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Chapter 10
Route Optimization
Once the match clause is satisfied, the set clause can manipulate the rout-
ing of the traffic by setting the next-hop or default interface or IP address,
setting the IP TOS (Type of Service), or setting the IP precedence of the traf-
fic. Note that route maps are set on the source router (the first router to
receive the packet), not the destination router. To better understand how
policy routing works, let's consider a couple of examples.
Policy-Routing TCP Services
As shown in Figure 10.12, Company A has two connections to the Internet:
one to ISP A and the other to ISP B. The connection to ISP A is much faster
than the connection to ISP B. Therefore, Company A wants to send all
latency-sensitive traffic over the link to ISP A and all non-interactive traffic
over the link to ISP B. So, for our example, we will configure RouterA to
direct SMTP (Simple Mail Transfer Protocol) traffic over the link to ISP B, and
all other traffic will be sent over the link to ISP A.
F I G U R E 1 0 . 1 2
Policy routing example 1
First we need to create an access list that will define the traffic we are
interested in, specifically SMTP traffic:
access-list 101 permit tcp any any eq 25
where 25 is the tcp port number for SMTP.
Next, we need to create a route map. In this example, we will name it
"routemail":
route-map routemail permit 10
Internet
172.16.2.2/24
172.16.1.2/24
56Kbps link
1.544Mbps link
172.16.1.1/24
172.16.2.1/24
s1
s0
ISP A
RouterB
ISP B
RouterC
Company A
RouterA
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