[29676] in North American Network Operators' Group
Re: bad idea?
daemon@ATHENA.MIT.EDU (Adrian Chadd)
Wed Jul 5 12:32:14 2000
Date: Thu, 6 Jul 2000 00:26:16 +0800
From: Adrian Chadd <adrian@creative.net.au>
To: "Greene, Dylan" <DGreene@NaviSite.com>
Cc: 'Jeremiah Kristal' <jkristal@on2.com>, nanog@merit.edu
Message-ID: <20000706002616.D71832@ewok.creative.net.au>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <7C06EA1D5AAAD311B4EB00508B550B99014F7ABF@navexc01.and.navisite.com>; from DGreene@NaviSite.com on Wed, Jul 05, 2000 at 11:53:13AM -0400
Errors-To: owner-nanog-outgoing@merit.edu
On Wed, Jul 05, 2000, Greene, Dylan wrote:
>
>
> Jeremiah,
>
> Hey there.. What you're describing is basically anycast, (rfc 1546) which is
> useful for single packet, connectionless UDP type things (dns lookups), but
> can make connection oriented / statefull protocols break.
>
> If you are advertising what appears to be two ways to get to the same
> prefix, you're relying on having stable paths through the internet to always
> deliver a packet via the same path the one before it took. If something
> outside of your control breaks / changes, you may end up changing paths and
> could start sending packets towards your 'other' (same destination) site mid
> session.
>
> Another thing to be careful of is inconsistent-as. If you plan to have
> multiple sites advertising the same prefix, they either need to be all part
> of the same asn, or you need to advertise a separate anycast asn padded w/
> unique per-site asns. (Also a good way to withdraw routes is necessary,
> using gated or something..)
>
> I think the anycast rfc mentioned setting aside a block of space for this
> purpose.
If you originate it from the same AS then yes, it works just fine.
I've run it for web servers before, without a complaint, and
a few people here have run it for streaming media and can give you
feedback. I haven't tested it for long-held streaming media connections
so I can't comment.
Adrian
