Chapter 12 QoS
57
Two subnetworks, A and B are accessed through the WAN1 interface as depicted in the figure i.e. all traffics
of these networks are passed through WAN1 interface. Again each of A and B have different types of traffic,
say Telnet, WWW, FTP or so on. Suppose Telnet of subnet A has high traffic rate and consume most of the
bandwidth of WAN1, other will be blocked, as WAN1 don’t have enough bandwidth compared to LAN1 and
eventually some traffic from LAN1 will be dropped. To solve this problem, Policy rate limit is installed on
WAN1 to control bandwidth distribution. Suppose subnet A will have 60% of the available WAN1 bandwidth
guaranteed; subnetwork B the rest (40%). Within each subnetwork the guarantee flows for each type of
service are as is indicated in the figure. Assume WAN1 has 1Mbps bandwidth, so telnet in subnet A will
have 60 Kbps (10% of 60% of 1Mbps) guaranteed bandwidth, while FTP will have 120 Kbps.
Corresponding commands for these Telnet and FTP for subnet A are as follows:
add rate_limit 192.168.1.0 24 any TCP 23 any 60-60 kbps
add rate_limit 192.168.1.0 24 any TCP 21 any 120 kbps
For other 2 class of traffic in subnet A, type following commands:
add rate_limit 192.168.1.0 24 any any 80 any 120-120 kbps (for www)
add rate_limit 192.168.1.0 24 any any 300 kbps (for other)
Following are the commands to setup traffic distribution control for subnet B:
add rate_limit 192.168.2.0 24 any TCP 23 any 60 kbps (for telnet)
add rate_limit 192.168.2.0 24 any TCP 21 any 120-120 kbps (for ftp)
add rate_limit 192.168.2.0 24 any any 80 120 kbps (for www)
add rate_limit 192.168.2.0 24 any any 100-100 kbps (for other)
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