Custom queueing

[Maarten Vervoorn]

Recently I performed a workbook lab with a question about custom queueing. The question was to give a percentage bandwidth to 4 types of traffice

20% FTP (1500bytes)

30% HTTP (600bytes)

40% UDP5001 (300 bytes)

10% all that is left

The bandwidth is devided by byte-count. But is this number meaning anything? I think its just a number you can take and devide it into percentages

queue-list 1 protocol ip 1 tcp ftp

queue-list 1 protocol ip 1 tcp ftp-data

queue-list 1 protocol ip 2 tcp www

queue-list 1 protocol ip 3 udp 5001

queue-list 1 default 4

Will both byte-count option do the same?

queue-list 1 queue 1 byte-count 3000

queue-list 1 queue 2 byte-count 4500

queue-list 1 queue 3 byte-count 6000

queue-list 1 queue 4 byte-count 1500

or

queue-list 1 queue 1 byte-count 200

queue-list 1 queue 2 byte-count 300

queue-list 1 queue 3 byte-count 400

queue-list 1 queue 4 byte-count 100

[Giuseppe Larosa]

Hello Maarten,

custom queueing is a legacy queueing scheduler where packet sizes and byte counts really counts for resources allocation

Clearly in current IOS routers everyone would use CBWFQ instead

see

http://www.cisco.com/en/US/docs/ios/12_0/qos/configuration/guide/qccq.html

generally calculations need to be performed with an iterative process

byte count should be big enough to accomodate a packet of size  = MTU on outgoing interface so it is better to use higher byte counts but not too big to avoid to increase jitter of packets waiting in the othe queues

at each round from each queue up to byte count bytes can be taken

custom queueing will take one or more packets causing distortion of BW distribution for this reason average packet size plays a role in the formula

that is if byte count is 501 and the packets are of size 500 bytes two packets are taken from the queue.

I may be wrong but I don't think that custom queueing is still part of current exams including CCIE level

Hope to help

Giuseppe