DSCP & Default Linux routing

Discussion in 'Linux Networking' started by itsanandr, Feb 13, 2006.

  1. itsanandr

    itsanandr Guest

    Hi all,
    I'd appreciate if someone can clarify this for me.

    From the source code (ip_forward.c), it seems that skb->priority is
    set from the "TOS bits" (mask 0x1E) in the TOS byte. Assume that an end
    point application sets the value 0xb8 in the TOS byte (for expedited
    forwarding). When this packet passes through a Linux router with
    default configuration, it will set the skb->priority to 4 (TOS bits
    will be binary 1100), as calculated by the function rt_tos2priority().

    If the egress link has 4 priority queues (for example IEEE 802.11e
    has 4 access categories), then skb->priority of 4 will map to access
    category #2 (Video). But expedited forwarding means it should map onto
    access category #3 (Voice), which means skb->priority should be set to
    6 or 7. Is this a bug or am I missing something?

    Thanks in advance.

    itsanandr, Feb 13, 2006
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