[j-nsp] ARP on unnumbered interfaces

[Mihai]

Hello,

  After the migration of a large network from a Cisco 7600 to a MX104 a 
lot of users started to have random problems with their connection.
The setup is based on unnumbered interfaces and /32 static routes 
through IFLs.
Basically, all clients with Cisco routers  will have at some point a 
missing ARP entry for their default gateway because the MX is changing 
the ARP source address from the gw_addr to the primary address.On Cisco 
i see the well known 'wrong cable' error.
Does anyone have a clue why is this happening beside a bug? I've made 
some tests on MX960,MX480 and MX5 and didn't see this behavior.
This is a lab simulation:


mx# show

interfaces {
     ge-1/1/8 {
         unit 55 {
             vlan-id 55;
             proxy-arp unrestricted;
             family inet {
                 unnumbered-address lo0.55;
             }
         }
         unit 56 {
             vlan-id 56;
             proxy-arp unrestricted;
             family inet {
                 unnumbered-address lo0.55;
             }
         }
     }
     lo0 {
         unit 55 {
             family inet {
                 address 5.5.5.5/32 {
                     primary;
                 }
                 address 10.10.10.1/24;
                 address 20.20.20.1/24;
             }
         }
     }
}
routing-options {
     static {
         route 20.20.20.2/32 {
             qualified-next-hop ge-1/1/8.55;
         }
         route 10.10.10.2/32 {
             qualified-next-hop ge-1/1/8.56;
         }
     }
     router-id 5.5.5.5;
}

mx> monitor traffic interface ge-1/1/8.55 detail no-resolve matching arp
Address resolution is OFF.
Listening on ge-1/1/8.55, capture size 1514 bytes

17:28:11.105586 Out arp who-has 20.20.20.2 tell 20.20.20.1
17:28:11.106100  In arp reply 20.20.20.2 is-at 00:1e:4a:fc:44:84
17:29:20.504891 Out arp who-has 20.20.20.2 tell 20.20.20.1
17:29:20.505375  In arp reply 20.20.20.2 is-at 00:1e:4a:fc:44:84
17:30:30.104188 Out arp who-has 20.20.20.2 tell 20.20.20.1
17:30:30.104632  In arp reply 20.20.20.2 is-at 00:1e:4a:fc:44:84

.....

17:53:01.790690 Out arp who-has 20.20.20.2 tell 5.5.5.5
17:54:05.690056 Out arp who-has 20.20.20.2 tell 5.5.5.5

Thanks!