[j-nsp] ARP on unnumbered interfaces

[Dave Bell]

Would the preferred-source-address statement work in your situation?

>From the link Madood posted:
interfaces {
  lo0 {
    unit 0 {
      family inet {
        address 2.2.2.1/32;
        address 3.3.3.1/32;
      }
    }
  }
}
interfaces {
    ge-4/0/0 {
      unit 0 {
        family inet {unnumbered-address lo0.0 preferred-source-address
3.3.3.1;
      }
    }
  }
}
On 11 Jan 2015 07:06, "Mihai" <mihaigabriel at gmail.com> wrote:

> Thank you for your response.If the document is true,then all ARPs should
> be originated with the primary address and as you can see this is not the
> case (tested on multiple platforms with different codes,Cisco included).
> One workaround i found is to delete/add the static route,but it doesn't
> work in all cases.
>
>
> On 01/11/2015 02:13 AM, Masood Ahmad Shah wrote:
>
>> 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 <http://5.5.5.5/32> {      //That
>> would be this in your case.
>>                      primary;
>>                  }
>>                  address 10.10.10.1/24 <http://10.10.10.1/24>;
>>                  address 20.20.20.1/24 <http://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
>> <mailto: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 <http://5.5.5.5/32> {
>>                          primary;
>>                      }
>>                      address 10.10.10.1/24 <http://10.10.10.1/24>;
>>                      address 20.20.20.1/24 <http://20.20.20.1/24>;
>>                  }
>>              }
>>          }
>>     }
>>     routing-options {
>>          static {
>>              route 20.20.20.2/32 <http://20.20.20.2/32> {
>>                  qualified-next-hop ge-1/1/8.55;
>>              }
>>              route 10.10.10.2/32 <http://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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