DHCP issue on Cisco 3750 Switch

[Pranav Gade]

Hi,

I configured an DHCP server on cisco 3750 switch . Wher in w3750 gets connected to plain l2 switch 2960 on floor  and machine gets connected to 2960 port.

w3750 -----trunk------w2960---- Machine 

DCHP Configuration on core switch

ip dhcp pool IT

origin file flash1:dhcp-it.txt

domain-name domain.com

dns-server 172.16.5.2 172.16.5.26

default-router 172.16.0.1

Below is the description of problem:

-> The Cisco 3750 switch is the DHCP server. VLAN 108 is named as internet vlan.

-> Ports in Cisco 2960 switch has been configured with "switchport access vlan 108".

-> There were no problems at all and everything had been working smoothly.

-> 3 days back, users started complaining that they couldn't access the internet. Up on troubleshooting the issue, I found out that there was an issue with the DHCP server as the computer couldn't get any IP address at all. After setting static IP address, the internet started working again.

If I bind IP to MAc address reservation on core 3750 switch for some time of moment it works but after that machine gets unreachable .

I restarted the 3750 switch and also all the 2960 switches over the weekend, however, the issue still hasn't been resolved yet. I did issue the command "clear ip dhcp conflict *", clear ip dhcp binding * but no joy at all.

I am stuck here and running out of ideas now. Can someone please help me out with this issue?

Please let me know if you want to have a look into the config/show command outputs.

Regards

Pranav

[anisaini]

Hi Pranav,

Please share the following

config

debug ip dhcp server packet

debug ip dhcp server event

check if the server is sending/replying the client broadcast/packets

then try to connect the pc directly to check if layer2 switch is causing the issue

you may also take wireshark captures on the PC to check what is being send and received in terms of DHCP.

hope this helps

[paul driver]

Hello
do you have dhcp snoopojg enabled?

is make sure its enabled.on all swithes that habe hosts attached and all swich intecomnects are trusted

have you ran out of ip addresses?
how.long is your dhcp lease time?

have you tried removing the origin file amd manually specifying a ip range?

res
paul

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