North American Network Operators Group

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Re: IP failover/migration question.

  • From: Christopher L. Morrow
  • Date: Sun Jun 11 23:37:40 2006

On Sun, 11 Jun 2006, Randy Bush wrote:
> > I'm fairly sure that what I would like to do is to arrange what is
> > effectively dual-homing, but with two geographically distinct homes:
> uh, that kinda inverts what we normally mean by 'multi-homing'.
> that's usually two upstream providers for a single site.

This almost sounds like an anycasted version of his site... only unicast
from one location then popping up at another location if the primary dies?

> > Assuming that I have an in-service primary site A, and an emergency
> > backup site B, each with a distinct link into a common provider AS, I
> > would configure B's link as redundant into the stub AS for A -- as if
> > the link to B were the redundant link in a (traditional single-site)
> > dual-homing setup.
> not clear what you mean by redundant.  as the common transit
> provider will not do well with hearing the same ip space from two
> sources, this type of hack might best be accomplished by B not
> announcing the space until A goes off the air and stops announcing
> it.  [ clever folk might try to automate this, but it would make me
> nervous. ]

I think there is some cisco magic you could do with 'dial backup'... you
may even be able to rig this up with an ibgp session (even if that goes
out over the external provider) to swing the routes.

NOTE: this could make your site oscillate if there are connectivity issues
between the sites, it could get messy FAST, and it could be hard to
troubleshoot. Basically look before you leap :)

This link may b e of assistance:

> i am sure others can come up with more clever hacks.  beware if
> they're too clever.

yes... this probably is...

> > I hope this is reasonably on-topic for the list.
> well, you left of mention of us legislative follies and telco and
> cable greed.  but maybe you can get away with a purely technical
> question once if you promise not to do it again. :-)

to get greed into it.. are you sure you want to be 'stuck' with a single
carrier? :) What if the carrier dies wouldn't you want redundant carrier
links as well?