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what's mx480 arp table size?

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  • 1.  what's mx480 arp table size?

    Posted 09-25-2018 09:06

    does anyone know what's size of arp table size?

    show version
    Model: mx480
    Junos: 15.1F6.9





  • 2.  RE: what's mx480 arp table size?

    Posted 09-25-2018 23:22



    Can you try to get the output of:-


    % sysctl -a | grep arp_cache


    I ready somewhere that medium-sized platforms like EX4300 or all MX device have a default value of 75000 but I can not find a document to confirm the same.


    Also if you think that no. of entries in your arp table is too high, you can use below command to set the aging timer:-


    set system arp aging-timer <value>








  • 3.  RE: what's mx480 arp table size?

    Posted 09-26-2018 20:45

    % sysctl -a | grep arp_cache
    net.link.ether.inet.arp_cache_retry_size: 377
    net.link.ether.inet.arp_cache_rearp_size: 13
    net.link.ether.inet.arp_cache_timeout_size: 12314
    net.link.ether.inet.arp_cache_size_threshold: 0
    net.link.ether.inet.arp_cache_perm_size: -1155
    net.link.ether.inet.arp_cache_size: 12700

  • 4.  RE: what's mx480 arp table size?

    Posted 09-26-2018 01:14

    The maximum arp table size on MX is around one million entries. IPv6 ND scaling a bit lower


    I would expect that you cannot do maximum arp scaling + ipv6 ND scaling at the same time. There the maximum will be a mix.


    Please note that the MPC in question only has one PFE which limits mac scale to 512K and you can only learn up to 128k mac-addresses on a single interface.


    ...but overall I think you are covered for most situations 🙂

  • 5.  RE: what's mx480 arp table size?

    Posted 09-26-2018 20:48

    ok, thanks so much. I understand mpc arp table size is 1M. how about RE? I see RE arp cache size is 12700.


    net.link.ether.inet.arp_cache_size: 12700

  • 6.  RE: what's mx480 arp table size?

    Posted 09-26-2018 21:12



    its 2M max for high end mx such mx480, mx960 and above.


    It's editable from junos 16.1 onwards:


    re0# set system arp-system-cache-limit ?
    Possible completions:
      <arp-system-cache-limit>  Set max system cache size for ARP nexthops (200..2000000)


    Please review the following link for details:



    The default behavior of ARP is to remove the cache entry if it is not used within a certain period of time, and not to allow the cache to grow too large. You can also manage the number of ARP cache next-hop entries by configuring a limit to the maximum number of next hops that can be created.


    numberIndicates the maximum number of routes to be held in the ARP cache.

    Range: 1 through 2,000,000


    Default: (ACX Series routers, EX2200, EX2200-C, EX3200, and EX3300 switches, SRX Series services gateways) 20,000

    (EX4200, EX4300, EX4500, EX4550, and EX6210 switches, MX Series routers) 75,000


    (Other platforms) 100,000



  • 7.  RE: what's mx480 arp table size?
    Best Answer

    Posted 09-26-2018 21:41

    Incoming arp goes to arp policer in the PFE (packet forwarding engine) on FPC/MPC and are forwarded to CPU complex and then up to RE. Arp table/cache is maintained by RE & takes resource from RE memory and not MPC/fpc specfic.  The mpc/fpc helps in terms of cps (call per sec) to process arp and uplift the arp req to RE.


    For numbers, follow this link:




  • 8.  RE: what's mx480 arp table size?

    Posted 09-27-2018 00:03

    thanks so much for the reply. in my understanding my Junos version is 15.1f6.9. so it's arp table size can't editable. and it's 2M ? right

  • 9.  RE: what's mx480 arp table size?

    Posted 09-27-2018 01:25

    Yes, its supported from 16.1 onwards.




  • 10.  RE: what's mx480 arp table size?

    Posted 09-30-2018 23:25

    When you are trying to change the default behavior; keep an eye on Default per-PFE ARP policer