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Priority Queuing 701
Dec 24,2008 00:00
by
alperen
Priority Queuing With priority queuing, data is placed into one of four different queues, defined as high, medium, normal, and low. These queues are emptied on a strict priority basis. Packets in the highest priority queue are always transmitted first, and packets in lower priority queues are not transmitted until the queues with higher priorities are emptied. Configuration options available to the administrator include how to define the traffic, what queue to place the traffic into, and how large each queue should be. To define the traffic for a particular priority queue, use the priority-list global command: Terry_3550(config)#priority-list 1 ? default Set priority queue for unspecified datagrams interface Establish priorities for packets from a named interface protocol priority queueing by protocol queue-limit Set queue limits for priority queues Terry_3550(config)#priority-list 1 protocol ? arp IP ARP bridge Bridging cdp Cisco Discovery Protocol compressedtcp Compressed TCP ip IP Terry_3550(config)#priority-list 1 protocol ip ? high medium normal low Terry_3550(config)#priority-list 1 protocol ip high ? fragments Prioritize fragmented IP packets gt Prioritize packets greater than a specified size list To specify an access list lt Prioritize packets less than a specified size tcp Prioritize TCP packets 'to' or 'from' the specified port udp Prioritize UDP packets 'to' or 'from' the specified port <cr> Terry_3550(config)#priority-list 1 prot ip high list ? <1-199> IP access list <1300-2699> IP expanded access list Terry_3550(config)#^Z Terry_3550# To define the maximum queue size for a particular priority queue, use the priority-list priority-queue queue-limit global command: Terry_3550(config)#priority-list 1 ? default Set priority queue for unspecified datagrams interface Establish priorities for packets from a named interface protocol Priority queueing by protocol queue-limit Set queue limits for priority queues Terry_3550(config)#priority-list 1 queue-limit ? <0-32767> High limit Terry_3550(config)#priority-list 1 queue-limit 5000 Terry_3550(config)#^Z Terry_3550# Allocating the priority queue to a particular outgoing interface is achieved using the priority-list priority-queue interface command: Terry_3550(config)#int fastEthernet 0/1 Terry_3550(config-if)#priority-group 1 Terry_3550(config)#^Z Terry_3550# It is common to make the queue sizes increasingly larger as the priority decreases. Naturally, packets in the lowest priority queue stand a statistically greater chance of spending more time in the queue, and it makes sense to allow the packets somewhere to wait The following configuration uses access list 101 to place Telnet traffic between any two hosts into the high-priority queue, uses access list 102 to place web traffic between any two hosts into the medium-priority queue, and places all other IP traffic into the normal-priority queue, while CDP traffic is placed into the low-priority queue. The list is applied to interface FastEthernet 0/24: Terry_3550(config)#priority-list 1 prot ip high list 101 Terry_3550(config)#priority-list 1 prot ip medium list 102 Terry_3550(config)#priority-list 1 prot ip normal Terry_3550(config)#priority-list 1 protocol cdp low Terry_3550(config)#access-list 101 permit tcp any any eq telnet Terry_3550(config)#access-list 102 permit tcp any any eq www Terry_3550(config)#int fastEthernet 0/24 Terry_3550(config-if)#priority-group 1 Terry_3550(config)#^Z Terry_3550# |