North American Network Operators Group

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Re: "Simple" Multi-Homing ? (was Re: CIDR Report)

  • From: Todd Sandor
  • Date: Wed May 17 00:40:25 2000

Thanks you for all the responses - the info has been educational
(special thanks to Chris and Greg) and its given us lots more things to
consider..(e.g. our SLA with our provider)..thanks...

We have always planned to co-locate (still a few months away), but
we just building  our "web-service" (we're a startup) and in the
short-term we need our boxes on-site and we need the service as
HA (Highly Available) as possible [the goal is 24x7, but ...].
We have considered most of the
other  alternatives that were discussed in the mails (e.g. run  effectively
two networks, each providing the  "web-service" and using some load-balancing
mechanism/products with other tricks/scripts when links fail) but  I wanted
to "flush-out" what the issues would be if we were to multi-home via BGP to
different  providers [its currently planned as a short-term solution] so we
could weigh the benefits/drawbacks of the approaches we were considering....

My hope was that the BGP approach would be "cleaner" ...maybe a little
more upfront work, but less on-going maintenance when a link fails [none
of the change the default routes on the fly hacks [and yes were running NT],
manual/scripted procedures when links fails - e.g. DNS changes, etc.).  But we
need to understand the issues before we can make the decision.

This brings me back to my original "operational" question of whether a
non-aggregated /24 will be globablly visiable when our primary link fails...The

"When a customer in one location is using a multi-homed setup to two providers A
B, with A being the primary (using a /24 from loaned from provider A)
and B being the secondary (updates via B would have a longer AS_path - using
default routes with
local-pref on the primary).  When the customers link to A fails, will the /24
needs to be now globably visible via B (a non-aggregate IP address for B) NOT be
visible because of the BGP filtering policies of some other provider somewhere,
say C ?