Understanding Routing Policy Match Conditions and Actions

A match condition defines the criteria that a route must match for an action to take place. Each term can have one or more match conditions. If a route matches all the match conditions for a particular term, the actions defined for that term are processed.

This topic contains the following sections:

Match Conditions
Actions

Match Conditions

Each term can consist of two statements, from and to, that define match conditions:

In the from statement, you define the criteria that an incoming route must match. You can specify one or more match conditions. If you specify more than one, all conditions must match the route for a match to occur.
In the to statement, you define the criteria that an outgoing route must match. You can specify one or more match conditions. If you specify more than one, all conditions must match the route for a match to occur.

The order of match conditions in a term is not important, because a route must match all match conditions in a term for an action to be taken.

Table 14 summarizes key routing policy match conditions.

Table 14: Summary of Key Routing Policy Match Conditions

Match Condition	Description
aggregate-contributor	Matches routes that are contributing to a configured aggregate. This match condition can be used to suppress a contributor in an aggregate route.
area area-id	Matches a route learned from the specified OSPF area during the exporting of OSPF routes into other protocols.
as-path name	Matches the name of the path regular expression of an autonomous systems (AS). BGP routes whose AS path matches the regular expression are processed.
color preference	Matches a color value. You can specify preference values that are finer-grained than those specified in the preference match conditions. The color value can be a number from 0 through 4,294,967,295 (2³² – 1). A lower number indicates a more preferred route.
community	Matches the name of one or more communities. If you list more than one name, only one name needs to match for a match to occur. (The matching is effectively a logical OR operation.)
external [type metric-type]	Matches external OSPF routes, including routes exported from one level to another. In this match condition, type is an optional keyword. The metric-type value can be either 1 or 2. When you do not specify type, this condition matches all external routes.
interface interface-name	Matches the name or IP address of one or more router interfaces. Use this condition with protocols that are interface-specific. For example, do not use this condition with internal BGP (IBGP). Depending on where the policy is applied, this match condition matches routes learned from or advertised through the specified interface.
internal	Matches a routing policy against the internal flag for simplified next-hop self policies.
level level	Matches the IS-IS level. Routes that are from the specified level or are being advertised to the specified level are processed.
local-preference value	Matches a BGP local preference attribute. The preference value can be from 0 through 4,294,967,295 (2³² – 1).
metric metric metric2 metric	Matches a metric value. The metric value corresponds to the multiple exit discriminator (MED), and metric2 corresponds to the IGP metric if the BGP next hop runs back through another route.
neighbor address	Matches the address of one or more neighbors (peers). For BGP export policies, the address can be for a directly connected or indirectly connected peer. For all other protocols, the address is for the neighbor from which the advertisement is received.
next-hop address	Matches the next-hop address or addresses specified in the routing information for a particular route. For BGP routes, matches are performed against each protocol next hop.
origin value	Matches the BGP origin attribute, which is the origin of the AS path information. The value can be one of the following: egp—Path information originated from another AS. igp—Path information originated from within the local AS. incomplete—Path information was learned by some other means.
preference preference preference2 preference	Matches the preference value. You can specify a primary preference value (preference) and a secondary preference value (preference2). The preference value can be a number from 0 through 4,294,967,295 (2³² – 1). A lower number indicates a more preferred route.
protocol protocol	Matches the name of the protocol from which the route was learned or to which the route is being advertised. It can be one of the following: aggregate, bgp, direct, dvmrp, isis, local, ospf, pim-dense, pim-sparse, rip, ripng, or static.
route-type value	Matches the type of route. The value can be either external or internal.

Actions

An action defines what the router does with the route when the route matches all the match conditions in the from and to statements for a particular term. If a term does not have from and to statements, all routes are considered to match and the actions apply to all routes.

Each term can have one or more of the following types of actions. The actions are configured under the then statement.

Flow control actions, which affect whether to accept or reject the route and whether to evaluate the next term or routing policy
Actions that manipulate route characteristics
Trace action, which logs route matches

If you do not specify an action, one of the following results occurs:

The next term in the routing policy, if one exists, is evaluated.
If the routing policy has no more terms, the next routing policy, if one exists, is evaluated.
If there are no more terms or routing policies, the accept or reject action specified by the default policy is executed.

Table 15 summarizes the routing policy actions.

Table 15: Summary of Key Routing Policy Actions

Action	Description
Flow Control Actions	These actions control the flow of routing information into and out of the routing table.
accept	Accepts the route and propagates it. After a route is accepted, no other terms in the routing policy and no other routing policies are evaluated.
reject	Rejects the route and does not propagate it. After a route is rejected, no other terms in the routing policy and no other routing policies are evaluated.
next term	Skips to and evaluates the next term in the same routing policy. Any accept or reject action specified in the then statement is ignored. Any actions specified in the then statement that manipulate route characteristics are applied to the route.
next policy	Skips to and evaluates the next routing policy. Any accept or reject action specified in the then statement is ignored. Any actions specified in the then statement that manipulate route characteristics are applied to the route.
Route Manipulation Actions	These actions manipulate the route characteristics.
as-path-prepend as-path	Appends one or more AS numbers at the beginning of the AS path. If you are specifying more than one AS number, include the numbers in quotation marks. The AS numbers are added after the local AS number has been added to the path. This action adds AS numbers to AS sequences only, not to AS sets. If the existing AS path begins with a confederation sequence or set, the appended AS numbers are placed within a confederation sequence. Otherwise, the appended AS numbers are placed with a nonconfederation sequence.
as-path-expand last-as count n	Extracts the last AS number in the existing AS path and appends that AS number to the beginning of the AS path n times. Replace n with a number from 1 through 32. The AS numbers are added after the local AS number has been added to the path. This action adds AS numbers to AS sequences only, not to AS sets. If the existing AS path begins with a confederation sequence or set, the appended AS numbers are placed within a confederation sequence. Otherwise, the appended AS numbers are placed with a nonconfederation sequence.
class class-name	Applies the specified class-of-service (CoS) parameters to routes installed into the routing table.
color preference color2 preference	Sets the preference value to the specified value. The color and color2 preference values can be a number from 0 through 4,294,967,295 (2³² – 1). A lower number indicates a more preferred route.
damping name	Applies the specified route-damping parameters to the route. These parameters override BGP's default damping parameters. This action is useful only in import policies.
local-preference value	Sets the BGP local preference attribute. The preference can be a number from 0 through 4,294,967,295 (2³² – 1).
metric metric metric2 metric metric3 metric metric4 metric	Sets the metric. You can specify up to four metric values, starting with metric (for the first metric value) and continuing with metric2, metric3, and metric4. For BGP routes, metric corresponds to the MED, and metric2 corresponds to the IGP metric if the BGP next hop loops through another router.
next-hop address	Sets the next hop. If you specify address as self, the next-hop address is replaced by one of the local router's addresses. The advertising protocol determines which address to use.

Understanding Routing Policy Match Conditions and Actions

Match Conditions

Actions

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