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BGP Load Sharing Scenarios

March 05, 2024 , ,

BGP Load Sharing Scenarios

BGP is used to exchange routing information between multiple autonomous systems (AS) on the Internet. An autonomous system is a group of networks that share a common administrative area. 

BGP is used to route traffic across multiple independent systems and is the protocol used by Internet Service Providers (ISPs) to communicate routing information with one another.

⭐Related : BGP Cheat Sheet for Network Engineers
⭐Related : 51 facts about BGP routing Protocol for Network Engineers

 What is BGP Load Sharing ?

BGP load sharing is a mechanism that allows BGP to divide traffic across multiple paths to a same destination.

BGP load sharing varies between dual homed, single multihomed, and dual multihomed networks based on the number and type of ISP connections.

BGP Load Sharing
Fig 1.1- BGP Load Sharing

 BGP Single homed Scenario

The single-homed design means that you only have one connection to one ISP. BGP is not required in this architecture because your network has only one exit path. You might as well use a static default route to the ISP.

BGP Single homed Scenario

 BGP Single multihomed Scenario

You have one connection to two different ISPs, and you can use BGP attributes such as MED, weight, local preference, or AS path prepending to influence the path selection for both inbound and outbound traffic.

BGP Single multihomed Scenario

  • You cannot use the maximum-paths command to enable load balancing, as BGP selects only a single best path among different ASs.
  • The advantage of this scenario is that you have redundancy and reliability with multiple ISPs.
  • The disadvantage is that you may have compatibility and interoperability issues with different ISPs.

 BGP Dual homed Scenario

You have two connections to the same ISP, and you may utilize BGP features like MED, weight, local preference, or AS path prepending to influence the path selection for both inbound and outgoing traffic.

BGP Dual homed Scenario

  • You can also use the maximum-paths command to enable per-destination or per-packet load balancing.
  • The advantage of this scenario is that you have redundancy and load sharing with a single ISP.
  • The disadvantage is that you still depend on a single ISP.

 BGP Dual multihomed Scenario

You have at least two connections to two different ISPs, and you can use BGP attributes such as MED, weight, local preference, or AS path prepending to influence the path selection for both inbound and outbound traffic.

BGP Dual multihomed Scenario

  • You can also use the maximum-paths command to enable per-destination or per-packet load balancing.
  • The advantage of this scenario is that you have the highest level of redundancy, reliability, and performance with multiple ISPs and links.
  • The disadvantage is that you have the highest level of complexity, resource consumption, and management.
When comparing all these together, you can check the below table to understand more