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Unicast ARP

  • 1.  Unicast ARP

     
    Posted 02-04-2021 01:55
    Hi.

    Is there a way for me to have Junos send out a unicast ARP Request?   

    (For example to verify whether an entry in its ARP table is current or not).


    Thanks,
    Deepak


  • 2.  RE: Unicast ARP

    Posted 02-04-2021 10:13
    Hello!


    To verify current state of ARP table

    > show arp no-resolve | no-more


    To check ARP packets ingress/egress the box (put interested interface instead)

    some-box> monitor traffic interface xe-0/1/0.13 detail no-resolve
    Address resolution is OFF.
    Listening on xe-0/1/0.13, capture size 1514 bytes

    18:08:45.808977 Out arp who-has 4.4.4.4 tell 4.4.4.1
    18:08:45.810106 In arp reply 4.4.4.4 is-at 58:00:bb:1b:b0:00


    Best regards
    Vladimir



    ------------------------------
    VLADIMIR A
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  • 3.  RE: Unicast ARP

     
    Posted 02-04-2021 12:24
    Hi Vladimir.

    But how do I get Junos to send a unicast ARP request? (The ARP request you've pasted is a broadcast one).

    Thanks,
    Deepak


  • 4.  RE: Unicast ARP

    Posted 02-04-2021 12:29
    Hello Deepak,

    A bit strange question, may be ping from junos box to resolve interested address first by ARP?

    Best regards
    Vladimir

    ------------------------------
    Vladimir
    ------------------------------



  • 5.  RE: Unicast ARP

     
    Posted 02-04-2021 12:33
    Hi Vladimir.

    Doesn't seem strange to me. Here's an example of a unicast ARP request. I'm just trying to get Junos to send one.

    https://www.cloudshark.org/captures/1e62881aa75b

    Regards,
    Deepak


  • 6.  RE: Unicast ARP

    Posted 02-04-2021 13:14

    Hello Deepak,

    If we are talking about real scenario with ARP suppression,
    please provide next outputs

    > show configuration interfaces =exact-interface= | display inheritance no-comments

    > show interfaces =exact-interface=

    > show arp no-resolve interface =exact-interface=

    and please point us wich IP you want to request by ARP.

    Best regards
    Vladimir



    ------------------------------
    Vladimir
    ------------------------------



  • 7.  RE: Unicast ARP

     
    Posted 02-04-2021 14:16
    Hi Deepak,

    I think this is the option you are looking for, please check below link,
    https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/arp-edit-interfaces.html 

    unicast-mode-on-expire-Send a unicast ARP request instead of the default broadcast request when an ARP cache entry ages out. When you include this option, the host device sends the requests only to the expected (currently cached) address. The ARP retry requests are unicast at intervals of 5 seconds. When you do not configure the unicast-mode-on-expire option, ARP retries are broadcast at intervals of 800 milliseconds.

    The default behavior of a Juniper device will be to send a broadcast to confirm if host is still active, you can change the behavior using this option, however this applies only the update requests.

    Please mark as "Solved" if this worked for you.

    Regards,
    Jeff




  • 8.  RE: Unicast ARP

     
    Posted 02-04-2021 14:55
    Thanks Jeff.

    That would've been what I was looking for, but I don't see that option on my vQFX running 18.1R3, so I think it's been deprecated.

    --Deepak


  • 9.  RE: Unicast ARP

     
    Posted 02-04-2021 15:04
    Deepak,

    Yes, just test it out on the lab and option is not available, tried to look under feature explorer and found that this one specifically seems to be available only on MX devices,
    https://apps.juniper.net/feature-explorer/feature-info.html?fKey=9807&fn=Unicast%20ARP%20request%20on%20table%20entry%20expiration

    Regards,
    Jeff