User Manual

BGP Configuration Examples
204 Enterasys X-Pedition User Reference Manual
•If the as-count option is entered for an active BGP session, routes will not be resent to reflect
the new setting. To have routes reflect the new setting, you must restart the peer session. To do
this:
a. Enter Configure mode.
b. Negate the command that adds the peer-host to the peer-group. (If this causes the number
of peer-hosts in the peer-group to drop to zero, then you must also negate the command
that creates the peer group.)
c. Exit Configure mode.
d. Re-enter Configure mode.
e. Add the peer-host back to the peer-group.
If the as-count option is part of the startup configuration, the above steps are unnecessary.
BGP Configuration Examples
This section presents sample configurations illustrating BGP features. The following features are
demonstrated:
• BGP peering
• Internal BGP (IBGP)
• External BGP (EBGP) multihop
• BGP community attribute
• BGP local preference (local_pref) attribute
• BGP Multi-Exit Discriminator (MED) attribute
• BGP load-sharing configuration
• EBGP aggregation
• Route reflection
BGP Peering Session Example
The router process used for a specific BGP peering session is known as a BGP speaker. A single
router can have several BGP speakers. Successful BGP peering depends on the establishment of a
neighbor relationship between BGP speakers. The first step in creating a BGP neighbor relationship
is the establishment of a TCP connection (using TCP port 179) between peers.
A BGP Open message can then be sent between peers across the TCP connection to establish
various BGP variables (BGP Version, AS number (ASN), hold time, BGP identifier, and optional