Some Questions on BIND and IPv4 Anycast

Barry Margolin barmar at
Sat Mar 10 02:09:37 UTC 2007

In article <esrrio$2cl5$1 at>,
 "Archimedes S. Gaviola" <agaviola at> wrote:

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> 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.

Barry Margolin, barmar at
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

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