DNS resolution issues

[BBA]

I usually don't post questions like this but we are all stumped.

The symptom is one of our client servers (HP DL380 G6 for this particular one) has developed a randomly issue where it loses name resolution, causing the server to fail to communicate with the domain controllers and any other network resources you try to ping. Our environment is running in native 2003 functional level with about 28 thousand servers, we have multiple DNS servers that use BigIP VIPs for round robin, etc...

DNS settings are on the particular client server are verified correct, all tcp settings appear good, teaming set to failover only, etc... When it happens, nslookup queries fail, even when you specify the DNS server. We can get around the AD issue by adding the DCs to the hosts file but that only addresses the AD communications, other communications requiring name resolution still fails (we can't add all target systems in the hosts file, as the servers application has to open connections to thousands of agent PC's that use DHCP).


We have done dnsclient restarts, winsock and tcp/ip resets, changed network drivers, updated firmware, etc. So far, the only workaround we have is rebooting the particular client server, then everything works fine for a few weeks to a month but the issue returns eventually.


Anyone been able to find a cause for such a weird issue? So far we have only had about three servers over the last few years that developed this issue.

 

[BBA]

This was quick...finally figured it out. The application was exhausting the available ports. Recylcing the application released the ports and name resolution works again, netstat verified ports that were in use are now available...etc.

For some reference on DNS and ports:

Dynamic Port Range is reserved by the Operating System. This range is assigned by the Internet Assigned Numbered Authority (IANA). The applications can't hard-code this port range for network communication. Microsoft developers have increased the default Dynamic Port range in Windows Vista and Windows Server 2008. The range is:

49152 through 65535
For Windows Vista and Windows Server 2008
1024 through 5000
For Windows 2003 and earlier

To show the Dynamic Port Range:

Netsh int, ipv4 show dynamicport udp
Netsh int, ipv4 show dynamicport tcp
Netsh int, ipv6 show dynamicport udp
Netsh int, ipv6 show dynamicport tcp

To set the Dynamic Port Range:

Netsh int, ipv4 set dynamicport tcp start=xxxxx num=xxxxx
Netsh int, ipv4 set dynamicport udp start=xxxxx num=xxxxx
Netsh int, ipv6 set dynamicport tcp start=xxxxx num=xxxxx
Netsh int, ipv6 set dynamicport udp start=xxxxx num=xxxxx