round robin dns for outside access to exchange OWA possible somehow?
We ran into this rare case, where one of our two internet service providers connection went down, rolling us over to the secondary. Primary is wan1.domainname.com and secondary is wan2.domainname.com These are also MX records out in the wild. The problem with this rollover, is that it occurred on a weekend, so the email i sent to everyone didnt get received by anyone until monday morning when they were in the building. We have a lot of people that work offsite and connect either via VPN (and then to the server) or via HTTP over RCP via wan1 or via OWA via https://wan1 etc So those offsite people didnt know to change their settings on their iphone to wan2 or in their browser etc. Is there some way to design this architecture with exchange/dns, so that a sortof round robin search can occur via one dns name? Granted we are small and this is rare, but if there is a way i'd like to configure it. Surely there is, for larger companies to get by... or maybe they just have multiple pipes on one dns name somehow? Thanks
July 2nd, 2009 5:37pm

Round-robin DNS may not work and may cause more grief than its worth... You will run into session issues due to the connections not being persistent on the same OWA server. I would suggest a load-balancer of some sort which could pull the non-responding node out of service. You may be able to get something going with NLB, ISA or a hardware solution.
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July 2nd, 2009 5:53pm

Round-robin DNS may not work and may cause more grief than its worth... You will run into session issues due to the connections not being persistent on the same OWA server. I would suggest a load-balancer of some sort which could pull the non-responding node out of service. You may be able to get something going with NLB, ISA or a hardware solution. We sortof have the NLB right now with our router, i think.. it has failover ability (a sonicwall gateway with dual wan ports).. so if the primary dies, it rolls to the secondary, but this doesnt solve the issue of the fact that dns wise, the external ip is bound to the port that dies. Perhaps there is another type of NLB setup that would fix the dns balancing issue? I dont see how it could be overcome though. Not sure if i described this quite right either :)
July 2nd, 2009 6:10pm

DNS round robin isnt the correct approach. Round robin will give users different IPs for their host name every other time (not an exact science). This means that 50% of your users will be sent to pipe 1 and 50% sent to pipe 2 regardless of an outtage. You need something that can sense when pipe1 is down. I used a cisco global dns site selector on one project. this device senses when a link is down and can update the ip address of owa.yourdomain.com with the ip of the new pipe.cons:-expensive-even after the dns address is updated it could still take time for users to get the new IP as caching and other natural dns delays. you can reduce the impact of this by making the ttl on the record like 5 minutes or something, but it still wont be instant swtich over because of other factors. Mike Crowley A+, Network+, Security+, MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator
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July 2nd, 2009 6:17pm

BTW... the poor mans way of doing this could be just make the TTL as low as possible and update the record manually during an outage. if you host your own DNS it also seems feesable you could script this somehow. Mike Crowley A+, Network+, Security+, MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator
July 2nd, 2009 6:19pm

here is what im talking about: http://www.cdw.com/shop/products/default.aspx?EDC=1027163 Mike Crowley A+, Network+, Security+, MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator
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July 2nd, 2009 6:21pm

Interesting product...very cool. Thanks.
July 2nd, 2009 8:35pm

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