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ipv4 ToS matches traffic class field of ipv6 but flow label?

Discussion in 'Networks' started by kobem, Jan 2, 2008.

  1. kobem

    kobem Megabyte Poster

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    hey people as you see in the title ToS in ipv4 is equal to traffic class field of ipv6
    though , flow label is similar to them too.

    "difference"?

    then

    regarding to article i have read somewhere there is no QoS in ipv4 but ToS
    does provide it , "is this wrong"?
     
    Certifications: CCNA
  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Yes and no. The TOS field was never really used - hence the statements that IPv4 doesn't have QoS.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  3. kobem

    kobem Megabyte Poster

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    and what is the difference exactly ?

    the other is that QoS is not in main header(ipv4) but it could be added soon , right?
     
    Certifications: CCNA
  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Er - the difference between what and what?

    I would think it exceeding unlikely that IPv4 will be modified much these days.

    The TOS field was changed to DSCP about 10 years ago - but I don't know who uses this. The IPv6 field is effectively DSCP I believe.

    The normal way to get QoS on IPv4 these days is via MPLS.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  5. kobem

    kobem Megabyte Poster

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    -------difference between "flow label" and "traffic class" field ?-----------------

    - although you explain there is no QoS in ipv4 , ToS definition doesn't tell the same .

    according to definition of ToS , " this field specifies the QoS services desired."

    ------i thought that traffic class field is concerned with real-time traffic and non-real time,
    however, flow label field is just interested in QoS (labeling flows required) ?-------
     
    Certifications: CCNA
  6. MacAllan

    MacAllan Byte Poster

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    I thought it was used in VOIP???
     
    Certifications: A+, N+, CCNA
    WIP: CCNP, Linux+
  7. Spice_Weasel

    Spice_Weasel Kilobyte Poster

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    QoS, in various forms, is widely used in ipv4. Every modern router or switch will be using some form of QoS internally, and of course decent networking equipment typically supports a number of QoS options. QoS is an essential tool (collection of tools, actually) in a modern network - voip is a classic example of a service that demands QoS to function properly. In ipv4 the ToS byte is defined as 8 bits in the ipv4 header, and as Harry points out was not widely used originally. Currently the bit field is used for dscp (6 bits) and ecn (2 bits) - although ecn is rarely used. The DSCP bits, however, are quite useful and frequently used.

    IPv6 uses the same DSCP and ecn bits as IPv4 and is essentially the same at this time. IPv6 also has a 20 bit flow field to help identify traffic belonging to a common flow, a feature that IPv4 does not have. However, it is not clear right now how widespread the use of the flow field will be.

    In summary, IPv4 and IPv6 in their current forms offer the same QoS field in the header (6 bits DSCP +2 bits ECN), and IPv6 also has a 20 bit flow header, but that field is currently unused, making IPv4 and IPv6 very similar functionally regarding QoS.

    Spice_Weasel
     
    Certifications: CCNA, CCNP, CCIP, JNCIA-ER, JNCIS-ER,MCP
    WIP: CCIE

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