Can't create proxy-arp entries for subnet

[Matthew Hudson]

Hello everybody,

I believe I may have stumbled across a bug in the arp program and
the reproduction is simple (and should be easy to verify) so I'll
just jump to the point. 

This is on 6.1-RELEASE-p3 i386

I discovered this while trying to create proxy-arp entries for a
subnet of a network I was directly connected to.  The smaller subnet
is forwarded over a tun interface.

Basically, the network plugged into fxp0 is 2.2.2.0/24 however
there's a small subnet (2.2.2.8/30) that lives on the other side
of the tun2 interface and I want to proxy arp for it so other hosts
on the wire can reach it without static routes.

Basic repro instructions:

  # dd if=/dev/zero of=/dev/tun count=0    ## create new tun interface
  # ifconfig tun2 1.1.1.1 1.1.1.2
  # ifconfig fxp0 2.2.2.1/24
  # route add 2.2.2.8/30 1.1.1.2
  add net 2.2.2.8: gateway 1.1.1.2
  # arp -s 2.2.2.9 auto pub
  using interface fxp0 for proxy with address 00:90:27:a5:cd:33
  cannot intuit interface index and type for 2.2.2.9

The "cannot intuit interace index and type" is the failure.

The workaround is to add the static arp entries before you add the
subnet route, however it seems like this is still a bug.   Can
anyone else verify that this shouldn't be?
  
Here's a more detailed log of the reproduction along with comments.
Comments are preceded by ']]'

---- script(1) start ----

   # netstat -rn
   Routing tables
   
   Internet:
   Destination     Gateway            Flags    Refs      Use  Netif Expire
   default         192.168.48.254     UGS         0     3066    em0
   127.0.0.1       127.0.0.1          UH          0        0    lo0
   192.168.48      link#2             UC          0        0    em0
   
   Internet6:
   Destination           Gateway        Flags      Netif Expire
   ::1                   ::1            UH          lo0
   ff01:4::/32           ::1            UC          lo0
   ff02::%lo0/32         ::1            UC          lo0
   
   ]] simple enough.  Note that fxp0 is completely unconfigured. 
   ]] The network on em0 should be entirely unrelated here but is shown 
   ]] to illustrate 'nothing up my sleeve'
   
   # ifconfig -a
   fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
       options=8<VLAN_MTU>
       ether 00:90:27:a5:cd:33
       media: Ethernet autoselect (100baseTX <full-duplex>)
       status: active
   em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
       options=b<RXCSUM,TXCSUM,VLAN_MTU>
       inet 192.168.48.154 netmask 0xffffff00 broadcast 192.168.48.255
       ether 00:08:74:38:3f:ef
       media: Ethernet autoselect (100baseTX <full-duplex>)
       status: active
   lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
       inet6 ::1 prefixlen 128
       inet 127.0.0.1 netmask 0xff000000
   tun2: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1500
   
   ]] Again, we see fxp0 is unconfigured. tun2 is unconfigured as well.
   
   # ifconfig tun2 1.1.1.1 1.1.1.2
   # ifconfig fxp0 2.2.2.1/24
   # route add 2.2.2.8/30 1.1.1.2
   add net 2.2.2.8: gateway 1.1.1.2
   
   ]] We configure an address on tun2, fxp0, and set up the /30 subnet to
   ]] route over tun2.
   
   # arp -s 2.2.2.9 auto pub
   using interface fxp0 for proxy with address 00:90:27:a5:cd:33
   cannot intuit interface index and type for 2.2.2.9
   
   ]] Here's the problem.  
   ]]   "cannot intuit interface index and type for 2.2.2.9"

   # route delete 2.2.2.8/30
   delete net 2.2.2.8
   # arp -s 2.2.2.9 auto pub
   using interface fxp0 for proxy with address 00:90:27:a5:cd:33
   
   ]] However if we delete the route, we can add the proxy arp no problem.
   
   # route add 2.2.2.8/30 1.1.1.2
   add net 2.2.2.8: gateway 1.1.1.2
   
   ]] We can even add the route *back* once the proxy arp is created. 
   
   # arp -d 2.2.2.9
   2.2.2.9 (2.2.2.9) deleted
   # arp -s 2.2.2.9 auto pub
   using interface fxp0 for proxy with address 00:90:27:a5:cd:33
   cannot intuit interface index and type for 2.2.2.9
   
   ]] However if we try to delete the proxy arp and then re-create it, no dice.
   ]]   note the broken-symmetry.
   
---- script(1) end ----


Cheers,
Matthew