[cisco-bba] DHCP max-lease-time and default-lease-time

[Frank Bulk]

For those using an external DHCP server for their BRAS, what's been your
practice in setting the max-lease-time and default-lease-time for PPPoA/E
clients?

I had the first set to 6 days and the second set to 3 days, and the 'sh dhcp
leases' shows that it's using a 3-day lease time.
	Lease: 259200 secs,  Renewal: 129600 secs,  Rebind: 226800 secs

But what I've been experiencing is that our Cisco 7206VXR (12.2(31)SB11) is
not consistently forcing PPPoX clients to renew their IP.  Our DHCP server
leases file shows an expired lease and there's no entry on the router's 'sh
dhcp leases', yet the PPPoX session remains up with that expired IP.  So
what happens is that a new session establishes and the DHCP server happily
hands out that "unused" IP address, which is, unfortunately, still in use.
The session fails to complete, and the PPPoX client tries again and again.
It's obvious in our RADIUS logs when this is happening.

It's also possible that the PPPoX client supports the max-lease-time, and
uses that as its lease length.  I'm really not sure if the PPP client is
supposed to use IPCP to renew or if the router handles that on the PPP
client's behalf.

Any ideas?  For now, I've set the max-lease-time to 3 days and we'll see
what happens.  It will take several days to know if it's making a
difference.

Frank