User guide

Configuring BGP Setting Global BGP Parameters
OmniSwitch AOS Release 7 Advanced Routing Configuration Guide March 2015 page 4-21
Setting the Router AS Number
The router takes a single Autonomous System (AS) number. The user can assign one and only one AS
number to a router using the ip bgp autonomous-system command. That same router may contain peers
that belong to a different AS than the AS you assign your router. In such a case these BGP peers with a
different AS would be considered external BGP (EBGP) peers and the communication with those peers
would be EBGP.
The following command would assign an AS number of 14 to a router:
-> ip bgp autonomous-system 14
This command requires that you first disable the BGP protocol. If BGP were already enabled, you would
actually need to issue two commands to assign the router’s AS number to 14:
-> ip bgp admin-state disable
-> ip bgp autonomous-system 14
Setting the Default Local Preference
A route’s local preference is an important attribute in the path selection process. In many cases, it will be
the most important criteria in determining the selection of one route over another. A route obtains its local
preference in one of two ways:
• By taking the default local preference established globally in the router.
• By having this default local preference manipulated by another command. The BGP peer, aggregate
route, and network commands allow you to assign a local preference to a route. It is also possible to
manipulate the local preference of a route through BGP policy commands.
If you want to change the default local preference value, use the ip bgp default local-preference
command. For example, if you wanted to change the default local preference for all routes to 200, you
would issue the following command:
-> ip bgp default local-preference 200
This command requires that you first disable the BGP protocol. If BGP were already enabled, you would
actually need to issue two commands to change the default local preference to 200:
-> ip bgp admin-state disable
-> ip bgp default local-preference 200