I have a router that I have added ip helper addresses to for dhcp use. It is up and working but I ran into a snag in the process that I have yet to figure out. Originally I had planned on adding the helper addresses to the existing 172.16.21.1/24 range (gig 0/1.2) & segmenting the dhcp scope to retain some static IPs that were still in the range. For a reason I have yet to identify with the helper addresses applied to gig 0/1.2 the router would not pass dhcp requests upstream through the tunnel. I then added the range 172.16.27.1/24 (gig 0/1.4) to the router, added permits to the PIX as needed & configured IP helper addresses pointing to our dhcp servers & it worked.
The tunnel terminates into a cisco PIX firewall.
Any ideas as to why dhcp requests would not be passed on gig 0/1.2?
The config below is from the live running config, it doesn't show it now, but I did have the helper addresses on gig 0/1.2 prior to creation of gig 0/1.4.
Are there any common causes that would prevent ip helper addresses from working?
Looks weird indeed. What you could try is to reapply the helper-address on Gi0/1.2, generate a DHCP request on both VLANs and trace the packets generated by the router. A debug ip packets detailed associated to an ACL could help.
You can also try to catch the packets behind the FW, closer to the DHCP server.
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