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Re: [eng/rtg] changing loopbacks

  • From: Stacy W. Smith
  • Date: Thu Sep 29 15:56:53 2005 
On Sep 29, 2005, at 12:05 PM, Randy Bush wrote:

so i have junipers, ciscos, and a few <gasp> zebras in an ospf
and ibgp mesh.  they're peering via loopbacks, of course.
unfortunately, i need to recover the space from which the
loopbacks are taken.  of course, i would like to do so with
minimal disruption.  i am thinking of something like the
following:

  o add second loopbacks to all routers with new address in new
    block
  o set up ibgp peerings to new addresses from existing
    peerings
  o change the source of routing updates to new addresses
  o remove old peerings
  o remove old loopbacks

what [else] am i missing?
I vaguely remember going through this exercise in a previous life...

As people have already mentioned, some things that are generally tied to loopback address (router-id for one) require a reboot on some vendors equipment. Because of that, we followed a procedure something like this:

1) for all routers:
Add IBGP sessions to new loopback IPs. Don't add new loopback IP to the router, or change IBGP source address. At this point, all added sessions will be down.

2) for each router:
Change "startup config" to the new loopback IP and reload the router on the new config. Router still has IBGP sessions for both old and new loopback IPs of each IBGP peer.

3) for all routers:
Remove all IBGP sessions to old loopback IPs. At this point all sessions to old IPs will be down and all sessions to new IPs will be up.


Each IBGP sessions ends up transitioning through these stages:

old <-> old
reboot one of the routers on new loopback
new <-> old
reboot other router on new loopback
new <-> new

--Stacy