BGP Communities has to be one of my favorite features added to the BGP protocol. As you should know by now, BGP passes several attributes between peers that help influence the BGP best path selection algorithm. One of these is the BGP Community attribute. Think of this as another tag placed on the route advertisement […]
AS-Path Filtering
Before we get into the how, let’s talk about the why. According to the CIDR Report, the global IPv4 routing table sits at about 525,000 routes, it has doubled in size since mid 2008 and continues to press upwards at an accelerated rate. This momentum, which in my estimate started around 2006, will most likely […]
BGP Essentials – The Art of Path Manipulation
Most enterprise networks use BGP to peer with their Internet Service Providers if they want to be multi-homed. Many factors come into play when determining how traffic should flow, but no matter what policies are put into place, at some point in time you’re going to need some control over how your external traffic is […]
BGP Tips! multipath load balancing
Previous thoughts on load balancing BGP were that it is not a load balancing protocol and in order to achieve any sort of balanced traffic you would have to perform some sort of route balancing. These days with BGP finding its way into our core IGP ( think MPLS VRF WAN ) a number of […]
More BGP tricks
At times, the ‘rules of BGP’ don’t fit the needs of our productions networks. When we get into today’s production networks how often do book configurations apply? I’ll tell you one thing. I don’t see many book examples with 450+ line BGP configs, but I’ve worked on a number of networks where this was the […]
Route Selection
One of the most common questions I get concerns path selection within the router. Everyone knows (or at least they should know) that a more specific prefix will be preferred, but until you learn the basics, you’ll never be able to debug why a router is using a sub optimal path. There are a couple […]
