Arista BGP Peering Options (1)

In this series of blogs, I will discuss a bit on the Arista EOS BGP peering options. As of March 2019, the EOS has the following peering options:



Here is the Arista official TOI links:

• BGP IPv4 NLRI over IPv6 Transport
• BGP IPv4 NLRI over IPv6 NH
• BGP IPv6 Link-local Peering

So, why do we need them, what's the difference and how to configure them?

1) Why
Today's network needs to support dual address spaces - IPv4 and IPv6, which requires providers to run 2 parallel control/forward planes. So the purpose of all the above features is to decrease the complexity by reducing control plane even forward plane.

For example, a data center with public ipv4/ipv6 address and needs support worldwide ipv4 and ipv6 access. Is that possible to use ipv4/ipv6 address space at the server pool and service routers, and only ipv6 infrastructure? The answer is yes.

2)  What's the difference between the above 3 options?

1. The basic way is to have dual ipv4/ipv6 infrastructures and control planes, which means, 2 BGP sessions and 2 address planes. 
2. IPv4 NRLI over IPv6 Transport is to send v4 prefixes over v6 peering. So it saves 1 just 1 control plane - ipv6 bgp but still needs ipv4 next hop as ipv4 prefixes, which means 2 data planes or dual v4/v6 stack. 
3. RFC 5549 - IPv4 NRLI over IPv6 NH, this feature is one step further, ipv4 prefixes can use ipv6 NH. So 1 BGP session and 1 data planes (v6 infrastructure)
4. BGP IPv6 link-local peering, this utilizes the ipv6 link-local address to establish BGP peering w/o assigning global IPv6 interface addresses. 

3) How to configure them? In the following blogs, I will show the configuration 1 by 1. (Please note that I use vrf under router bgp, in order to configure them together in one place. But it is not required and most of the time, you only need ONE)