Sunday, July 17, 2016

switch - DHCP snooping prevents client server from receiving IP

The issue that I am experiencing is that DHCP requests can't be delivered from DHCP server on sw1 to DHCP client server on sw2 when DHCP snooping is enabled. Client servers on the same switch as DHCP server are able to receive DHCP with no problem. Both switches are connected to a router through which traffic between them is transported. I have seen solutions for Cisco switches, but I am using dell switches and I can not find a solution to this. Disabling DHCP snooping on either of the switches fixes the problem oddly. I've also enabled snooping trust on DHCP server and client ports as well as uplink from sw1 to sw2. I am working with dell S4810 switches. Any suggestions?



UPDATE:



To eliminate the possibility of router issue I did the same thing simply by connecting 2 switches of the same model and of the same configuration with each other and trusting all ports and uplinks for dhcp snooping. My client server is still unable to receive DHCP server reply packet. I tracked packet pathway between switches and noticed that client server is able to send DHCP request packet to the DHCP server which the server receives, however when the DHCP server tries to send a reply, the packet reaches the switch on which the client server resides but it never reaches the client server itself. It seems like the client switch drops the reply packet. With dhcp snooping disabled everything works in order.

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