Triangular Routing



Triangular Routing

In the world of networking, efficient data transmission is paramount. Innovative routing techniques have emerged with the increasing demand for faster and more reliable networks. One such technique is triangular routing, which optimizes network performance and enhances the overall user experience. This blog post will explore triangular routing, how it works, and its benefits in network optimization.


  • Ingress Site Selection

An essential requirement for business continuity is to support distributed applications. Different types of applications, be they legacy or nonlegacy, will provide particular challenges for ingress site selection. One of the main challenges designers face is workload virtualization between different geographic locations. Workload virtualization requires location independence for server resources and the ability to move these resources from one geographic location to another. This is where triangular routing comes to play.

  • The LISP protocol

What is triangular routing? Triangular routing is a method for transmitting packets of data in communications networks. It uses a form of routing that sends a packet to a proxy system before transmission to the intended destination. The LISP Protocol used as an Internet locator can be used as a proxy.


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

  1. Network Security Components
  2. LISP Hybrid Cloud
  3. Remote Browser Isolation
  4. Dynamic Workload Scaling
  5. Active Active Data Center Design
  6. Identity Security


Triangular Routing

Key Triangular Routing Discussion Points:

  • Introduction to triangular routing and what is involved.

  • Highlighting the details of the LISP traffic flow.

  • Technical details on Ingress and Egress traffic flows.

  • Scenario with a DC extension use case.

  • LISP Host mobility solution. 


  • A key point: Hand-on video on LISP and Triangular routing

The following video is a hands-on demonstration that illustrates all the main components of LISP in operation and interactions.LISP is a Layer 3 overlay protocol that addresses the challenges of the scalability of the Internet and mobility by separating the identity and location namespaces, decoupling the control plane and data plane, and managing family versatility.



Virtualized Workload Mobility

Virtualized Workload Mobility allows live migration between “Twin” data centers and presents several challenges. Firstly, it brings the challenge of route optimization once the workload has moved to the new location. When virtual machines are migrated between data centers, the traffic flow for client-server may become suboptimal, leading to application performance degradation.

How do existing and new connections get directed to the new location? Traditional methods, such as Route Health Injection ( RHI ) and DNS, are available but don’t suit all requirements. They can place unnecessary workloads over the data center interconnect link ( DCI ), creating a triangular routing effect discussed below.


A Key Point: Knowledge Check 


Back to Basics: Triangular Routing

  • A key point: Back to basics with IP Routing.

A router’s primary function is to move an IP packet from one network to a different network. Routers try to select the best loop-free path in a network that forwards a packet to its destination IP address. A router understands nonattached networks through static configuration or dynamic IP routing protocols. So we have two routing protocols, static and dynamic.

Dynamic IP routing protocols distribute network topology information between routers and provide updates without intervention when a topology change occurs. On the other hand, IP routing with static routes only accommodates topology changes well and can burden network engineers depending on the network size.

IP Routing example
Diagram: IP routing example. The source is Study CCNA.


  • A key point: A network routing technique

So, what is triangular routing? Triangular routing is a network routing technique that involves sending traffic through three or more points on the network. It is often used to increase the network’s reliability, security, or performance by reducing the load on any single point. In triangular routing, the data is sent from the source node to a middle node, then to the destination node. Depending on the network configuration, the middle node may be a router, switch, or hub.


Avoid congestion

Triangular routing is a common technique on the Internet. It is used to avoid congestion and increase reliability. When a connection is established between two nodes, the traffic is sent from the source to the middle node via a shorter route. If the connection between the middle node and the destination node is interrupted, the data can be re-routed through another node. This ensures the data is delivered to the destination without interruption.

Triangular routing is also used in private networks, such as corporate networks. It reduces the load on a single point, reduces latency, and increases the network’s security. In addition, each node in the triangular routing is configured with different routing protocols, making it difficult for intruders to penetrate the network.

Triangular routing is a reliable and secure routing technique that can be used to improve the performance of a network. It can be used to avoid congestion and increase reliability by routing data through multiple points on the network. The following figure shows an example of triangular routing.



Hair-pinning & Triangular routing – Ingress and Egress traffic flows.

Triangular routing

  1. The external client queries its configured DNS server. The Global Load Balancing ( GLB ) device receives the request, which is authoritative for the queried domain. The GLB responds with the VIP_1 address of the local Load Balancer ( LLB ) in DC1. The VIP_1 represents the application in DC1.
  2. Traffic gets directed toward the active LLB in DC1.
  3. The LLB performs a Source-NAT translation. Source-NAT changes the source IP address to the internal IP address of the LLB. This enables return traffic to be routed back through the correct Load balancer. This step is necessary to retain existing established sessions.
  4. The Virtual Machine ( VM ) receives the packet and replies with the destination address of the Local Load Balancer ( due to Source-NAT ).
  5. The LLB performs reverse translation and returns the packet to the external client.

Let’s assume that DC1 is overutilized and the network administrator wants to move the VM from DC1 to DC2. This move will be a hot move, a “live migration,” so all established sessions must remain intact. This is mainly because of the presence of stateful devices and the fact that we are not stretching the state of these stateful devices between the two data centers.

There is also a requirement for a LAN extension, such as OTV or vPC, between the two data centers. The LAN extension stretches VLANs and the layer 2 traffic between the two data centers.

triangular routing

  1. The client-server flows are still directed to VIP_1 from the global load balancers, as there have been no changes to site selection for existing connections. We are traversing the same stateful device as in the earlier example.
  2. The local load balancer performs Source-NAT and changes the source IP address to its inside address.
  3. The packet can reach the moved VM by leveraging the L2 LAN extension between both DCs.
  4. Any existing or new sessions using the VIP_1 of DC1 will follow the suboptimal path through DC1 to get to DC2.

You would hope there can be immediate changes to DNS and any new sessions ingress to DC2. This would follow the optimum path to the VIP_2, and egress traffic would follow the local gateway in DC2.


Triangular routing: The challenge

The main problem with this approach is that it works for only name-based connections, and previously established connections are hair pinned. The hair-pinning effect implies that there have been active connections to the VIP_1 ( old address ) and some new connections to the VIP_2 in the second data center for some time. Hair-pinning can put an additional load on the DCI and creates a triangular routing effect.


The Solution? Locator Identity Separation Protocol ( LISP )

A new routing architecture called Locator Identity Separation Protocol ( LISP ) was developed to overcome the challenges of workload mobility and triangular routing previously discussed. LISP overcomes the problems faced with route optimization when workloads migrate. It creates a new paradigm by splitting the device identity, an Endpoint Identifier ( EID ), and its location, known as its Routing Locator ( RLOC ), into two different numbering spaces.

This means we have a separate protocol representing where and who you are. The existing number scheme based on IP does not offer this flexibility, and both roles ( who and where ) are represented by one address.

LISP Control plane
LISP Control plane


  • A key point: Additional information on the LISP protocol 

RFC 6830, LISP is described as a routing and addressing architecture for the Internet Protocol. The LISP routing architecture addressed scalability, multihoming, inter-site traffic engineering, and mobility.

Internet addresses today combine location (how a device is connected to the network) and identity semantics into a single 32-bit or 128-bit number. In LISP, the location is separated from the identity. LISP allows you to change your location in a network (your network layer locator), but your identity remains the same (your network layer identifier).

A LISP separates the identifiers of end users from the routing locators used to reach them. The LISP routing architecture design separates device identity – endpoint identification (EID) – from its location – routing locator (RLOC). To further understand how LISP does the locator/ID separation, it is essential to first learn about the architectural components of LISP. The following are some of the functions or features that form the LISP architecture:

LISP Components
Diagram: LISP Components. Source Cisco Press.

LISP Host Mobility

LISP Host Mobility provides an automated solution that enables IP end-points, for example, Virtual Machines ( VM ), to change location while keeping their assigned IP address. As a result, the LISPs detection and mapping system guarantees optimal routing between clients and the IP end-points that moved. The critical point to note is that it’s an automated system.

There is no need to change DNS once the VM moves to the new location. The LISP control plane does not make any changes to DNS and does not require any agents installed on the clients. It’s completely transparent.

LISP VM-mobility provides a transparent solution to end hosts and guarantees optimal path routing to the moving endpoints. It decouples the identity from the topology but creates two separate namespaces, RLOC and EID. The RLOCs remain associated with the topology and are reachable via traditional routing methods. The EID, which describes the end host, can dynamically change location and associate with different RLOCs. This allows the End-point Identifier space to be mobile without impacting the routing interconnecting the locator’s IP space.


LISP VM-Mobility solution:

  • VM migrations are automatically detected by the LISP Tunnel Router ( xTR ). This is accomplished by comparing the source in the IP header of traffic received from the hosts against a range of configured prefixes allowed to roam.
  • No changes are required to DNS or to install any agents. Transparent to end-users.
  • Once the move is detected, the mappings between EIDs and RLOCs are updated by the new xTR.
  • Updating the RLOC-to-EID mappings allows traffic to be redirected to the new locations without causing any updates or churn in the underlying routing. Transparent to the core.


Additional information

  • Load Balancing:

By distributing data packets across multiple paths, triangular routing helps balance the network load. This ensures that no single path becomes overwhelmed with traffic, preventing congestion and optimizing network performance. Load balancing improves network efficiency and minimizes latency, resulting in faster data transmission.

  • Fault Tolerance:

One of the critical advantages of triangular routing is its fault tolerance capabilities. In the event of a link failure or network congestion on one path, the other two paths can still carry the data packets to their destination. This redundancy ensures that the network remains operational despite adverse conditions, reducing the risk of data loss and maintaining uninterrupted connectivity.

Benefits of Triangular Routing:

1. Improved Network Performance: Triangular routing enhances network performance by distributing traffic across multiple paths, reducing congestion, and minimizing latency.

2. Enhanced Reliability: With fault tolerance capabilities, triangular routing ensures uninterrupted connectivity, even in the face of link failures or network congestion.

3. Scalability: Triangular routing provides a scalable solution for network optimization. As the network expands, additional paths can be added to accommodate the increased traffic, ensuring efficient data transmission.

4. Cost-Efficiency: By optimizing network performance, triangular routing helps reduce operational costs associated with network maintenance and upgrades.


Triangular routing offers a robust solution for network optimization, providing improved performance, enhanced reliability, scalability, and cost-efficiency. As network demands continue to grow, adopting innovative routing techniques like triangular routing becomes increasingly crucial. By implementing this strategy, organizations can maximize their network’s potential, ensuring seamless data transmission and an enhanced user experience.


Matt Conran
Latest posts by Matt Conran (see all)

2 Responses