Meshed topology. Finally, the third topology is the Hub and Spoke with Partial Mesh topology.  To create these DMVPN topologies, we have phases, such as DMVPN Phase 3, that are the most flexible enabling a pull mesh of on-demand tunnels that can use IPsec for security.

 

Concept of Reverse Routing Injection (RRI)

For network and host endpoints protected by a remote tunnel endpoint, reverse route injection (RRI) allows static routes to be automatically injected into the routing process. These protected hosts and networks are called remote proxy identities.

The next hop to the remote proxy network and mask is the remote tunnel endpoint, and each route is created based on these parameters. Traffic is encrypted using the remote Virtual Private Network (VPN) router as the next hop.

Static routes are created on the VPN router and propagated to upstream devices, allowing them to determine the appropriate VPN router to send returning traffic to maintain IPsec state flows. When multiple VPN routers are used to provide load balancing or failover, or remote VPN devices cannot be accessed via a default route, choosing the right VPN router is crucial. Global routing tables or virtual route forwarding tables (VRFs) are used to create routes.

 

IPsec fault tolerance
Diagram: IPsec fault tolerance with multiple areas to consider.

 

The Networks Involved

Backbone network

IPsec uses an underlying backbone network for endpoint connectivity. It does not deploy its underlying packet-forwarding mechanism and relies on backbone IP packet-routing functions. Usually, the backbone is controlled by a 3rd-party provider, ensuring IPsec gateways trust redundancy and high availability methods applied by separate administrative domains.

 

Access link 

Adding a second link to terminate IPsec sessions and enabling both connections for IPsec termination improves redundant architectures. However, access link redundancy requires designers to deploy either Multiple IKE identities or Single IKE identities. Multiple IKE identity design involves two different peer IP addresses, one peer for each physical access link. The IKE identity of the initiator is derived from the source IP of the initial IKE message, and this will remain the same. Single IKE identity involves one peer neighbor, potentially terminating on a logical loopback address.

 

  • Physical interface redundancy

Design physical interface redundancy by terminating IPsec on logical interfaces instead of multiple physical interfaces. Useful when the router has multiple exit points and you do not want the other side to use multiple peers’ addresses. Single IPsec session terminating on loopback instead of multiple IPsec sessions terminating on physical interfaces. You still require the crypto map configured on two physical interfaces. Issue the command to terminate IPsec on the loopback: “crypto map VPN local-address lo0.”

 

  • A key point: Link failure

In the event of a single physical link failure, Phase 1 and 2 do not converge. Convergence is based on an underlying network routing protocol. No IKE convergence occurs if one of the physical interfaces goes down.

 

Asymmetric Routing

Routing protocol convergence

Asymmetric routing may occur in multipath environments. For example, in the diagram below, traffic leaves spoke A, creating an IPsec tunnel to interface Se1/1:0 on Hub A. Asymmetric routing occurs when return traffic flows via Se0:0. The effect is a new IPsec SA between Se0:0 and Spoke A, introducing additional memory usage on peers. Overcome this by proper routing mechanism and IPsec state replication ( discussed later ).

Asymmetric routing
Diagram: Asymmetric routing.

 

Design to ensure routing protocol convergence does not take longer than IKE dead peer detection. Routing protocols should not introduce repeated disruptions to IPsec processes. If you have control of the underlying routing protocol, deploy fast convergence techniques so that routing protocols converge faster than IKE detects a dead peer.

 

IPsec Fault Tolerance and IPsec Gateway

A redundant gateway involves a second IPsec gateway in standby mode. It does not have any IPsec state or replicate IPsec information between peers. Because either gateway may serve as an active gateway for spoke return traffic, you may experience asymmetric traffic flows. Also, due to the failure of the hub peer gateway, all traffic between sites drops until IKE and IPSec SAs are rebuilt on the standby peer.

 

Routing mechanism at gateway nodes

A common approach to overcome asymmetric routing is to deploy a routing mechanism at gateway nodes. IPsec’s high availability can be incorporated with HSRP, which pairs two devices with a single VIP address. VIP address terminates IPsec tunnel. HSRP and IPsec work perfectly fine as long as the traffic is symmetric.

Asymmetric traffic occurs when the return traffic does not flow via the active HSRP device. To prevent this, enable HSRP on the other side of IPsec peers, resulting in Front-end / Back-end HSRP design model. Or deploy Reverse Route Injection ( RRI ), and static routes are injected only by active IPsec peer. You no longer need Dead Peer Detection ( DPD ) as you use VIP for IPsec termination. In the event of a node failure, the IPsec peer does not change. A different method to resolve the asymmetric problem is implementing Reverse Route Injection. 

Reverse Route Injection
Diagram: Routing mechanisms and Reverse Route Injection.

 

Reverse Route Injection (RRI)

RRI is a method that synchronizes return routes for the spoke to the active gateway. The idea behind RRI is to make routing decisions dependent on the IPsec state. For end-to-end reachability, a route to a “secure” subnet must exist with a valid network hop. RRI inserts a route to the “secure” subnet in the RIB and associates it with an IPsec peer. Then, it injects based on the Proxy ACL; matches the destination address in the proxy ACL.

  •  RRI injects a static route for the upstream network.

 HSRPs’ or RRI IPsec is limited because it does not carry any state between the two IPsec peers. A better high-availability solution is to carry state ( Security Association Database ) between the two gateways, offering stateful failover.

 

Implementing IPsec Fault Tolerance:

1. Redundant VPN Gateways: Deploying multiple VPN gateways in a high-availability configuration is fundamental to achieving IPsec fault tolerance. These gateways work in tandem, with one as the primary gateway and the others as backups. In case of a failure, the backup gateways seamlessly take over the traffic, guaranteeing uninterrupted, secure communication.

2. Load Balancing: Load balancing mechanisms distribute traffic across multiple VPN gateways, ensuring optimal utilization of resources and preventing overloading of any single gateway. This improves performance and provides an additional layer of fault tolerance.

3. Automatic Failover: Implementing automatic failover mechanisms ensures that any failure or disruption in the primary VPN gateway triggers a swift and seamless switch to the backup gateway. This eliminates manual intervention, minimizing downtime and maintaining continuous network security.

4. Redundant Internet Connections: Organizations can establish redundant Internet connections to enhance fault tolerance further. This ensures that even if one connection fails, the IPsec infrastructure can continue operating using an alternate connection, guaranteeing uninterrupted, secure communication.

Conclusion:

IPsec fault tolerance is a crucial aspect of maintaining uninterrupted network security. Organizations can ensure that their IPsec infrastructure remains operational despite failures or disruptions by implementing redundancy, failover, and load-balancing mechanisms. Such measures enhance reliability and enable seamless scalability as the organization’s network grows. With IPsec fault tolerance, organizations can rest assured that their sensitive information is protected and secure, irrespective of unforeseen circumstances.

 

IPsec Fault Tolerance

ASA failover

ASA Failover

ASA Failover

Cisco ASA (Adaptive Security Appliance) firewalls are widely used by organizations to protect their networks from unauthorized access and threats. One of the key features of Cisco ASA is failover, which ensures uninterrupted network connectivity and security even in the event of hardware failures or other issues. In this blog post, we will explore the concept of Cisco ASA failover and its importance in maintaining network resilience.

Cisco ASA failover is a mechanism that allows two Cisco ASA firewalls to work together in an active-passive setup. In this setup, one firewall assumes the role of the primary unit, while the other serves as the secondary unit. The primary unit handles all network traffic and actively performs firewall functions, while the secondary unit remains in standby mode, ready to take over in case of primary unit failure.

Table of Contents

Highlights: ASA Failover

Cisco ASA is a stateful inspection firewall that combines firewall, antivirus, intrusion prevention, and virtual private network (VPN) capabilities. It provides proactive threat defense that stops attacks before they spread through the network. The Cisco ASA failover enables firewall failover and offers the following:

Link High Availability: A generic solution achieved by dynamic routing running between interfaces. Dynamic routing enables rerouting around failures. ASA offers up to three equal-cost routes per interface to the same destination network. However, it does not support ECMP ( Equal Cost Multipath ) on multiple interfaces.

Reliable static routing with IP SLA instance: Redundancy achieved through enhanced object tracking and floating static routes.

Redundancy interface: Bind multiple physical interfaces together into one logical interface. Not the same as EtherChannel. One interface is active and forwarding at any time, unlike EtherChannel, which can forward over all interfaces in a bundle. ASA redundancy interface is an active / standby technology; one interface is active, and the other is on standby.

Node Availability: Firewall Failover, which is the focus of this post.

 

Related: Before you proceed, you may find the following helpful:

  1. Context Firewall
  2. Stateful Inspection Firewall
  3. Data Center Failover
  4. Virtual Data Center Design
  5. GTM Load Balancer
  6. Virtual Device Context



ASA Failover

Key ASA Failover Discussion Points:


  • Introduction to ASA failover and what is involved.

  • Highlighting the details of the different types of failover modes.

  • Critical points on the failover link.

  • Technical details on the challenges with asymmetric routing. 

  • A final note on ASA health monitoring. 

Back to Basics: Cisco ASA Failover

Stateful inspection Firewalls

Compared to simple packet-filtering firewalls, stateful inspection firewalls offer enhanced benefits. By verifying that every packet passing through their interfaces is a good, established connection, they track every packet passing through them. In addition to the packet header contents, they examine the application layer information within the payload. The firewall can then be configured to permit or deny traffic based on specific payload patterns.

A stateful firewall, such as the Cisco ASA, goes beyond traditional packet-filtering firewalls by inspecting and maintaining context-aware information about network connections. It examines the entire network conversation, not just individual packets, to make informed decisions about allowing or blocking traffic. This approach provides enhanced security and helps prevent malicious attacks.

 

Lab Guide Cisco ASA firewall and NAT

In the following lab guide, we have a typical firewall setup. There are inside, outside, and DMZ networks. These are security zones, and they govern how traffic flows by default. For example, the interface connected to R2 is the outside, and R1 is the inside. So, by default, traffic cannot flow from Outside to Inside. In this lab, we demonstrate NAT, where traffic from Inside to Outside is NATD. View the output below in the screenshots.

Firewall traffic flow
Diagram: Firewall traffic flow and NAT

Generic failover information

Failover is an essential component of any high-availability system, as it ensures that the system will remain operational and provide services even when the primary system fails. When a system fails, the failover system will take over, allowing operations to continue with minimal interruption.

Several types of failover systems are available, such as active/passive, active/active, and cluster-based. Each type has its advantages and disadvantages, and the type of system used should be determined based on the system’s specific requirements.

Lab guide on ASA failover: 

In this lab, we will address Active / Standby ASA configuration. We know that the  ASA supports active/standby failover which means one ASA becomes the active device, it handles everything while the backup ASA is the standby device. There needs to be a failure event for something to happen. 

In our example, ASA1 is ( was ) the primary, and ASA2 is the standby. I disconnected the switch links connected to Gi0//0 on ASA1, triggering the failover event. Notice that in the screenshot, we have the protocol SCPS exchanged between the two ASA nodes. The hello packets are exchanged between active and standby to detect failures using messages sent using IP protocol 105. IP protocol 105 refers to SCPS (Space Communications Protocol Standards).”

The failover mechanism is stateful, meaning the active ASA sends all stateful connection information to the standby ASA. This includes TCP/UDP states, NAT translation tables, ARP tables, and VPN information.

ASA Failover

Highlighting Cisco ASA Failover

The Cisco ASA failover is the high availability mechanism that mainly provides redundancy rather than capacity scaling. While Active/Active failover can help distribute traffic load across a failover pair or devices, its scalability has significant practical implications. With this design, we can leverage failover to group identical ASA appliances or modules into a fully redundant firewall entity with centralized configuration management and stateful session replication ( if needed ).

When one unit in the failover pair can no longer pass transit traffic, its identical peer seamlessly assumes firewall functionality with minimal impact on traffic flows. This type of firewalling design is helpful for an active active data center design.

Cisco ASA failover
Diagram: Cisco ASA failover. Source Grandmetric

Unit Roles and Functions in Firewall Failover

If configuring a firewall failover pair, designate one unit as primary and the other as secondary. The roles are statically configured and do not change during failover. The failover subsystem could use this designation to resolve some operational conflicts. Still, either the primary or secondary units may pass transit traffic while in an active role while their peers remain on standby. Depending on the operational state of the failover pair, dynamic active and standby roles pass between the statically defined primary and secondary units.

Adaptive Security Appliance: ASA Failover

For ASA high availability, a failover group consists of a pair of identical ASA connected via a dedicated failover link and an optional state link. Two failover modes, Active / Standby or Active / Active, work in Routed and Transparent modes. Depending on the IOS version, you can use a mixture of routed and transparent modes per context.

There are two types of Cisco ASA failover: Active/Standby failover and Active/Active failover.

  • Active / Standby

In an Active/Standby failover configuration, the primary unit handles all traffic while the secondary unit remains idle, continuously monitoring the primary unit’s status. If the primary unit fails, the secondary unit becomes the new active unit. This failover process occurs seamlessly, ensuring uninterrupted network connectivity and minimal downtime.

Active / Standby: One-forwarding path and active ASA. The standby forwards traffic when the active device fails over. Traffic is not evenly distributed over both units. Active / standby uses single or multiple context modes. Failover allows two firewall units to operate in hot standby mode.

For two units to operate as a firewall failover pair, their hardware and software configurations must be identical (flash disk and minor software version differences are allowed for zero downtime upgrade of a failover pair). One firewall unit is designated as primary and another as secondary, and by default, the primary unit receives the active role, and the secondary receives the standby role.

  • Active / Active for context groups

Active/Active failover, as the name suggests, allows both Cisco ASA firewalls to handle network traffic simultaneously actively. Each firewall can have its own set of interfaces and IP addresses, providing load balancing and increased throughput. In a failure, the remaining active firewall takes over the failed unit’s responsibilities, ensuring uninterrupted network services.

Active / Active for context groups: Not supported in single context mode. Only available in multiple context mode. When configuring failover, it is mandatory to set both firewalls in single or multiple context modes simultaneously, with multiple context modes supporting a unique failover function known as Active/Active failover.

With Active/Active failover, the primary unit is active for the first group of security contexts and standby for the second group, whereas the secondary unit is active for the second group of security contexts and standby for the first group; only two failover groups are supported because there are only two ASAs within a failover pair, and the admin context is always a member of group one.

Both ASAs forward simultaneously by splitting the context into logical failover groups. Still, technically active / standby. Not like Gateway Load Balancing Protocol ( GLBP ). Two units do not forward for the same context at the same time.

ASA failover
Diagram: ASA failover.

Permits a maximum of two failover groups. For example, one group was active on primary ASA; and another was active on secondary ASA. Active / Active failover occurs in a group and not on a system basis.

Upon failover event, either by primary unit or context group failure, the secondary takes over the primary IP and Media Access Control Address ( MAC ) address and begins forwarding traffic immediately. The failover event is seamless; no change in IP or MAC results in zero refreshes to Address Resolution Protocol ( ARP ) tables at Layer 3 hosts. If the failover changed MAC addresses, all other Layer 3 devices on the network would have to flush their ARP tables.

 

ASA high availability: Type of firewall failover

For ASA high availability, there are two types of failovers are available

  1. Stateful failover and
  2. Stateless failover.

Cisco ASA Failover: Stateless failover

The default mode is Stateless; no state/connection information is maintained, and upon failover, existing connections are dropped and must be re-established. It uses a dedicated failover link to poll each other. Upon failover, which can be manual or detected, the unit changes roles, and standby assumes the IP and MAC of the primary unit.

Cisco ASA Failover: Stateful failover

Failover operates statelessly by default. The active unit only synchronizes its configuration with the standby device in this configuration. After a failover event, all stateful flow information remains local to the active ASA, so all connections must be re-established. In most high-availability configurations, stateful failover is required to preserve ASA processing resources. You must configure a stateful failover link to communicate state information to the standby ASA, as discussed in the “Stateful Link” section. When stateful replication is enabled, an active ASA synchronizes the following additional information to the standby peer.

Stateful table for TCP and UDP connections. Certain short-lived connections are not synchronized by default by ASA to preserve processing resources. For example, unless you configure the failover replication http command, HTTP connections over TCP port 80 remain stateless.

In the same way, ICMP connections synchronize only in Active/Active failover scenarios with configured Asymmetric Routing (ASR) groups. The maximum connection setup rate supported by the particular ASA platform may be reduced by up to 30 percent when stateful replication is enabled for all connections.

ASA stateful failover: Pass state/connection

Stateful failover: pass state/connection information to each other. Connection information could be Network Address Translation ( NAT ) tables, TCP / UDP connection states, IPSEC SA, and ARP tables. The active unit constantly replicates the state table. Whenever a new connection comes into the table, it’s copied to the standby unit. It is processor-intensive, so you need to understand design requirements.

Does your environment need-stateful redundancy? Does it matter if users must redial or establish a new AnyConnect session? Stateful failover requires a dedicated “stateful failover link.” The stateless failover link can be used, but separating these functions is recommended.

Dynamic routing protocols are maintained with stateful failover. The routes learned by the active unit are carried across to the Routing Information Base ( RIB ) table on the standby unit. However, hypertext Transfer Protocol ( HTTP ) connections are short-lived, and HTTP clients usually retry failed connection attempts. As a result, by default, the HTTP state is not replicated. The command failover replication HTTP enables HTTP connections in replication.

ASA failover
Diagram: Checking ASA failover status

 

Firewall Failover Link

The failover link is for Link-Local communication between ASAs and determines the status of each ASA. Layer 2 polling via HELLO Keepalives transmitted and configurations synchronized. Have the connecting switch ports in port fast mode, ensuring if a flap of the link occurs, no other Layer 2 convergence will affect the failover convergence.

For redundancy purposes, use port channels and do not use the same link used for stateless connectivity. It is recommended to connect the failover and data links through different physical paths. Failover links should not use the same switch as the data interfaces, as the state information may generate excessive traffic. In addition, you don’t want the replication of the state information to interfere with normal Keepalives.

 

Failover link connectivity

The failover link can be connected directly or by an Ethernet switch. If the failover link connects via an ethernet switch, use a separate VLAN with no other devices in that Layer 2 broadcast domain. ASA supports Auto-MDI/MDIX, enabling crossover or straight-through cable. MDI-MDIX automatically detects the cable type and swaps transmit/receive pairs to match the cable seen.

 

ASA’s high availability and asymmetric routing

Asymmetric routing means that a packet does not follow the same logical path both ways (outbound client-to-server traffic uses one path, and inbound server-to-client uses another path). Because firewalls track connection states and inspect traffic, asymmetric routing is not firewall-friendly by default, traffic is dropped, and TCP traffic is significantly affected.

The problem with asymmetric traffic flows is that if ASA receives a packet without connection/state information, it will drop it. The issue may arise in the case of an Active / Active design connected to two different service providers. It does not apply to Active / Standby as the standby is not forwarding traffic and, as a result, will not receive returning traffic sent from the active unit. It is possible to allow asymmetrically routed packets by assigning similar interfaces to the same ASR group.

Asymmetric Traffic
Diagram: Asymmetric traffic.

ASA Failover and Traffic Flow Considerations

  • An outbound session exists to ISP-A through the Primary-A context.

  • In this instance, return traffic flows from ISP-B to Primary-B context.

  • Traffic dropped as Primary-B does not have state information for the original flow.

  • However, due to interfaces configured in the same ASR Group, session information for the original outbound flow has been replicated to the Primary-B context. 

  • Layer 2 header rewritten and traffic redirected to Primary-B. Resulting in asymmetrically routed packets being restored to the correct interface.

 

Stateful failover and HTTP replication are required.

Although in all real deployments, you should avoid asymmetric routing (with or without a firewall in the path), there are certain cases when this is required or when you need more control. If a firewall is in the path, there are several options to still allow traffic through:

  • If outbound traffic transits the firewall, but inbound traffic does not, use TCP state bypass for the respective connection or use static NAT with nailed option (effectively disables TCP state tracking and sequence checking for the connection).
  • If both outbound and inbound traffic transit the firewall but on different interfaces, use the exact solutions as above.
  • If outbound traffic transits one context of the ASA and inbound traffic transits another context of the ASA, use ASR groups; this applies only for multi-context mode and requires active-active stateful failover configured.

ASA’s high availability and health monitoring

Unit Monitoring

The failover link determines the health of the overall unit. HELLO, packets are sent over the failover link. The lack of three consecutive HELLOs causes ASA to send an additional HELLO packet out of ALL data interfaces, including the failover link. Rules out the failure of the actual failover link.

The resulting action of ASA depends on the additional HELLO packets. No action occurs if a response is received over the failover or data links. Failover actions occur if no response is received on any of the links. With interface monitoring, the number of monitored interfaces depends on the IOS version. It would help if you always tried to monitor essential interfaces.

A final note on ASA’s high availability: In an IPv6 world, ASA uses IPv6 neighbor discovery instead of ARP for its health monitoring tests. If it has to broadcast to all nodes, it uses IPv6 FE02::1. FE02::1 is an all-IPv6 speakers-multicast group.

Benefits of Cisco ASA Failover:

Implementing Cisco ASA failover provides several benefits, including:

1. High Availability: Failover ensures continuous network connectivity and security, even in the event of hardware failures or other issues. This enhances the network’s overall availability and minimizes the impact of potential disruptions.

2. Redundancy: By having a secondary unit ready to take over, failover provides redundancy and eliminates single points of failure. This ensures that network services remain uninterrupted and minimizes the risk of downtime.

3. Enhanced Performance: Active/Active failover allows both firewalls to handle network traffic simultaneously, leading to increased throughput and improved performance. This is particularly beneficial for organizations with high network traffic demands.

4. Simplified Maintenance: With failover, organizations can perform maintenance tasks on one firewall without impacting network services. The secondary unit takes over during maintenance, ensuring continuous network operation.

 

Highlights: ASA Failover

In today’s fast-paced digital landscape, network downtime can be catastrophic for businesses. As companies rely heavily on their network infrastructure, having a robust failover mechanism is crucial to ensure uninterrupted connectivity. In this blog post, we delved into the world of ASA failover and explored its importance in achieving network resilience and high availability.

Section 1: Understanding ASA Failover

ASA failover refers to the capability of Cisco Adaptive Security Appliances (ASAs) to automatically switch to a backup unit in the event of a primary unit failure. It creates a seamless transition, maintaining network connectivity without any noticeable interruption. ASA failover operates in Active/Standby and Active/Active modes.

Section 2: Active/Standby Failover Configuration

In an Active/Standby failover setup, one ASA unit operates as the active unit, handling all traffic. In contrast, the standby unit remains hot, ready to take over instantly. This configuration ensures network continuity even if the active unit fails. The standby unit constantly monitors the health of the active unit, ensuring a swift failover when needed.

Section 3: Active/Active Failover Configuration

Active/Active failover allows both ASA units to process traffic simultaneously, distributing the load and maximizing resource utilization. This configuration is ideal for environments with high traffic volume and resource-intensive applications. In a failure, the remaining active unit seamlessly takes over the entire workload, offering uninterrupted connectivity.

Section 4: Configuring ASA Failover

Configuring ASA failover involves several steps, including interface and IP address configuration, failover link setup, and synchronization settings. Cisco provides a comprehensive set of commands to configure ASA failover efficiently. Following best practices and thoroughly testing the failover configuration is essential to ensure its effectiveness during real-world scenarios.

Section 5: Monitoring and Troubleshooting Failover

Proactive monitoring and regular testing are essential to maintain the reliability and effectiveness of ASA failover. Cisco ASA provides various monitoring tools and commands to monitor failover status, track synchronization, and troubleshoot any issues that may arise. Establishing a monitoring routine and promptly address any detected problems to prevent potential network disruptions is crucial.

Conclusion:

ASA failover is a critical component of network resilience and high availability. By implementing an appropriate failover configuration, organizations can minimize downtime, ensure uninterrupted connectivity, and provide a seamless experience to their users. Whether it is Active/Standby or Active/Active failover, the key lies in proper configuration, regular monitoring, and thorough testing. Invest in ASA failover today and safeguard your network against potential disruptions.

Diagram: Default Firewall Inspection.

Stateful Inspection Firewall

 

 

Stateful Inspection Firewall

Network security is crucial in safeguarding businesses and individuals from cyber threats in today’s interconnected world. One of the critical components of network security is a firewall, which acts as a barrier between the internal and external networks, filtering and monitoring incoming and outgoing network traffic. Among various types of firewalls, one that stands out is the Stateful Inspection Firewall.

Stateful Inspection Firewall, also known as dynamic packet filtering, is a security technology that combines the benefits of traditional packet filtering and advanced inspection techniques. It goes beyond simply examining individual packets and considers the context and state of the network connection. Doing so provides enhanced security and greater control over network traffic.

Stateful Inspection Firewalls offer several key advantages over other firewall technologies.

Firstly, they provide increased network visibility by monitoring the entire communication session. This visibility allows administrators to identify and investigate suspicious activities more effectively. Secondly, Stateful Inspection Firewalls are more efficient in handling network traffic. By maintaining a connection state table, they can quickly process packets without the need for complex rule-matching algorithms.

Highlights: Stateful Firewall

This post will focus on the stateful firewall and stateful inspection firewall. We will briefly touch on basic packet filtering, firewall traffic flow, reflexive access list, and where they fit in the world of the stateful firewall. What is a stateful firewall? In short, firewalls are network functions specifically tailored to inspect network traffic. Upon inspection, the firewall will decide to carry out specific actions, such as forwarding or blocking it according to some criteria. In such a way, we can see firewalls as security network entities with several different firewall types.

 

  • Different Firewall Types

The different firewall types will be used in other network locations in your infrastructure, such as distributed firewalls at a hypervisor layer. You may have a stateful firewall close to workloads while a packet-filtering firewall is at the network’s edge. As identity is now the new perimeter, many opt for a stateful inspection firewall nearer to the workloads. With virtualization, you can have a stateful firewall per workload, commonly known as virtual firewalls.

  • Stateful Firewall

A stateful firewall is a form of firewall technology that monitors incoming and outgoing network traffic and keeps track of the state of each connection passing through it. It acts as a filter, allowing or denying traffic based on configuration. Stateful firewalls are commonly used to protect private networks from potential malicious activity.

The primary function of a Stateful Inspection Firewall is to inspect the headers and contents of packets passing through it. It maintains a state table that keeps track of the connection state of each packet, allowing it to identify and evaluate the legitimacy of incoming and outgoing traffic. This stateful approach enables the firewall to differentiate between legitimate packets from established connections and potentially malicious packets.

Unlike traditional packet filtering firewalls, which only examine individual packets based on predefined rules, Stateful Inspection Firewalls analyze the entire communication session. This means that they can inspect packets in the context of the entire session, allowing them to detect and prevent various types of attacks, including TCP/IP-based attacks, port scanning, and unauthorized access attempts.

  • Combining Security Features

They can be combined with other security measures, such as antivirus software and intrusion detection systems. Stateful firewalls can be configured to be both restrictive and permissive and can be used to allow or deny certain types of traffic, such as web traffic, email traffic, or FTP traffic. They can also control access to web servers, databases, or mail servers. Additionally, stateful firewalls can detect and block malicious traffic, such as files, viruses, or port scans.

 

Before you proceed, you may find the following helpful post for pre-information:

  1. Network Security Components
  2. Virtual Data Center Design
  3. Context Firewall
  4. Cisco Secure Firewall

 



Stateful Inspection Firewall

Key Stateful Inspection Firewall Discussion Points:


  • Also, known as dynamic packet filtering.

  • Discussion of how a firewall monitors the state of active connections.

  • Discussion based on filtering based on state and context.

  • Primarily used at the Transport and Network layers of the OSI model.

  • Better security than a stateless firewall that does not hold state.

 

  • A key point – Video 1: Stateful firewall inspection.

In the following video, we will address stateful firewall inspection. Generally, we interact directly with the application layer and have networking and security devices working at the lower layers. So when host A wants to talk to host b, it will go through several communication layers with devices working at each layer. A device that works at one of these layers is a stateful firewall that can perform the stateful inspection.

Another significant advantage of Stateful Inspection Firewalls is their ability to perform deep packet inspection. This means that they can analyze the content of packets beyond their headers. By examining the payload of packets, Stateful Inspection Firewalls can detect and block potentially harmful content, such as malware, viruses, and suspicious file attachments. This advanced inspection capability adds an extra layer of security to the network.

 

Stateful Inspection Firewall
Prev 1 of 1 Next
Prev 1 of 1 Next

 

Back to basics with the firewall concept

The term “Firewall.”

The term “firewall” comes from a building and automotive construction concept of a wall built to prevent the spread of fire from one area into another. This concept was then taken into the world of network security. The firewall’s assignment is to set all restrictions and boundaries described in the security policy on all network traffic that passes the firewall interfaces. Then we have the concept of firewall filtering that compares each packet received to a set of rules that the firewall administration configures.

These exception rules are derived from the organization’s security policy. The firewall filtering rules state that the contents found in the packet are either allowed or denied. Therefore, based on firewall traffic flow, it continues to its destination if the packet matches an allowed rule. If the packet matches a deny rule, the packet is dropped.

 

Firewalling acts as a barrier

The firewall is the barrier between a trusted and untrusted network, often used between your LAN and WAN. It’s typically placed in the forwarding path so that all packets have to be checked by the firewall, where we can drop or permit them.

 

  • A key point: Lab guide on Cisco ASA firewall

In the following lab guide, you can see we have an ASA working in routed mode. In routed mode, the ASA is considered a router hop in the network. Each interface that you want to route between is on a different subnet. You can share Layer 3 interfaces between contexts.

Traditionally, a firewall is a routed hop and acts as a default gateway for hosts that connect to one of its screened subnets. On the other hand, a transparent firewall is a Layer 2 firewall that acts like a “bump in the wire” or a “stealth firewall” and is not seen as a router hop to connected devices. However, like any other firewall, access control between interfaces is controlled, and the usual firewall checks are in place.

The Adaptive Security Algorithm considers the state of a packet when deciding to permit or deny the traffic. One enforced parameter for the flow is that traffic enters and exits the same interface. The ASA drops any traffic for an existing flow that enters a different interface. Traffic zones let you group multiple interfaces so that traffic entering or exiting any interface in the zone fulfills the Adaptive Security Algorithm security checks.

The command:  show asp table routing displays the accelerated security path tables for debugging purposes and the zone associated with each route. See the following output for the show asp table routing command:

Cisco ASA configuration
Diagram: Cisco ASA Configuration

Firewall filtering rules

Firewall filtering rules help secure a network from unauthorized access and malicious activity. These rules protect by controlling traffic flow in and out of the network. Firewall filtering rules can allow or deny traffic based on source and destination IP addresses, ports, and protocols.

Firewall filtering rules should be tailored to the specific needs of a given network. Generally, it is recommended to implement a “deny all” rule and then add rules to allow only the specific traffic that is necessary. This helps to block any malicious activity while legitimate traffic is allowed. When creating firewall filtering rules, it is essential to consider the following:

  • Make sure to use the most up-to-date protocols and ports.
  • Be aware of any potential risks associated with the traffic being allowed.
  • Use logging to monitor traffic and ensure that expected behavior is occurring.
  • Ensure that the rules are implemented consistently across all firewalls.
  • Ensure that the rules are regularly reviewed and updated as needed.

 

  • A key point: Lab Guide on default firewall inspection

The Cisco ASA Firewall uses so-called “security levels” that indicate how trusted an interface is compared to another. The higher the security level, the more trusted the interface is. Each interface on the ASA is a security zone, so by using these security levels, we have different trust levels for our security zones. Therefore we have da default firewall inspection. We will discuss this more later.

Below we have 3 routers and subnets with 1 ASA firewall.

  • Interface G0/0 as the INSIDE.
  • Interface G0/1 as the OUTSIDE.
  • Interface G0/2 as our DMZ.

The name command is used to specify a name for the interface. As you can see, the ASA recognizes INSIDE, OUTSIDE, and DMZ names. And sets the security level for that interface to a default level. Therefore, restriction of traffic flow.

Remember that the ASA can reach any device in each security zone. This doesn’t work since we are trying to go from a security level of 0 (outside) to 100 (inside) or 50 (DMZ). We will have to use an access list if you want to allow this traffic.

Firewall inspection
Diagram: Default Firewall Inspection.

 

What Is a Stateful Firewall?

The stateful firewall examines Layer 4 headers and above, analyzing firewall traffic flow and enabling support for Application-aware inspections. Stateful inspection keeps track of every connection passing through their interfaces by analyzing packet headers and additional payload information.

Stateful Firewall
Diagram: Stateful firewall. Source Cisco.

 

Stateful Firewall Operation

You can see how filtering occurs at layers 3 and 4 and that the packets are examined as a part of the TCP session.

The topmost part of the diagram shows the three-way handshake, which takes place before the commencement of the session and is explained as follows.

  1. Syn refers to the initial synchronization packet sent from one host to another; in this case, the client to the server.
  2. The server sends an acknowledgment of the syn, and this known as syn-ack
  3. The client again sends an acknowledgment of this syn-ack, thereby completing the process and initiation of the TCP session.
  4. Both parties can end the connection anytime by sending a FIN to the other side. This is similar to a telephone call where the caller or the receiver could hang up.

 

  • A key point: Video on TCP and UDP scanning

In this whiteboard session, we will address port scanning. Now. Port scanning can be performed against TCP and UDP ports. Identifying open ports on a target system is the stage that a bad actor has to carry out when understanding and defining the attack surface of a target.

 

Port Scanning: UDP and TCP
Prev 1 of 1 Next
Prev 1 of 1 Next

 

State and Context.

The two important terms to understand are state and context information. Filtering is based on the state and context information the firewall derives from a session’s packets. The firewall will store state information in its state table, which is updated regularly. For example, in TCP, this state is reflected in specific flags such as SYN, ACK, and FIN. Then we have the context. This includes source and destination port, IP address, and sequence numbers of any metadata. The firewall also stores this information and updates regularly based on traffic flowing through the firewall.

 

Firewall state table

A firewall state table is a data structure that stores information about the connection state of a network firewall. For example, it determines which packets are allowed to pass through the firewall and which are blocked. The table contains entries for each connection, including source and destination IP addresses, port numbers, and other related information.

The firewall state table is typically organized into columns, with each row representing an individual connection. Each row contains the source and destination IP address, the port numbers, and other related information.

For example, the source IP address and port number indicate the origin of the connection, while the destination IP address and port number indicate the destination of the connection. Additionally, the connection’s state is stored in the table, such as whether the connection is established, closed, or in transit.

The state table also includes other fields that help the firewall understand how to handle the connection, such as the connection duration, the type of connection being established, and the protocol used.

 

Stateful inspection firewall
Diagram: Stateful inspection firewall. Source: Science Direct.

 

So whenever a packet arrives at a firewall to seek permission to pass through it, the firewall checks from its state table if there is an active connection between the two points of source and destination of that packet. The endpoints are identified by something known as sockets. A socket is similar to an electrical socket at your home which you use to plug your appliances into the wall.

Similarly, a network socket consists of a unique IP address and a port number and is used to plug in one network device to the other. The packet flags are matched against the state of the connection to which it belongs, which is allowed or denied based on that. For example, if a connection already exists and the packet is a Syn packet, it must be denied since Syn is only required at the beginning.

 

Stateful Firewall and Interface Configuration

It would be best to consider the interfaces in firewall terms when considering a stateful inspection firewall. For example, some interfaces are connected to protected networks, where data or services must be secured. Others connect to public or unprotected networks, where untrusted users and resources are located.

The top portion of the diagram below shows a stateful firewall with only two interfaces connecting to the inside (more secure) and outside (less secure) networks. The bottom portion of the figure shows the stateful inspection firewall with three interfaces connected to the inside (most secure), DMZ (less secure), and outside (least secure) networks. The firewall has no concept of these interface designations or security levels; these concepts are put into play by the inspection processes and policies configured.

So you need to explain to the firewall which interface is at what security level. And this will effect the firewall traffic flow. Some traffic will be denied by default between specific interfaces with default security levels.

stateful inspection firewall

Interface configuration specific to ASA

Since version 7.0 of the ASA code, configuring interfaces in the firewall appliance is very similar to configuring interfaces in IOS-based platforms. If the firewall connection to the switch is an 802.1q trunk (the ASA supports 802.1q only, not ISL), you can create sub-interfaces corresponding to the VLANs carried over the trunk. Do not forget to assign a VLAN number to the sub-interface. The native (untagged) VLAN of the trunk connection maps to the physical interface and cannot be assigned to a sub-interface.

 

Stateful Inspection and full state of active network connections

So we know that the stateful firewall monitors the full state of active network connections and constantly analyses the complete context of traffic and data packets. Then we have the payload to consider. The payload is part of transmitted data that is the intended message, along with the headers and metadata sent only to enable payload delivery.

Payloads offer transaction information, which can protect against some of the most advanced network attacks. For example, deep packet inspection configures the stateful firewall to deny specific Hypertext Transfer Protocol ( HTTP ) content types or specific File Transfer Protocol ( FTP ) commands, which may be used to penetrate networks.

Stateful inspection and Deep Packet Inspection (DPI)

The following diagram shows the OSI layers involved in the stateful inspection. As you can see, Stateful inspection operates primarily at the transport and network layers of the Open Systems Interconnection (OSI) model for how applications communicate over a network. However, it can also examine application layer traffic, if only to a limited degree. Deep Packet Inspection (DPI) is higher up in the OSI layers.

DPI is considered to be more advanced than stateful packet filtering. It is a form of packet filtering that locates, identifies, classifies, and reroutes or blocks packets with specific data or code payloads that conventional packet filtering, which examines only packet headers, cannot detect. Many firewall vendors will have the stateful inspection and DPI on the same appliance. However, a required design may require a separate appliance for compliance or performance reasons.

Stateful Inspection Firewall
Diagram: Stateful inspection firewall.

 

Stateful Inspection Firewall

What is a stateful firewall?

A stateful firewall keeps track of and monitors the state of active network connections while analyzing incoming traffic and looking for potential traffic and data risks. The state is a process or application’s most recent or immediate status. In a firewall, the state of connections is stored, providing a list of connections against which to compare the connection a user is attempting to make.

Stateful packet inspection is a technology stateful firewalls use to determine which packets to allow through the firewall. It works by examining the contents of a data packet and then comparing them against data about packets that have previously passed through the firewall.

 

Stateful Firewall Feature

Stateful Firewall 

Better logging than standard packet filters

Protocols with dynamic ports


TCP SYN cookies


TCP session validation


No TCP fingerprinting

Not present

 

Stateful firewall and packet filters

The stateful firewall contrasts packet filters that match individual packets based on their source/destination network addresses and transport-layer port numbers. Packet filters have no state or check the validity of transport layer sessions such as sequence numbers, Transmission Control Protocol ( TCP ) control flags, TCP acknowledgment, or fragmented packets. The critical advantage of packet filters is that they are fast and processed in hardware.

Reflexive access lists are closer to a stateful tool than packet filters. Whenever TCP or User Datagram Protocol ( UDP ) session permits, matching return traffic is automatically added. The disadvantage of reflexive access lists is they cannot detect / drop-malicious fragments or overlapping TCP segments. Transport layer session inspection goes beyond reflexive access lists and addresses fragment reassembly and transport-layer validation.

Application-level gateways ( ALG ) add additional awareness. They can deal with FTP or Session Initiation Protocol ( SIP ) applications that exchange IP addresses and port numbers in the application payload. These protocols operate by opening additional data sessions and multiple ports.

Packet filtering
Diagram: Packet filtering. Source Research Gate.

 

Simple packet filters for a perfect world

In a perfect world where most traffic exits the data center, servers are managed with regular patching, servers listen on standard TCP or UDP ports, and designers could get away with simple packet filters. But in the real world, each server is a distinct client, has multiple traffic flows to and from the data center and back-end systems, and unpredictable source TCP or UDP port number makes using packet filters impractical.

Instead, implement additional control with deep packet inspection for unpredictable scenarios and poorly managed servers. Stateful firewalls keep state connections and allow traffic to return dynamically. Return traffic is permitted if the already state for that flow is in the connection table. The traffic needs to be part of a return flow. If not, it’s dropped.

 

  • A stateless firewall – predefined rule sets

A stateless firewall uses a predefined set of rules. If the arriving data packet conforms to the rules, it is considered “safe.” The data packet is allowed to pass through. With this approach to firewalling, traffic is classified instead of inspected. The process is less rigorous compared to what a stateful firewall does.

Remember that a stateless firewall does not differentiate between certain kinds of traffic, such as Secure Shell (SSH) versus File Transfer Protocol (FTP). A stateless firewall may classify these as “safe” and allow them to pass through, which can result in potential vulnerabilities.

A stateful firewall holds context across all its current sessions rather than treating each packet as an isolated entity, as with a stateless firewall. With stateless inspection, lookup functions impact the processor and memory resources much less, resulting in faster performance even if traffic is heavy.

 

The Stateful Firewall and Security Levels

Regardless of the type of firewall mode, or single or multiple contexts, Adaptive Security Appliance ( ASA ) permits traffic based on a concept of security levels configured per interface. And is an important point to note for ASA failover and how you design your failover firewall strategy. The configurable range is from level 0 to 100. Every interface on ASA must have a security level.

The security level allows configured interface trust-ability and can range from 0, which is the lowest, to 100, which is the highest—offering ways to control traffic flow based on security level numbering. The default security level is “0”, configuring the name on the interface “inside” without explicitly entering a security level; then, the ASA automatically sets the security level to 100 ( highest ).

By default, based on the configured nameif, ASA assigns the following implicit security levels to interfaces:

  • 100 to a nameif of inside.
  • 0 to a nameif of outside.
  • 0 to all other nameifs.

 

Without any configured access lists, ASA implicitly allows or restricts traffic flows based on the security levels:

Securty Levels and Traffic Flows

  • Traffic from high-security level to low-security level is allowed by default (for example, from 100 to 0, or in our case, from 60 to 10)

  • Traffic from low-security level to the high-security level is denied by default; to allow traffic in this direction, an ACL must be configured and applied (at the interface level or global level)

  • Traffic between interfaces with an identical security level is denied by default (for example, from 20 to 20, or in our case, from 0 to 0); to allow traffic in this direction, the command same-security-traffic permit inter-interface must be configured

 

Firewall traffic flow between security levels

By default, traffic can flow from highest to lowest without explicit configuration. Also, interfaces on the same security level cannot directly communicate, and packets cannot enter and exit the same interface. Override the defaults, permit traffic by allowing high to low; explicitly configure ACLs on the interface or newer version use-global ACL. Global ACL affects all interfaces in all directions.

Firewall traffic flow

Firewall traffic flows

Inter-Interface communication ( Routed Mode only ); enter the command “same-security-traffic permit inter-interface” or permit traffic explicitly with an ACL. This will give design granularity and allows the configuration of more-communicating interfaces. Intra-Interface communication; configured for traffic hair-pining ( leaves on the outside interface and goes back out the outside interface ).

Useful for Hub and Spoke VPN deployments; traffic enters an interface and routes back out the same interface – Spoke to Spoke communication. To enable Intra-Interface communication, enter the command “same-security-traffic permit intra-interface.”

 

Default inspection and Modular Policy Framework ( MPF )

ASA implements what is known as Modular Policy Framework ( MPF ). MPF controls WHAT traffic is inspected, such as Layer 3 or Layer 4 inspection of TCP, UDP, ICMP, an application-aware inspection of HTTP, or DNS. It also controls HOW traffic is inspected based on connection limits and QoS parameters.

ASA inspects TCP / UDP from the inside (higher-security level ) to the outside ( lower-security level ). This cannot be disabled. No traffic inspection from outside to inside unless it is from an original flow.

An entry is created in the state table, so when flows return, it checks the state table before it goes to implicit deny ACL. The state is created during traffic leaves, so it checks the specific connection and application data when the return flows come back. It does more than Layer 3 or 4 inspections and depends on the application.

It does not, by default, inspect ICMP traffic. Enable ICMP inspection with a global inspection policy or explicitly allow with an interface or Global ACLs. ASA global policy affects all interfaces in all directions. The state table is checked before any ACL. A good troubleshooting tool, Packet Tracer, goes through all inspections and displays the order the ASA is processing.

 

modular policy framework
Diagram: Modular Policy Framework

 




Key Stateful Inspection Firewall Summary Points:

Main Checklist Points To Consider

  • Firewalls carry out specific actions based on policy. The default policy can exist. Different firewall types exist for different parts of the network.

  • The stateful firewall monitors the full state of the connections. The state is held in a state table.

  • Standard packet filters don't state or check the valid nature of the transport layer sessions. They do not do a stateful inspection.

  • Firewalls will have default rules based on interface configurations. Default firewall traffic flow is based on an interface security level.

  • The Cisco ASA operates with a Modular Policy Framework (MPF) technology. ASA is a popular stateful firewall.

 

  • A key point – Video 2: Discussing the Secure Web Gateway (SWG)

In your layers of defense, you will have a stateful firewall working alongside a Secure Web Gateway. One of the primary functions of a secure web gateway is to prevent malware and malicious code from entering the network through web traffic. It leverages advanced threat detection techniques, such as signature-based scanning, heuristic analysis, and machine learning algorithms, to identify and block known and unknown threats. By inspecting web traffic in real time, SWG can detect and mitigate threats before they can reach the end-user.

 

Technology Brief : Cloud Security - Introducing Secure Web Gateways
Prev 1 of 1 Next
Prev 1 of 1 Next

 

Furthermore, secure web gateways provide secure access to web applications. They enable organizations to securely enable remote access to web-based applications by providing features such as secure sockets layer (SSL) decryption and inspection. This ensures encrypted web traffic is correctly inspected for potential threats or policy violations.

Firewalls and secure web gateways (SWGs) play a similar and overlapping role in securing your network. Both analyze incoming information and seek to identify threats before they enter your system. Despite sharing a similar function, they have some key differences. Look at the “classical” distinction between secure web gateways and firewalls.

The basic distinctions:

  • Firewalls inspect data packets
  • Secure web gateways inspect applications
  • Secure web gateways set and enforce rules for users

 

  • A key point: Lab Guide on traffic flows and NAT

I have the Cisco ASA configured with Dynamic NAT in the following guide. This is the same setup as before. In the middle, we have our ASA, its G0/0 interface belongs to the inside, and the G0/1 interface belongs to the outside.  I have not configured anything on the DMZ interfaces.

For this ASA version, you need to configure object groups. I have configured a network object that defines the pool with public IP addresses we want to use for translation. The IP address that has been translated too is marked in the red box below.

The show nat command shows us that some traffic has been translated from the inside to the outside.

The show xlate command shows that the IP address 192.168.1.1 has been translated to 192.168.2.196. It also tells us what kind of NAT we are doing here (dynamic NAT in our example) and how long this entry has been idle.

Firewall traffic flow
Diagram: Firewall traffic flow and NAT

 

Closing Points on Stateful Inspection Firewall.

A stateful inspection firewall is a crucial component of network security that helps protect computer networks from unauthorized access and malicious activities. It acts as a barrier between internal and external networks, examining incoming and outgoing network traffic to determine whether it should be allowed or blocked based on predetermined security rules. This document provides an overview of stateful inspection firewalls, their features, and how they enhance network security.

 

Definition and Working Principle:

A stateful inspection firewall is a type of firewall that operates at the network layer of the OSI model. Unlike traditional packet-filtering firewalls that only examine individual packets, stateful inspection firewalls keep track of the state of network connections, allowing them to make more informed decisions about allowing or denying network traffic.

Stateful inspection firewalls maintain a state table that records information about each network connection passing through the firewall. This information includes source and destination IP addresses, port numbers, and connection states. When a packet arrives at the firewall, it is compared against the information in the state table to determine whether it belongs to an established connection or is part of a new connection attempt.

 

Key Features:
1. Packet Filtering: Stateful inspection firewalls analyze packets based on their source and destination IP addresses, port numbers, and other header information. This allows them to filter out potentially malicious traffic based on predefined rules.
2. Connection Tracking: By monitoring the state of network connections, stateful inspection firewalls can differentiate between legitimate traffic and suspicious activity. They keep track of the connection’s state, such as established, new, or closed, and use this information to make informed decisions.
3. Deep Packet Inspection: Stateful inspection firewalls inspect the contents of packets beyond their headers, allowing them to detect and prevent advanced threats such as malware, viruses, and intrusion attempts. This level of inspection provides enhanced security compared to traditional packet-filtering firewalls.
4. Application Layer Filtering: Stateful inspection firewalls can analyze network traffic at the application layer to identify and block specific types of traffic. This feature helps prevent unauthorized access to vulnerable applications and services.

 

Benefits:
1. Improved Security: Stateful inspection firewalls protect against unauthorized access, network attacks, and data breaches. By analyzing the state of network connections, they can detect and block suspicious activity, reducing the risk of security incidents.
2. Increased Performance: Compared to traditional packet-filtering firewalls, stateful inspection firewalls offer better performance by reducing the processing overhead associated with each packet. By maintaining a state table, they can quickly match packets to established connections, improving network efficiency.
3. Flexibility and Scalability: Stateful inspection firewalls can be configured to meet the specific security requirements of different networks. They can be easily scaled to accommodate growing network traffic and adapt to changing security needs.

 

Apply a multi-layer approach to security. 

When it comes to network security, organizations must adopt a multi-layered approach. While Stateful Inspection Firewalls provide essential protection, they should be used in conjunction with other security technologies, such as intrusion detection systems (IDS), intrusion prevention systems (IPS), and virtual private networks (VPNs). This combination of security measures ensures comprehensive protection against various cyber threats.

In conclusion, Stateful Inspection Firewalls are integral to network security infrastructure. With their ability to inspect packets in the context of the entire communication session, these firewalls offer enhanced security and greater control over network traffic. By leveraging advanced inspection techniques, deep packet inspection, and a stateful approach, Stateful Inspection Firewalls provide a robust defense against evolving cyber threats. Organizations prioritizing network security should consider implementing Stateful Inspection Firewalls as part of their security strategy.

 

firewall traffic flow