DHCPv6 Option 18 (interface-id) relay problem (fwd)

Christian Kratzer ck-lists at cksoft.de
Thu Nov 8 16:18:38 UTC 2012


On Thu, 8 Nov 2012, Andreas Hanke wrote:

> Hello again,
> I did an other test now and now I am very confused...
> The test steps:
> 1.) CLIENT PC (without DLSAM) <----> CISCO <------> DHCP Server
> 2.) Client PC get IP
> 3.) Insert the host-identifier option....
> 4.) Client PC get IP, but not the IP which is configured by the DHCP
> config host-identifier option, the same that in step 2.)
> 5.) Delete lease files, restart etc...remove range configuration, so
> that just the host-identifier option is there
> 6.) client PC get IP, already the same like at 4.)
> 7.) remove the DHCP Server from network (just CLIENT PC <-----> CISCO)
> 8.) Client PC get IP, the same that in the last steps but from my range
> which is configured in DHCP server which is disconnected!!!!!
> -> what makes me confused: at 2.) + 4.) + 6.) the DHCP server always do
> the log messages and show my the interface-id from Client PC (without
> DSLAM/DSL Modem).
> Any ideas?....

there should be no need at all to remove the lease file as hosts are not recorded in the lease file and are also checked before leases.

In case the PC gets an ip from a range then the host with the host identifier obviously was not matched.

The best way to proceeed would be to first be absolutely sure that you have the correct host-identifier specified in your config file.

So run a packet capture on the dhcp server so you see exactly the packet as the dhcp server is getting them and also check exactly what the dhcp server is sending back to the client.

Then post both you dhcpd.conf and the packet capture (preferably in pcap format).

It is entirely possible that there is no matching logic in the dhcpd to match these kinds of options.  But the code being complex it's good to have proof first before starting to debug.


> Hope this night there will be a solution in my dreams...
> cheers andy
> R-KOM Regensburger Telekommunikationsgesellschaft mbH & Co. KG,
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Christian Kratzer                      CK Software GmbH
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