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Re: Question on IP address used by anycast DNS cache server

  • From: Edward B. Dreger
  • Date: Mon Oct 11 09:35:21 2004

JS> Date: Mon, 11 Oct 2004 17:23:19 +0800 (CST)
JS> From: Joe Shen

JS> 1. As it's descripted in J.Abley's paper, DNS server
JS> in anycast group should be configured with a real IP
JS> on its NIC and one or two service IP on loopback

Service IP addresses also are "real IP" addresses.

JS> interface(s). BIND listen on both real IP and service
JS> IPs. Any DNS answer packet will be encapsulated with
JS> source address as service IP.  To my understanding,

s/encapsulated with/sourced from/

JS> this is OK for root servers because they do not invoke
JS> recursive lookup procedure. But, if the DNS server is
JS> a member of  ISP's DNS Cache server farm, recursive
JS> lookup packets to other DNS server MUST be
JS> encapsulated with real IP address.

s/encapsulated with real/sourced from unicast/

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

Not sure what you're asking, but it's probably OT.  If I
understand you correctly, RFC 1034 or 1035 would be the place you
should start; it sounds like you're asking a protocol question.

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

Standard routing rules apply.  Think of anycast as multihoming
with a disjoint backend.

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