Working with a Cisco router

[Simon Hobson]

Tim Gavin wrote:
>I have just identified a problem where a small group of people are
>'stealing' their IPs.  It appears that they're grabbing their DHCP
>assigned address and setting it in their router as a static.  This has
>the obvious consequences.
>
>What I'm wondering is if anyone knows of a script or app that will
>work with ISC DHCP that can set a static ARP in my Cisco router based
>on the DHCP lease.  Maybe using SNMP or something. . . I know it's a
>strange request, but am hoping someone has dealt with this before.

If your leases are long enough, then you could periodically scan the 
leases file to get a list of IP-MAC pairs and script an update to a 
switch or router. Or possibly more useful, compare this with the 
router ARP table and build a blacklist of devices to redirect into a 
walled garden.

Actually, this could be a reasonably safe way to do it - you could 
include logic that would include expired leases less than a certain 
age which would avoid false blockings just after a lease expires. 
However, a lease would disappear if the address got reallocated to 
another customer, but in that case, the faster you deal with the 
offender the better.

-- 
Simon Hobson

WANTED: "Software CD ROM Kit" for Canon CLBP 360-PS printer (Canon 
part no RH6-3612, or possibly RH6-3810, or RH6-3610 might do). I've a 
dead HD and need this CD so I can replace the disk and re-install the 
printer OS on it. If anyone knows where I might get hold of one I'd 
be grateful - requests to Canon drew a blank, it's been out of 
support for years.
Alternatively, if anyone has one of these and would let me image 
their hard disk ...

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.