Uhm it seems to me people are trying to make this whole AS112-thing sound more complex than it really is... We use the BGP anycast-method in our backbone, and have been doing so for a long time. Basically, we have multiple caching DNS-servers scattered around our network, but all of them use the same IP-adress (well, actually two - since customers expect to configure a primary and a secondary DNS on their computers). The DNS resolvers all run zebra and identify themselves as a private AS, announcing two single host routes (the two DNS resolver-IP's) to the border-router they are connected to. Our customers' DNS queries will be routed to the nearest available server, by the same mechanisms as any other hot-potato routing setup (i.e. MEDs). This works beautifully since we are only dealing with DNS UDP packets. (The servers do also have a unique IP adress for management traffic etc, and these are normally routed in the IGP - but they do not respond to DNS traffic on this IP). That way, we have both "load-balancing" (customer queries are spread out to the servers who are closest to the customer) and redundancy - if one resolver fails, BGP will use the next available route to get to this prefix. The only difference with the AS112 setup is the fact that you are doing it across several AS'es instead of just inside a single one, but the principle is the same - and just as simple. This is an extremely simple anycast setup for DNS servers, and potentially other simple UDP-based services, we have been using it for a couple of years, and it works beautifully. No new protocols, no complex setups, just normal BGP operation. I even think someone wrote a very good paper on setting up DNS resolvers this way once, though I can't remember where I saw it. --Lars Erik On Friday 05 July 2002 15:05, Marshall Eubanks wrote:
On Fri, 5 Jul 2002 13:36:49 +0100 (BST)
"Stephen J. Wilcox" <steve@opaltelecom.co.uk> wrote:
Doesnt announcing the same routing prefix into BGP from multiple locations do the same thing without needing a new range or enhancement in IGMP etc ?
We do this in IGP currently..
Steve
As I see it, the problems with doing this in BGP are
- it's static - no failover. If AS 701 and AS 1239 are both announcing a route to foo, and your preferred route is "through" AS701, and the AS701 foo goes down, then you do not automatically switch over to the AS1239 foo, even if you could reach it.
- there is no way to have multiple anycast addresses within an AS
- load balancing is tough
These may all be solved, though... it's hard to tell without a protocol description.
Regards Marshall Eubanks
On Fri, 5 Jul 2002, Barry Raveendran Greene wrote:
FYI - for those scratching their heads on "anycast" .....
I just pushed out a paper on anycast by Chris Metz. Good foundation material.
http://www.cisco.com/public/cons/isp/essentials/ip-anycast-cmetz-03.pdf
-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu]On Behalf Of Bill Woodcock Sent: Friday, July 05, 2002 4:56 AM To: Marshall Eubanks Cc: nanog@merit.edu Subject: Re: Internet vulnerabilities
> But the only IPv4 anycast > that I know of does use MSDP :
http://www.ietf.org/internet-drafts/draft-ietf-mboned-anycast-rp-08.t xt
> Is there a different proposal ? What's the RFC / I-D name ?
You seem to be confusing anycast with something complicated. It's not a protocol, it's a method of assigning and routing addresses.
-Bill