# phpman > man > tc-skbprio(8)

[SKBPRIO(8)](https://www.chedong.com/phpMan.php/man/SKBPRIO/8/markdown)                                      Linux                                     [SKBPRIO(8)](https://www.chedong.com/phpMan.php/man/SKBPRIO/8/markdown)



## NAME
       skbprio - SKB Priority Queue


## SYNOPSIS
       **tc** **qdisc** **...** **add** **skbprio** **[** **limit** packets **]**


## DESCRIPTION
       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 pack‐
       ets in the queue, it is dropped.

       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 indi‐
       vidual 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)](https://www.chedong.com/phpMan.php/man/tc-skbedit/8/markdown).  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  at‐
       tack.   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
       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 bandwidth.


## PARAMETERS
       limit  Maximum queue size specified in packets. It defaults to 64.  The range for this param‐
              eter is [0, UINT32_MAX].


## SEE ALSO
       [**tc-prio**(8)](https://www.chedong.com/phpMan.php/man/tc-prio/8/markdown), [**tc-skbedit**(8)](https://www.chedong.com/phpMan.php/man/tc-skbedit/8/markdown)


## AUTHORS
       Nishanth Devarajan <<devarajn@uci.edu>>, Michel Machado <<michel@digirati.com.br>>

       This manpage maintained by Bert Hubert <<ahu@ds9a.nl>>



iproute2                                   13 August 2018                                 [SKBPRIO(8)](https://www.chedong.com/phpMan.php/man/SKBPRIO/8/markdown)