[nsp] RBE and DHCP relay deleting manually added static routes.

[Miquel van Smoorenburg]

Hello,

	we're terminating our ADSL subscribers with RBE on a 6400
with NRP-1s. We're using RFC1483 encapsulation by means of RBE.

All our customers have static IP addresses, but we encourage the use of
DHCP so that everything works "plug and play".

So we have set up the config like

interface lo 1
  ip address 192.168.8.1 255.255.255.0
!
interface ATM 0/0/0.40 point-to-point
  bandwidth 2048
  ip unnumbered lo 1
  ip helper-address 192.168.1.10
  atm route-bridged ip
  pvc 0/40
    class-vc atm-2048
!
ip route 192.168.8.40 255.255.255.255 ATM 0/0/0.40

.. and so on, a subinterface for each client. Using option 82 in the DHCP
server we make sure that this client indeed gets assigned the right
IP address (192.168.8.40), netmask, gateway etc if they happen to use DHCP.

So clients can configure their CPE or router statically or dynamically.
It all works.

However now for the problem.

If someone uses DHCP, the IOS relay agent adds an interface route for
the IP address that is in the DHCP reply packet - replacing the existing
route. And as soon as the lease expires or is released, that route is
deleted. At that point, the original static route is gone too.

Which means that as soon as a client uses DHCP, even if just once, it is
impossible to switch back to the static config - since part of it is now
gone on the c6400 side (the static route over the interface).

Anyone know of a workaround ? Best would be if the DHCP route was added with
a larger metric, not replacing an existing route with a smaller metric,
and if the DHCP route was only deleted if it was indeed a DHCP route.
But that is not what happens now (this is with 12.2(15)T7 )

Mike.