In some cases with DHCP snooping enabled, the switch can cause a DHCP request to be blocked.
This is appears to be a corner case but it has happened to me with two different pieces of hardware in two different scenarios.
First, I have a printer on a VLAN where other computers can get an IP address fine but when DHCP snooping is enabled, the printer is unable to obtain an IP.
Second, I created a separate VLAN for an isolated network and enabled DHCP snooping on that VLAN. A modem was hooked up to one port and added as a trusted interface. A computer was hooked up to another port and with DHCP snooping enabled, the computer was unable to obtain an IP address.
In both cases, the DHCP snooping binding table shows an IP of 0.0.0.0 for the port with a very low renew time (~100sec). Also, as soon as I disabled DHCP snooping for either of the above VLANs, the devices are able to obtain IP address. It appears that the DHCP OFFER is never making its way back to the device with DHCP snooping enabled.
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