Bgp Peers; Bgp Sessions; Dynamic As Numbers For Prefix Peers - Cisco Nexus 3000 Series Configuration Manual

Chapter 5 Configuring Basic BGP
S e n d d o c u m e n t c o m m e n t s t o n e x u s 3 k - d o c f e e d b a c k @ c i s c o . c o m
The administrative distance does not influence the BGP path selection algorithm, but it does influence
Note
whether BGP-learned routes are installed in the IP routing table.
For more information, see the

BGP Peers

A BGP speaker does not discover another BGP speaker automatically. You must configure the
relationships between BGP speakers. A
to another BGP speaker.

BGP Sessions

BGP uses TCP port 179 to create a TCP session with a peer. When a TCP connection is established
between peers, each BGP peer initially exchanges all of its routes—the complete BGP routing
table—with the other peer. After this initial exchange, the BGP peers send only incremental updates
when a topology change occurs in the network or when a routing policy change occurs. In the periods of
inactivity between these updates, peers exchange special messages called keepalives. The
the maximum time limit that can elapse between receiving consecutive BGP update or keepalive
messages.
Cisco NX-OS supports the following peer configuration options:
•
•
•

Dynamic AS Numbers for Prefix Peers

Cisco NX-OS accepts a range or list of AS numbers to establish BGP sessions. For example, if you
configure BGP to use IPv4 prefix 192.0.2.0/8 and AS numbers 33, 66, and 99, BGP establishes a session
with 192.0.2.1 with AS number 66 but rejects a session from 192.0.2.2 with AS number 50.)
Cisco NX-OS does not associate prefix peers with dynamic AS numbers as either interior BGP (iBGP)
or external BGP (eBGP) sessions until after the session is established. See
Advanced BGP,"
The dynamic AS number prefix peer configuration overrides the individual AS number configuration
Note
that is inherited from a BGP template. See
information on templates.
Individual IPv4 or IPv4 address—BGP establishes a session with the BGP speaker that matches the
remote address and AS number.
IPv4 prefix peers for a single AS number—BGP establishes sessions with BGP speakers that match
the prefix and the AS number.
Dynamic AS number prefix peers—BGP establishes sessions with BGP speakers that match the
prefix and an AS number from a list of configured AS numbers.
for more information on iBGP and eBGP.
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, NX-OS Release 5.0(3)U1(1)
"Administrative Distance" section on page
is a BGP speaker that has an active TCP connection
BGP peer
Chapter 6, "Configuring Advanced BGP,"
Information About Basic BGP
1-7.
hold time
Chapter 6, "Configuring
for more
5-3
is