Some Questions on BIND and IPv4 Anycast

Archimedes S. Gaviola agaviola at
Mon Mar 12 11:05:42 UTC 2007

To all of you who answered my questions, thank you very much! At least it is
already clear to my mind that IPv4 anycasting heavily involves with routing
rather than just a sort of configuration parameter on the operating system

Sincerely Yours,

Archimedes S. Gaviola

-----Original Message-----
From: Bill Larson [mailto:wllarso at] 
Sent: Saturday, March 10, 2007 10:33 AM
To: comp-protocols-dns-bind at
Cc: Archimedes S. Gaviola
Subject: Re: Some Questions on BIND and IPv4 Anycast

On Mar 9, 2007, at 7:09 PM, Barry Margolin wrote:

> In article <esrrio$2cl5$1 at>,  "Archimedes S. Gaviola" 
> <agaviola at> wrote:
>> Content-Type: text/plain;
>> 	charset="us-ascii"
>> Content-Transfer-Encoding: 7bit
>> To Whom It May Concerned:
>> Anycast address is commonly used for root nameservers for 
>> geographical failover. How does BIND handles anycast address? How to 
>> determine that certain IPv4 address is an anycast? Does this type of 
>> address being advertised by routers on the Internet? Or just a 
>> configuration parameter on the underlying operating system just like 
>> with IPv6?
> Anycast (in this context) is implemented simply by having multiple 
> servers configured with the same IP, and advertising the route via a 
> routing protocol (or having their upstream router do this for them).
> The routing protocol then arranges for client traffic to be directed 
> to the nearest server that advertises the address.
> As far as any other devices on the network can tell, there's nothing 
> special about anycast -- it looks to the rest of the network as if 
> it's just multiple paths to the same host.  It's kind of the opposite 
> of virtual hosting -- instead of one host with many IPs, it's many 
> hosts with the same IP.  Of course, for management purposes the hosts 
> also have their own, unique IPs.

You might want to look at, a Tech Note from ISC about how ISC is using
anycast for DNS services.  Anycasting is managed completely at the routing
level and not processed by BIND in any special manner.

Barry, your description is excellent.  Thank you.

Bill Larson

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