The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.
The MPLS LDP-IGP Synchronization feature ensures that the Label Distribution Protocol (LDP) is fully established before the Interior Gateway Protocol (IGP) path is used for switching.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Packet loss can occur because the actions of the IGP and LDP are not synchronized. Packet loss can occur in the following situations:
The MPLS LDP-IGP Synchronization feature does the following:
To enable LDP-IGP synchronization on each interface that belongs to an OSPF or IS-IS process, enter the mpls ldp sync command. If you do not want some of the interfaces to have LDP-IGP synchronization enabled, issue the no mpls ldp igp sync command on those interfaces.
If the LDP peer is reachable, the IGP waits indefinitely (by default) for synchronization to be achieved. To limit the length of time the IGP session must wait, enter the mpls ldp igp sync holddown command. If the LDP peer is not reachable, the IGP establishes the adjacency to enable the LDP session to be established.
When an IGP adjacency is established on a link but LDP-IGP synchronization is not yet achieved or is lost, the IGP advertises the max-metric on that link.
When the MPLS LDP-IGP Synchronization feature is enabled on an interface, LDP determines if any peer connected by the interface is reachable by looking up the peer's transport address in the routing table. If a routing entry (including longest match or default routing entry) for the peer exists, LDP assumes that LDP-IGP synchronization is required for the interface and notifies the IGP to wait for LDP convergence.
LDP-IGP synchronization with peers requires that the routing table be accurate for the peer's transport address. If the routing table shows there is a route for the peer's transport address, that route must be able to reach the peer's transport address. However, if the route is a summary route, a default route, or a statically configured route, it may not the correct route for the peer. You must verify that the route in the routing table can reach the peer's transport address.
When the routing table has an inaccurate route for the peer's transport address, LDP cannot set up a session with the peer, which causes the IGP to wait for LDP convergence unnecessarily for the sync hold-down time.
The MPLS LDP-IGP Synchronization feature provide the option to configure a delay time for MPLS LDP and IGP synchronization on an interface-by-interface basis. If you want to configure a delay time on an interface, use the mpls ldp igp sync delay delay-timecommand in interface configuration mode. To remove the delay timer from a specified interface, enter the no mpls ldp igp sync delay command. This command sets the delay time to 0 seconds, but leaves MPLS LDP IGP synchronization enabled.
When LDP is fully established and synchronized, LDP checks the delay timer:
If you configure a new delay time while a timer is running, LDP saves the new delay time but does not reconfigure the running timer.
The MPLS LDP-IGP Synchronization feature is not supported during the startup period if IGP nonstop forwarding (NSF) is configured. The MPLS LDP-IGP Synchronization feature conflicts with IGP NSF when the IGP is performing NSF during startup. After the NSF startup is complete, the MPLS LDP-IGP Synchronization feature is supported.
LDP Graceful Restart protects traffic when an LDP session is lost. If an interface that supports a Graceful Restart-enabled LDP session fails, MPLS LDP-IGP synchronization is still achieved on the interface while it is protected by Graceful Restart. MPLS LDP-IGP synchronization is eventually lost under the following circumstances:
Packet loss can occur because the actions of the IGP and LDP are not synchronized. Packet loss can occur in the following situations:
The MPLS LDP-IGP Synchronization feature does the following:
To enable LDP-IGP synchronization on each interface that belongs to an OSPF or IS-IS process, enter the mpls ldp sync command. If you do not want some of the interfaces to have LDP-IGP synchronization enabled, issue the no mpls ldp igp sync command on those interfaces.
If the LDP peer is reachable, the IGP waits indefinitely (by default) for synchronization to be achieved. To limit the length of time the IGP session must wait, enter the mpls ldp igp sync holddown command. If the LDP peer is not reachable, the IGP establishes the adjacency to enable the LDP session to be established.
When an IGP adjacency is established on a link but LDP-IGP synchronization is not yet achieved or is lost, the IGP advertises the max-metric on that link.
To configure MPLS LDP-Autoconfiguration with OFPF interfaces, perform the following steps.
When you issue the mpls ldp sync command, all of the interfaces that belong to an OSPF process are enabled for LDP-IGP synchronization. To remove LDP-IGP synchronization from some interfaces, use the no form of the mpls ldp igp sync command on those interfaces.
Perform the following task to disable LDP-IGP synchronization from some OSPF interfaces after they are configured with LDP-IGP synchronization through the mpls ldp sync command.
After you configure the interfaces for LDP, OSPF, and LDP-IGP synchronization, verify that the configuration is working correctly using the show mpls ldp igp syncand show ip ospf mpls ldp interfacecommands.
The following sections contain the steps and examples for configuring MPLS LDP-IGP synchronization for interfaces running IS-IS processes:
Perform the following task to configure the MPLS LDP-IGP Synchronization feature on all interfaces running IS-IS processes.
This section contains the steps for configuring the MPLS LDP-IGP Synchronization feature on an interface that is running an IS-IS process.
When you issue the mpls ldp sync command, all of the interfaces that belong to an IS-IS process are enabled for LDP-IGP synchronization. To remove LDP-IGP synchronization from some interfaces, use the no form of the mpls ldp igp sync command on those interfaces.
Perform the following task to disable LDP-IGP synchronization from some IS-IS interfaces after they are configured with LDP-IGP synchronization through the mpls ldp sync command.
You can verify that the MPLS LDP Autoconfiguration feature is working correctly with the show isis mpls ldp command.
Use the debug mpls ldp igp sync command to display events related to MPLS LDP-IGP synchronization.
The following sections show examples for the MPLS LDP-IGP synchronization feature with OSPF and IS-IS processes:
The following task shows how to enable LDP for OSPF process 1. The mpls ldp syncand the OSPF network commands enable LDP on interfaces POS0/0/0, POS0/1/0, and POS1/1/0, respectively. The no mpls ldp igp sync command on interface POS1/0/0 prevents LDP from being enabled on interface POS1/0/0, even though OSPF is enabled for that interface.
Router# configure terminal Router(config)# interface POS0/0/0 Router(config-if)# ip address 10.0.0.1 Router(config-if)# mpls ip ! Router(config)# interface POS0/1/0 Router(config-if)# ip address 10.0.1.1 Router(config-if)# mpls ip ! Router(config)# interface POS1/1/0 Router(config-if)# ip address 10.1.1.1 Router(config-if)# mpls ip ! Router(config)# interface POS1/0/0 Router(config-if)# ip address 10.1.0.1 Router(config-if)# mpls ip ! Router(config)# router ospf 1 Router(config-router)# network 10.0.0.0 0.0.255.255 area 3 Router(config-router)# network 10.1.0.0 0.0.255.255 area 3 Router(config-router)# mpls ldp sync Router(config-router)# exit Router(config)# interface POS1/0/0 Router(config-if)# no mpls ldp igp sync
The following examples show the configuration commands you can use to configure MPLS LDP-IGP synchronization on interfaces POS0/2 /0 and POS0/3/0, which are running IS-IS processes:
Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# interface POS0/2/0 Router(config-if)# ip router isis Router(config-if)# exit Router(config)# router isis Router(config-router)# mpls ldp sync Router(config-router)# exit . . . Router(config)# interface POS0/3/0 Router(config-if)# ip router isis Router(config-if)# exit Router(config)# router isis Router(config-router)# mpls ldp sync Router(config-router)# exit Router(config) exit Router#
Related Topic |
Document Title |
---|---|
MPLS LDP |
MPLS Label Distribution Protocol |
MPLS LDP-IGP synchronization |
MPLS LDP-IGP Synchronization |
LDP autoconfiguration |
LDP Autoconfiguration |
Standards |
Title |
---|---|
None |
-- |
MIBs |
MIBs Link |
---|---|
MPLS LDP MIB |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs |
Title |
---|---|
RFC 3036 |
|
RFC 3037 |
Description |
Link |
---|---|
The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password. If you have a valid service contract but do not have a user ID or password, you can register on Cisco.com. |
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1 | Feature Information for MPLS LDP-IGP Synchronization |
Feature Name |
Releases |
Feature Information |
---|---|---|
MPLS LDP-IGP Synchronization |
12.0(30)S 12.0(32)SY 12.2(33)SB 12.2(33)SRB 15.0(1)M 12.3(14)T Cisco IOS XE Release 2.1 |
The MPLS LDP-IGP Synchronization feature ensures that LDP is fully established before the IGP path is used for switching. In 12.0(30)S, this feature was introduced. In 12.0(32)SY, support for enabling synchronization on interfaces running Intermediate System-to-System (IS-IS) processes was added. In 12.2(33)SB, the feature was integrated. MPLS LDP-IGP synchronization for IS-IS is not supported in this release. In 12.2(33)SRB, the feature was integrated. MPLS LDP-IGP synchronization for IS-IS is not supported in this release. In 12.3(14)T, this feature was integrated. MPLS LDP-IGP synchronization for IS-IS is not supported in this release. In 15.0(1)M, support for enabling synchronization on interfaces running IS-IS processes was added. In XE 2.1, this feature was implemented on Cisco ASR 1000 Series Routers. The following commands were modified: debug mpls ldp igp sync, mpls ldp igp sync, mpls ldp igp sync holddown, mpls ldp sync, show ip ospf mpls ldp interface, show isis mpls ldp, and show mpls ldp igp sync. |
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.