Routing - Using Anycast with BGP Multipath

When configuring BGP in an environment where there are multiple servers leveraging Anycast addresses, it may be considered beneficial to incorporate the use of BGP Multipath to allow multiple equal cost paths to be leveraged simultaneously.

However, this is not a desirable scenario for various reasons.

BGP Multipath is used to allow multiple paths to be installed in the BGP table, resulting in load balancing of traffic via these multiple paths. When IPv6 anycast is used, because the location of the multiple servers sharing that same IPv6 address will typically be distributed geographically, it is unlikely that multipath will install multiple paths to the IPv6 anycast addresses, simply because the BGP multipath prerequisites are unlikely to be met.

However, even if it does, this is undesirable because then that would result in BGP trying to load balance a single session of traffic across two or more different servers. This would result in one server receiveing half of the session packets while the other server receiving the other half.

However, anycast on its own will simply allow BGP to route traffic to the single closest server that shares that IPv6 address.