Bug 217978 - Dhclient does not support supersede statement for option 54
Summary: Dhclient does not support supersede statement for option 54
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: bin (show other bugs)
Version: CURRENT
Hardware: Any Any
: --- Affects Some People
Assignee: freebsd-bugs (Nobody)
Keywords: patch
Depends on:
Reported: 2017-03-21 14:59 UTC by fabian.kurtz
Modified: 2020-04-27 14:02 UTC (History)
4 users (show)

See Also:

Changes to enable supersede statement for option 54 (75.52 KB, text/plain)
2017-03-21 14:59 UTC, fabian.kurtz
no flags Details
clean patch for 11.0 (1.57 KB, patch)
2017-04-24 04:14 UTC, Franco Fichtner
no flags Details | Diff

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Description fabian.kurtz 2017-03-21 14:59:07 UTC
Created attachment 181028 [details]
Changes to enable supersede statement for option 54

The German cable internet provider Unitymedia (and possibily other ISPs from the Liberty Global group) uses DHCP relays which only answer to broadcasts. Dhclient renews WAN leases by sending unicasts to the relay, which doesn't forward them to the DHCP server. If, in the rebind phase, the broadcast packet is lost, the WAN IP expires, all connections are dropped and Dhclient needs to aquire a new lease.

The problem can be avoided by setting DHCP option 54 (dhcp-server-identifier) to However, the required supersede statement for this option is not implemented in dhclient.c. Thus the DHCP client does not use the option and the value given by the DHCP server remains in effect (which points to the IP of the relay), which then results in the observed problem.

To solve this a section which checks if "supersede dhcp-server-identifier" is set has been added to dhclient.c (see "Start of the updated section" at line 855 in the attached file).
Comment 1 Franco Fichtner 2017-04-24 04:14:49 UTC
Created attachment 182031 [details]
clean patch for 11.0

I believe the attached patch is the essence of this request.  The author hasn't given feedback yet, maybe Fabian could do this via this tracker instead?

Comment 2 fabian.kurtz 2017-04-30 16:40:38 UTC
(In reply to Franco Fichtner from comment #1)
Thanks, the patch looks good to me.