Daily Archives: March 10, 2015

What is Routing?

Routing is like a network’s GPS. It involves directing data packets from their source to their destination across multiple networks. Think of it as the process of determining the best possible path for data to travel. Routers, the key devices responsible for routing, use various algorithms and protocols to make intelligent decisions about where to send data packets next.

The Role of Switching

While routing deals with data flow between networks, switching comes into play within a single network. Switches serve as the traffic managers within a local area network (LAN). They connect devices, such as computers, printers, and servers, allowing them to communicate with one another. Switches receive incoming data packets and use MAC addresses to determine which device the data should be forwarded to. This efficient and direct communication within a network makes switching so critical.

The Role of Optimal Layer 3 Forwarding:

Optimal Layer 3 forwarding ensures that data packets are transmitted through the most efficient path, improving network performance. It minimizes packet loss, latency, and jitter, enhancing user experience. By selecting the best path, optimal Layer 3 forwarding also enables load balancing, distributing the traffic evenly across multiple links, thus preventing congestion.

Benefits of Implementing Optimal Layer 3 Forwarding

a) Enhanced Network Performance: Optimal layer three forwarding reduces packet loss, congestion, and delays, improving network performance and user experience.

Several factors can impact network performance, and identifying them is crucial for optimizing your network. From bandwidth limitations and network congestion to hardware limitations and improper configurations, each element plays a role in determining the overall performance. This section will explore these factors in detail, providing insights into how they can affect your network and steps to mitigate their impact.

One key challenge in network performance is identifying and resolving bottlenecks. These bottlenecks can occur due to congested network links, outdated hardware, or inefficient routing protocols. Organizations can optimize their bandwidth utilization by conducting thorough network assessments and employing intelligent traffic management techniques, ensuring smooth data flow and reduced latency.

GRE and Next Hops

Generic Routing Encapsulation (GRE) is a tunneling protocol that enables the encapsulation of various network protocols within IP packets. It provides a flexible and scalable solution for deploying virtual private networks (VPNs) and connecting disparate networks over an existing IP infrastructure. By encapsulating multiple protocol types, GRE allows for seamless network communication, regardless of their underlying technologies. Notice the next hop below is the tunnel interface.

Implementing Quality of Service (QoS) Policies

Implementing quality of service (QoS) policies is essential to prioritizing critical applications and ensuring optimal user experience. QoS allows network administrators to allocate network resources based on application requirements, guaranteeing a minimum level of service for high-priority applications. By classifying and prioritizing traffic flows, organizations can prevent congestion, reduce latency, and deliver consistent performance.

Leveraging Load Balancing Techniques

b) Load Balancing: Distributing traffic across multiple paths optimizes resource utilization and prevents bottlenecks.

Load balancing is crucial in distributing network traffic across multiple servers or links, optimizing resource utilization, and preventing overload. By implementing intelligent load-balancing algorithms, organizations can achieve better network performance, fault tolerance, and enhanced scalability. Load balancing techniques, such as round-robin, least connections, or weighted distribution, ensure efficient utilization of network resources.

Example: EIGRP configuration

EIGRP is an advanced distance-vector routing protocol developed by Cisco Systems. It is known for its fast convergence, efficient bandwidth use, and support for IPv4 and IPv6 networks. Unlike traditional distance-vector protocols, EIGRP utilizes a more sophisticated Diffusing Update Algorithm (DUAL) to determine the best path to a destination. This enables networks to adapt quickly to changes and ensures optimal routing efficiency.

EIGRP load balancing enables routers to distribute traffic among multiple paths, maximizing the utilization of available resources. It is achieved through the equal-cost multipath (ECMP) mechanism, which allows for the simultaneous use of multiple routes with equal metrics. By leveraging ECMP, EIGRP load balancing enhances network reliability, minimizes congestion, and improves overall performance

Enhanced Network Scalability

c) Improved Scalability: Optimal layer three forwarding allows networks to scale seamlessly, accommodating growing traffic demands while maintaining high performance.

Network scalability refers to a network’s capacity to grow and adapt to changing requirements without sacrificing performance or efficiency. It involves handling increased traffic, data volume, and user demands. Traditional networks often struggle with scalability, leading to bottlenecks, slow connections, and compromised user experiences.

Enhanced network scalability brings numerous benefits to businesses and organizations. Firstly, it allows for seamless expansion as the network can accommodate additional devices, users, and data traffic without performance degradation. This scalability fosters growth and supports future business needs. Secondly, enhanced scalability improves reliability and uptime. With redundant systems and load-balancing capabilities, network failures can be minimized, ensuring uninterrupted operations. Lastly, scalability enables efficient resource allocation, optimizing network resources and reducing costs.

Technologies Driving Enhanced Network Scalability

Several technologies play a crucial role in achieving enhanced network scalability. Software-defined networking (SDN) allows centralized network management, flexibility, and simplified configuration. Network function virtualization (NFV) decouples network functions from physical devices, enabling greater scalability and agility. Cloud computing and virtualization also contribute to enhanced scalability by providing on-demand

Implementing Optimal Layer 3 Forwarding

a) Choosing the Right Routing Protocol: An appropriate routing protocol, such as OSPF or BGP, is crucial for implementing optimal layer three forwarding.

b) Network Segmentation: Breaking down large networks into smaller subnets enhances routing efficiency and reduces network complexity.

c) Traffic Engineering: Network operators can further optimize layer three forwarding by leveraging traffic engineering techniques, such as MPLS or segment routing.

Challenges and Considerations

Security: Layer 3 forwarding introduces potential security risks involving routing packets across different networks. Implementing robust security measures, such as access control lists (ACLs) and firewall policies, is essential to protect against unauthorized access and network attacks.

Network congestion: In complex network environments, layer 3 forwarding can lead to congestion if not correctly managed. Network administrators must carefully monitor and analyze traffic patterns to proactively address congestion issues and optimize routing decisions.

Example: Arista with Large Layer-3 Multipath

Arista EOS supports hardware for Leaf ( ToR ), Spine, and Spline data center design layers. Its wide product range supports significant layer-3 multipath ( 16 – 64-way ECMP ) with excellent optimal Layer 3-forwarding technologies. Unfortunately, multi-protocol Label Switching ( MPLS ) is limited to static MPLS labels, which could become an operational nightmare. Currently, no Fibre Channel over Ethernet ( FCoE ) support exists.

Arista supports massive Layer-2 Multipath with ( Multichassis Link aggregation ) MLAG. Validated designs with Arista Core 7508 switches ( offer 768 10GE ports ) and Arista Leaf 7050S-64 support over 1980 x 10GE server ports with 1:2,75 oversubscription. That’s a lot of 10GE ports. Do you think layer 2 domains should be designed to that scale?

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

1. Scaling Load Balancers
2. Virtual Switch
3. Data Center Network Design
4. Layer-3 Data Center
5. What Is OpenFlow

Back to Basics: Router operation and IP forwarding

Every IP host in a network is configured with its IP address and mask and the IP address of the default gateway. Suppose the host wants to send traffic, which, in our case, is to a destination address that does not belong to a subnet to which the host is directly attached; the host passes the packet to the default gateway, which would be a Layer 3 router.

The Role of The Default Gateway 

A standard misconception is how the address of the default gateway is used. People mistakenly believe that when a packet is sent to the Layer 3 default router, the sending host sets the destination address in the IP packet as the default gateway router address. However, if this were the case, the router would consider the packet addressed to itself and not forward it any further. So why configure the default gateway’s IP address?

First, the host uses the Address Resolution Protocol (ARP) to find the specified router’s Media Access Control (MAC) address. Then, having acquired the router’s MAC address, the host sends the packets directly to it as data link unicast submissions.

Benefits of Optimal Layer 3 Forwarding:

1. Enhanced Scalability: Optimal Layer 3 forwarding allows networks to scale effectively by efficiently handling a growing number of connected devices and increasing traffic volumes. It enables seamless expansion without compromising network performance.

2. Improved Network Resilience: Optimized Layer 3 forwarding enhances network resilience by selecting the most efficient path for data packets. It enables networks to quickly adapt to network topology or link failure changes, rerouting traffic to ensure uninterrupted connectivity.

3. Better Resource Utilization: Optimal Layer 3 forwarding optimizes resource utilization by distributing traffic across multiple links. This enables efficient utilization of available network capacity, reducing the risk of bottlenecks and maximizing the network’s throughput.

4. Enhanced Security: Optimal Layer 3 forwarding contributes to network security by ensuring traffic is directed through secure paths. It also enables the implementation of firewall policies and access control lists, protecting the network from unauthorized access and potential security threats.

Implementing Optimal Layer 3 Forwarding:

To achieve optimal Layer 3 forwarding, various technologies and protocols are utilized, such as:

1. Routing Protocols: Dynamic routing protocols, such as OSPF (Open Shortest Path First) and BGP (Border Gateway Protocol), enable networks to exchange routing information automatically and determine the best path for data packets.

2. Quality of Service (QoS): QoS mechanisms prioritize network traffic, ensuring that critical applications receive the necessary bandwidth and reducing the impact of congestion.

3. Network Monitoring and Analysis: Continuous network monitoring and analysis tools provide real-time visibility into network performance, enabling administrators to identify and resolve potential issues promptly.

Arista deep buffers: Why are they important?

A vital switch table you need to be concerned with for large 3 networks is the size of Address Resolution Protocol ( ARP ) tables. When ARP tables become full, and packets are offered with the destination ( next hop ) that isn’t cached, the network will experience flooding and suffer performance problems.

Arista Spine switches have deep buffers, ideal for bursty- and latency-sensitive environments. They are also perfect when you have little knowledge of the application traffic matrix, as they can handle most types efficiently.

Finally, deep buffers are most useful in spine layers as traffic concentration occurs in these layers. If you are concerned that ToR switches do not have enough buffers, physically direct servers to chassis-based switches in the Core / Spine layer.

Knowledge Check: Cisco PfR

Understanding Cisco PfR

Cisco PfR, also known as Cisco Performance Routing, is an intelligent network optimization technology that dynamically manages traffic flows to ensure optimal performance. It combines sophisticated algorithms, real-time monitoring, and path selection to intelligently route network traffic, leveraging multiple paths and network resources.

The Benefits of Cisco PfR

Enhanced Network Resilience and Redundancy

By continuously monitoring network conditions and dynamically adapting to changes, Cisco PfR ensures network resilience. It automatically reroutes traffic when network congestion, link failures, or other performance issues occur, minimizing downtime and disruptions.

Improved Application Performance

With Cisco PfR, network traffic is intelligently distributed across multiple paths based on application requirements. This optimization ensures critical applications receive the necessary bandwidth and low latency, enhancing the overall user experience.

Cost-Efficient Bandwidth Utilization

By intelligently distributing traffic across available network resources, Cisco PfR optimizes bandwidth utilization. It can dynamically choose the path with the lowest cost or least congestion, resulting in significant cost savings for organizations.

Optimal layer 3 forwarding  

Every data center has some mix of layer 2 bridging and layer 3 forwardings. The design selected depends on layer 2 / layer 3 boundaries. Data centers that use MAC-over-IP usually have layer 3 boundaries on the ToR switch. While fully virtualized data centers require large layer two domains ( for VM mobility ); VLANs span Core or Spine layers.

Either of these designs can result in suboptimal traffic flow. Layer 2 forwarding in ToR switches and layer 3 forwarding in Core may result in servers in different VLANs connected to the same ToR switches being hairpinned to the closest Layer 3 switch.

Solutions that offer optimal Layer 3 forwarding in the data center were available. These may include stacking ToR switches, architectures that present the whole fabric as a single layer 3 elements ( Juniper QFabric ), and controller-based architectures (NEC’s Programmable Flow ). While these solutions may suffice for some business requirements, they don’t have optimal Layer 3 forward across the whole data center while using sets of independent devices.

Arista Virtual ARP does this. All ToR switches share the same IP and MAC with a common VLAN. Configuration involves the same first-hop gateway IP address on a VLAN for all ToR switches and mapping the MAC address to the configured shared IP address. The design ensures optimal Layer 3 forwarding between two ToR endpoints and optimal inbound traffic forwarding.

Load balancing enhancements

Arista 7150 is an ultra-low latency 10GE switch ( 350 – 380 ns ). It offers load-balancing enhancements other than the standard 5-tuple mechanism. Arista supports new load-balancing profiles. Load-balancing profiles allow you to decide what bit and byte of the packet you want to use as the hash for the load-balancing mechanism—offering more scope and granularity than the traditional 5-tuple mechanism. 

LACP fallback

With traditional Link Aggregation ( LAG ), LAG is enabled after receiving the first LACP packet. This is because the physical interfaces are not operational and are down / down before receiving LACP packets. This is viable and perfectly OK unless you need auto-provisioning. What does LACP fallback mean?

If you don’t receive an LACP packet and the LACP fallback is configured, one of the links will still become active and will be UP / UP. Continue using the Bridge Protocol Data Unit ( BPDU ) guard on those ports, as you don’t want a switch to bridge between two ports, create a forwarding loop.

Direct server return

7050 series supports Direct Server Return. The load balancer in the forwarding path does not do NAT. Implementation includes configuring VIP on the load balancer’s outside IP and the internal servers’ loopback. It is essential not to configure the same IP address on server LAN interfaces, as ARP replies will clash. The load balancer sends the packet unmodified to the server, and the server sends it straight to the client.

Requires layer 2 between the load balancer and servers; load balancer needs to use MAC address between the load balancer and servers. It is possible to use IP called Direct Server Return IP-in-IP. Requires any layer 3 connectivity between the load balancer and servers.

Arista 7050 IP-in-IP Tunnel supports essential load balancing, so one can save the cost of not buying an external load-balancing device. However, it’s a scaled-down model, and you don’t get the advanced features you might have with Citrix or F5 load balancers.

Link flap detection

Networks have a variety of link flaps. Networks can experience fast and regular flapping; sometimes, you get irregular flapping. Arista has a generic mechanism to detect flaps so you can create flap profiles that offer more granularity to flap management. Flap profiles can be configured on individual interfaces or globally. It is possible to have multiple profiles on one interface.

Detecting failed servers

The problem is when we have scale-out applications, and you need to detect server failures. When no load balancer appliance exists, this has to be with application-level keepalives or, even worse, Transmission Control Protocol ( TCP ) timeouts. TCP timeout could take minutes. Arista uses Rapid Indication of Link Loss ( RAIL ) to improve performance. RAIL improves the convergence time of TCP-based scale-out applications.

OpenFlow support

• Support OpenFlow Protocol 1.0. Available on 7050 series.

Arista matches 750 complete entries or 1500 layer 2 match entries, which would be destination MAC addresses. They can’t match IPv6 or any ARP codes or inside ARP packets, which are part of OpenFlow 1.0. Limited support enables only VLAN or layer 3 forwardings. If matching on layer 3 forwarding, match either the source or destination IP address and rewrite the layer 2 destination address to the next hop.

Arista offers a VLAN bind mode, configuring a certain amount of VLANs belonging to OpenFlow and another set of VLANs belonging to standard Layer 3. Openflow implementation is known as “ships in the night.”

Arista also supports a monitor mode. Monitor mode is regular forwarding with OpenFlow on top of it. Instead of allowing the OpenFlow controller to forward forwarding entries, forwarding entries are programmed by traditional means via Layer 2 or Layer 3 routing protocol mechanism. OpenFlow processing is used parallel to conventional routing—openflow then copies packets to SPAN ports, offering granular monitoring capabilities.

DirectFlow

Direct Flow – I want all traffic from source A to destination A to go through the standard path, but any HTTP traffic goes via a firewall for inspection. i.e., set the output interface to X and a similar entry for the return path, and now you have traffic going to the firewall but for port 80 only.

It offers the same functionality as OpenFlow but without a central controller piece. DirectFlow can configure OpenFlow with forwarding entries through CLI or REST API and is used for Traffic Engineering ( TE ) or symmetrical ECMP. Direct Flow is easy to implement as you don’t need a controller. Just use a REST API available in EOS to configure the flows.

Optimal Layer 3 Forwarding: Final Points

Optimal Layer 3 forwarding is a critical network architecture component that significantly impacts network performance, scalability, and reliability. Efficiently routing data packets through the best paths enhances network resilience, resource utilization, and security.

Implementing optimal Layer 3 forwarding through routing protocols, QoS mechanisms, and network monitoring ensures a robust and efficient network infrastructure. Embracing this technology allows organizations to deliver seamless connectivity and a superior user experience in today’s increasingly interconnected world.