Route next-hop interface behaviour

[Richard Tector]

Hi,

I'm not sure if it is expected behaviour but when configuring a static 
route (default or otherwise) the outbound interface recorded in the 
table does not update when the system's IP changes interface, even when 
removing and re-adding it.

Fairly simple topology, system running 9.1-STABLE (30th March) with just 
one of four 'em' interfaces in use - em0 with 10.0.2.199. Default route 
to 10.0.2.1.

Whilst troubleshooting some odd TCP behaviour I thought I'd try a 
different interface and so downed the active interface and brought up 
one on a PCI card, and swapped the cable over:

# ifconfig em0 down
# ifconfig em2 inet 10.0.2.199/24
# ifconfig em2 up


#####
If I then ping an external host it shows as the destination network 
being inaccessible:

root at daffy:~ # ping 212.23.6.76
PING 212.23.6.76 (212.23.6.76): 56 data bytes
ping: sendto: Network is down


#####
Can contact the next hop just fine:

root at daffy:~ # ping 10.0.2.1
PING 10.0.2.1 (10.0.2.1): 56 data bytes
64 bytes from 10.0.2.1: icmp_seq=0 ttl=64 time=0.211 ms


#####
Routing table shows that the default route is still bound to em0 even 
though the next hop is on em2:

root at daffy:~ # netstat -rfinet -n
Routing tables

Internet:
Destination        Gateway            Flags    Refs      Use  Netif Expire
default            10.0.2.1           UGS         0     3141    em0
                                                                 ^^^
10.0.2.0/24        link#4             U           1      255    em2
10.0.2.199         link#1             UHS         1        0    lo0
127.0.0.1          link#9             UH          0        0    lo0


#####
Removing the default route and re-adding also leaves it on the old 
interface:

root at daffy:~ # route delete default
delete net default
root at daffy:~ # route add default 10.0.2.1
add net default: gateway 10.0.2.1
root at daffy:~ # netstat -rfinet -n
Routing tables

Internet:
Destination        Gateway            Flags    Refs      Use  Netif Expire
default            10.0.2.1           UGS         0        0    em0
10.0.2.0/24        link#4             U           0      688    em2
10.0.2.199         link#1             UHS         1        0    lo0
127.0.0.1          link#9             UH          0        0    lo0



I can understand the initial problem, but surely when I re-add the route 
it should do a lookup against the table for the next hop, ie. 
10.0.2.0/24, and use the associated Netif?

What's interesting is that if I remove the IP configuration from em0 it 
removes the default route above (even though the interface is downed). 
Re-adding the route works.

Regards,

Richard