tc-skbprio(8) — Linux manual page


SKBPRIO(8)                        Linux                       SKBPRIO(8)

NAME         top

       skbprio - SKB Priority Queue

SYNOPSIS         top

       tc qdisc ... add skbprio [ limit packets ]

DESCRIPTION         top

       SKB Priority Queue is a queueing discipline intended to
       prioritize the most important packets during a denial-of-service
       ( DoS ) attack. The priority of a packet is given by
       skb->priority , where a higher value places the packet closer to
       the exit of the queue. When the queue is full, the lowest
       priority packet in the queue is dropped to make room for the
       packet to be added if it has higher priority. If the packet to be
       added has lower priority than all packets in the queue, it is

       Without SKB priority queue, queue length limits must be imposed
       on individual sub-queues, and there is no straightforward way to
       enforce a global queue length limit across all priorities.
       SKBprio queue enforces a global queue length limit while not
       restricting the lengths of individual sub-queues.

       While SKB Priority Queue is agnostic to how skb->priority is
       assigned. A typical use case is to copy the 6-bit DS field of
       IPv4 and IPv6 packets using tc-skbedit(8).  If skb->priority is
       greater or equal to 64, the priority is assumed to be 63.
       Priorities less than 64 are taken at face value.

       SKB Priority Queue enables routers to locally decide which
       packets to drop under a DoS attack.  Priorities should be
       assigned to packets such that the higher the priority, the more
       expected behavior a source shows.  So sources have an incentive
       to play by the rules.

ALGORITHM         top

       Skbprio maintains 64 lists (priorities go from 0 to 63).  When a
       packet is enqueued, it gets inserted at the tail of its priority
       list. When a packet needs to be sent out to the network, it is
       taken from the head of the highest priority list. When the queue
       is full, the packet at the tail of the lowest priority list is
       dropped to serve the ingress packet - if it is of higher
       priority, otherwise the ingress packet is dropped. This algorithm
       allocates as much bandwidth as possible to high priority packets,
       while only servicing low priority packets when there is enough

PARAMETERS         top

       limit  Maximum queue size specified in packets. It defaults to
              64.  The range for this parameter is [0, UINT32_MAX].

SEE ALSO         top

       tc-prio(8), tc-skbedit(8)

AUTHORS         top

       Nishanth Devarajan <>, Michel Machado

       This manpage maintained by Bert Hubert <>

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling
       TCP/IP networking and traffic) project.  Information about the
       project can be found at 
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iproute2                     13 August 2018                   SKBPRIO(8)