multi homing pressure

Thu Oct 20 04:16:27 UTC 2005

--On October 19, 2005 11:17:02 PM -0400 Jon Lewis <jlewis at lewis.org> 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 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".
>
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
business.

> 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?

Owen
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