ARP resolution fails when MSG_DONTROUTE flag is set

[<puneet.mehta%wipro.com@localhost>]

Hi,

Environment:
NetBSD  1.6.1 NetBSD 1.6.1 (GENERIC) #1: Thu Jun 14 04:52:29 PDT 2007

root@:/usr/src/sys/arch/i386/compile/GENERIC i386


I have the following two routes installed on kernel routing table of my
NetBSD
machine, for the same destination:

1. A directly connected route, with outgoing interface as Inf1
2. A host specific ?/32? route via an alternate path with outgoing
interface as
Inf2.

In this scenario, if a packet is sent to the destination, the packets
egresses
from Inf2.(longest prefix match)
If a packet is sent on interface Inf1 setting the MSG_DONTROUTE flag (to
bypass
the routing table), arp resolution is failing and I am getting the
following
error message logged in /var/log/messages:

>>>>>>>>>>>> /netbsd: arpresolve: can't allocate llinfo on fxp2 for
23.23.23.23


This problem exists only when we have a directly connected route and a
'/32'
route (via an alternate path) to the same destination. ARP resolution
fails for
the directly connected interface, an the packet gets dropped.

>How-To-Repeat:

+--------+ 21.21.21.22         21.21.21.21 +----------+
|  PC1   |-----------------------------------------|   PC2    |
+--------+                                                 +----------+
     \  23.23.23.24             25.25.25.26 /
      \                                                   /
       \                                                /
        \                                             /
         \                                           /
          \                                         /
           \                                       /
            \                                     /
             \                                   /
              \                                 /
               \                               /
                \                             /
                 \                           /
                  \                         /
                   \                       /
                    \                     /
                     \                   /
                      \                 /
                       \               /
                        \             /
                         \           /
                          \         /
                           \       /
                            \     /
         23.23.23.23 \   / 25.25.25.25
                         +----------+
                         |   PC3    |
                         +----------+

On PC1
======
bash-3.2# route show
Routing tables

Internet:
Destination       Gateway            Flags
10.11.0.0         link#1             U
10.11.1.59        00:10:18:82:09:66  UH
10.11.6.150       00:19:d1:5e:62:46  UH
10.11.8.204       00:10:18:82:02:f7  UH
21.21.21.0        link#2             U
21.21.21.21       link#2             UH
21.21.21.22       00:02:b3:28:52:61  UH
23.23.23.0        link#3             U
23.23.23.23       21.21.21.21        UG
localhost         127.0.0.1          UH

bash-3.2# traceroute 23.23.23.23
traceroute to 23.23.23.23 (23.23.23.23), 30 hops max, 40 byte packets
 1  21.21.21.21 (21.21.21.21)  0.243 ms  0.120 ms  0.113 ms
 2  23.23.23.23 (23.23.23.23)  0.332 ms  0.206 ms  0.233 ms


On PC2
======
bash-3.2# route show
Routing tables

Internet:
Destination       Gateway            Flags
default           100.0.2.3          UG
1.0.0.1           1.0.0.1            UH
1.0.0.1           link#5             U
10.11.0.0         link#1             U
10.11.6.150       00:19:d1:5e:62:46  UH
21.21.21.0        link#2             U
21.21.21.22       link#2             UH
23.23.23.0        21.21.21.22        UG
23.23.23.23       25.25.25.25        UG
25.25.25.0        link#4             U
25.25.25.25       link#4             UH
100.0.2.0         link#3             U
loopback          link#5             U
localhost         127.0.0.1          UH


On PC3
======
bash-3.2# route show
Routing tables

Internet:
Destination       Gateway            Flags
10.11.0.0         link#1             U
10.11.6.11        00:02:a5:84:95:62  UH
10.11.6.150       00:19:d1:5e:62:46  UH
21.21.21.0        25.25.25.26        UG
23.23.23.0        link#2             U
25.25.25.0        link#3             U
25.25.25.26       link#3             UH
loopback          link#5             U
localhost         127.0.0.1          UH


ping 23.23.23.23 is successful from PC1.
ping -r 23.23.23.23 is unsuccessful from PC1.

(ping -r is used to bypass the routing table and send the packet through

interface 23.23.23.24).

tail -f /var/log/messages (on PC1)
==================================
arpresolve: can't allocate llinfo on fxp2 for 23.23.23.23
arplookup: unable to enter address for
23.23.23.23@01:01:46:5c:17:17:17:18:17:17:17:17:08:00:7d:45 on null
(host is
not on local network)
arpresolve: can't allocate llinfo on fxp2 for 23.23.23.23
arplookup: unable to enter address for
23.23.23.23@01:01:46:5a:17:17:17:18:17:17:17:17:08:00:7c:44 on null
(host is
not on local network)
arpresolve: can't allocate llinfo on fxp2 for 23.23.23.23
arplookup: unable to enter address for
23.23.23.23@01:01:46:58:17:17:17:18:17:17:17:17:08:00:7b:43 on null
(host is
not on local network)

Please give me some way to bypass the routing table and send the packets
directly on an interface.

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