See the accepted solution in http:Q_24009750.html to make a DHCP filter in wireshark. Much easier than sorting through the megabytes of data it can capture in just a few minutes on the average network.
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Wireshark Capture DHCP Packets
I am troubleshooting dhcp failure between my cisco wireless phones and my call manager server. Cisco tech support has asked me to get a sniffer capture at my access point and dhcp server to verify packets are being passed between. He pointed me to Wireshark to use for the capture.
Because the Cisco techs usually speak two or three levels above me and I can't get them to come down, i'm hoping someone here can point me in the right direction to get the right capture.
i've installed wireshark to my pc but when i run a capture (wide open) i don't see any traffic bound for any of my voice network. (i have statically assigned the ip of the pc to the voice network).
Tips? Guidance?
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Answers
I read the closed question and created the filter. (I wasn't sure if I was supposed to follow the first comment with all the settings and options). with the filter I get very few packets and none of them are from the voice network.
My data network is in the 172.16.200.0/24 subnet and voice is 172.17.0.0/16.
DHCP for the voice net is provided by my call manager server. Got the laptop to get an IP from that DHCP and I am now getting packets on the voice net.
Is this the correct capture filter string (minus the quotes): "udp port 68 and port 67"
Just want to be sure I'm getting both sides of the conversation. I do see "DHCP Discover" and "DHCP Offer" packets from the server and from the phone. Not sure what else I'm looking to see to verify everything is doing what it should. Phone still gets DHCP timeout.
Informed Cisco TAC of results. This was response (after a week):
>Please send me the unfiltered capture at the WLC port and at the DHCP server concurrently so we can >see if all the packets make from one end to the other. Also capture the output of the following debugs >at the same time.
>debug client <xxxxxxxxxxxxx> (Clients mac address)
>debug dhcp message enable
>debug aaa all enable
How do I specify where I want the capture? Where am I issuing these debug commands (my AP doesn't recognize some of this syntax)?
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by: bec0sPosted on 2009-01-06 at 09:11:05ID: 23306561
Hello,
Wireshark is a great trouble shooting tool. The first step to begin is to sniff packets from the two endpoints,i.e. the DHCP server and the wireless network.
DHCP is broadcast traffic so you could snif it from any port in the voice vlan. Maybe you pc is not connected to the voice vlan. In any case please provide more topology info on equipment used so we can direct you in the proper way to peform snifs and troubleshoot the problem.
Another usefull cisco feature is that you can make a "monitor session" in a switch or router to get all traffic flowing replayed to a certain port and then you can use wireshark in that port to see the packets.
Thanks.