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Controlling DNS Record for Multi-homed Client (wireless/wired)

Posted on 2005-04-21
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Last Modified: 2013-12-19
My network has 750 Windows XP laptops all with both an Ethernet and a wireless network adapter. On the server side we use standard Windows 2000 AD with Windows DHCP and DNS.

The problem is that each host gets two A records. For example, the wireless NIC for "host1.domain.com" might get assigned an IP which then results in an A record matching "host1.domain.com" to 10.100.10.50 while the Ethernet NIC gets and IP matching "host1.domain.com" to 10.100.10.60 for the Ethernet card.

This is problematic for two reasons. First, I have no control over which NIC I connect to when using the hostname "host1.domain.com". Of course, I could lookup the DHCP lease and determine which adapter is which by the hardware address, but this hardly convenient. Secondly, I have a need to be able to do a reverse lookup on an IP and know whether the IP was from a wireless or wired NIC. Currently a reverse lookup for either 10.100.10.50 or .60 would both yield "host1.domain.com".

What I'd like is to have the Ethernet NIC IP matched to an A record for "host1.domain.com" with the Wireless NIC IP matched to an A record for "host1.wifi.domain.com" or some solution similar to this which alters the hostname in the DNS record. Any suggestions for how to make this happen short of managing 1500 DHCP reservations which isn't an option?

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Question by:glebn
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by:ccomley
ID: 13838470
Eek. I can see it would be a problem.

Can you not get the users to disable the WiFi when they're using Wired connections?

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by:glebn
ID: 13851570
I'm not actually worried about both being active simultaneously, it's DNS not being able to distinguish between the two that is the problem.

Your comment does bring up a good point. Any solution that requires 1,000 users to do anything isn't a solution ;)
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Michael Pfister earned 1500 total points
ID: 13857782
If you can live with the fixed LANs registration, clear the "register this connection's Ip address in DNS" for the wireless lan adapters TCP/IP DNS config. Maybe someone can do a script to do this on 750 machines.

Or you could assing the wireless lan a DHCP range of its own so you can tell the difference by the clients ip address.
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Author Comment

by:glebn
ID: 13858378
I can't believe I overlooked a simple checkbox which solved my problem.

From the start, I thought that setting a DNS suffix for this connection would solve the problem registering the connection using the connection suffix. However, again I can't believe I missed the little check box below this which says "Use this connections DNS suffix in DNS registration".

Placed a checkbox in this setting and problem solved.

Thanks for all who replied
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by:glebn
ID: 13860580
I'll give mpfister the points because s/he was closest to the answer.

However, the advice to solve the problem by "assigning the wireless lan a DHCP range of its own so you can tell the difference by the clients ip address" is not complete. How would the DHCP server know which type of adapter was requesting the IP and thereby assign an IP from the correct range given all hosts are on the same physical and logical network? The only way I could see to do this would be to put all my Wireless AP's in a VLAN so that all request from wireless clients originated from the wireless VLAN which could then be set to assign IPs from one range with hosts from everywhere else getting IPs from the other range. Of course isolating the wireless network like this isn't a bad idea for many reasons not the least of which is security, but unfortunately it isn't an option given our current infrastructure. Nontheless, thanks for offering the advice :)
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Expert Comment

by:Michael Pfister
ID: 13864829
thanks for the points, glebn.

Of course if putting your wireless lan in a separate IP range is not an option, you are stuck. Still you should think about it, especially for security. I'd rather put an extr firewall between lan and wireless lan...

There might be a way to send these clients to different DNS zones. If you look at the IP config you see there are fields for a connection specific DNS FQDN. I've never played with it but it sounds like you could put wireless.domain.com to the wireless adapter and cable.domain.com to the regular lan adapter.

Michael (still he ...;-))


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