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Buffer sizes on EX4200

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  • 1.  Buffer sizes on EX4200

    Posted 12-12-2009 10:15

    I am trying to get some questions answered for a customer. One of them has to do with the port buffer size for the EX4200. The Juniper documentation states that port buffers for the EX8200 series switches are:

    - Buffer per 10-Gigabit Ethernet port: 512 MB

    - Buffer per 1-Gigabit Ethernet port: 42 MB

    I can't seem to find any documentation in regards to the EX4200. Can anyone comment or validate that it is the same on this platform as with the 8200? I am looking or buffer size and it is per port or shared pool?


  • 2.  RE: Buffer sizes on EX4200
    Best Answer

    Posted 12-13-2009 02:34

    Hi Kevin,


    each PFE (24 ports) on EX3200/EX4200 has approximately 2.5 MB.


    *** Buffer Mgmt on EX4200 platform ***


    Each port gets resources from two pool types:


      - "Dedicated" pool

      - "Shared" pool

    The allocation of buffers from the Dedicated pool is controlled by configuration:

      - If a buffer-size percentage is configured for a class, the number of buffers assigned will be proportional to that percentage

      - If no buffer-size is configured for a class or classes, the remaining percentage will be equally shared between those classes


    The allocation of buffers from the Shared pool is dynamically performed according to the queueing needs of a class, and it cannot be controlled by configuration


    - When a queue needs to buffer traffic, it first consumes the allocated resources from the Dedicated pool. Once those resources are consumed, it may get assigned more buffers from the Shared pool


    - Only PLP low traffic may get buffers from the Shared pool

    - Thus the number of PLP high packets that may be queued is bounded by the size of the Dedicated pool


    Kind Regards

    Michael Pergament


    If this worked for you please flag my post as an "Accepted Solution" so others can benefit. A kudo would be cool if you think I earned it.



  • 3.  RE: Buffer sizes on EX4200

    Posted 12-17-2009 10:16

    I think your post is nice, but you neglected to mention from which user facing document you pulled this information.  Would you mind?  If there are no user facing docs, it would be helpful to know how to adjust the dedicated pool size as well the releases that support this configuration, should it not be universally supported.  Thanks in advance.

  • 4.  RE: Buffer sizes on EX4200

    Posted 01-02-2013 07:54

    Here is the knowledge Base that is the source for the above information :



  • 5.  RE: Buffer sizes on EX4200

    Posted 11-07-2013 11:07

    Does anybody know how the buffers are allocated by different MTUs on an interface?


    Eg. you have 1MB of buffer in a class and a 1514 Byte MTU, and an average packetsize of 800 Byte

     => Does this mean you can queue 693 Packets (1*1024*1025/1514) or 1312 Packets (1*1024*1025/800)?


    Thanks in advance



  • 6.  RE: Buffer sizes on EX4200

    Posted 06-23-2017 15:37
      |   view attached

    If anyone still trying to figure out the buffer size for EX4200. It is described as follows.


    24 ports on EX4200= 1PFE (Packet-Forwarding-Engine) 


    My EX4200-has 48 ports + 4 uplink ports = 3PFE


    Every 1PFE = has 3MB  of buffer size.


    Hence, EX4200 with 48ports + 4 uplink ports = 3PFE = 3 x 3MB = 9MB total buffer space available for shared buffer.


    (Note: Found above info based on 2010 Junos CoS document, couldn't find any latest. Please also check attached gif, has explaination also for EX2200, EX3200, EX8200 or go http://www.juniper.net/us/en/local/pdf/implementation-guides/8010073-en.pdf )


    Hope this Helps. Cheers!


    - AJ