Subject: Anycast address implementations

From: John Wells <[email-masked]>
Date: Wed, 25 Apr 2001 18:12:10 +0200

Hi-
I'd like to know if anyone can shed light on this matter.

RFC 2373 (IPv6 Addressing Architecture) defines IPv6 anycast addresses and
notes that a "packet sent to an anycast address is routed to the 'nearest'
interface having that address, according to the routing protocols' measure
of distance".  Who defines nearest and how is it defined?  Do the anycast
routers communicate with each other and elect a router to perform the
metrics?  I assume these metrics are measured with respect to the source
address?

I'd also be interested in hearing any real world experiences with anycast
addresses, such as inefficiencies, etc., and how anycast addresses are
limited in practice, such as if anycast address participants must be defined
on a router a priori elected to serve as the address coordinator, etc.

Best regards,
John Wells

-- 
John WELLS
ENSIMAG/3A Télécomm/Réseaux - INRIA Rhône-Alpes
Virginia Tech MS/Computer Engineering - Networking and Visualization Lab
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From: "Tony Hain" <[email-masked]>
Date: Wed, 25 Apr 2001 16:05:13 -0700

Anycast is implemented as a host route, and as such the anycast routers
don't communicate anything other than their normal routing updates. The
distance is not measured, and is strictly a matter of normal routing finding
the closest router that has some host behind it willing to answer to the
anycast address. As you might guess any long running connection with one of
these hosts is subject to routing flaps, with the resulting connection reset
when packets appear at a different host than the previous ones did. As such
it is much better suited to transaction applications like DNS than long
lived applications like FTP.

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of John Wells
Sent: Wednesday, April 25, 2001 9:12 AM
To: [email-masked]
Subject: Anycast address implementations

Hi-

Best regards,
John Wells

--
John WELLS
ENSIMAG/3A Tilicomm/Riseaux - INRIA Rhtne-Alpes