BGP routes originated through redistribution have incomplete origin

router (config)# router bgp <AS>

router (config-router)# redistribute <IGP>

router (config-router)# di stribute-list *CACL> out router (config-router)# exit router (config)# access-list <ACL> permit <network>

Routes redistributed into BGP will carry the origin attribute "incomplete". In most cases this situation does not jeopardize BGP functionality. It could pose a problem if the route selection process has to decide on the best route toward a particular destination based on the MED attribute. In the case of receiving two routes, one with the "IGP" origin (inserted with the network command), and another one with the "incomplete" origin, the first route would always be selected, no matter what value that the MED attribute is set to (according to the BGP route selection rules).

redistribute (IP)

To redistribute routes from one routing process into another routing process, use the redistribute router configuration command.

■ redistribute protocol [process-id] {level-1 | level-1-2 | level-2} [metric metric-value] [match {internal | external 1 | external 2}] [tag tag-value] [route-map map-tag] [weight weight] [subnets]

To disable redistribution, use the no form of this command.

■ no redistribute protocol [process-id] {level-1 | level-1-2 | level-2} [metric metric-value] [match {internal | external 1 | external 2}] [tag tag-value] [route-map map-tag] [weight weight] [subnets]

1-82 Configuring BGP on Cisco Routers (BGP) v3.1 Copyright © 2004, Cisco Systems, Inc.

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be used in commercial training, and may not be distributed for purposes other than individual self-study.

Syntax Description

Parameter

Description

protocol

Source protocol from which routes are being redistributed. It can be one of the following keywords: bgp

process-id

(Optional) For bgp, egp, or igrp, this is an AS number, which is a 16-bit decimal number.

For isis, this is an optional tag that defines a meaningful name for a routing process. You can specify only one Intermediate System-to-Intermediate System (IS-IS) process per router. Creating a name for a routing process means that you use names when configuring routing.

For ospf, this is an appropriate OSPF process ID from which routes are to be redistributed. This ID identifies the routing process. This value takes the form of a nonzero decimal number.

For rip, no process ID value is needed.

level-1

For IS

level-1-2

For IS

level-2

For IS

metric metric-value

(Optional) Metric that is used for the redistributed route. If a value is not specified for this option, and no value is specified using the default

match {internal | external 1 | external 2}

(Optional) For OPSF, the criteria by which OSPF routes are redistributed into other routing processes. It can be one of the following:

■ internal: Routes that are internal to a specific AS.

■ external 1: Routes that are external to the AS but are imported into OSPF as a type 1 external route.

■ external 2: Routes that are external to the AS but are imported into OSPF as a type 2 external route.

route-map

(Optional) The route-map should be interrogated to filter the importation of routes from this source routing protocol to the current routing protocol. If not specified, all routes are redistributed. If this keyword is specified, but no route-map tags are listed, no routes will be imported.

map-tag

(Optional) Identifier of a configured route-map.

weight weight

(Optional) Network weight when you are redistributing into BGP. An integer from 0 to 65535.

subnets

Indicates that not only networks with a natural mask should be redistributed but also subnets.

Copyright © 2004, Cisco Systems, Inc. BGP Overview 1-83

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be used in commercial training, and may not be distributed for purposes other than individual self-study.

distribute-list out (IP)

To suppress networks from being advertised in updates, use the distribute-list out router configuration command with routing-process specified.

■ distribute-list {access-list-number | access-list-name} out [interface-name | routing-process | autonomous-system-number]

To cancel this function, use the no form of this command.

■ no distribute-list {access-list-number | access-list-name} out [interface-name | routing-process | autonomous-system-number]

The access-list referred to by the distribute-list command permits those routes that should be redistributed.

1-84 Configuring BGP on Cisco Routers (BGP) v3.1 Copyright © 2004, Cisco Systems, Inc.

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be used in commercial training, and may not be distributed for purposes other than individual self-study.

Redistribution Using Route-Maps

• Origin can be set to "IGP" with a route-map

• Other BGP path attributes can also be set:

- Metric

- Next-hop

- Community

© 2004 Cisco Systems, Ii

© 2004 Cisco Systems, Ii

Route-maps can be configured on the router to filter updates and modify various attributes. A configured route-map can be applied to routes being redistributed from the IGP.

Only the routes permitted by the route-map will be redistributed. Using the set command in the route-map, you can modify specific path attributes that are attached to the redistributed routes. Thus, only selected routes will be advertised, and they will have the desired attribute values.

The route-map must be given a name. This name is a case-sensitive string, which is used when you are referring to it. Any string could be used, but a meaningful name is suggested.

Use the route-map global configuration command and the match and set route-map configuration commands to define the conditions for redistributing routes. Each repetition of the route-map command has a list of match and set commands that are associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map command. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met.

When you are passing routes through a route-map, it can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised. If you want to modify only some data, you must configure a second route-map section with an explicit match specified.

Copyright © 2004, Cisco Systems, Inc. BGP Overview 1-85

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be used in commercial training, and may not be distributed for purposes other than individual self-study.

Was this article helpful?

+1 0

Post a comment