In this Community Roundtable episode, returning guests Russ White and Nick Russo continue our three part deep dive into the Border Gateway Protocol, or BGP, with a look at the mechanisms within the protocol to perform traffic engineering.

Show Notes

Influence Ingress

* Classic bestpath options to influence ingress

* AS-path prepend outbound to influence inbound traffic

* Why AS Path prepend doesn’t always work

* In many areas, ISPs are in a full or almost full mesh and connected to common backbones making AS Path prepend largely irrelevant

* Providers normally use their own local preference for outbound traffic back to a customer

* MED

* MED is a hint, it’s often stripped or ignored

* MED only works if the AS Path is the same on all routes

* MED is non-transitive and doesn’t mean anything beyond the next hop

* Longest Match

* Be careful about this, as it pollutes the DFZ

* DFZ = default free zone

* A router belongs to the DFZ if it doesn’t need a 0.0.0.0 route to reach everything on the internet

* Tragedy of the commons here

* An enterprise can force inbound traffic to be load-balanced better but it pushes the processing of that traffic engineering onto the internet

* This is the “big hammer”

* Using RFC 1998 communities for influence ingress traffic

* This is a way to signal your provider to take some sort of BGP action

* You need to find the specific communities used by each provider

* Make certain the provider accepts communities on their eBGP edge

Influence egress

* Local Pref

* Overrides pretty much everything other than weight

* Used to implement hot/cold potato routing

* hot potato routing is when a provider chooses to get the traffic out of its network as quickly as possible at the closest egress point

* cold potato routing is when a provider chooses to control some traffic as long as possible for some reason

*  Weight

* Local to a device

* Other handy stuff:

* Cost community: IGP and pre-bestpath POI

* Accumulated IGP (AIGP)

* iBGP tie breakers

* Using RFC 1998 communities for influence ingress traffic

* This is a way to signal your provider to take some sort of BGP action

* You need to find the specific communities used by each provider

* Make certain the provider accepts communities on their eBGP edge

* BGP deterministic MED

 

Outro Music:

Danger Storm Kevin MacLeod (incompetech.com)

Licensed under Creative Commons: By Attribution 3.0 License

http://creativecommons.org/licenses/by/3.0/