Bug 26833

The attached transcript says it about as well as I can hope to:  when
you ifconfig an interface down, the kernel removes the routes for
networks directly attached to that interface.  (Or, in the case of a
point-to-point interface, the route for the remote end of the link.)

After ifconfigging an interface down, you can add a route whose 
gateway is on a directly attached network, with `route add'.

However, `route change' under these conditions, when invoked to change
the route to what it already is, failed with EDQUOT.

I have reproduced this with both broadcast and point-to-point
interfaces, on FreeBSD 4.2 and 4.3, and on a number of different
machines.

How-To-Repeat: # netstat -rn -f inet
Routing tables

Internet:
Destination        Gateway            Flags     Refs     Use     Netif Expire
default            xxx.xxx.xxx.81     UGSc        1        0      ep0
127.0.0.1          127.0.0.1          UH         15   665693      lo0
xxx.xxx.xxx.80/28  link#9             UC          0        0      ep0 =>
# netstat -rn -f inet
Routing tables

Internet:
Destination        Gateway            Flags     Refs     Use     Netif Expire
default            xxx.xxx.xxx.81     UGSc        1        0      ep0
127.0.0.1          127.0.0.1          UH         15   665693      lo0
xxx.xxx.xxx.80/28  link#9             UC          0        0      ep0 =>
# ifconfig ep0 down
# netstat -rn -f inet
Routing tables

Internet:
Destination        Gateway            Flags     Refs     Use     Netif Expire
default            xxx.xxx.xxx.81     UGSc        1        0      ep0
127.0.0.1          127.0.0.1          UH         15   665693      lo0
# route delete default
delete net default
# netstat -rn -f inet
Routing tables

Internet:
Destination        Gateway            Flags     Refs     Use     Netif Expire
127.0.0.1          127.0.0.1          UH         15   665693      lo0
# route add default xxx.xxx.xxx.81
add net default: gateway xxx.xxx.xxx.81
# route change default xxx.xxx.xxx.81
route: writing to routing socket: Disc quota exceeded
change net default: gateway xxx.xxx.xxx.81: Disc quota exceeded