[31166] in North American Network Operators' Group
RE: Confussion over multi-homing
daemon@ATHENA.MIT.EDU (Tony Tauber)
Thu Sep 14 18:11:35 2000
Date: Thu, 14 Sep 2000 18:09:41 -0400 (EDT)
From: Tony Tauber <ttauber@genuity.net>
To: "Roeland M.J. Meyer" <rmeyer@MHSC.com>
Cc: David Lott <dlott@msncomm.com>, nanog@merit.edu
In-Reply-To: <1148622BC878D411971F0060082B042C36C2@hawk.lvrmr.mhsc.com>
Message-ID: <Pine.GSO.4.21.0009141804360.14064-100000@mesa.bbnplanet.com>
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Errors-To: owner-nanog-outgoing@merit.edu
On Thu, 14 Sep 2000, Roeland M.J. Meyer wrote:
>
> David Lott: Thursday, September 14, 2000 10:34 AM wrote:
>
> > First, allow me to state the assumptions that I'm under. I understand
> > the policy to state that if a business needs to multi-home
> > and requires
> > less space than a /20, then they should request this space from their
> > ISP. I also understand that there are filters at the /20
> > boundaries in
> > order to minimize the size of the routing table.
Not *all* boundaries, see below.
> >
> > Question: Doesn't this break multi-homing for end users that
> > need less
> > than a /20?
>
> Yep, this has been a topic here before...no real resolution. You didn't
> really need to prove the case, it has already been proven.
No. From a post I made to this list on 6/22/2000:
++> Here's the deal. If you number out of Provider1's CIDR block
++> but advertise your more-specific to Provider2 and the two Providers
++> touch and Provider1 accepts the more-specific route from Provider2,
++> you should have no problem reaching anyone.
++>
++> Here's the reason: Everyone accepts Provider1's announcement of the block.
++> When your link to P1 is up, any traffic they recieve for your prefix
++> gets routed over that link since they carry your more-specific internally.
++> However, if other providers here the more-specific from P2, they'll
++> send directly via P2 who sends it over the link to you.
++> If your link to P1 goes down, P1 won't see the direct route to you
++> but should see the route via P2 if P1 is accepting it. (Some
++> may either block the announcement or have anti-spoofing packet filters
++> at their borders that block the traffic itself).
++>
As long as Provider1 sees the more-specific from Provider2,
the length is irrelevant.
Does someone disagree?
++> There are many misconceptions about this topic.
++> Hopefully this explanation has helped someone.
Tony
