[j-nsp] ARP on unnumbered interfaces

[Masood Ahmad Shah]

AFAIK, router uses the preferred source address when it is configured for
an unnumbered Eth interface, for arp requests and replies. arp requests
need to match the preferred source address, which is by default primary
interfaces

    lo0 {
        unit 55 {
            family inet {
                address 5.5.5.5/32 {      //That would be this in your
case.
                    primary;
                }
                address 10.10.10.1/24;
                address 20.20.20.1/24;
            }
        }
    }

More here:
http://www.juniper.net/documentation/en_US/junos13.2/topics/usage-guidelines/interfaces-configuring-an-unnumbered-interface.html

Cheers,
Masood

On Sun, Jan 11, 2015 at 2:34 AM, Mihai <mihaigabriel at gmail.com> wrote:

> 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!
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