OSPF routerID and loopback int

[Brad_199]

Originally the OSPF router-ID set on my OSPF switches were using the lowest IP address assigned to a VLAN.

I've since created a new loopback interface (int 1) and assigned it an IP address expecting the switch to use it as the routerID.  But it didn't.

The only way I could set the router-ID to the address given to the loopback interface was to manually set it from the CLI.

Do you know why?

Snippet of my routing table:

130.130.130.1/32     lo1                  connected            1          0
 127.0.0.0/8                 reject              static                     0          0
 127.0.0.1/32               lo0                  connected            1          0

[Pete W]

Did you restart the ospf process (or restart the switch)?

Pete

[paulgear]

Morning Brad. :-)

The router ID is only set at startup or when manually configured.  Check out http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c02610033/c02610033.pdf page 5-16 for more info about this.

[Pete W]

Taken from the HP 5400zl routing guide:

If no router ID is configured, then, by default, the router ID on a ProCurve 
routing switch is the first IP address that becomes physically active at reboot. 
This is usually the lowest numbered IP interface configured on the device. 
However, if no router ID is configured and one or more user-configured 
loopback interfaces are detected at reboot, then the lowest-numbered (user­
configured) loopback interface becomes the router ID. If the lowest numbered
loopback interface has multiple IP addresses, then the lowest of 
these addressees will be selected as the router ID. Once a router ID is selected, 
it will not automatically change unless a higher-priority interface is configured.

The router id does not seem to be OSPF specific - but an ID that is specified at switch startup (after a reboot!). On Cisco I believe that the router id IS ospf specific, and is dynamically selected upon initialising or resetting the OSPF processes.

Hope this helps.

Pete.

[Brad_199]

Opps I never saw that part in the documentation. Thanks for pointing it out guys.

Is lo0 a user configured loopback int? It wouldn't let me change the ip so I created a new loopback int (int 1)