multi homing pressure

Jon Lewis jlewis at lewis.org
Thu Oct 20 03:17:02 UTC 2005


On Wed, 19 Oct 2005, Owen DeLong wrote:

> I've done simple ASN/BGP based multihoming for a number of businesses, and,
> it can be done on a mostly set-and-forget basis.  If you have your upstreams
> supply 0.0.0.0/0 via BGP and no other routes, and, you advertise your
> networks, believe it or not, that's a pretty stable configuration.  If
> your upstreams are reasonably reliable, that works pretty well.  If not,
> and, you care about knowing what your upstreams can't reach at the moment,
> then, you need a full feed and life becomes slightly more complicated.

There's really nothing more complicated about taking 2 (or more) full 
views, other than keeping an eye on available memory.  The C&W/PSI 
incident a few years ago and the more recent Cogent/Level3 incident are 
perfect examples of why taking two 0/0's really doesn't cut it if you want 
reliable connectivity to the "whole internet".

Cisco burned a lot people by building routers with needlessly limited RAM 
capacities (planned obsolescence?).  Because of that, one customer 
wouldn't buy another cisco, and instead went Imagestream.  They have 3 
full views and no worries now.  They were so happy with that Imagestream, 
they ended up buying a bunch more for internal WAN needs.

Another customer I dealt with recently was fairly typical of the "small 
multihomer" I'd guess.  They were multihomed to two Tier1 providers and 
wanted to replace one of them with us.  Their BGP had been done either by 
a consultant or former employee and was definitely set and forgot on 
autopilot.  Their router (cisco 3640) kept "dying" and they'd just power 
cycle it as needed.  When I got in to take a look, I found it was taking 
full views and had pretty much no RAM left...and it was announcing all 
their space deaggregated as /24s for no reason.  They weren't willing to 
shell out the $ for a bigger router, so I ended up configuring them for 
full routes from us and customer routes from their other (a Tier1) 
provider (and fixing their advertisements).  Other than expansion (more 
network statements), running out of RAM again, or changing providers, I 
doubt their BGP config will need to be touched in the forseeable future.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                | 
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________



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