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Policy Based Routing

July 25th, 2017 in ROUTE 300-101 Go to comments

Question 1

Explanation

Normal policy based routing (PBR) is used to route packets that pass through the device. Packets that are generated by the router (itself) are not normally policy-routed. To control these packets, local PBR should be used. For example: Router(config)# ip local policy route-map map-tag (compared with normal PBR: Router(config-if)# ip policy route-map map-tag)

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfpbr.html

Question 2

Explanation

The set command specifies the action(s) to take on the packets that match the criteria. You can specify any or all of the following:

* precedence: Sets precedence value in the IP header. You can specify either the precedence number or name.
* df: Sets the “Don’t Fragment” (DF) bit in the ip header.
* vrf: Sets the VPN Routing and Forwarding (VRF) instance.
* next-hop: Sets next hop to which to route the packet.
* next-hop recursive: Sets next hop to which to route the packet if the hop is to a router which is not adjacent.
* interface: Sets output interface for the packet.
* default next-hop: Sets next hop to which to route the packet if there is no explicit route for this destination.
* default interface: Sets output interface for the packet if there is no explicit route for this destination.

route_map_set_command1.jpg

route_map_set_command.jpg

(Reference: http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfpbr_ps1835_TSD_Products_Configuration_Guide_Chapter.html)

Question 3

Explanation

The “show route-map “route-map name” displays the policy routing match counts so we can learn if PBR reacts to packets sourced from 172.16.0.0/16 or not.

show_route-map_divert.jpg

Question 4

Explanation

First we should check the access-list log, if the hit count does not increase then no packets are matched the access-list -> the policy based routing match counts will not increase.

Comments
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    September 22nd, 2017

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    September 29th, 2017

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