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Custom Queuing

Custom Queuing

Custom Queuing (CQ) is a Congestion Management technique which is round-robin like where frames from each queue are serviced until a byte-counter limit threshold is met. Once this threshold is met, the frames from next queue are serviced.

There are 17 queues in CQ- queue 0 is the System Queue while queues 1-16 are user-defined. Queue 0 is used for keepalives, some routing protocols whose traffic is generated by the router. These are ISIS Hellos, EIGRP/IGRP Hellos, OSPF Hellos, Spanning-tree keepalives, Router Syslog messages, SLARP address resolution, etc. Queue 0 is always serviced first. Queues 1 through 16 are then serviced in round-robin fashion.


Network topology:

We will use 4 different queues (although 16 queues can be used) and assign traffic to each queue-

  1. Using Iperf, TCP traffic will be generated from PC1 to PC2 on TCP Port 5001 – Queue 1
  2. Using Iperf, TCP traffic will be generated from PC1 to PC2 on TCP Port 5002 – Queue 2
  3. Using Iperf, TCP traffic will be generated from PC1 to PC2 on TCP Port 5003 – Queue 3
  4. ICMP traffic originating from PC1 to PC2 – Queue 4

Configuration:

CQ is configured using queue-list command from global configuration mode.

Allocating traffic to Queues

!---- Defining Access-Lists to match traffic
!
access-list 101 permit tcp host 192.168.1.10 host 192.168.2.10 eq 5001
!
access-list 102 permit tcp host 192.168.1.10 host 192.168.2.10 eq 5002
!
access-list 103 permit tcp host 192.168.1.10 host 192.168.2.10 eq 5003
!
access-list 104 permit icmp host 192.168.1.10 host 192.168.2.10
!
queue-list 1 protocol ip 1 list 101
queue-list 1 protocol ip 2 list 102
queue-list 1 protocol ip 3 list 103
queue-list 1 protocol ip 4 list 104

!

By default, the size of each queue is 20 packets. The size of a queue can be changed using¬†queue-list¬†<list-number>¬†queue¬†<queue-number>¬†limit <value>¬†global configuration command. The range of the “value” keyword is 0 to 32767 where 0 indicates unlimited size of the queue.

Changing Queue size

queue-list 1 queue 1 limit 40
queue-list 1 queue 2 limit 30
queue-list 1 queue 3 limit 20
queue-list 1 queue 4 limit 20
!

Now each queue is set with a byte-count threshold which specifies how many bytes the system allows to be delivered from a given queue during one cycle before servicing the next queue. By default, this value is 1500 bytes. To change this value, use queue-list <list-number> queue <queue-number> byte-count <byte-count-number> global configuration command.

Queue Byte-count

queue-list 1 queue 1 byte-count 1400
queue-list 1 queue 2 byte-count 1450
!

By default, Queue 0 is always served first (like High Queue in Priority Queuing). However, Cisco IOS allows user-defined queues to become priority queues. It is done using¬†queue-list <list-number> lowest-custom <no._of_queues>¬†global configuration command. The “number of queues” keyword specifies the number of queues to be considered Priority Queues including Queue 0. The range is 0 to 16.

Specifying PQ in Custom Queuing

queue-list 1 lowest-custom 2
!

Monitoring Custom Queuing:

The show queueing custom displays custom queuing on R1 router.

show queueing custom on R1

R1# show queueing custom
Current custom queue configuration:

List   Queue  Args
1      1      protocol ip          list 101
1      2      protocol ip          list 102
1      3      protocol ip          list 103
1      4      protocol ip          list 104
1      1      byte-count 1400 limit 40
1      2      byte-count 1450 limit 30

The show interface Serial 1/0 command shows CQ applied on the interface.

show interface serial 1/0

R1# show interface serial 1/0
Serial1/0 is up, line protocol is up
  Hardware is M4T
  Internet address is 10.1.1.1/30
  MTU 1500 bytes, BW 128 Kbit/sec, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input 00:00:02, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: custom-list 1
  Output queues: (queue #: size/max/drops)
     0: 0/20/0 1: 0/40/0 2: 0/30/0 3: 0/20/0 4: 0/20/0
     5: 0/20/0 6: 0/20/0 7: 0/20/0 8: 0/20/0 9: 0/20/0
     10: 0/20/0 11: 0/20/0 12: 0/20/0 13: 0/20/0 14: 0/20/0
     15: 0/20/0 16: 0/20/0
...
...output omitted

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