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North American Network Operators Group

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

  • From: Chris Williams
  • Date: Tue May 16 12:16:37 2000

> IP allocation is essentially meaningless in your case.  You are not
> going to benefit from any kind of IP routing redundancy unless you can
> pull your own fibre down different routes to different locations in the
> USA.  Period.  Don't even think about BGP -- it won't help you unless
> you're willing to pay mega-bucks for your own long-haul links and unless
> you've got incredibly "secure" facilities.  "multi-homing" to two
> different providers in the same city isn't really going to be any more
> reliable than simply paying one good provider enough incentive to sign a
> decent service level agreement with you and let them deal with the
> redundancy issues to the rest of the Internet.

Although I agree that co-locating is probably the right solution in this
guy's case, I _strongly disagree_ with the assertion that having links
to two different providers is not helpful, even if somewhere futher up
the line there is still a single point of failure (just as the fibre
trunk to the US, or whatever).
There is a whole class of human-error and miscommunication problems
which can cause an interruption of service from one provider, regardless
of how technically redundant your links to that provider are. Examples
I've directly experienced in the past year:
  -- The provider finds a cancellation for an old circuit floating
around in their DB, and confusing it with your current service, shuts
down your connection (I had this happen with a prominent tier-1 provider
-- these kinds of mistakes are not just made by small no-name ISPs)
  -- The provider sends your bill to the wrong address, and so your
accounting dept doesn't pay it, and they suspend your service.
  -- A box on your network is cracked and used to send SPAM. The
providers shuts you down for spamming without warning, or with warnings
sent to the wrong address.

Given, these types of things can be largely prevented by maintaining
good lines of communication with your provider. But, in the real world,
miscommunication and mistakes do happen, especailly if you are busy and
understaffed, as I think most small high-tech companies are.
In the time I recently worked with a small multihomed company (about 2
years), I would say the outages we experienced were 30% downed circuits,
40% incompetance on the part of our tier-2 upstream, 10% our own
incompetance, and 20% legitimate miscommunication as described above (if
you count by duration of the outage -- if you counted number of discrete
outages, you would see us rebooting our flakey router a lot ;)). If you
assumed we had gone with a competant backup provider, that would leave
1/3 of all downtime to "human factors" other than our own foul-ups,
rather than actual hardware and/or software failures.

Of course, my experience in this type of scenario may not be universal.
;)

In any case, it seems to me we've veered significantly from the original
topic. I thought we had pretty well established that "there are some
legitimate needs for multihomed /24s" -- the question brought to the
list was really "will my /24 work if I multihome it?", not "please tell
me I don't know what I want".

[BTW, thanks Rob for pointing out my date problem -- somebody here
thought it was clever for our login script to get the date from a server
with a dead CMOS battery..]





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