Samsung Ubigate iBG2016 Configuration Manual page 147

Ubigate iBG2016 Configuration Guide
CHAPTER 6. BGP
The Border Gateway Protocol(BGP) is an exterior gateway protocol(EGP)
that is used to exchange routing information among routers in different
autonomous systems(ASs). BGP routing information includes the complete
route to each destination. BGP uses the routing information to maintain a
database of network reachability information, which it exchanges with other
BGP systems. BGP uses the network reachability information to construct a
graph of AS connectivity, thus allowing BGP to remove routing loops and
enforce policy decisions at the AS level.
BGP allows for policy-based routing. You can use routing policies to choose
among multiple paths to a destination and to control the redistribution of
routing information. BGP uses the Transmission Control Protocol(TCP) as its
transport protocol, using port 179 for establishing connections. Running over a
reliable transport protocol eliminates the need for BGP to implement update
fragmentation, retransmission, acknowledgment, and sequencing. BGP
supports classless interdomain routing(CIDR), which eliminates the concept
of network classes. Instead of assuming which bits of an address represent the
network by looking at the first octet, CIDR allows you to explicitly specify the
number of bits in the network address, thus providing a means to decrease the
size of the routing tables. BGP also supports aggregation of routes, including
the aggregation of AS paths.
BGP is esentially a Distance Vector protocol that uses TCP as its transport
protocol. It runs between exactly two nodes. These two nodes establish a BGP
session between them and are known as BGP peers of each other.
On connection start, BGP peers exchange complete copies of their routing
tables, which can be quite large. However, only changes(deltas) are
subsequently exchanged, which makes long running BGP sessions more
efficient than shorter ones.
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