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DNS and DHCP issues

By james.white2 ·
I have an interesting issue here at my job.
When I ping a workstation on the network, it gives me my ip address.
If I Ping -a my IP address, it gives me a different workstation name. there is an example listed below. Any idea on what can be done to fix this problem?

C>ping dsms2-7331-696

Pinging dsms2-7331-696.northgrum.com [10.45.100.34] with 32 bytes of data:

Reply from 10.45.100.34: bytes=32 time<10ms TTL=127
Reply from 10.45.100.34: bytes=32 time<10ms TTL=127
Reply from 10.45.100.34: bytes=32 time<10ms TTL=127
Reply from 10.45.100.34: bytes=32 time<10ms TTL=127

Ping statistics for 10.45.100.34:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms

C>pign -a 10.45.100.34

Pinging rssms2-flx001.ingalls.com [10.45.100.34] with 32 bytes of data:

Reply from 10.45.100.34: bytes=32 time<10ms TTL=127
Reply from 10.45.100.34: bytes=32 time<10ms TTL=127
Reply from 10.45.100.34: bytes=32 time<10ms TTL=127
Reply from 10.45.100.34: bytes=32 time<10ms TTL=127

Ping statistics for 10.45.100.34:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms

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by 1 Sane Nerd@Work In reply to DNS and DHCP issues

are these valid workstations in your network?
dsms2-7331-696.northgrum.com ?
rssms2-flx001.ingalls.com ?

are u running VPN?
Did you setup firewall in the network to block IP resolve?

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by james.white2 In reply to DNS and DHCP issues

Yes these both systems are valid computers. The original one pinged at least was on the network. because it is responding with a bogus IP address, it is difficult to tell if it is on the network or not. That is why this is such an issue for me.

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by djbrown62 In reply to DNS and DHCP issues

Assuming that you have done something to change the default name resolution order, it looks like you have an invalid entry in your reverse lookup table on the DNS server. Check there for the record that associates "rssms2-flx001.ingalls.com" to "10.45.100.34"

Delete or correct that entry.

name resolution: http://www.altusnet.com/lti/154web/name.htm

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by smight In reply to DNS and DHCP issues

Yeah this is certainly a DNS issue. Here is what happens:

Your first Ping to the NAME dsms2-7331-696 uses DNS to resolve that hostname to an IP address. The machine you are using is set to append its parent DNS suffix to the hostname so the Windows DNS devolver eventually tries to do a dns lookup on the NAME dsms2-7331-696.northgrum.com. In your zone file for the domain northgrum.com there is an A record for the hostname dsms2-7331-696 which says that it is at IP 10.45.100.34. This may or may not be true. In fact, DNS basically tells the Ping utility to try pinging that IP address, but as long as you have ANY device at that IP address that has ICMP (ping) turned on you will get a reply. So a good troubleshooting step is to go to dsms2-7331-696 and find out what IP address it is actually on.

Secondly, when you do a PING -a to the IP 10.45.100.34, the Ping utility again queries DNS to do a reverse lookup on the IP 10.45.100.34. In your reverse lookup zone file on your DNS servers, there is a PTR record which says that the IP 10.45.100.34 resolves to the NAME rssms2-flx001.ingalls.com. But then the Ping utility pings the IP 10.45.100.34 anyway. Ping never actually pings a NAME. When you do a ping -a you are just asking ping to do a reverse lookup for you, but it still pings the IP address. Again, you get a successful reply from the IP 10.45.100.34. The successful ping reply doesn't tell us anything since we already know from above that there is a device on that IP that replies. The point is that you still don't know which machine is actually on that IP. So you could also go to the machine rssms2-flx001.ingalls.com and see what IP it is using.

<answer continued in next post>

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by smight In reply to

<answer continued from previous post>

Once you fingure out which machine is actually using the IP 10.45.10.34, then go to your DNS server and update either the forward zone A record or the reverse zone PTR record, depending on which one is incorrect.

You can also use the nslookup utility to do forward and reverse lookups into your DNS zone regardless of whether the IP pings or not. This will help you resolve the DNS inconsistency.

Hope this helps,
Chris Britt

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by james.white2 In reply to

Poster rated this answer.

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by james.white2 In reply to DNS and DHCP issues

Is there a DNS flush that can be done to resolve them all at once? This is not an isolated issue with just a 1 or 2 pcs. We are talking probably 50 or more that I have seen.

FYI: I hope no one thinks i'm a total idiot because I don't know the answers to these questions. I am a Domain Admin but my skills in networking with DNS is a little lacking. This is not my job to fix this, i'm just tired of having troubles because of this problem. Any help is greatly appretiated.

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by smight In reply to DNS and DHCP issues

To answer your question about DNS flush, there is a flushdns option but it doesn't do what you want it to. You have some erroes in your DNS zone file itself. When a WinXP machine (for example) queries a name for DNS resolution it will cache that answer in its internal DNS cache until the TTL (time to live) value expires and it has to resolve that name again. When you use the command line switch ipconfig /flushdns it will tell Windows XP to manually clear its entire DNS cache. This will force it to do new queries against the DNS zone file to look up name.

However, you will still have not fixed your zone file and so as soon as you do a flushdns it will simple requery the wrong information again. To fix your issue you need to:

1) go to both machines and find out which one had which ip address.
2) Armed with this new informaiton, go to your DNS zone files on your DNS servers and fix those entires.

If you are using all domain mahcines connected to active driectory, and you set your zone file for secure updates, you can tell the machines to automatically update their DNS registrations. Furthermore, you can go to each machine manually and type ipconfig /registerdns to force a manual update of the information in DNS.

<Answer continued>

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by smight In reply to

<Answer continued>

You haven't said whether you are running Unix DNS or BIND or what. So I don't know from your post whether you have these AD options available to you or not. I am just answering your question about why you are seeing conflicting information when you do your ping queries.

If you use AD, you can set it up so that the DNS entires will be fairly automated within DHCP and everything. But until you get it setup right, you will have to go to each machine and double check everything.

Hope this helps,
Chris

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by james.white2 In reply to

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