Opened 4 years ago

#17279 new defect

DHCP renewal issues w/ cable provider

Reported by: hrncn Owned by:
Priority: normal Milestone: Chaos Calmer 15.05
Component: documentation Version: Trunk
Keywords: dhcp renewal Cc:


I'm running OpenWrt Barrier Breaker r41777 / LuCI Trunk (svn-r10459) on a TP-Link TL-WR841N/ND v9 which is attached to a Cisco EPC3212 cable modem.
The first issue is that the dhcp server does not respond to unicast renewal requests, so udhcpc eventually panics when the lease time is <60 seconds and resorts to a broadcast which (depending on timing, i've had this fail once) succeeds, this issue with cable providers is apparently not uncommon.

I've fixed this for the time with an iptables rule,

iptables -t nat -A OUTPUT -d -o eth1 -p udp -m udp --dport 67 -j DNAT --to-destination

but I think a better way would be to provide a fix like the dhclient "supersede dhcp-server-identifier" option.

The second issue is that after the broadcast succeeds openwrt answert the dhcp ack with icmp port unreachable, which i believe shouldn't happen.

See the attached pcap (vanilla state without my iptables fix) for details.

Attachments (1)

dhcp_problem_.pcapng (6.1 KB) - added by hrncn 4 years ago.

Download all attachments as: .zip

Change History (1)

Changed 4 years ago by hrncn

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