In BGP, routing information is exchanged between autonomous systems. The BGP router ID, expressed like an IPv4 address, uniquely identifies the router. It can be set to be the same as the system interface address.
It is possible to configure an SRĀ OS to operate with an IPv6 only BOF and no IPv4 system interface address. When configured in this manner, the operator must explicitly define IPv4 router IDs for protocols such as OSPF and BGP as there is no mechanism to derive the router ID from an IPv6 system interface address.
If a new or different router ID value is entered in the BGP context, then the new router ID value is used instead of the router ID configured on the router level, system interface level, or inherited from the MAC address. The router-level router ID value remains intact. The router ID used by BGP is selected in the following order:
the router-id configured under config>router>bgp
the router-id configured under config>router
the system interface IPv4 address
the last 4 bytes of the system MAC address
When configuring a new router ID outside of the config>router>bgp context, BGP is not automatically restarted with the new router ID; the next time BGP is (re) initialized the new router ID is used. An interim period of time can occur when different protocols use different router IDs. To force the new router ID, issue the shutdown and no shutdown commands for BGP or restart the entire router. Use the following CLI syntax to configure the router ID for multiple protocols.
CLI syntax
config>router# router-id router-id
The following example displays router ID configuration command usage.
Example
config>router# router-id 10.10.10.104
The following example displays the router ID configuration:
ALA-B>config>router# info
----------------------------------------------
# IP Configuration
#------------------------------------------
interface "system"
address 10.10.10.104/32
exit
interface "to-103"
address 10.0.0.104/24
port 1/1/1
exit
autonomous-system 100
router-id 10.10.10.104
#------------------------------------------
...
ALA-B>config>router#