How to check or debug dhcp request and IP renew logs

[getaway51]

Hi,

May I  knw how to check ALL DHCP debug messages? I wish to find out if DHCP error was cause by DHCP server or clients issue. DHCP client not getting IP address

[luis_cordova]

Hi @getaway51 ,

Check this:

https://learningnetwork.cisco.com/thread/63652

Regards

[Francesco Molino]

Hi

Is your switch/router acting as dhcp server?

There’re different commands to run:
- debug ip packet details filtered with an acl
- debug ip udp
- debug ip dhcp server packet

On what device are you troubleshooting on? You can run a capture (wireshark) to see the whole dhcp process or if not able to do a capture, you can do a span and capture udp packets for ports 67 and 68.

[getaway51]

Router is acting as DHCP relay with ip-helper configuration at int Gi0/5

Can i view those DHCP ack, request, offer,etc traffic? So as verify whether DHCP traffic send and received

[getaway51]

1)Do you mean i issue these 3 cmds?
- debug ip packet 
- debug ip udp
- debug ip dhcp server packet

2) How to do a span and capture udp packets for ports 67 and 68? DHCP is udp port 67 & 68 only? Is it same as bootp?

[Francesco Molino]

At least, as your DHCP isn't local to your device, you can run the 2 commands:
- debug ip packet detail filtered with an acl. I believe if you search for DHCP troubleshooting on Cisco website you'll find a documentation explaining it.
- debug ip udp

For SPAN, the goal is to replicate all traffic from 1 interface to another interface. Like you want to replicate traffic from your host to another port where your laptop will be connected to and running wireshark with commands like monitor session.

[dimigav1977]

What the following debug message means??

*Aug 30 17:26:59.631: DHCP: Try 9 to acquire address for GigabitEthernet0/0.837
*Aug 30 17:26:59.635: DHCP: allocate request
*Aug 30 17:26:59.635: DHCP: new entry. add to queue, interface GigabitEthernet0/0.837
*Aug 30 17:26:59.635: DHCP: SDiscover attempt # 1 for entry:
*Aug 30 17:26:59.635: Temp IP addr: 0.0.0.0 for peer on Interface: GigabitEthernet0/0.837
*Aug 30 17:26:59.635: Temp sub net mask: 0.0.0.0
*Aug 30 17:26:59.635: DHCP Lease server: 0.0.0.0, state: 3 Selecting
*Aug 30 17:26:59.635: DHCP transaction id: A3C
*Aug 30 17:26:59.635: Lease: 0 secs, Renewal: 0 secs, Rebind: 0 secs
*Aug 30 17:26:59.635: Next timer fires after: 00:00:04
*Aug 30 17:26:59.635: Retry count: 1 Client-ID: cisco-a0ec.f97f.9288-Gi0/0.837
*Aug 30 17:26:59.635: Client-ID hex dump: 636973636F2D613065632E663937662E
*Aug 30 17:26:59.635: 393238382D4769302F302E383337
*Aug 30 17:26:59.635: Hostname: Router
*Aug 30 17:26:59.635: DHCP: SDiscover placed class-id option: 636973636F706E70
*Aug 30 17:26:59.635: DHCP: SDiscover: sending 309 byte length DHCP packet
*Aug 30 17:26:59.635: DHCP: SDiscover 309 bytes
*Aug 30 17:26:59.635: B'cast on GigabitEthernet0/0.837 interface from 0.0.0.0

I don't have IP address from DHCP Server and the debug ip udp gives the following

*Aug 30 17:42:44.215: Released port 58034 in Transport Port Agent for IP type 1
*Aug 30 17:42:44.215: Released port 58034 in Transport Port Agent for IP type 1
*Aug 30 17:42:44.215: UDP unique_ipport: using ephemeral max 65535
*Aug 30 17:42:44.215: UDP: Random local port generated 59807, network 1
*Aug 30 17:42:44.215: Reserved port 59807 in Transport Port Agent for UDP IP type 1
*Aug 30 17:42:44.215: UDP: sent src=192.168.2.254(59807), dst=8.8.8.8(53), length=37
*Aug 30 17:42:47.215: UDP: sent src=192.168.2.254(59807), dst=8.8.8.8(53), length=37
*Aug 30 17:42:50.215: UDP: sent src=192.168.2.254(59807), dst=8.8.8.8(53), length=37
*Aug 30 17:42:53.215: UDP: sent src=192.168.2.254(59807), dst=8.8.8.8(53), length=49
*Aug 30 17:42:56.215: UDP: sent src=192.168.2.254(59807), dst=8.8.8.8(53), length=49
*Aug 30 17:42:59.215: UDP: sent src=192.168.2.254(59807), dst=8.8.8.8(53), length=49
*Aug 30 17:43:02.215: Released port 59807 in Transport Port Agent for IP type 1
*Aug 30 17:43:02.215: Released port 59807 in Transport Port Agent for IP type 1
*Aug 30 17:43:02.215: UDP unique_ipport: using ephemeral max 65535