Question on IP address used by anycast DNS cache server

Joe Shen joe_hznm at
Mon Oct 11 09:23:19 UTC 2004


I'm , but I met some questions when reading those
paper from ISC on F-root anycasting.

1. As it's descripted in J.Abley's paper, DNS server
in anycast group should be configured with a real IP
on its NIC and one or two service IP on loopback
interface(s). BIND listen on both real IP and service
IPs. Any DNS answer packet will be encapsulated with
source address as service IP.  To my understanding,
this is OK for root servers because they do not invoke
recursive lookup procedure. But, if the DNS server is
a member of  ISP's DNS Cache server farm, recursive
lookup packets to other DNS server MUST be
encapsulated with real IP address. 

Is BIND or other DNS software capable of
distinguishing between DNS answer back packet and
recursive lookup packets? or could this be done
automatically by operating system like Solaris, Linux,

2. If we want to design a hierachical DNS service
system which distribute across multiple private AS of
an ISP, is there any problem to select service IP
randomly from unused address pool? 

thanks in advance.


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