Question about DOCSIS DHCP vs ARP

Jean-Francois Mezei jfmezei_nanog at
Sat Jan 12 01:29:23 UTC 2013

On 13-01-11 19:59, Karl Brumund wrote:
> JF,
> Long ago been fixed. Look at Cisco CMTS config documentation, particularly cable-source-verify.

Many thanks. In particular, you need "cable-source-verify dhcp" to
prevent self assigned IPs that are unused by neighbours.

Is this something that is now basically a default for all cable
operators ? Or does this command add sufficient load to the CMTS that
some cable operators choose to not use it for performance purposes ?

What happens when a CMTS reboots and has an enpty database of DHCP
leases ? Does it then query the DHCP server for every IP/MAC it sees
that it doesn't yet know about ?

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