[Kea-users] KEA handling malformed packets

[Francis Dupont]

Marcin Jurczuk writes:
> I have lab system with isc-dhcp-server and kea installed.
> I stuck on issue of handling malformed packets.
> ISC-DHCP handles them flawlesly yet kea throws weird error:
> DEBUG DHCP4_LEASE_QUERY_PACKET_UNPACK_FAILED failed to parse query from
> 10.0.0.1 to 172.16.0.10, received over interface ens18, reason: Option
> parse failed. Tried to parse 161 bytes from 158-byte long buffer.
>
> This is not LEASE QUERY packet at all.

=> when you load the lease query hook the unpack/parsing is performed
by the hook because it is the right place to intercept lease query
messages. Outside the log which is a bit different the lease query hook
does not apply lenient parsing even when enabled: this is a known defect
described in the #4105 ticket which is currently in backlog (i.e. waiting
for someone to request it to be fixed).

> pcap shows this is malformed packet
> where option125 length reported by CableModem is just wrong.
> Below is wireshark text about exactly that packet that causes problem - it
> was captured on dhcpd server.

=> so Kea is right in complaining about the packet to be malformed....

> To emphasise - turning off kea, starting isc-dhcp - and modem gets IP,
> turning off isc-dhcp enabling kea - I'm getting this error and modem is not
> getting IP.

=> you have at least 4 solutions:
 - to get client fixed (I am afraid this can't be done...)
 - fix packets on the flight (not so easy)
 - move the lease query service to another box and enable linient parsing:
  if it is not critical to not step parsing at the malformed option this
  should fix your problem
 - make #4105 to be addresseed (unfortunately could take time as the next
  release is scheduled for next year...).

Thanks

Francis Dupont <fdupont at isc.org>