Results 1 to 4 of 4

Thread: MSS Size

  1. #1

    MSS Size

    Philip,

    Just would like to confirm:

    TCP Connection

    MSS = MTU - (IP header + TCP Header)

    UDP Connection

    MSS = MTU - (IP header + UDP Header)

    Why is it Ethernet Header of 18 bytes is not considered?
    Are there any other variables to consider?

  2. #2
    Administrator Philip's Avatar
    Join Date
    May 1999
    Location
    Jacksonville, Florida, United States
    Posts
    10,300
    Blog Entries
    6
    You are correct.

    As to Ethernet headers, in Ethernet v2 the payload is 1500 bytes. The rest is just CRC (4 bytes) and inter-frame spacing (12 bytes) that cannot be used. There are more bytes that exist in an Ethernet frame (MAC soruce/destination) but they are not part of the payload. Jumbo frames and other variants are not supported through all the switches/nodes that packets travel through, so anything larger than 1500 will get fragmented by some router before transmission, causing additional delay.
    Linux is user friendly, it's just picky about its friends...
    Disclaimer: Please use caution when opening messages, my grasp on reality may have shaken loose during transmission (going on rusty memory circuits).
    ๑۩۞۩๑

  3. #3
    Thanks for confirming.

    I would assume MSS = MSSfix of Openvpn. Are the overhead the same?

  4. #4
    Administrator Philip's Avatar
    Join Date
    May 1999
    Location
    Jacksonville, Florida, United States
    Posts
    10,300
    Blog Entries
    6
    VPN ads its own encapsulation headers, often reducing the maximum possible payload per packet from 1460 down to 1200-1300 bytes, depending on the particular protocol/options.

Similar Threads

  1. RWIN Same Size as LAN Request Buffer Size
    By DRRobinson in forum Broadband Tweaks Help
    Replies: 2
    Last Post: 12-27-08, 08:01 PM
  2. MTU size
    By ismedave in forum Networking Forum
    Replies: 1
    Last Post: 01-03-06, 01:55 PM
  3. Size Up!! (Flash Size Estimator)
    By A_old in forum General Discussion Board
    Replies: 0
    Last Post: 08-20-02, 06:36 PM
  4. psu size?
    By vc_wannabe in forum Hardware & Overclocking
    Replies: 2
    Last Post: 05-21-02, 08:00 PM
  5. MTU size ?
    By HackMcDivot in forum Broadband Tweaks Help
    Replies: 1
    Last Post: 04-18-01, 07:21 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •