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New Member

DHCP offer packets don't get sent to switchport

We have a 3750X switch stack in one building and it is connected to another building using Ten gig portchannel to a 7K.  DHCP traffic has been sniffed and confirmed that the offer packet makes it to the 3750X but it doesn't make it to the switchport where a Cisco IP phone resides.  The IP phone is stuck in Configuring IP because it never receives the offer packet that the 3750 gets from the DHCP server.  Desktops on the same port work fine.  Been on a TAC call for 7 hours.

3 REPLIES
VIP Purple

DHCP offer packets don't get sent to switchport

How is your switch port configuration looks like ? Does this happen to all your cisco phones or particular phones ?

Did you try to put a phone to a simple access port (without voice vlan config) & see whether it get an IP ?

Rasika

DHCP offer packets don't get sent to switchport

Hi Steven,

what configuration you applyed on the access switch interfaces? in this case you should configure the interfaces to support data and voice traffic.

you can apply below command in on of the interfaces;

show int fa 0/2 switchport

show run int fa 0/2

best regards,

New Member

DHCP offer packets don't get sent to switchport

All the ports have the same voice vlan and data vlan.  Two of the phones are 7937's and just have the voice vlan as access valn.  The DHCP offers make it to the 3750X but do not get seen by the phone.  We have DHCP snooping and ARP inspection turned on but for different VLANs, not voice or data vlans.  But we found disabling DHCP snooping and ARP inspection globally fixed the issue.  There must be some kind of bug.  We are using a specific encryption module that has been the bain of our existence since we implemented it.  I think we are looking into just brining in a 5K, to connect this building to the 7K across the street, so we can pull the encryption module on our 3750X switch stack.

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