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If it was not turned on, DLSw+ would queue this traffic on the router's outbound ports. As soon
as the traffic started traversing an internetwork, the service classifications would be lost.

If there is a reason to change the default values, you can override them using the command dlsw
tos map or by using policy-based routing. For example, you could use this command:

dlsw tos map high 5 medium 2 normal 1 low 0

Policy-Based Routing

CCDPs must know where and when to use Policy-Based Routing (PR). Policy-Based Routing
could be called Static Routes Version 2, because in essence it is another flavor of static routing.
Policy routing is the ability to specify the path that traffic will take through the network based
on user-specific parameters. An added bonus is that the priority packets can be modified.

Policy Routing classifies packets through the use of extended access lists. ACLs, IP Precedence,
queuing, and other QoS capabilities work together to carry out the network management policy
framework. CCDPs can control the traffic path using extended ACLs, bypassing the lookup in
the routing table.

Policy Routing comes in handy when you have transmission lines between two points that have
different characteristics. Figure 14-19 shows a low-bandwidth terrestrial link from Router A to
Router B and a high-bandwidth, high-propagation-delay satellite link. Policy routing is also
used in a particular situation in which the need is to route based on the source address and the
traditional destination address.

Figure 14-19

Policy-Based Routing

SNA traffic would best be served by being directed over the low-propagation delay link.

RSVP

RSVP is an IETF standard (RFC 2205) for allowing an application to dynamically reserve
network bandwidth. RSVP lets an application dynamically reserve network bandwidth from

Token Ring

ISBN S/370

56 K

Satellite

Router B

SNA

Host

Router A

87200333.book Page 536 Wednesday, August 22, 2001 1:41 PM