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Subject
- Posted on
problem with dhcp on 2960 switches
- 04-02-2008
- SIMON WATSON
April 2, 2008, 3:29 pm

Hi All
I need your help
We have a dhcp server that was connected to Cisco 2960 which in turn was
connected to alcatel switches, all worked fine. we changed the alcatel
switches to cisco 2960's. We now have a problem that only devices directly
connected to the original 2960(where the dhcp server is connected to) is
receiving IP addresses we have now 4 other 2960's onthe network but we
cannot get a IP address when we connect to any of the ports. doing a sniffer
trace on the working switch the DHCP four way handshake is performed,
discovery>>offer>>request>>>ack
On one of the other switches only the discovery is seen but no offer
response from the dhcp server is seen therefore no ip address is received.
the new switches only have portfast set and an ip address for vlan1 so I
cannot understand what is stopping the dhcp traffic
Any Ideas
Thanks
Simon
I need your help
We have a dhcp server that was connected to Cisco 2960 which in turn was
connected to alcatel switches, all worked fine. we changed the alcatel
switches to cisco 2960's. We now have a problem that only devices directly
connected to the original 2960(where the dhcp server is connected to) is
receiving IP addresses we have now 4 other 2960's onthe network but we
cannot get a IP address when we connect to any of the ports. doing a sniffer
trace on the working switch the DHCP four way handshake is performed,
discovery>>offer>>request>>>ack
On one of the other switches only the discovery is seen but no offer
response from the dhcp server is seen therefore no ip address is received.
the new switches only have portfast set and an ip address for vlan1 so I
cannot understand what is stopping the dhcp traffic
Any Ideas
Thanks
Simon

Re: problem with dhcp on 2960 switches
Check for "DHCP Snooping" on both switches. Basically, just do a "show run |
inc dhcp". If you have DHCP Snooping implemented, configure uplink as a
"trusted port".
Good luck,
Mike
CCNP, CCDP, CCSP, Cisco Voice, MCSE W2K, MCSE+I, Security+, etc.
CCIE R&S (in progress), CCIE Voice (in progress)
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