When prepend fails, what next? (2)
This week’s post was written by Johnny Britt over at FreedomPay. I’ve edited in some small places to add more information, etc., but I think Johnny needs to start blogging…
Once you have determined that AS-Path prepending can no longer help us what are our next steps? Routing is based on the longest matched prefix, this is true when BGP routes are being compared as well regardless of the AS-PATH. So one option you have is to split your address space into longer advertised prefixes and advertise a slice to each of our upstream providers. In Fig. 1, AS65000 splits its /44 IPv6 into 2 prefixes and advertises them out to AS65001 and AS65004 respectively. This forces half of AS65000 subnet traffic to flow inbound from one specific provider and we can combine both this technique and AS-Path prepending to give us more load sharing capabilities.

Using longer prefixes to direct traffic to a more preferred inbound link can take us a long way in creating the desired inbound traffic pattern. Sometimes there are scenarios where you may need to direct traffic at a more granular level.
But what if you don’t have the ability to create longer prefixes Continue reading