BGP Load Sharing Scenarios
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.
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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.
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 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.
- 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.
- 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.
- 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.
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