kern/119432: route add -host <host> -iface <nic> causes arp entry with nic's arp address

[Axel Scheepers]

>Number:         119432
>Category:       kern
>Synopsis:       route add -host <host> -iface <nic> causes arp entry with nic's arp address
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Jan 07 19:20:03 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Axel Scheepers
>Release:        7.0-PRERELEASE
>Organization:
Private Home User
>Environment:
System: FreeBSD taliesin.thuis.net 7.0-PRERELEASE FreeBSD 7.0-PRERELEASE #1: Sun Jan 6 14:44:59 CET 2008 root at taliesin.thuis.net:/usr/obj/usr/src/sys/TALIESIN i386
>Description:
I use a xs4all connection at home for which I have to use sip spoofing 
(http://www.sterenborg.org:81/docs/alcatel_sip_spoof.html). To make it usefull
I have to set a route to my speedtouch modem with the -iface option to route
like this:
- ifconfig <extNic> <extIp> netmask 255.255.255.255
- route add <modemIp> -iface <extNic>
- route add default <modemIp>

This worked on 4.x as above, on 7.0-PRERELEASE however an arp entry for modemIp
containing the mac adress of extNic is added as soon as I add the route with 
-iface. Pinging the modem causes icmp redirects and ttl expires. I get messages
on the console that modemIp wan't to overwrite the existing arp entry.
I have to enter the correct mac address in the arp table for things to work 
correctly like;
- arp -s <modemIp> <modemMac>
- route add default <modemIp>

I'm not sure if this is intended behaviour but the former way seems more 
intuitive.

>How-To-Repeat:
Connect 2 boxes with crosscable, on box a: (simulates my modem)
- ifconfig fxp0 192.168.0.1 netmask 255.255.255.0
on box b: (simulates my router)
- ifconfig fxp0 10.10.10.1 netmask 255.255.255.255
- route add 192.168.0.1 -iface fxp0
- ping 192.168.0.1
- arp -na
(- arp -s 192.168.0.1 <mac of box a>)
(- ping 192.168.0.1)

>Fix:
You can work around it by setting the correct mac adress in the arp table.


>Release-Note:
>Audit-Trail:
>Unformatted: