OECG – Chapter 12


path attribute – a BGP update field that any number of things about the included prefix

BGP table – the router’s table of BGP prefixes, not the same as the IP routing table

BGP Update – a message sent from one BGP router to another, contain prefixes with matching path attributes

established – the state in which BGP neighbors are able to sent updates to one another

iBGP – internal BGP. BGP neighbors that are members of the same ASN are internal.

eBGP – external BGP. BGP neighbors that are members of different ASNs are external.

EGP – exterior gateway protocol, a legacy predecessor to BGP.

BGP – border gateway protocol

peer group – configuring multiple neighbors as a group, easing configuration and reducing the amount of BGP overhead since the router only has to compute Updates once for routers in the same peer group

eBGP multihop – adding additional TTL so that eBGP neighbors can peer without being physically adjacent

autonomous system – a group of BGP routers administrated by a common body, to define routing policies together

AS number – autonomous system number, identifying a BGP AS

AS_PATH – BGP PA containing all ASNs along the way that a prefix has been advertised through since its origin

ORIGIN – BGP PA describing how the prefix came to be in the BGP table – IGP, EGP or incomplete

NLRI – network layer reachability information – BGP’s technical term for a prefix and prefix length

NEXT_HOP – the BGP PA describing the IP address of the router that can route the prefix

MULTI_EXIT_DISC – commonly referred to as MED, it is the BGP PA that allows routers in one AS to advertise a value into another AS, and therefore influence the routing in that other AS. Thought of as the “BGP metric”.

LOCAL_PREF – a BGP PA that tells an AS what route is the best route to take when leaving an AS. A larger number is better.

routing black hole – when routes converge on a path that cannot forward the prefix. Packets die when the end up at a router than cannot forward them.

synchronization – in BGP, where a router will not put a route into his BGP table unless that route is in his IP routing tables learned via some IGP.

confederation – a BGP feature that saves you from having to fully mesh iBGP peers by breaking the AS up into sub-ASs

route reflector – a BGP feature where a router will learn routes, and then forward those routes to all configured iBGP peers, while following logic that will prevent routing loops.

confederation identifier – the “parent” or tier-1 ASN that will be seen by eBGP neighbors outside of the confederation.

sub-AS – iBGP routers grouped in confederation will be a part of a sub-AS

route reflector server – the same as a route-reflector
route reflector client – a BGP router that receives routes from a route-reflector. This router does not know that he is a RR client

route reflector nonclient – a BGP router in an AS with RRs, but isn’t updated by that RR

confederation AS – the number assigned to a confederation sub-AS, often a private ASN.

confederation eBGP – a connection between 2 different sub-AS routers within a confederation

weight – a local BGP setting that is not advertised to any peers. Larger is better. This is a Cisco proprietary feature.

About the author

Ethan Banks

Most people know me because I write & podcast about IT on the Packet Pushers network. I also co-authored "Computer Networks Problems & Solutions" with Russ White.

Find out more on my about page.


Most people know me because I write & podcast about IT on the Packet Pushers network. I also co-authored "Computer Networks Problems & Solutions" with Russ White.

Find out more on my about page.

Subscribe via Email

Receive complete, ad-free posts in your inbox as I publish them here.