Configuring RSVP
Configuring RSVP is simple—so simple, in fact, that the temptation is to enable RSVP without fully understanding how it works. This is not a good idea, which is why this chapter covers the mechanics before it discusses the configuration.
RSVP is enabled on router interfaces, not on the router as a whole. This gives you the flexibility to enable RSVP on some interfaces but leave other interfaces alone.
Figure 5-7 WFQ on Outbound Interfaces Ensures Data Is Delivered at the Desired QoS
Queuing/QoS (Weighted Fair Queuing)
Receiver
Queuing/QoS (Weighted Fair Queuing)
Receiver
To configure RSVP on an interface, simply issue the bandwidth and ip rsvp bandwidth commands, like this:
2503#conf t
Enter configuration commands, one per line. End with CNTL/Z.
2503(config)#int s0
2503(config- if)#bandwidth 768
2503(config- if)#ip rsvp bandwidth
2503(config-if)#*Z
By default, the router limits the amount of bandwidth that can be reserved for RSVP sessions to 75% of the interface bandwidth. This prevents RSVP sessions from hogging all of the bandwidth on the interface and allows non-RSVP traffic at least 25% of the bandwidth. Note that the bandwidth command is used to specify the amount of bandwidth in kilobits per second available on this interface. Configuring this is very important because the router will use the number configured with this command to calculate the maximum bandwidth RS VP can reserve (75% of the number configured with the bandwidth command). Without this command, most serial interfaces default to a bandwidth equal to 1544 kbps (Tl), which might not be a proper representation of the real bandwidth on the interface.
You can look at the router configuration to see what RSVP bandwidth was calculated. The following is a partial listing of a router configuration, using the show running-config command:
interface Serial© ip address 192.168.1.2 255.255.255.0 ip rsvp bandwidth 576 576 bandwidth 768
in the preceding example configuration, you can verify that 75 percent of 768 kbps is 576 kbps. The first number after ip rsvp bandwidth is the maximum amount of bandwidth RSVP can reserve for RSVP sessions. The second number is the maximum amount of bandwidth that any one session (a single reservation) can reserve. If you want to change these numbers, you can issue the command with different bandwidth numbers:
2503(config-if)#ip rsvp bandwidth 400 200
The preceding eonfiguration restricts RSVP to a maximum of 400 kbps on this interface and states that no single reservation may exceed 200 kbps.
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