20-3
Cisco Nexus 1000V Troubleshooting Guide, Release 5.2(1)SV3(1.1)
OL-31593-01
Chapter 20 DHCP, DAI, and IPSG
Problems with DHCP Snooping
Problems with DHCP Snooping
The following are symptoms, possible causes, and solutions for problems with DHCP snooping.
Symptom Possible Causes Solution
With snooping
configured, the
DHCP client is not
able to obtain an IP
address from the
server.
The IP address was not added to the binding
database.
A faulty connection is between the DHCP
server and client.
1. Verify the connection between the DHCP
server(s) and the host connected to the client.
vmkping
2. If the connection between the DHCP server and
the host is broken, do the following:
–
Check the configuration in the upstream
switch, for example, verifying that the
VLAN is allowed.
–
Make sure that the server is up and running.
The interface of the DHCP server(s) connected
to the DVS as a VM is not trusted.
1. On the Virtual Supervisor Module (VSM), verify
that the interface is trusted.
show ip dhcp snooping
2. On the VSM, verify that the vEthernet interface
attached to the server is trusted.
module vem mod# execute vemcmd show
dhcps interfaces
DHCP requests from the VM are not reaching
the server for acknowledgement.
On the DHCP server, log in and use a packet capture
utility to verify requests and acknowledgements in
packets.
DHCP requests and acknowledgements are not
reaching the Cisco Nexus 1000V.
• From the client vEthernet interface, SPAN the
packets to verify they are reaching the client.
• On the host connected to the client, enable VEM
packet capture to verify incoming requests and
acknowledgements in packets.
The Cisco Nexus 1000V is dropping packets. On the VSM, verify DHCP statistics.
show ip dhcp snooping statistics
module vem mod# execute vemcmd show
dhcps stats
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