Multihomed Server hostname resolution problem.

Hi,

tldr version:

On multihomed server with 2 NICs when trying to resolve it's own hostname to IP I always get IP of NIC with higher interface index which is not a domain NIC and can't find a setting that would allow me to control this. This is a problem if an app uses server hostname to get it's IP address.

Full version.

I've got Windows Servers 2012 R2 (and 2012) in my infrastructure. Some are VM and others use windows nic teaming. All have 2 NICs (or virtual NICs) in two different networks - Domain network and Management network.

 

Let's say my server hostname is dpm01 and domain is contoso.com. Domain network address is 172.23.1.1/16 and Management address is 172.29.0.2/24.

So dpm1.contoso.com is 172.23.1.1

 

When I'm trying to resolve the name "dpm1" or "dpm01.contoso.com" to IP address I get 172.29.0.2. I'm doing it by using ping and I know that I have an application that is also doing such a resolution and getting the same result as I am with ping.

Question is what do I do to get 172.23.1.1 for "dpm01.contoso.com" when pinging from it ???

 

What I know or tried:

1. This is NOT a DNS problem. nslookup returns proper result from dns server. DNS registration is disabled on all NICs and on DNS server.

2. Tried adding dpm1 and dpm01.contoso.com in hosts file - nothing.

3. 172.29.0.2/24 does not have a default gateway, has NetBIOS disabled and for testing I disabled in NIC properties everything besides IPv4 and "QoS packet scheduler". There are no DNS servers configured for this NIC. LMHOSTS lookup is also disabled.

4. I've changed interface binding order so that Domain network is on top, confirmed in registry and rebooted. No help.

5. Every other server when pinging dpm01 uses DNS so they get proper address of 172.23.1.1 so as in 1 - this is NOT a DNS problem.

6. Domain NIC has interface index 12, Management NIC has index 13, if I switch them then I get proper results, but I'm looking for a solution that does not require me to reconfigure NICs on all my servers based on random order they get (in VM). Seriously I should not have to address NIC based on its interface index...

I would appreciate any help with this issue.

 

February 20th, 2015 8:14pm

Hi,

According to your description, my understanding is that multi-homed server with 2 NICs, always gets IP of NIC with higher interface index when trying to resolve its own hostname to IP address. And you want to resolve its name to the IP address which connects to domain network.

In general, when you ping another hostname on a server, it will first send DNS packets to ask the DNS server to resolve the hostname, then the server broadcasts ARP packets and try to get answers from the destination after getting the corresponding IP address of the hostname. If ping the server itself, packets will not send out of the NICs and as you said that it has nothing to do with DNS Server.

Change interface binding order will not affect NIC index.

I have not find related official KBs/articles detailed described this, but based on my tests, manually change the index number of NICs might be the only way to resolve this problem.

Best Regards,
Eve Wang

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February 22nd, 2015 10:13pm

Hello,

please see the following article about multihoming, here especially DCs.

http://blogs.msmvps.com/acefekay/2009/08/17/multihomed-dcs-with-dns-rras-and-or-pppoe-adapters/

If you really have the need for it please assure to follow the above mentioned article.

February 23rd, 2015 4:21am

Hi,

your understanding is correct. Thank you for looking around, it's good to know that I'm not the only one having trouble finding any documentation about this :)

The issue I have with this solution is that if I add new network adapter it gets bigger index, and the problem returns :(

Are you aware of a method to change NIC index ? Or do I have to switch addresses between NICs ?

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February 23rd, 2015 4:35am

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