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.