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Strange issue after changing out backbone switch

I have a Cisco 3005 Concentrator with a public and private IP addres. Private IP address is 172.22.0.3 . Backbone switch Cisco 4506 is 172.22.0.5 255.255.0.0

Client connect to VPN via IPSEC using Radius-Auth with expry to IAS server inside the network. Once connectted they get an IP from a static pool (172.31.1.x 255.255.255.0).

After that they typically launch Outlook and get email. Problem is that many of them cannot get to the Exchange server until they run an ipconfig /flushdns and ipconfig /registerdns after connection. DNS Server for the VPN concentrator is 172.22.0.14 and 172.22.8.1 which are on the LAN and are my DC's for AD.

You can ping by IP just fine and tracert to and from the clients and from my network to them. But until you do the ipconfig commands from the client at the command prompt - DNS does not seem to want to work. Any ideas??

Additional info is that I have a PIX 515E as well on the network (172.22.0.1) The VPN and PIX's public IP's are different.

The group that the users are associated with has static DNS entries in there for them with the corresponding IP's above.

I have tested with IPSEC , IPSEC/UDP , and IPSEC/TCP from several different endpoints.

Any ideas or suggestions?? Tks.

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Re: Strange issue after changing out backbone switch

Try to configure static ARP entry for DNS server. Do this using the command arp -s command in the client dos window.

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