I am searching for any links, experiences or materials describing the problem with DHCP rebindings problems of clients. The DHCP broadcast works fine, only unicast DHCP request is not working as it should.
broadcasts work because the CMTS takes the broadcast message and unicasts to the ip specified in cable helper-address
when the DHCP server responds however it unicasts the response back to the CPE to the CPE gateway (typically on the IP-bundle), this is almost certainly a different path than the cable helper address ip. So while i suspect you can ping the cable helper address just fine, I suspect you cannot ping from the DHCP server to the CPE gateway address.
You should do a packet capture at the dhcp server, find out what interface it is using to send the traffic towards the CPE GW and then test with ping/tracroute to find your issue.
From there is should be pretty easy to find the issue.
if you need help post the PCAP at the DHCP server and the traceroute from there to the CMTS and we should be able to help you.
Hi,
the network setup is this: switch - docsis - LAN. Clients in the LAN can get IP address when docsis is reset but when the clients try to rebind they cannot. The DHCP is behind the switch and the helper address is on the switch where is default gateway for LAN clients.
almost certainly a routing/acl problem.
broadcasts work because the CMTS takes the broadcast message and unicasts to the ip specified in cable helper-address
when the DHCP server responds however it unicasts the response back to the CPE to the CPE gateway (typically on the IP-bundle), this is almost certainly a different path than the cable helper address ip. So while i suspect you can ping the cable helper address just fine, I suspect you cannot ping from the DHCP server to the CPE gateway address.
You should do a packet capture at the dhcp server, find out what interface it is using to send the traffic towards the CPE GW and then test with ping/tracroute to find your issue.
From there is should be pretty easy to find the issue.
if you need help post the PCAP at the DHCP server and the traceroute from there to the CMTS and we should be able to help you.
Hi,
the network setup is this: switch - docsis - LAN. Clients in the LAN can get IP address when docsis is reset but when the clients try to rebind they cannot. The DHCP is behind the switch and the helper address is on the switch where is default gateway for LAN clients.