Table Of Contents
MPLS Scalability Enhancements for the ATM LSR
This feature was introduced.
This feature was integrated to Cisco IOS Release 12.0(22)S.
This document describes how to prevent label-switched paths (LSPs) from being created in an MPLS network. This document includes the following sections:
Some LSPs are often unnecessary between some label-switched edge routers (LERs) in an MPLS network. Every time a new destination is created, LSPs are created from all LERs in the MPLS network to the new destination. You can use the mpls ldp request-tags for command with an access list at an LER to restrict the destinations for which a downstream-on-demand request is issued. You specify the destination IP addresses that you want to enable/disable from creating LSPs.
This command allows you to permit/deny creation of some LSPs, while preventing the creation of others. Using this command reduces the number of LSPs in an MPLS network, which reduces the VC usage in the network.
This section details some of the restrictions of this feature.
•Do not use the mpls disable headend-vc command.
When using access lists to prevent the creation of LSPs, do not disable the router from acting as an edge router with the mpls disable headend-vc command, which prevents all LSPs from being established.
•Cisco 12000 routers need special LVC configuration for efficient use of VCs.
A Cisco 12000 router (GSR) ATM interface used for MPLS cannot use the entire virtual path identifier (VPI) range configured on the subinterface. Attempts to create label switched controlled virtual circuits (LVCs) within the configured range may be rejected by the line card drivers. This can occur when you use the GSR ATM OC-3 or OC-12 interfaces running MPLS.
The following paragraphs show the commands for efficiently using LVC space. For a configuration example, see "Efficiently Using LVC space for Cisco 12000 Series Routers".
–For the Quad OC-3 or Quad OC-12
On the main interface, use 512 VCs per VPI. Enter the following command:atm vc-per-vp 512
On the MPLS subinterface, match the hardware limit of 7 VPIs and set the control-vc to within that range by entering the following commands:mpls atm control-vc 2 32mpls atm vpi 2-8
–For the Single-Port OC-12
On the main interface, use 1024 VCs per VPI . Enter the following command:atm vc-per-vp 1024
On the MPLS subinterface, match the hardware limit of 15 VPIs and set the control-vc to fall within that range by entering the following commands:mpls atm control-vc 2 32mpls atm vpi 2-16
You must configure the control-vc of the LDP neighbor so that it uses the same VPI and VCI.
For more information about standard and extended access lists, see the following documents:
•Cisco IOS Security Configuration Guide, Release 12.2, Access Control Lists: Overview and Guidelines
This feature is supported on the following platforms:
•Cisco 7200 series
•Cisco 7500 series
•Cisco 12000 series (engine 0)
Determining Platform Support Through Cisco Feature Navigator
Cisco IOS software is packaged in feature sets that are supported on specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Cisco Feature Navigator is a web-based tool that enables you to quickly determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.
To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to firstname.lastname@example.org. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Availability of Cisco IOS Software Images
Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.
Supported Standards, MIBs, and RFCs
The MPLS LSC supports no new or modified standards.
The MPLS LSC supports no new or modified MIBs.
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
If Cisco MIB Locator does not support the MIB information that you need, you can also obtain a list of supported MIBs and download MIBs from the Cisco MIBs page at the following URL:
To access Cisco MIB Locator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to email@example.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
The MPLS LSC supports no new or modified RFCs.
The following sections explain how to configure the network to prevent the creation of LSPs from specified IP addresses:
Sample MPLS ATM Network
Figure 1 is an MPLS ATM network that consists of the following elements:
•The PE routers in the virtual private network require LSPs to communicate with each other.
•All the PE routers are in network 1 (198.x.x.x).
•All the IGP IP addresses are in network 2 (192.x.x.x).
•If numbered interfaces are required (for network management or other purposes), they are placed in network 2 (192.x.x.x).
Figure 1 Sample MPLS ATM Network
The following configuration tasks use mpls ldp request-tags for commands to accomplish the following:
•Allow the PE routers in network 1 to create LSPs and communicate with each other, but prevent creation of LSPs from the PE routers to the MPLS ATM network,
•Prevent LSPs from being created in the MPLS ATM network (network 2) and prevent from the MPLS ATM network to the PE routers.
Performing these tasks reduces the number of LSPs in the MPLS ATM network, which reduces the VC usage in the network.
Configuring the MPLS ATM Network
In the configuration file of the routers in the MPLS ATM network, enter the following commands:
Configuring the PE Routers
In the configuration file of the PE routers, enter the following commands:
Verifying the Configuration
Use the following commands to verify the configuration:
This section contains the following configuration examples:
Disabling the Creation of LSPs
The following examples of the mpls ldp request-tags for command use Figure 2 as a basis. The examples show different ways to disable the creation of LSPs from the LSC to the edge GSR, and from the edge GSRs to the LSC.
Note In this example, the LSCs are running 12.1(5)T software. Cisco IOS Release 12.0(14ST) does not support LSCs.
Figure 2 Sample Configuration
Using a Numbered Access List
The following examples use a numbered access list to restrict creation of LSPs.
Note With LSCs, you disable the LSC from acting as an edge router with the mpls disable headend-vc command, which prevents all LSPs from being established. The following examples use the mpls ldp request-tags for command on the LSC. However, it is recommended that you use the mpls disable headend-vc command.
Preventing LSPs from the LSC to the Edge LSRs
The following example prevents LSPs from being established from the LSC to all 198.x.x.x destinations. However, transit LSPs are allowed between 198.x.x.x destinations. Add the following commands to the LSC configuration:mpls ldp request-tags for 1access-list 1 deny 18.104.22.168 0.255.255.255access-list 1 permit any
Preventing LSPs from the Edge LSRs to the LSC
The following example prevents headend LVCs from being established from edge LSR 1 and edge GSR 2 to the LSC (192.x.x.x). However, transit LSPs are allowed between 198.x.x.x destinations. Add the following commands to the edge GSR 1 and 2 configurations:mpls ldp request-tags for 1access-list 1 deny 192.0.0.0 0.255.255.255access-list 1 permit any
Using a Named Access List
The following examples use a named access list to perform the same tasks as the previous examples.mpls ldp request-tags for nolervcsip access-list standard nolervcsdeny 22.214.171.124 0.255.255.255permit anympls ldp request-tags for nolervcsip access-list standard nolervcsdeny 192.0.0.0 0.255.255.255permit any
Specifying Exact Match IP Addresses with an Access List
The following examples use exact IP addresses to perform the same tasks as the previous examples.mpls ldp request-tags for 1access-list 1 deny 126.96.36.199 0.0.0.0access-list 1 deny 188.8.131.52 0.0.0.0access-list 1 permit anympls ldp request-tags for 1access-list 1 deny 184.108.40.206 0.0.0.0access-list 1 permit any
Efficiently Using LVC space for Cisco 12000 Series Routers
The following configuration shows how to set up the ATM interfaces so that LVC space is optimized on a Cisco 12000 series router.
Figure 3 Cisco 12000 Series Router Configuration Example
LSC1 Configurationip routingip cefmpls ip!int loopback0ip address 220.127.116.11.255.255.255.255!int atm1/0tag-control-protocol vsi slaves 18!interface XTagATM101ip unnumbered Loopback0extended-port ATM2/0 vsi 0x000A0100mpls atm control-vc 2 32mpls atm vpi 2-8mpls ip!interface XTagATM103ip unnumbered Loopback0extended-port ATM2/0 vsi 0x000A0300mpls atm control-vc 2 32mpls atm vpi 2-8mpls ip
Port 9.1uptrk 9.1cnfrscr 9.1 256 248207 N y 1 e 512 5000 2 15 26000 100000addshelf 9.1 V
Port 10.1uptrk 10.1cnfrscr 10.1 256 248207 N y 1 e 512 5000 2 15 26000 100000
Port 10.3uptrk 10.3cnfrscr 10.3 256 248207 N y 1 e 512 5000 2 15 26000 100000
Routing Protocol Configurationrouter ospf 100network 18.104.22.168.0.255.255.255.255 area 100
GSR1 Configurationip routingip cefmpls ip!int loopback0ip address 10.10.10.10.255.255.255.255int atm5/0atm vc-per-vp 512!interface ATM5/0.1 tag-switchingip unnumbered Loopback0no ip directed-broadcastno atm enable-ilmi-trapmpls atm control-vc 2 32mpls atm vpi 2-8mpls ip!router ospf 100network 10.0.0.0.0.255.255.255.255 area 100
GSR2 Configurationip routingip cefmpls ip!int loopback0ip address 22.214.171.124.255.255.255.255!int atm5/0atm vc-per-vp 512interface ATM5/0.1 tag-switchingip unnumbered Loopback0no ip directed-broadcastno atm enable-ilmi-trapmpls atm control-vc 2 32mpls atm vpi 2-8mpls ip!router ospf 100router (config-router)# network 126.96.36.199.0.255.255.255.255 area 100
This section describes the CLI commands that you can use to disable the creation of LSPs:
All other commands used with this feature are documented in the Cisco IOS command reference publications.
mpls ldp request-tags for
To restrict the creation of LVCs through the use of access lists on the label edge router, use the mpls ldp request-tags for global configuration command. Use the no form of this command to disable this feature.
mpls ldp request-tags for access list
no mpls ldp request-tags for access list
No default behavior or values
This command was introduced as tag-switching request-tags for.
This command was changed to reflect MPLS terminology.
This command was integrated into Cisco IOS Release 12.0(22)S.
The command includes the following usage guidelines:
•You can specify either an access list number or name.
•When creating an access list, the end of the access list contains an implicit deny statement for everything if it did not find a match before reaching the end.
•If you omit the mask from an IP host address access list specification, 0.0.0.0 is assumed to be the mask.
In the following example, headend LVCs are prevented from being established from the core router to all 198.x.x.x destinations. The following commands are added to the core router configuration:mpls ldp request-tags for 1access-list 1 deny 188.8.131.52 0.255.255.255access-list 1 permit any