Table Of Contents
BGP Support for Sequenced Entries in Extended Community Lists
How to Sequence Extended Community Lists
Configuring Extended Community-list Sequencing
IP Extended Community-list Configuration Mode
Resequencing Extended Community-lists
Verifying Extended Community-list Sequences
Configuration Examples for Sequenced Entries in Extended Community-lists
Sequenced Extended Community-list Entry Configuration: Example
Resequenced Extended Community-list Entry Configuration: Example
Sequenced Extended Community-list Entry Verification: Example
BGP Support for Sequenced Entries in Extended Community Lists
This feature introduces automatic sequencing of individual entries in Border Gateway Protocol (BGP) extended community lists. This feature also introduces the ability to remove or resequence extended community list entries without deleting the entire existing extended community list.
Feature History for the BGP Support for Sequenced Entries in Extended Community Lists Feature
Finding Support Information for Platforms and Cisco IOS Software Images
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Contents
•How to Sequence Extended Community Lists
•Configuration Examples for Sequenced Entries in Extended Community-lists
How to Sequence Extended Community Lists
This section contains the following tasks:
•Configuring Extended Community-list Sequencing
•Verifying Extended Community-list Sequences
Configuring Extended Community-list Sequencing
Perform this task to sequence and resequence extended community lists.
IP Extended Community-list Configuration Mode
This feature introduces IP Extended community-list configuration mode. Both named and numbered extended community lists can be configured in IP Extended community-list configuration mode. To enter IP Extended community-list configuration mode, the ip extcommunity-list command is entered with either the expanded or standard keyword followed by the extended community-list name. This configuration mode supports all of the functions that are available in global configuration mode. In addition, you can perform the following operations:
•Configure sequence numbers for extended community list entries
•Resequence existing sequence numbers for extended community list entries
•Configure an extended community list to use default values
Default Sequence Numbering
Extended community list entries start with the number 10 and increment by 10 for each subsequent entry when no sequence number is specified, when default behavior is configured, and when an extended community list is resequenced without specifying the first entry number or the increment range for subsequent entries.
Resequencing Extended Community-lists
Extended community-list entries are sequenced and resequenced on a per-extended community-list basis. The resequence command can be used without any arguments to set all entries in a list to default sequence numbering. The resequence command also allows you to set the sequence number of the first entry and increment range for each subsequent entry. The range of configurable sequence numbers is from 1 to 2147483647.
Restrictions
A sequence number is applied to all extended community-list entries by default regardless of the configuration mode. Explicit sequencing and resequencing of extended community list entries can only be configured in IP Extended community-list configuration mode and not in global configuration mode.
SUMMARY STEPS
1. enable
2. configure terminal
3. ip extcommunity-list {expanded-list-number | expanded list-name | standard-list-number | standard list-name }
4. [sequence-number] { deny [regular-expression] | exit | permit [regular-expression] | resequence [starting-sequence] [sequence-increment]}
5. [sequence-number] {deny [rt extcom-value] [soo extcom-value] | exit | permit [rt extcom-value] [soo extcom-value] | resequence [starting-sequence] [sequence-increment] }
6. end
DETAILED STEPS
Verifying Extended Community-list Sequences
Perform this task to verify the configuration of extended community-list sequences.
SUMMARY STEPS
1. show ip extcommunity-list [list-number | list-name]
DETAILED STEPS
Command or Action PurposeStep 1
show ip extcommunity-list [list-number | list-name]
Example:Router# show ip extcommunity-list
Displays routes that are permitted by an extended community list.
Configuration Examples for Sequenced Entries in Extended Community-lists
The following examples show how to configure and verify this feature:
•Sequenced Extended Community-list Entry Configuration: Example
•Resequenced Extended Community-list Entry Configuration: Example
•Sequenced Extended Community-list Entry Verification: Example
Sequenced Extended Community-list Entry Configuration: Example
The following example creates and configures a named extended community list that will permit routes only from route target 64512:10, 65000:20, 64535:30, and site of origin 65535:40. All other routes implicitly denied.
Router(config)# ip extcommunity-list standard NAMED_LIST
Router(config-extcom-list)# 1 permit rt 64512:10
Router(config-extcom-list)# 2 permit rt 65000:20
Router(config-extcom-list)# 3 permit rt 64535:30
Router(config-extcom-list)# 4 permit soo 65535:40
Router(config-extcom-list)# end
Resequenced Extended Community-list Entry Configuration: Example
The following example resequences the extended community list entries in the named community list. The first entry is resequenced to the number 50 and the range for each subsequent entry to follow by 100 (for example, 150, 250, 350, etc):
Router(config)# ip extcommunity-list standard NAMED_LIST
Router(config-extcom-list)# resequence 50 100
Router(config-extcom-list)# end
Sequenced Extended Community-list Entry Verification: Example
The following example uses the show ip extcommunity-list Exec command to display routes that are permitted by the named extended community list. This example also shows the configuration from the first example after it has been resequence with user-defined values.
Router# show ip extcommunity-list
Standard extended community-list NAMED_LIST50 permit RT:64512:10150 permit RT:64512:10250 permit RT:64512:10350 permit RT:64512:10Additional References
The following sections provide references related to the BGP Support for Named Extended Community Lists feature.
Related Documents
Related Topic Document TitleBGP commands
Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3T
BGP configuration tasks
Cisco IOS IP Configuration Guide, Release 12.3
Regular Expressions
"Regular Expressions" appendix of the Cisco IOS Terminal Services Configuration Guide, Release 12.3T
Standards
Standards TitleNo new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
—
MIBs
RFCs
RFCs TitleNo new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.
—
Technical Assistance
Description LinkTechnical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, tools, and lots more. Registered Cisco.com users can log in from this page to access even more content.
TAC Home Page:
http://www.cisco.com/public/support/tac/home.shtml
BGP Support Page:
http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Internetworking:BGP
Command Reference
This section documents modified commands.
ip extcommunity-list
To create an extended community list to configure Virtual Private Network (VPN) route filtering, use the ip extcommunity-list command in global configuration mode. To delete the extended community list, use the no form of this command.
Global Configuration Mode CLI
ip extcommunity-list expanded-list [ expanded list-name {permit | deny} [regular-expression] | standard-list | standard list-name {permit | deny} [rt value] [soo value] ]
no ip extcommunity-list expanded-list [ expanded list-name | standard-list | standard list-name]
To enter IP Extended community-list configuration mode to create or configure an extended community-list, use the ip extcommunity-list command in global configuration mode. To delete the entire extended community list, use the no form of this command. To delete a single entry, use the no form in IP Extended community-list configuration mode.
ip extcommunity-list expanded-list [expanded list-name | standard-list | standard list-name ]
no ip extcommunity-list expanded-list [expanded list-name | standard-list | standard list-name ]
Expanded IP Extended Community-List Configuration Mode CLI
[sequence-number] deny [regular-expression] [exit | permit [regular-expression] | resequence] [starting-sequence] [sequence-increment]
default {sequence-number | deny [regular-expression] | exit | permit [regular-expression] | resequence [starting-sequence] [sequence-increment]}
no {sequence-number | deny [regular-expression] | permit [regular-expression] | resequence [starting-sequence] [sequence-increment]}
Standard IP Extended Community-List Configuration Mode CLI
[sequence-number] deny [rt value] [soo value] [ exit | permit [rt value] [soo value] | resequence] [starting-sequence] [sequence-increment]
default {sequence-number | deny [rt value] [soo value] | exit | permit [rt value] [soo value] | resequence [starting-sequence] [sequence-increment]}
no {sequence-number | deny [rt value | soo value] | permit [rt value] [soo value] | resequence [starting-sequence] [sequence-increment]}
Syntax Description
Defaults
Extended community exchange is not enabled by default. It is enabled on a per-neighbor basis with the neighbor send-community command.
Once a permit value has been configured to match a given set of extended communities, the extended community list defaults to an implicit deny for all other values.
Extended community list entries start with the number 10 and increment by ten for each subsequent entry when no sequence number is specified, when default behavior is configured, and when an extended community list is resequenced without specifying the first entry number or the increment range for subsequent entries.
Command Modes
Global configuration
IP Extended community-list configurationCommand History
Usage Guidelines
The ip extcommunity-list command is used to configure named or numbered extended community lists. Extended community attributes are used to filter routes for VPN routing and forwarding instances (VRFs) and Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs). All of the standard rules of access lists apply to the configuration of extended community lists. The route target (RT) and site of origin (SOO) extended community attributes are supported by the standard range of extended community lists. Regular expressions are supported in expanded extended community lists. For information about configuring regular expressions, see the Regular Expressions appendix of the Cisco IOS Terminal Services Configuration Guide.
Route Target Extended Community Attribute
The route target (RT) extended community attribute is configured with the rt keyword. This attribute is used to identify a set of sites and VRFs that may receive routes that are tagged with the configured route target. Configuring the route target extended attribute with a route allows that route to be placed in the per-site forwarding tables that are used for routing traffic that is received from corresponding sites.
Site of Origin Extended Community Attribute
The site of origin (SOO) extended community attribute is configured with the soo keyword. This attribute uniquely identifies the site from which the provider edge (PE) router learned the route. All routes learned from a particular site must be assigned the same site of origin extended community attribute, regardless if a site is connected to a single PE router or multiple PE routers. Configuring this attribute prevents routing loops from occurring when a site is multihomed. The SOO extended community attribute is configured on the interface and is propagated into BGP through redistribution. The SOO should not be configured for stub sites or sites that are not multihomed.
IP Extended Community-List Configuration Mode
Named and numbered extended community lists can be configured in IP Extended community-list configuration mode. To enter IP Extended community-list configuration mode, enter the ip extcommunity-list command with either the expanded or standard keyword followed by the extended community list name. This configuration mode supports all of the functions that are available in global configuration mode. In addition, you can perform the following operations:
•Configure sequence numbers for extended community list entries
•Resequence existing sequence numbers for extended community list entries
•Configure an extended community list to use default values
Extended Community List Processing
When multiple values are configured in the same extended community list statement, a logical AND condition is created. All extended community values must match to satisfy an AND condition. When multiple values are configured in separate extended community list statements, a logical OR condition is created. The first list that matches a condition is processed.
Examples
Standard Extended Community-List Configuration Example
In the following example, an extended community list is configured that permits routes from route target 64512:10 and site of origin 65400:20 and denies routes from route target 65424:30 and site of origin 64524:40. List 1 shows a logical OR condition; the first match is processed. List 2 shows a logical AND condition; all community values must match in order for list 2 to be processed.
Router(config)# ip extcommunity-list 1 permit rt 64512:10
Router(config)# ip extcommunity-list 1 permit soo 65400:20
Router(config)# ip extcommunity-list 2 deny rt 65424:30 soo 64524:40
Expanded Extended Community-List Configuration Example
In the following example, an expanded extended community list is configured to deny advertisements from any path through or from autonomous system 65534 from being advertised to the 192.168.1.2 neighbor:
Router(config)# ip extcommunity-list 500 deny _65412_
Router(config)# router bgp 50000
Router(config-router)# address-family vpnv4
Router(config-router-af)# neighbor 172.16.1.1 remote-as 65412
Router(config-router-af)# neighbor 172.16.1.1 neighbor send-community extended
Router(config-router-af)# neighbor 192.168.1.2 remote-as 65534
Router(config-router-af)# neighbor 192.168.1.2 neighbor send-community extended
Router(config-router-af)# end
Named Extended Community-List Configuration Example
In the following example, a named extended community list is configured that will permit routes only from route target 65505:50. All other routes are implicitly denied.
Router(config)# ip extcommunity-list standard NAMED_LIST permit rt 65505:50
IP Extended Community-List Configuration Mode Example
In the following example, an expanded named extended community list is configured in IP Extended community-list configuration mode. A list entry is created with a sequence number 10 that will permit a route target or route origin pattern that matches any network number extended community from autonomous system 65412.
Router(config)# ip extcommunity-list RED
Router(config-extcom-list)# 10 permit 65412:[0-9][0-9][0-9][0-9][0-9]_
Router(config-extcom-list)# exit
Extended Community-List Resequencing Example
In the following example, the first list entry is resequenced to the number 50 and each subsequent entry is configured to increment by 100:
Router(config)# ip extcommunity-list BLUE
Router(config-extcom-list)# resequence 50 100
Router(config-extcom-list)# exit
Related Commands
show ip extcommunity-list
To display routes that are permitted by an extended community list, use the show ip extcommunity-list command in EXEC mode.
show ip extcommunity-list [list-number | list-name]
Syntax Description
Defaults
If a specific extended community list number is not specified when the show ip extcommunity-list command is entered, all locally configured extended community lists will be displayed by default.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip extcommunity-list command in EXEC mode:
Router# show ip extcommunity-listStandard extended community-list 110 permit RT:64512:1020 permit SoO:65400:2030 deny RT:65424:30 SoO:64524:40Standard extended community-list 9910 permit RT:65504:40 SoO:65505:5020 deny RT:65406:60 SoO:65307:70Expanded extended community-list LIST_NAME10 permit 0-9* A-Z* a-z*Table 1 describes the significant fields shown in the display.
Related Commands
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