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Re: multi homing pressure

  • From: Owen DeLong
  • Date: Thu Oct 20 00:18:30 2005

--On October 19, 2005 11:17:02 PM -0400 Jon Lewis <[email protected]> wrote:

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 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".

Yes and no.  Most people that will spend the $$ for routers with enough
memory to handle multiple full feeds are also looking to get a certain
amount of TE capability out of the deal, and, at that point, babysitting
the TE becomes more than 0.01 FTE (closer to 0.30 in my experience).

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.

That's an interesting way to look at it.  I think that at the time those
routers were designed (I'm assuming you are talking AGS+ here), there
was no concept of why anyone would ever need that much memory, and,
designing a board to accommodate it would have seriously increased the
size and price of the router.  If you're talking about more recent,
then, it's a marketing decision to not facilitate full tables on
low-end routers lest they start eating into their high-end router

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
Lol... Yep, that happens.

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.

That could be true, but, how long do you really think the RAM will last?


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