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

[Chris Kawchuk]

I think that's precisely what he's trying to avoid. =)

What we did is to use RVIs (vlan.xxx), but had a series of VLANs (VLAN 2000, 2001, 2002, 2003 etc..) setup as point-to-point /30s between the EXes inside a VLAN. Switch 1 to Switch 2 would be VLAN 2002. Switch 2 to Switch 3 would be VLAN 2003, etc. 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').

We could also re-use the same point-to-point VLAN IDs elsewhere in the network to link other switches together OSPF-wise (as the VLAN ID was only locally significant to a pair of switches). I could re-use 2001/2002/2003 elsewhere, perhaps in a different group of switches.

Hence, on each switch, we turned on OSPF on those RVIs, allocated some private /30s between the switches, and exported lo0.0 into the ospf area. Ended up with something that looks alot like what you're trying to do.

Nice thing is that you can discover the switched network topology easily via a simple traceroute. Makes reachability troubleshooting easy for my new guys; esp if you do the reverse DNS properly:

> traceroute loopback.switch5.mynetwork.net

1 10ms 10ms 10ms ge-0/0/22.switch1.mynetwork.net [10.222.1.2]
2 10ms 10ms 10ms ge-0/0/24.switch2.mynetwork.net [10.222.2.2]
3 10ms 10ms 10ms ge-0/1/0.switch3.mynetwork.net  [10.222.3.2]
4 10ms 10ms 10ms xe-0/1/1.switch4.mynetwork.net  [10.222.4.2]
5 10ms 10ms 10ms loopback.switch5.mynetwork.net  [10.111.5.1]

^^ fake traceroute, but you get the idea of what's possible. each link between the switches is a /30. Map your reverse DNS appropriately to which interface is shared between the two switches.

- Chris.

P.S. If you want to get really fancy (or dislike burning a bunch of IP space for /30 connections), use IP unnumbered instead /30s on the vlan.x interfaces. OSPF will form an adjacency and learn. traceroutes will then show the loopback IPs of each switch as you trace through the network instead.



>> I don't want to make a giant vlan and put all the devices loopbacks in it, one for
>> scalability issues but also for broadcast related issues.
> 
> Could you achieve what you want using RVIs rather than loopback interfaces?
> 
> i.e. on your dot1q trunks, carry an extra "management" VLAN and attach
> a "family inet" RVI to it?