Anycast DNS - LB/LTM

[ju wusuo]

so the script would run on the LTM, it will periodically check each physical DNS node, if one cannot resolve then takes it out of the pool; it will also check the VIP, if the VIP cannot resolve, pool is empty or LTM issue, stop the advertising?


________________________________
 From: David Klein <root at nachtmaus.us>
To: ju wusuo <juwusuo at yahoo.com> 
Cc: "bind-users at lists.isc.org" <bind-users at lists.isc.org> 
Sent: Wednesday, March 7, 2012 11:18 PM
Subject: Re: Anycast DNS
 


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). 



HTH,

 -DTK



On Wed, Mar 7, 2012 at 2:34 PM, ju wusuo <juwusuo at yahoo.com> 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servers behind LBs, 1) would the LTMs be able to announce the routes dynamically for the DNS servers, and a VIP can be withdrawn when the site is gone? 2) would the LTMs be able to detect a DNS service failure and stop sending over DNS queries, i.e., in the case a named is still up but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)
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