RSS
Twitter
Facebook
v
The
de facto standard for inter-AS routing,
v
BGP:
glues the whole Internet together
v
Path
Vector protocol
Uses TCP (service port: 179)
v
Similar
to Distance Vector protocol. Each Border Gateway broadcast to neighbors (peers)
entire path (i.e., sequence of AS’s) to destination
v
BGP
is an exterior gateway protocol (EGP), which means that it performs routing between
multiple autonomous systems or domains and exchanges routing and reachability
information with other BGP systems.
v
The
information exchanged among BGP routers allow a router to construct a graph of AS’s
and each AS is identified by Autonomous System Number (ASN).
v
BGP
routes to networks (ASs), not individual hosts
v
BGP
messages exchanged using TCP and BGP messages are:
o OPEN: opens TCP
connection to peer and authenticates sender
o UPDATE:
advertises
new path (or withdraws old)
o KEEPALIVE keeps connection
alive in absence of UPDATES; also ACKs OPEN request
o NOTIFICATION: reports errors
in previous msg; also used to close connection
v
Session
is established between two BGP speakers to exchange information regarding
- New active
routes
- Old inactive
routers or
- To report
error conditions
The below figure
illustrates core routers using BGP to route traffic between autonomous Systems
v
All
BGP message types use the basic packet header. Open, update, and notification messages
have additional fields, but keep-alive messages use only the basic packet header.
v The
below figure illustrates the fields used in the BGP header.
0 comments