Anycast DNS

David Klein root at
Thu Mar 8 04:18:45 UTC 2012

You would need to create a custom script to use as your monitor, which does
a lookup of an address that you know will always be in your domain. If that
fails, force-down/inactive the node, and tie this script as a monitor to
the pool holding the DNS server nodes.

You can advertise the /32 containing the VIPA to the up-stream router via
either OSPF or IBGP, and if the pool goes empty, stop advertising the route
(the only option is stop advertising, not actively withdraw the route,
since that could cause a massive reconvergence cycle in your
enterprise-wide RIB, if done wrong, just because of a flapping interface).



On Wed, Mar 7, 2012 at 2:34 PM, ju wusuo <juwusuo at> wrote:

> thanks everyone for all responses with the great inputs ..
> now if I want to put the DNS servers behind LBs, 1) would the LTMs be able
> to announce the routes dynamically for the DNS servers, and a VIP can be
> withdrawn when the site is gone? 2) would the LTMs be able to detect a DNS
> service failure and stop sending over DNS queries, i.e., in the case a
> named is still up but just not able to resolve names (assuming LTM can
> detect a named is down)?
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david t. klein

Cisco Certified Network Associate (CSCO11281885)
Linux Professional Institute Certification (LPI000165615)
Redhat Certified Engineer (805009745938860)

Quis custodiet ipsos custodes?
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