BGP Commands

Syntax Description

address	Aggregate address.
mask	Aggregate mask.
as-set	(Optional) Generates autonomous system set path information.
summary-only	(Optional) Filters all more specific routes from updates.
suppress-map map-name	(Optional) Name of route map used to select the routes to be suppressed.
advertise-map map-name	(Optional) Name of route map used to select the routes to create AS-SET origin communities.
attribute-map map-name	(Optional) Name of route map used to set the attribute of the aggregate route.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

You can implement aggregate routing in BGP either by redistributing an aggregate route into BGP or by using this conditional aggregate routing feature.

Using the aggregate-address command with no arguments will create an aggregate entry in the BGP routing table if there are any more-specific BGP routes available that fall in the specified range. The aggregate route will be advertised as coming from your autonomous system and has the atomic aggregate attribute set to show that information might be missing. (By default, the atomic aggregate attribute is set unless you specify the as-set keyword.)

Using the as-set keyword creates an aggregate entry using the same rules that the command follows without this keyword, but the path advertised for this route will be an AS_SET consisting of all elements contained in all paths that are being summarized. Do not use this form of aggregate-address when aggregating many paths, because this route must be continually withdrawn and re-updated as autonomous system path reachability information for the summarized routes changes.

Syntax Description

This command has no arguments or keywords.

Defaults

Enabled (the software summarizes subprefixes to the classful network boundary when crossing classful network boundaries).

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

Route summarization reduces the amount of routing information in the routing tables.

By default, BGP does not accept subnets redistributed from Interior Gateway Protocol (IGP). To advertise and carry subnet routes in BGP, use an explicit network command or the no auto-summary command. If you disable auto-summarization and have not entered a network command, you will not advertise network routes for networks with subnet routes unless they contain a summary route.

In the following example, network numbers are not summarized automatically:

router bgp 6
 no auto-summary

Syntax Description

This command has no arguments or keywords.

Defaults

The Cisco IOS software does not compare MEDs for paths from neighbors in different autonomous systems.

Command Modes

Router configuration

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

The MED is one of the parameters that is considered when selecting the best path among many alternative paths. The path with a lower MED is preferred over a path with a higher MED.

By default, during the best-path selection process, MED comparison is done only among paths from the same autonomous system. This command changes the default behavior by allowing comparison of MEDs among paths regardless of the autonomous system from which the paths are received.

Examples

The following example configures the BGP speaker in autonomous system 100 to compare MEDs among alternative paths, regardless of the autonomous system from which the paths are received:

router bgp 109
 bgp always-compare-med

Syntax Description

This command has no arguments or keywords.

Defaults

The router considers as-path in choosing a route.

Command Modes

Router configuration

Command History

Release	Modification
12.0	This command was introduced.

Examples

The following example prevents the BGP router from considering as-path as a factor in choosing a route.

router bgp 210 
 bgp bestpath as-path ignore

Related Commands

Command	Description
show ip bgp neighbors	Displays information about the TCP and BGP connections to neighbors.

Syntax Description

This command has no arguments or keywords.

Defaults

The software does not consider the MED attribute when choosing among paths learned from confederation peers.

Command Modes

Router configuration

Command History

Release	Modification
12.0	This command was introduced.

Usage Guidelines

The comparison between MEDs is only made if there are no external autonomous systems in the path (an external autonomous system is an autonomous system that is not within the confederation). If there is an external autonomous system in the path, then the external MED is passed transparently through the confederation, and the comparison is not made.

For example, assume that AS 65000, 65001, 65002, and 65004 are part of the confederation; AS1 is not; and we are comparing route A with four paths. If the bgp bestpath med-confed command is enabled, path 1 would be chosen. The fourth path has a lower MED, but it is not involved in the MED comparison because there is an external autonomous system in this path.

path= 65000 65004, med=2

path= 65001 65004, med=3

path= 65002 65004, med=4

path= 65003 1, med=1

Examples

The following command enables the BGP router to compare MED values for paths learned from confederation peers.

router bgp 210
 bgp bestpath med-confed

Related Commands

Command	Description
show ip bgp	Display entries in the BGP routing table.
show ip bgp neighbors	Displays information about the TCP and BGP connections to neighbors.

Syntax Description

This command has no arguments or keywords.

Defaults

The software assigns a value of 0 to the missing MED, causing the path with the missing MED attribute to be considered the best path.

Command Modes

Router configuration

Command History

Release	Modification
12.0	This command was introduced.

Examples

The following command specifies that the Border Gateway Protocol (BGP) router to consider a missing MED attribute in a path as having a value of infinity, making this path the least desirable path.

router bgp 210
 bgp bestpath missing-as-worst

Related Commands

Command	Description
show ip bgp	Display entries in the BGP routing table.
show ip bgp neighbors	Displays information about the TCP and BGP connections to neighbors.

Syntax Description

This command has no arguments or keywords.

Defaults

When a route reflector is configured, the route reflector reflects routes from a client to other clients.

Command Modes

Router configuration

Command History

Release	Modification
11.1	This command was introduced.

Usage Guidelines

By default, the clients of a route reflector are not required to be fully meshed and the routes from a client are reflected to other clients. However, if the clients are fully meshed, route reflection is not required. Use the no bgp client-to-client reflection command to disable client-to-client reflection.

Examples

In the following example, the local router is a route reflector. The three neighbors are fully meshed, so client-to-client reflection is disabled.

router bgp 5
 neighbor 155.24.95.22 route-reflector-client
 neighbor 155.24.95.23 route-reflector-client
 neighbor 155.24.95.24 route-reflector-client
 no bgp client-to-client reflection

Related Commands

Command	Description
bgp cluster-id	Configures the cluster ID if the BGP cluster has more than one route reflector.
neighbor route-reflector-client	Configures the router as a BGP route reflector and configures the specified neighbor as its client.
show ip bgp	Displays entries in the BGP routing table.

Syntax Description

cluster-id

Cluster ID of this router acting as a route reflector; maximum of 4 bytes.

Defaults

The router ID of the single route reflector in a cluster

Command Modes

Router configuration

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

Together, a route reflector and its clients form a cluster.

Usually a cluster of clients will have a single route reflector. In that case, the cluster is identified by the router ID of the route reflector. In order to increase redundancy and avoid a single point of failure, a cluster might have more than one route reflector. In this case, all route reflectors in the cluster must be configured with the 4-byte cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster.

If the cluster has more than one route reflector, use this command to configure the cluster ID.

Examples

In the following example, the local router is one of the route reflectors serving the cluster. It is configured with the cluster ID to identify the cluster.

router bgp 5
 neighbor 198.92.70.24 route-reflector-client
 bgp cluster-id 50000

Related Commands

Command	Description
bgp client-to-client reflection	Restores route reflection from a BGP route reflector to clients.
neighbor route-reflector-client	Configures the router as a BGP route reflector and configures the specified neighbor as its client.
show ip bgp	Display entries in the BGP routing table.

Syntax Description

autonomous-system

Autonomous system number that internally includes multiple autonomous systems.

Defaults

No confederation identifier is configured.

Command Modes

Router configuration

Command History

Release	Modification
10.3	This command was introduced.

Usage Guidelines

Examples

In the following example, the autonomous system is divided into autonomous systems 4001, 4002, 4003, 4004, 4005, 4006, and 4007 and identified by the confederation identifier 5. Neighbor 1.2.3.4 is someone inside your routing domain confederation. Neighbor 3.4.5.6 is someone outside your routing domain confederation. To the outside world, there appears to be a single autonomous system with the number 5.

router bgp 4001
 bgp confederation identifier 5
 bgp confederation peers 4002 4003 4004 4005 4006 4007
 neighbor 1.2.3.4 remote-as 4002
 neighbor 3.4.5.6 remote-as 510

Related Commands

Command	Description
bgp confederation peers	Configures the autonomous systems that belong to the confederation.

Syntax Description

autonomous-system

Autonomous system numbers for BGP peers that will belong to the confederation.

No confederation peers are configured.

Defaults

No Border Gateway Protocol (BGP) peers are identified as belonging to the confederation.

Command Modes

Router configuration

Command History

Release	Modification
10.3	This command was introduced.

Usage Guidelines

Syntax Description

half-life	(Optional) Time (in minutes) after which a penalty is decreased. Once the route has been assigned a penalty, the penalty is decreased by half after the half-life period (which is 15 minutes by default). The process of reducing the penalty happens every 5 seconds. The range of the half-life period is 1 to 45 minutes. The default is 15 minutes.
reuse	(Optional) If the penalty for a flapping route decreases enough to fall below this value, the route is unsuppressed. The process of unsuppressing routes occurs at 10-second increments. The range of the reuse value is 1 to 20000; the default is 750.
suppress	(Optional) A route is suppressed when its penalty exceeds this limit. The range is 1 to 20000; the default is 2000.
max-suppress-time	(Optional) Maximum time (in minutes) a route can be suppressed. The range is 1 to 20000; the default is 4 times the half-life. If the half-life value is allowed to default, the maximum suppress time defaults to 60 minutes.
route-map map	(Optional) Name of route map that controls where BGP route dampening is enabled.

Defaults

Disabled by default.

half-life is 15 minutes.
reuse is 750.
suppress is 2000.
max-suppress-time is 4 times half-life.

Command Modes

Global configuration

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

If this command is used with no arguments, it enables BGP route dampening. The arguments half-life, reuse, suppress, and max-suppress-time are position-dependent. Therefore, if any of them are used, they must all be specified.

Examples

The following example sets the half-life to 30 minutes, the reuse value to 1500, the suppress value to 10000; and the maximum suppress time to 120 minutes:

bgp dampening 30 1500 10000 120

Related Commands

Command	Description
clear ip bgp dampening	Clears BGP route dampening information and unsuppresses the suppressed routes.
clear ip bgp flap-statistics	Clears BGP flap statistics.
show ip bgp dampened-paths	Displays BGP dampened routes.
show ip bgp flap-statistics	Displays BGP flap statistics.

Syntax Description

value

Local preference value from 0 to 4294967295. Higher is more preferred.

Defaults

Local preference value of 100

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

Generally, the default value of 100 allows you to easily define a particular path as less preferable than paths with no local preference attribute. The preference is sent to all routers and access servers in the local autonomous system.

Examples

The following example raises the default local preference value from the default of 100 to 200:

router bgp 200
 bgp default local-preference 200

Related Commands

Command	Description
set local-preference	Specifies a preference value for the autonomous system path.

Syntax Description

This command has no arguments or keywords.

Defaults

Enabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Examples

The following example disables the automatic resetting of BGP sessions:

router bgp 109
 no bgp fast-external-fallover

Syntax Description

This command has no arguments or keywords.

Defaults

No BGP neighbor changes are logged.

Command Modes

Router configuration

Command History

Release	Modification
11.1 CC and 12.0	This command was introduced.

Usage Guidelines

The bgp log-neighbor-changes command enables logging of BGP neighbor status changes (up or down) and resets for troubleshooting network connectivity problems and measuring network stability. Unexpected neighbor resets might indicate high error rates or high packet loss in the network and should be investigated.

Using the bgp log-neighbor-changes command to enable status change message logging does not create a significant performance hit, unlike, for example, enabling per BGP update debugging. If the UNIX syslog facility is enabled, messages are sent to the UNIX host running the syslog daemon so that the messages can be stored and archived. If the UNIX syslog facility is not enabled, the status change messages are retained in the router's internal buffer, and are not stored to disk. You can set the size of this buffer, which is dependent upon the available RAM, using the logging buffered command.

The neighbor status change messages are not tracked if bgp log-neighbor changes is not enabled, except for the reset reason, which is always available as output of the show ip bgp neighbor command.

The log messages display the following reasons for changes in a neighbor's status:

BGP protocol initialization

No memory for path entry

No memory for attribute entry

No memory for prefix entry

No memory for aggregate entry

No memory for dampening info

No memory for BGP updates

BGP Notification received

Erroneous BGP Update received

User reset request

Peer timeout

Password change

Error during connection collision

Peer closing down the session

Peer exceeding maximum prefix limit

Interface flap

Router ID changed

Neighbor deleted

Member added to peergroup

Administratively shutdown

Remote AS changed

RR client configuration modification

Soft reconfiguration modification

The eigrp log-neighbor-changes command enables logging of Enhanced IGRP neighbor adjacencies, but messages for BGP neighbors are logged only if they are specifically enabled with the bgp log-neighbor-changes command.

Use the show logging command to display the log for the BGP neighbor changes.

Examples

The following configuration will log neighbor changes for BGP:

bgp router 100
    bgp log-neighbor-changes

Related Commands

Command	Description
logging buffered	Logs messages to an internal buffer.
show ip bgp neighbors	Displays information about the TCP and BGP connections to neighbors.
show logging	Displays the state of logging (syslog).

Syntax Description

*	Resets all current BGP sessions.
address	Resets only the identified BGP neighbor.
peer-group-name	Resets the specified BGP peer group.
soft	(Optional) Soft reset. Does not reset the session.
in | out	(Optional) Triggers inbound or outbound soft reconfiguration. If the in or out option is not specified, both inbound and outbound soft reset are triggered.

Defaults

No reset is initiated.

Command Modes

EXEC

Command History

Release	Modification
10.0	This command was introduced.
12.0(6)T	The dynamic inbound soft reset capability was added.

Usage Guidelines

You can reset inbound routing table updates dynamically or by generating new updates using stored update information. Using stored update information required additional memory for storing the updates.

To reset inbound routing table updates dynamically, all BGP routers must support the route refresh capability. To determine whether a BGP router supports this capability, use the show ip bgp neighbors command. If a router supports the route refresh capability, the following message is displayed:

Received route refresh capability from peer.

If all BGP routers support the route refresh capability, use the clear ip bgp {*|address|peer-group name} in command. You need not use the soft keyword, because soft reset is automatically assumed when the route refresh capability is supported.

To generate new inbound updates from stored update information (rather than dynamically), without resetting the BGP session, you must first preconfigure the local BGP router using the neighbor soft-reconfiguration inbound command. This preconfiguration causes the software to store all received updates without modification regardless of whether an update is accepted by the inbound policy. Storing updates is memory intensive and should be avoided if possible.

Outbound BGP soft configuration does not have any memory overhead and does not require any preconfiguration. You can trigger an outbound reconfiguration on the other side of the BGP session to make the new inbound policy take effect.

Use this command whenever any of the following changes occur:

• Additions or changes to the BGP-related access lists

• Changes to BGP-related weights

• Changes to BGP-related distribution lists

• Changes to BGP-related route maps

Examples

The following example clears the inbound session with the neighbor 131.108.1.1 without resetting the session:

clear ip bgp 131.108.1.1 soft in
 

The following example clears the outbound session with the peer-group corp without resetting the session:

clear ip bgp corp soft out

Related Commands

Command	Description
neighbor soft-reconfiguration	Configures the Cisco IOS software to start storing updates.
show ip bgp	Displays entries in the BGP routing table.

Syntax Description

address	(Optional) IP address of the network about which to clear dampening information.
mask	(Optional) Network mask applied to the address.

Command Modes

EXEC

Command History

Release	Modification
11.0	This command was introduced.

Examples

The following example clears route dampening information about the route to network 150.0.0.0 and unsuppresses its suppressed routes. When the address and mask arguments are not specified, the clear ip bgp dampening command clears route dampening information for the entire BGP routing table.

clear ip bgp dampening 150.0.0.0 255.255.0.0

Related Commands

Command	Description
bgp dampening	Enables BGP route dampening or changes various BGP route dampening factors.
show ip bgp dampened-paths	Displays BGP dampened routes.

Syntax Description

regexp regexp	(Optional) Clears flap statistics for all the paths that match the regular expression.
filter-list list	(Optional) Clears flap statistics for all the paths that pass the access list.
address	(Optional) Clears flap statistics for a single entry at this IP address. If this argument is placed before flap-statistics, the router clears flap statistics for all paths from the neighbor at this address.
mask	(Optional) Network mask applied to the address.

Defaults

No statistics are cleared.

Command Modes

EXEC

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

If no arguments or keywords are specified, the router clear flap statistics for all routes.

The flap statistics for a route are also cleared when a BGP peer is reset. Although the reset withdraws the route, there is no penalty applied in this instance even though route flap dampening is enabled.

Examples

The following example clears all of the flap statistics for paths that pass filter list 3:

clear ip bgp flap-statistics filter-list 3

Related Commands

Command	Description
bgp dampening	Enables BGP route dampening or changes various BGP route dampening factors.

Syntax Description

tag	Name of the BGP peer group to clear.

Defaults

No BGP peer group members are cleared.

Command Modes

EXEC

Command History

Release	Modification
11.0	This command was introduced.

Examples

The following example clears all members from the BGP peer group internal:

clear ip bgp peer-group internal

Related Commands

Command	Description
neighbor peer-group (assigning members)	Configures a BGP neighbor to be a member of a peer group.

Syntax Description

name	(Optional) The name of the prefix list from which the hit count is to be cleared.
network/len	(Optional) The network number and length (in bits) of the network mask.

Defaults

Does not clear the hit count.

Command Modes

Router configuration

Command History

Release	Modification
12.0	This command was introduced.

Usage Guidelines

The hit count is a value indicating the number of matches to a specific prefix list entry.

Examples

The following example clears the hit count from the prefix list entries for the prefix list named first_list that match the network mask 35.0.0.0/8.

clear ip prefix-list first_list 35.0.0.0/8

Related Commands

Command	Description
distribute-list in (IP)	Filters networks received in updates.
distribute-list out	Suppresses networks from being advertised in updates.
ip prefix-list	Creates an entry in a prefix list
ip prefix-list description	Adds a text description of a prefix list.
ip prefix-list sequence-number	Enables the generation of sequence numbers for entries in a prefix list
redistribute (IP)	Redistributes routes from one routing domain into another routing domain.
show ip bgp regexp	Displays information about a prefix list or prefix list entries

Syntax Description

This command has no arguments or keywords.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Examples

The following example configures BGP to redistribute network 0.0.0.0 into BGP:

router bgp 164
 default-information originate

Related Commands

Command	Description
neighbor ebgp-multihop	Accepts and attempts BGP connections to external peers residing on networks that are not directly connected.
network (BGP)	Specifies the list of networks for the BGP routing process.

Syntax Description

number

Default metric value appropriate for the specified routing protocol.

Defaults

Built-in, automatic metric translations, as appropriate for each routing protocol

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

In BGP, this command sets the Multi Exit Discriminator (MED) metric. (The name of this metric for BGP Versions 2 and 3 is INTER_AS.)

Examples

The following example shows a router in autonomous system 109 using both the BGP and the Open Shortest Path First (OSPF) routing protocols. In the example, OSPF-derived routes are advertised by BGP with a default metric of 10.

router bgp 109
 default-metric 10
 redistribute ospf

Related Commands

Command	Description
redistribute (IP)	Redistributes routes from one routing domain into another routing domain.

Syntax Description

external-distance	Administrative distance for Border Gateway Protocol (BGP) external routes. External routes are routes for which the best path is learned from a neighbor external to the autonomous system. Acceptable values are from 1 to 255. The default is 20. Routes with a distance of 255 are not installed in the routing table.
internal-distance	Administrative distance for BGP internal routes. Internal routes are those routes that are learned from another BGP entity within the same autonomous system. Acceptable values are from 1 to 255. The default is 200. Routes with a distance of 255 are not installed in the routing table.
local-distance	Administrative distance for BGP local routes. Local routes are those networks listed with a network router configuration command, often as back doors, for that router or for networks that are being redistributed from another process. Acceptable values are from 1 to 255. The default is 200. Routes with a distance of 255 are not installed in the routing table.

Defaults

external-distance: 20
internal-distance: 200
local-distance: 200

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual router or a group of routers. Numerically, an administrative distance is an integer between 0 and 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.

Use this command if another protocol is known to be able to provide a better route to a node than was actually learned via external BGP, or if some internal routes should really be preferred by the BGP.

Note Changing the administrative distance of BGP internal routes is considered dangerous and is not recommended. One problem that can arise is the accumulation of routing table inconsistencies, which can break routing.

Examples

In the following example, internal routes are known to be preferable to those learned through the Interior Gateway Protocol (IGP), so the administrative distance values are set accordingly:

router bgp 109
 network 131.108.0.0
 neighbor 129.140.6.6 remote-as 123
 neighbor 128.125.1.1 remote-as 47
 distance bgp 20 20 200

Syntax Description

access-list-number | name	Standard IP access list number or name. The list defines which networks are to be received and which are to be suppressed in routing updates.
prefix-list	Name of a prefix list. The list defines which networks are to be received and which are to be suppressed in routing updates, based upon matching the network prefix to the prefixes in the list.
in	Applies the access list to incoming routing updates.
type	(Optional) Interface type.
number	(Optional) Interface number on which the access list should be applied to incoming updates. If no interface is specified, the access list will be applied to all incoming updates.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
11.2	The access-list-name, type, and number arguments were added.
12.0	The prefix-list argument was added.

Usage Guidelines

This command is not supported in IS-IS or OSPF.

Using a prefix list allows filtering based upon the prefix length, making it possible to filter either on the prefix list, the gateway, or both for incoming updates.

Do not use both access-list and prefix-list with the distribute-list in command.

To suppress networks from being advertised in updates, use the distribute-list out command.

Examples

In the following example, the BGP routing process accepts only two networks---network 0.0.0.0 and network 131.108.0.0:

access-list 1 permit 0.0.0.0
access-list 1 permit 131.108.0.0
access-list 1 deny 0.0.0.0 255.255.255.255
router bgp
 network 131.108.0.0
 distribute-list 1 in

In the following example, the BGP routing process accepts only networks with prefixes that match those in the prefix list firstlist on the interface ethernet 0.

router bgp
distribute-list prefix list firstlist in ethernet 0

Related Commands

Command	Description
access-list (IP extended)	Defines an extended IP access list.
clear ip prefix-list	Resets the hit count of the prefix list entries.
distribute-list out	Suppresses networks from being advertised in updates.
ip prefix-list	Creates an entry in a prefix list
ip prefix-list description	Adds a text description of a prefix list.
ip prefix-list sequence-number	Enables the generation of sequence numbers for entries in a prefix list
redistribute (IP)	Redistributes routes from one routing domain into another routing domain.
show ip bgp regexp	Displays information about a prefix list or prefix list entries

Syntax Description

access-list-number | name	Standard IP access list number or name. The list defines which networks are to be received and which are to be suppressed in routing updates.
prefix-list	Name of a prefix list. The list defines which networks are to be received and which are to be suppressed in routing updates, based upon matching the network prefix to the prefixes in the list.
out	Applies the access list to outgoing routing updates.
interface-name	(Optional) Name of a particular interface.
routing-process	(Optional) Name of a particular routing process, or the keyword static or connected.
autonomous-system- number	(Optional) Autonomous system number.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
11.2	The access-list-name argument was added.
12.0	The prefix-list argument was added.

Usage Guidelines

When redistributing networks, a routing process name can be specified as an optional trailing argument to the distribute-list command. This causes the access list to be applied to only those routes derived from the specified routing process. After the process-specific access list is applied, any access list specified by a distribute-list command without a process name argument will be applied. Addresses not specified in the distribute-list command will not be advertised in outgoing routing updates.

Do not use both prefix-list and access-list with the distribute-list out command.

Note To filter networks received in updates, use the distribute-list in command.

Examples

The following example causes only one network (network 131.108.0.0) to be advertised by a RIP routing process.

access-list 1 permit 131.108.0.0
access-list 1 deny 0.0.0.0 255.255.255.255
router rip
 network 131.108.0.0
 distribute-list 1 out
 

In the following example, access list 1 is applied to outgoing routing updates, and IS-IS is enabled on Ethernet interface 0. Only network 131.131.101.0 will be advertised in outgoing IS-IS routing updates.

router isis
 redistribute ospf 109
 distribute-list 1 out
interface Ethernet 0
 ip router isis
access-list 1 permit 131.131.101.0 0.0.0.255
 

In the following example, the BGP routing process advertises only networks with prefixes that match those in the prefix list firstlist on the interface ethernet 0.

router bgp
distribute-list prefix list firstlist out ethernet 0

Related Commands

Command	Description
access-list (IP extended)	Defines an extended IP access list.
clear ip prefix-list	Resets the hit count of the prefix list entries.
distribute-list in	Filters networks received in updates.
ip prefix-list	Creates an entry in a prefix list
ip prefix-list description	Adds a text description of a prefix list.
ip prefix-list sequence-number	Enables the generation of sequence numbers for entries in a prefix list
redistribute (IP)	Redistributes routes from one routing domain into another routing domain.
show ip bgp regexp	Displays information about a prefix list or prefix list entries

Syntax Description

access-list-number	Integer from 1 to 199 that indicates the regular expression access list number.
permit	Permits access for matching conditions.
deny	Denies access to matching conditions.
as-regular-expression	Autonomous system in the access list using a regular expression. See the "Regular Expressions" appendix in the Cisco IOS Dial Services Command Reference for information about forming regular expressions.

Defaults

No access lists are defined.

Command Modes

Global configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

You can specify an access list filter on both inbound and outbound BGP routes. Each filter is an access list based on regular expressions. If the regular expression matches the representation of the autonomous system path of the route as an ASCII string, then the permit or deny condition applies. The autonomous system path does not contain the local autonomous system number. Use the ip as-path access-list global configuration command to define an BGP access list, and the neighbor router configuration command to apply a specific access list.

Examples

The following example specifies that the BGP neighbor with IP address 128.125.1.1 is not sent advertisements about any path through or from the adjacent autonomous system 123:

ip as-path access-list 1 deny _123_
ip as-path access-list 1 deny ^123$
 
router bgp 109
 network 131.108.0.0
 neighbor 129.140.6.6 remote-as 123
 neighbor 128.125.1.1 remote-as 47
 neighbor 128.125.1.1 filter-list 1 out

Related Commands

Command	Description
neighbor distribute-list	Distributes BGP neighbor information as specified in an access list.
neighbor filter-list	Sets up a BGP filter.

Syntax Description

community-list-number	Integer from 1 to 99 that identifies one or more permit or deny groups of communities.
permit	Permits access for a matching condition.
deny	Denies access for a matching condition.
community-number	Community number configured by a set community command. Valid value is one of the following: A number from 1 to 4294967200. You can specify a single number or multiple numbers separated by a space. internet---The Internet community. no-export---Routes with this community are sent to peers in other sub-autonomous systems within a confederation. Do not advertise this route to an EBGP peer. External systems are those outside the confederation. If there is no confederation, an external system is any EBGP peer. local-as ---Send this route to peers in other sub-autonomous systems within the local confederation. Do not advertise this route to an external system. no-advertise---Do not advertise this route to any peer (internal or external).

Defaults

Once you permit a value for the community number, the community list defaults to an implicit deny for everything else that has not been permitted.

Command Modes

Global configuration

Command History

Release	Modification
10.3	This command was introduced.
12.0	The local-as attribute was added.

Examples

In the following example, Cisco IOS software permits all routes except the routes with the communities 5 and 10 or 10 and 15:

ip community-list 1 deny 5 10
ip community-list 1 deny 10 15
ip community-list 1 permit internet
 

The following example permits all routes within the local autonomous system:

ip community-list 1 permit local-as

Related Commands

Command	Description
set community	Sets the BGP COMMUNITIES attribute.
show ip bgp community	Displays routes that belong to specified BGP communities.

Syntax Description

list name	Prefix list name.
text	Text description of te prefix list.

Defaults

There is no text description.

Command Modes

Global configuration

Command History

Release	Modification
10.0	This command was introduced.
11.2	The access-list-name, type, and number arguments were added.
12.0	The prefix-list argument was added.

Usage Guidelines

This command is not supported in IS-IS or OSPF.

To suppress networks from being advertised in updates, use the distribute-list out command.

Examples

The following example shows a prefix list description that indicates what routes are permitted by the prefix list:

ip prefix-list customerA description Permit routes from customer A

Related Commands

Command	Description
clear ip prefix-list	Resets the hit count of the prefix list entries.
distribute-list out	Suppresses networks from being advertised in updates.
ip prefix-list	Creates an entry in a prefix list.
ip prefix-list sequence-number	Enables the generation of sequence numbers for entries in a prefix list.
match ip address	Distributes any routes that have a destination network number address that is permitted by a standard or extended access list, and performs policy routing on packets.
neighbor prefix-list	Distributes BGP neighbor information as specified in a prefix list.
show ip prefix-list	Displays information about a prefix list or prefix list entries.

Syntax Description

This command has no arguments or keywords.

Defaults

There is no text description.

Command Modes

Global configuration

Command History

Release	Modification
12.0	This command was introduced.

Examples

The following example disables the default automatic generation of sequence numbers for prefix list entries:

no ip prefix-list sequence-number

Related Commands

Command	Description
clear ip prefix-list	Resets the hit count of the prefix list entries.
distribute-list in	Filters networks received in updates.
distribute-list out	Suppresses networks from being advertised in updates.
ip prefix-list	Creates an entry in a prefix list.
ip prefix-list sequence-number	Enables the generation of sequence numbers for entries in a prefix list.
match ip address	Distributes any routes that have a destination network number address that is permitted by a standard or extended access list, and performs policy routing on packets.
neighbor prefix-list	Distributes BGP neighbor information as specified in a prefix list.
show ip prefix-list	Displays information about a prefix list or prefix list entries.

Syntax Description

path-list-number

Autonomous system path access list. An integer from 1 to 199.

Defaults

No path lists are defined.

Command Modes

Route-map configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

Syntax Description

community-list-number	Community list number in the range 1 to 99.
exact	(Optional) Indicates an exact match is required. All of the communities and only those communities in the community list must be present.

Defaults

No community list is defined.

Command Modes

Route-map configuration

Command History

Release	Modification
10.3	This command was introduced.

Usage Guidelines

Matching based on community list is one of the types of match clauses applicable to BGP.

Examples

In the following example, the routes that match community list 1 will have the weight set to 100. Any route that has community 109 will have the weight set to 100.

ip community-list 1 permit 109
!
route-map set_weight
 match community-list 1
 set weight 100
 

In the following example, the routes that match community list 1 will have the weight set to 200. Any route that has community 109 alone will have the weight set to 200.

ip community-list 1 permit 109
!
route-map set_weight
 match community-list 1 exact
 set weight 200

Related Commands

Command	Description
route-map (IP)	Defines the conditions for redistributing routes from one routing protocol into another, or enables policy routing.
set weight	Specifies the BGP weight for the routing table.

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.
route-map map-name	(Optional) Name of the route map. The route map allows route 0.0.0.0 to be injected conditionally.

Defaults

No default route is sent to the neighbor.

Command Modes

Router configuration

Command History

Release	Modification
11.0	This command was introduced.
12.0	Modifications were added to permit extended access lists.

Usage Guidelines

This command does not require the presence of 0.0.0.0 in the local router. When used with a route map, the default route 0.0.0.0 is injected if the route map contains a match ip address clause and there is a route that matches the IP access list exactly. The route map can contain other match clauses also.

You can use standard or extended access lists with the neighbor default-originate command.

Examples

In the following example, the local router injects route 0.0.0.0 to the neighbor 160.89.2.3 unconditionally:

router bgp 109
 network 160.89.0.0
 neighbor 160.89.2.3 remote-as 200
 neighbor 160.89.2.3 default-originate
 

In the following example, the local router injects route 0.0.0.0 to the neighbor 160.89.2.3 only if there is a route to 198.92.68.0 (that is, if a route with any mask exists, such as 255.255.255.0 or 255.255.0.0):

router bgp 109
 network 160.89.0.0
 neighbor 160.89.2.3 remote-as 200
 neighbor 160.89.2.3 default-originate route-map default-map
!
route-map default-map 10 permit
 match ip address 1
!
access-list 1 permit 198.92.68.0
 

In the following example, the last line of the configuration has been changed to show the use of an extended access list. The local router injects route 0.0.0.0 to the neighbor 160.89.2.3 only if there is a route to 198.92.68.0 with a mask of 255.255.0.0:

router bgp 109
 network 160.89.0.0
 neighbor 160.89.2.3 remote-as 200
 neighbor 160.89.2.3 default-originate route-map default-map
!
route-map default-map 10 permit
 match ip address 1
!
access-list 100 permit ip host 198.92.68.0 host 255.255.255.0

Related Commands

Command	Description
neighbor ebgp-multihop	Accepts and attempts BGP connections to external peers residing on networks that are not directly connected.

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.
text	Text (up to 80 characters) that describes the neighbor.

Defaults

There is no description of the neighbor.

Command Modes

Router configuration

Command History

Release	Modification
11.3	This command was introduced.

Examples

In the following example, the description of the neighbor is "peer with abc.com":

router bgp 109
 network 160.89.0.0
 neighbor 160.89.2.3 description peer with abc.com

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.
access-list-number | name	Number or name of a standard or extended access list. It can be an integer from 1 to 199.
prefix-list-name	Name of a BGP prefix list.
in	Access list is applied to incoming advertisements to that neighbor.
out	Access list is applied to outgoing advertisements from that neighbor.

Defaults

No BGP neighbor is specified.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
11.0	The peer-group-name argument was added.
11.2	The access-list-name argument was added.
12.0	The prefix-list-name argument was added,

Usage Guidelines

Syntax Description

ip-address	IP address of the BGP-speaking neighbor.
peer-group-name	Name of a BGP peer group.
ttl	(Optional) Time-to-live in the range 1 to 255 hops.

Defaults

Only directly connected neighbors are allowed.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
11.0	The peer-group-name argument was added.

Usage Guidelines

This feature should only be used under the guidance of technical support staff.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

To prevent the creation of loops through oscillating routes, the multihop will not be established if the only route to the multihop peer is the default route (0.0.0.0).

Examples

The following example allows connections to or from neighbor 131.108.1.1, which resides on a network that is not directly connected:

router bgp 109
 neighbor 131.108.1.1 ebgp-multihop

Related Commands

Command	Description
neighbor default-originate	Allows a BGP speaker (the local router) to send the default route 0.0.0.0 to a neighbor for use as a default route.
neighbor peer-group (creating)	Creates a BGP peer group.
network (BGP)	Specifies the list of networks for the BGP routing process.

Syntax Description

ip-address	IP address of the neighbor.
peer-group-name	Name of a BGP peer group.
access-list-number	Number of an autonomous system path access list. You define this access list with the ip as-path access-list command.
in	Access list to incoming routes.
out	Access list to outgoing routes.

Defaults

No filter is used.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
12.1	The weight keyword was removed.

Usage Guidelines

This command establishes filters on both inbound and outbound BGP routes.

Syntax Description

ip-address	IP address of the neighbor.
peer-group-name	Name of a BGP peer group.
maximum	Maximum number of prefixes allowed from this neighbor.
threshold	(Optional) Integer specifying at what percentage of maximum the router starts to generate a warning message. The range 1 to 100; the default is 75 (percent).
warning-only	(Optional) Allows the router to generate log message when the maximum is exceeded, instead of terminating the peering.

Defaults

Disabled; there is no limit on the number of prefixes.

Command Modes

Router configuration

Command History

Release	Modification
11.3	This command was introduced.

Usage Guidelines

This command allows you to configure a maximum number of prefixes a BGP router is allowed to receive from a peer. It adds another mechanism (in addition to distribute lists, filter lists, and route maps) to control prefixes received from a peer.

When the number of received prefixes exceeds the maximum number configured, the router terminates the peering (by default). However, if the warning-only keyword is configured, the router instead only sends a log message, but continues peering with the sender. If the peer is terminated, the peer stays down until the clear ip bgp command is issued.

Examples

The following example sets the maximum number of prefixes allowed from the neighbor at 129.140.6.6 to 1000:

router bgp 109
 network 131.108.0.0
 neighbor 129.140.6.6 maximum-prefix 1000
 
 

Related Commands

Command	Description
clear ip bgp	Resets a BGP connection using BGP soft reconfiguration.

Syntax Description

ip-address	IP address of the BGP-speaking neighbor.
peer-group-name	Name of a BGP peer group.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
11.0	The peer-group-name argument was added.

Usage Guidelines

This command is useful in nonmeshed networks (such as Frame Relay or X.25) where BGP neighbors may not have direct access to all other neighbors on the same IP subnet.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command. Specifying the command with an IP address will override the value inherited from the peer group.

For a finer granularity of control, see the set ip next-hop command.

Examples

The following example forces all updates destined for 131.108.1.1 to advertise this router as the next hop:

router bgp 109
 neighbor 131.108.1.1 next-hop-self

Related Commands

Command	Description
neighbor peer-group (creating)	Creates a BGP peer group.
set ip next-hop (BGP)	Indicates where to output packets that pass a match clause of a route map for policy routing.

Syntax Description

ip-address	IP address of the BGP-speaking neighbor.
peer-group-name	Name of a BGP peer group.
string	Case-sensitive password of up to 80 characters. The first character cannot be a number. The string can contain any alphanumeric characters, including spaces. You cannot specify a password in the format number-space-anything. The space after the number causes problems.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

You can invoke authentication between two BGP peers, causing each segment sent on the TCP connection between them to be verified. This feature must be configured with the same password on both BGP peers; otherwise, the connection between them will not be made. The authentication feature uses the MD5 algorithm. Specifying this command causes the generation and checking of the MD5 digest on every segment sent on the TCP connection.

Configuring a password for a neighbor will cause an existing session to be torn down and a new one established.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

If a router has a password configured for a neighbor, but the neighbor router does not, a message such as the following will appear on the console while the routers attempt to establish a BGP session between them:

%TCP-6-BADAUTH: No MD5 digest from [peer's IP address]:11003 to [local router's IP address]:179
 

Similarly, if the two routers have different passwords configured, a message such as the following will appear on the console:

%TCP-6-BADAUTH: Invalid MD5 digest from [peer's IP address]:11004 to [local router's IP address]:179

Examples

The following example enables the authentication feature between this router and the BGP neighbor at 131.102.1.1. The password that must also be configured for the neighbor is bla4u00=2nkq.

router bgp 109
 neighbor 131.108.1.1 password bla4u00=2nkq

Related Commands

Command	Description
neighbor peer-group (creating)	Creates a BGP peer group.

Syntax Description

ip-address	IP address of the BGP neighbor who belongs to the peer group specified by the tag.
peer-group-name	Name of the BGP peer group to which this neighbor belongs.

Defaults

There are no BGP neighbors in a peer group.

Command Modes

Router configuration

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

The neighbor at the IP address indicated inherits all the configured options of the peer group.

Examples

The following example assigns three neighbors to the peer group named internal:

router bgp 100
 neighbor internal peer-group
 neighbor internal remote-as 100
 neighbor internal update-source loopback 0
 neighbor internal route-map set-med out
 neighbor internal filter-list 1 out
 neighbor internal filter-list 2 in
 neighbor 171.69.232.53 peer-group internal
 neighbor 171.69.232.54 peer-group internal
 neighbor 171.69.232.55 peer-group internal
 neighbor 171.69.232.55 filter-list 3 in

Related Commands

Command	Description
neighbor peer-group (creating)	Creates a BGP peer group.
neighbor shutdown	Disables a neighbor or peer group.

Syntax Description

peer-group-name

Name of the BGP peer group.

Defaults

There is no BGP peer group.

Command Modes

Router configuration

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

Often in a BGP speaker, there are many neighbors configured with the same update policies (that is, same outbound route maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be grouped into peer groups to simplify configuration and make update calculation more efficient.

Note Peer group members can span multiple logical IP subnets, and can transit, or pass along, routes from one peer group member to another.

Once a peer group is created with the neighbor peer-group command, it can be configured with the neighbor commands. By default, members of the peer group inherit all the configuration options of the peer group. Members can also be configured to override the options that do not affect outbound updates.

Peer group members will always inherit the following configuration options: remote-as (if configured), version, update-source, out-route-map, out-filter-list, out-dist-list, minimum-advertisement-interval, and next-hop-self. All the peer group members will inherit changes made to the peer group.

If a peer group is not configured with a remote-as, the members can be configured with the neighbor {ip-address | peer-group-name} remote-as command. This command allows you to create peer groups containing Exterior Border Gateway Protocol (EBGP) neighbors.

Examples

Example for an IBGP Peer Group

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.
prefix-listname	Name of a prefix list.
in	Access list is applied to incoming advertisements to that neighbor.
out	Access list is applied to outgoing advertisements from that neighbor.

Defaults

No BGP neighbor is specified.

Command Modes

Router configuration

Command History

Release	Modification
12.0	This command was introduced.

Usage Guidelines

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.
number	Autonomous system to which the neighbor belongs.

Defaults

There are no BGP neighbor peers.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
11.0	The peer-group-name argument was added.

Usage Guidelines

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.
map-name	Name of route map.
in	Apply to incoming routes.
out	Apply to outgoing routes.

Defaults

No route maps are applied to a peer.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

If an outbound route map is specified, it is proper behavior to only advertise routes that match at least one section of the route map.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command. Specifying the command for a neighbor overrides the inbound policy that is inherited from the peer group.

Examples

The following example applies a route map named internal-map to incoming route from 198.92.70.24:

router bgp 5
 neighbor 198.92.70.24 route-map internal-map in
!
route-map internal-map
 match as-path 1
 set local-preference 100
 
 

Related Commands

Command	Description
neighbor peer-group (creating)	Creates a BGP peer group.

Syntax Description

ip-address

IP address of the BGP neighbor being identified as a client.

Defaults

There is no route reflector in the autonomous system.

Command Modes

Router configuration

Command History

Release	Modification
11.1	This command was introduced.

Usage Guidelines

By default, all Interior Border Gateway Protocol (IBGP) speakers in an autonomous system must be fully meshed, and neighbors do not readvertise IBGP learned routes to neighbors, thus preventing a routing information loop.

If you use route reflectors, all IBGP speakers need not be fully meshed. In the route reflector model, an internal BGP peer is configured to be a route reflector responsible for passing IBGP learned routes to IBGP neighbors. This scheme eliminates the need for each router to talk to every other router.

Use the neighbor route-reflector-client command to configure the local router as the route reflector and the specified neighbor as one of its clients. All the neighbors configured with this command will be members of the client group and the remaining IBGP peers will be members of the nonclient group for the local route reflector.

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.

Defaults

No "communities" attribute is sent to any neighbor.

Command Modes

Router configuration

Command History

Release	Modification
10.3	This command was introduced.
11.0	The peer-group-name argument was added.

Usage Guidelines

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

Examples

In the following example, the router belongs to autonomous system 109 and is configured to send the "communities" attribute to its neighbor at IP address 198.92.70.23:

router bgp 109
 neighbor 198.92.70.23 send-community

Related Commands

Command	Description
match community-list	Matches a BGP community.
neighbor peer-group (creating)	Creates a BGP peer group.
set community	Sets the BGP COMMUNITIES attribute.

Syntax Description

ip-address	IP address of the BGP-speaking neighbor.
peer-group-name	Name of a BGP peer group.
inbound	(Optional) Keyword indicating that the update to be stored is an incoming update.

Defaults

Soft reconfiguration is not enabled

Command Modes

Router configuration

Command History

Release	Modification
11.2	This command was introduced.

Usage Guidelines

This command requires at least one keyword. Currently the only keyword available is inbound, so the use of the inbound keyword is not optional.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

Examples

The following example enables inbound soft-reconfiguration for the neighbor 131.108.1.1. All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is done later, the stored information will be used to generate a new set of inbound updates.

router bgp 100
 neighbor 131.108.1.1 remote-as 200
 neighbor 131.108.1.1 soft-reconfiguration inbound
 

Related Commands

Command	Description
clear ip bgp	Resets a BGP connection using BGP soft reconfiguration.
neighbor peer-group (creating)	Creates a BGP peer group.

Syntax Description

ip-address	IP address of the BGP-speaking neighbor.
peer-group-name	Name of a BGP peer group.
interface	Loopback interface.

Defaults

Best local address

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

This feature works in conjunction with the loopback interface feature described in the "Interface Configuration Overview" chapter of the Cisco IOS Interface Configuration Guide.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

Examples

The following example sources BGP TCP connections for the specified neighbor with loopback interface's IP address rather than the best local address:

router bgp 110
 network 160.89.0.0
 neighbor 160.89.2.3 remote-as 110
 neighbor 160.89.2.3 update-source Loopback0

Related Commands

Command	Description
neighbor peer-group (creating)	Creates a BGP peer group.

Syntax Description

ip-address	IP address of the BGP-speaking neighbor.
peer-group-name	Name of a BGP peer group.
value	BGP version number. The version can be set to 2 to force the software to only use Version 2 with the specified neighbor. The default is to use Version 4 and dynamically negotiate down to Version 2 if requested.

Defaults

BGP Version 4

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

Entering this command disables dynamic version negotiation.

Our implementation of BGP supports BGP Versions 2, 3, and 4. If the neighbor does not accept default Version 4, dynamic version negotiation is implemented to negotiate down to Version 2.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

Examples

The following example locks down to Version 4 of the BGP protocol:

router bgp 109
 neighbor 131.104.27.2 version 4

Related Commands

Command	Description
neighbor peer-group (creating)	Creates a BGP peer group.

Syntax Description

ip-address	Neighbor's IP address.
peer-group-name	Name of a BGP peer group.
weight	Weight to assign. Acceptable values are 0 to 65535.

Defaults

Routes learned through another BGP peer have a default weight of 0 and routes sourced by the local router have a default weight of 32768.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

All routes learned from this neighbor will have the assigned weight initially. The route with the highest weight will be chosen as the preferred route when multiple routes are available to a particular network.

Syntax Description

network-number	Network that BGP will advertise.
mask	(Optional) Network or subnetwork mask.
network-mask	(Optional) Network mask address.

Defaults

No networks are specified.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
12.0	The limit of 200 network commands per BGP router was removed.

Usage Guidelines

These types of networks can be learned from connected routes, dynamic routing, and from static route sources.

The maximum number of network commands you can use is determined by the router's resources, such as the configured NVRAM or RAM.

Examples

The following example sets up network 131.108.0.0 to be included in the BGP updates:

router bgp 120
 network 131.108.0.0

Related Commands

Command	Description
default-information originate (BGP)	Allows the redistribution of network 0.0.0.0 into BGP.
neighbor ebgp-multihop	Accepts and attempts BGP connections to external peers residing on networks that are not directly connected.
network backdoor	Specifies a backdoor route to a BGP border router that will provide better information about the network.
network weight	Assigns an absolute weight to a BGP network.
router bgps	Configures the BGP routing process.

Syntax Description

address

IP address of the network to which you want a backdoor route.

Defaults

No network is advertised.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

A backdoor network is treated as a local network, except that it is not advertised.

Examples

The following example configures network 131.108.0.0 as a local network and network 192.31.7.0 as a backdoor network:

router bgp 109
 network 131.108.0.0
 network 192.31.7.0 backdoor

Syntax Description

autonomous-system

Number of an autonomous system that identifies the router to other BGP routers and tags the routing information passed along.

Defaults

No BGP routing process is enabled by default.

Command Modes

Global configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

This command allows you to set up a distributed routing core that automatically guarantees the loop-free exchange of routing information between autonomous systems.

Examples

The following example configures a BGP process for autonomous system 120:

router bgp 120

Related Commands

Command	Description
network (BGP)	Specifies the list of networks for the BGP routing process.
timers bgp	Adjust BGP network timers.

Syntax Description

tag	Converts the tag of a route into an autonomous system path. Applies only when redistributing routes into BGP.
prepend as-path-string	Appends the string following the keyword prepend to the as-path of the route that is matched by the route map. Applies to inbound and outbound BGP route maps.

Defaults

Autonomous system path is not modified.

Command Modes

Route-map configuration

Command History

Release	Modification
11.0	This command was introduced.

Usage Guidelines

By allowing you to convert the tag into an autonomous system path, the set as-path tag variation of this command modifies the autonomous system length. The set as-path prepend variation allows you to "prepend" an arbitrary autonomous system path string to BGP routes. Usually the local autonomous system number is prepended multiple times, increasing the autonomous system path length.