packet or route using the match commands. If the conditions match, actions are taken to modify attributes of the packet or route. These actions are specified by the set commands. A collection of route map statements that have the same route map name is considered one route map. Within a route map, each route map statement is numbered and can be edited individually. The statements in a route map are analogous to the lines of an ACL. Specifying the match conditions in a route map is similar to specifying the source and destination addresses and masks in an ACL. One major difference between route maps and ACLs is that route maps can use the set commands to modify the packet or route. Web Links Understanding Policy Routing
http://www.cisco.com/warp/public/105/36.html
Content 5.4 Policy-based Routing 5.4.2 Route Map Applications Network administrators use the route map tool for a variety of purposes. Several of the more common applications for route maps are as follows:
Content 5.4 Policy-based Routing 5.4.3 Route Map Operation Route maps operate in a manner similar to ACLs. When determining which routes will be redistributed from one protocol to the next, the router checks each route against the route map, beginning with the top line. Each line is sequence-numbered, both for top-down processing purposes and for editing purposes. Lines can be added or removed from a route map as changes are required. Each line has a permit or deny statement. If a route is matched in the matching statements and the line statement is “permit,” the router sets the metrics or other defined conditions and permits the redistribution of that route. The route map stops processing at the first match. If the packet is matched and the route map line is “deny,” the router stops at the matched line in the map and does not redistribute that route. Routes are filtered by this method. Routes are checked from line to line looking for a match. If there is no match and the bottom of the route map is reached, the router denies the route from being redistributed. Like an ACL, there is an implicit “deny any” at the end of a route map. Matching statements in a route map can be complex. Multiple match criteria in the same line are processed with OR logic. Separate match criteria can also be applied vertically under a route map line. In this case, each match uses AND logic. A route map may consist of multiple route map statements. The statements are processed top down, like an ACL. The first match found for a route is applied. The sequence number is used for inserting or deleting specific route map statements in a specific place in the route map. The match route map configuration commands define the conditions to be checked. The set route map configuration commands define the actions that you should follow if there is a match. The single-match statement may contain multiple conditions. At least one condition in the match statement must be true to consider the statement a match (logical OR). A route map statement may contain multiple-match statements. All match statements in the route map statement must be true to consider the route map statement a match (logical AND). The sequence number specifies the order in which conditions are checked. For example, if there are two statements in a route map named MYMAP, one with sequence 10 and the other with sequence 20, sequence 10 is checked first. If the match conditions in sequence 10 are not met, sequence 20 is checked. Like an ACL, there is an implicit “deny any” at the end of a route map. The consequences of this deny depend on how the route map is used.
Content 5.4 Policy-based Routing 5.4.4 Using Route Map Commands The route-map command defines the conditions for route filtering and redistribution. Figure displays the command parameters. When used for redistribution filtering, a route map is applied to the route redistribution process by adding route-map map-tag at the end of the redistribute protocol command.
Content 5.4 Policy-based Routing 5.4.5 The match Command The match command is applied within a route map. Figure displays some of the match command parameters. The parameters represent a general list of match criteria. Some criteria are used for BGP policy, some for PBR, and some for redistribution filtering.
Content 5.4 Policy-based Routing 5.4.6 The set Command The set command is used within a route map to change or add characteristics, such as metrics, to any routes that have met a match criterion. Figure displays some of the set command parameters. Not all of the set options that are listed here are used for redistribution purposes. The table includes options for BGP and PBR.
Content 5.4 Policy-based Routing 5.4.7 Implementing Route Maps with Redistribution In Figure , RIPv1 is being redistributed into OSPF 10. A route map called “redis-rip” is attached to the redistribute rip command. Sequence number 10 of the route map is looking for an IP address match in ACL 23 or ACL 29. If a match is found, the router redistributes the route into OSPF with a cost metric of 500 and sets the new OSPF route to external type 1. If there is no match to line 10, move to line 20. If there is a match in ACL 37, do not let that route redistribute into OSPF because sequence number 20 is a deny. If there is no match to sequence number 20, move to 30. Because 30 is a permit and there is no match criterion, all remaining routes are redistributed into OSPF with a cost metric of 5000 and an external metric of type 2. Implementing Policy Routing
Figure presents a policy routing scenario. A route map can be used at RTA to implement policy routing. Assume for this example that the policy to be enforced is as follows: First, define the access lists that will be used in the route maps to match IP addresses. Then configure the route map itself using the syntax shown in Figure . The commands in the figure actually have two policies configured. The ISP1 route map matches access list 1 and routes traffic out S0 toward ISP1. The ISP2 route map matches access list 2 and routes that traffic out S1 toward ISP2. The final step is to apply each route map to the appropriate interface on RTA using the ip policy route-map command. With the route maps applied to the appropriate LAN interfaces, policy routing is successfully implemented. Frequently, route maps are used to control the exchange of routing information during redistribution.
Content 5.5 DHCP 5.5.1 The Purpose of DHCP DHCP is structured on the Bootstrap Protocol (BOOTP) server and BOOTP well-known ports in User Datagram Protocol (UDP). Previous to DHCP, IP