[j-nsp] Running OSPF to manage loopbacks, only have trunks

Chris Kawchuk juniperdude at gmail.com
Wed Aug 31 03:12:19 EDT 2011

> Chris,
> Could you elaborate on:
> Just need to be careful to bridge the VLAN across the trunk link as necessary. (i.e. only bridge what you need - switch to switch - don't use 'vlan members all').
> What would be the problem if I did all? I might have say tag 2001 going to a switch that doesn't play on that vlan, but I wouldn't have problems necessarily would I?
> Thanks,
> Morgan

You're right. It wouldn't necessarily be an issue.

What I'm trying to avoid is bridging VLAN 2001 everywhere (and we're back to the original '1 giant LAN' problem).

Switch 1 <> Switch 2 uses VLAN 2001
Switch 2 <> Switch 3 uses VLAN 2002
Switch 3 <> Switch 1 uses VLAN 2003

All inter-switch links declared 'family ethernet switching port-mode trunk members vlan all'.

Agreed, if switch 3 doesn't have tag 2001 declared, it'll just ignore it / not pass it back to switch 1.

However, if you're using a base RSTP topology (VLAN unaware), then one of those inter-switch links is going to block. 

You will not have routing/IP connectivity on one of the inter-switch links. However, this is not necessarily a problem.... If RSTP blocks between a pair of switches, OSPF will just lose the inter-switch adjacency - but not reachability of each switch in the OSPF database (The Type 1's are all still there). The traceroute simply follows the current RSTP forwarding topology.

- Chris.

More information about the juniper-nsp mailing list