MPLS Label Distribution Protocol

MPLS Label Distribution Protocol
MPLS Label Distribution Protocol (LDP) enables peer label switch routers (LSRs) in an Multiprotocol Label
Switching (MPLS) network to exchange label binding information for supporting hop-by-hop forwarding
in an MPLS network. This module explains the concepts related to MPLS LDP and describes how to configure
MPLS LDP in a network.
• Finding Feature Information, page 1
• Prerequisites for MPLS Label Distribution Protocol, page 1
• Information About MPLS Label Distribution Protocol, page 2
• How to Configure MPLS Label Distribution Protocol, page 6
• Configuration Examples for MPLS Label Distribution Protocol, page 21
• Additional References, page 24
• Feature Information for MPLS Label Distribution Protocol, page 26
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and
feature information, see Bug Search Tool and 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 module.
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.
Prerequisites for MPLS Label Distribution Protocol
Label switching on a device requires that Cisco Express Forwarding be enabled on that device.
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MPLS Label Distribution Protocol
Information About MPLS Label Distribution Protocol
Information About MPLS Label Distribution Protocol
Introduction to MPLS Label Distribution Protocol
MPLS Label Distribution Protocol (LDP) provides the means for label switch devices (LSRs) to request,
distribute, and release label prefix binding information to peer devices in a network. LDP enables LSRs to
discover potential peers and to establish LDP sessions with those peers for the purpose of exchanging label
binding information.
Multiprotocol Label Switching (MPLS) LDP enables one LSR to inform another LSR of the label bindings
it has made. Once a pair of devices communicate the LDP parameters, they establish a label switched path
(LSP). MPLS LDP enables LSRs to distribute labels along normally routed paths to support MPLS forwarding.
This method of label distribution is also called hop-by-hop forwarding. With IP forwarding, when a packet
arrives at a device the device looks at the destination address in the IP header, performs a route lookup, and
forwards the packet to the next hop. With MPLS forwarding, when a packet arrives at a device the device
looks at the incoming label, looks up the label in a table, and then forwards the packet to the next hop. MPLS
LDP is useful for applications that require hop-by-hop forwarding, such as MPLS VPNs.
MPLS Label Distribution Protocol Functional Overview
Cisco Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) provides the building blocks
for MPLS-enabled applications, such as MPLS Virtual Private Networks (VPNs).
LDP provides a standard methodology for hop-by-hop, or dynamic label, distribution in an MPLS network
by assigning labels to routes that have been chosen by the underlying Interior Gateway Protocol (IGP) routing
protocols. The resulting labeled paths, called label switch paths (LIPS), forward label traffic across an MPLS
backbone to particular destinations. These capabilities enable service providers to implement MPLS-based
IP VPNs and IP+ATM services across multivendor MPLS networks.
LDP and TDP Support
On supported hardware platforms and software releases, the Label Distribution Protocol (LDP) supercedes
Tag Distribution Protocol (TDP). See the table below for information about LDP and TDP support in Cisco
software releases.
Use caution when upgrading the image on a device that uses TDP. Ensure that the TDP sessions are established
when the new image is loaded. You can accomplish this by issuing the mpls label protocol tdp global
configuration command. Issue this command and save it to the startup configuration before loading the new
image. Alternatively, you can enter the command and save the running configuration immediately after loading
the new image.
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MPLS Label Distribution Protocol
Introduction to LDP Sessions
Table 1: LDP and TDP Support
Train and Release
LDP and TDP Support
12.0S Train
• TDP is enabled by default.
• Cisco IOS Release 12.0(29)S and earlier releases: TDP is
supported for LDP features.
• Cisco IOS Release 12.0(30)S and later releases: TDP is not
support for LDP features.
12.2S, SB, and SR Trains
• LDP is enabled by default.
• Cisco IOS Release 12.2(25)S and earlier releases: TDP is
supported for LDP features.
• Cisco IOS Releases 12.2(27)SBA, 12.2(27)SRA,
12.2(27)SRB and later releases: TDP is not supported for
LDP features.
12.T/Mainline Trains
• Cisco IOS Release 12.3(14)T and earlier releases: TDP is
enabled by default.
• Cisco IOS Releases 12.4 and 12.4T and later releases: LDP
is enabled by default.
• Cisco IOS Release 12.3(11)T and earlier releases: TDP is
supported for LDP features.
• Cisco IOS Release 12.3(14)T and later releases: TDP is not
support ed for LDP features.
Introduction to LDP Sessions
When you enable Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP), the label switch
routers (LSRs) send out messages to try to find other LSRs with which they can create LDP sessions. The
following sections explain the differences between directly connected LDP sessions and nondirectly connected
LDP sessions.
Directly Connected MPLS LDP Sessions
If a label switch router (LSR) is one hop from its neighbor, it is directly connected to its neighbor. The LSR
sends out Label Distribution Protocol (LDP) link Hello messages as User Datagram Protocol (UDP) packets
to all the devices on the subnet (multicast). A neighboring LSR may respond to the link Hello message,
allowing the two devices to establish an LDP session. This is called basic discovery.
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Introduction to LDP Sessions
To initiate an LDP session between devices, the devices determine which device will take the active role and
which device will take the passive role. The device that takes the active role establishes the LDP TCP connection
session and initiates the negotiation of the LDP session parameters. To determine the roles, the two devices
compare their transport addresses. The device with the higher IP address takes the active role and establishes
the session.
After the LDP TCP connection session is established, the LSRs negotiate the session parameters, including
the method of label distribution to be used. Two methods are available:
• Downstream Unsolicited: An LSR advertises label mappings to peers without being asked to.
• Downstream on Demand: An LSR advertises label mappings to a peer only when the peer asks for them.
Nondirectly Connected MPLS LDP Sessions
If the label switch router (LSR) is more than one hop from its neighbor, it is nondirectly connected to its
neighbor. For these nondirectly connected neighbors, the LSR sends out a targeted Hello message as a User
Datagram Protocol (UDP) packet, but as a unicast message specifically addressed to that LSR. The nondirectly
connected LSR responds to the Hello message and the two devices begin to establish a Label Distribution
Protocol (LDP) session. This is called extended discovery.
A Multiprotocol Label Switching (MPLS) LDP targeted session is a label distribution session between devices
that are not directly connected. When you create an MPLS traffic engineering tunnel interface, you need to
establish a label distribution session between the tunnel headend and the tailend devices. You establish
nondirectly connected MPLS LDP sessions by enabling the transmission of targeted Hello messages.
You can use the mpls ldp neighbor targeted command to set up a targeted session when other means of
establishing targeted sessions do not apply, such as configuring mpls ip on a traffic engineering (TE) tunnel
or configuring Any Transport over MPLS (AToM) virtual circuits (VCs). For example, you can use this
command to create a targeted session between directly connected MPLS LSRs when MPLS label forwarding
convergence time is an issue.
The mpls ldp neighbor targeted command can improve label convergence time for directly connected
neighbor LSRs when the links directly connecting them are down. When the links between the neighbor LSRs
are up, both the link and targeted Hellos maintain the LDP session. If the links between the neighbor LSRs
go down, and there is an alternate route between neighbors, the targeted Hellos would maintain the session,
allowing the LSRs to retain labels learned from each other. When a link directly connecting the LSRs comes
back up, the LSRs can immediately reinstall labels for forwarding use without having to reestablish their LDP
session and exchange labels.
The exchange of targeted Hello messages between two nondirectly connected neighbors can occur in several
ways, including the following:
• Device 1 sends targeted Hello messages carrying a response request to Device 2. Device 2 sends targeted
Hello messages in response if its configuration permits. In this situation, Device 1 is considered to be
active and Device 2 is considered to be passive.
• Device 1 and Device 2 both send targeted Hello messages to each other. Both devices are considered to
be active. Both, one, or neither device can also be passive, if they have been configured to respond to
requests for targeted Hello messages from each other.
The default behavior of an LSR is to ignore requests from other LSRs that send targeted Hello messages. You
can configure an LSR to respond to requests for targeted Hello messages by issuing the mpls ldp discovery
targeted-hello accept command.
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MPLS Label Distribution Protocol
Introduction to LDP Label Bindings Label Spaces and LDP Identifiers
The active LSR mandates the protocol that is used for a targeted session. The passive LSR uses the protocol
of the received targeted Hello messages.
Introduction to LDP Label Bindings Label Spaces and LDP Identifiers
A Label Distribution Protocol (LDP) label binding is an association between a destination prefix and a label.
The label used in a label binding is allocated from a set of possible labels called a label space.
LDP supports two types of label spaces:
• Interface-specific—An interface-specific label space uses interface resources for labels. For example,
label-controlled ATM (LC-ATM) interfaces use virtual path identifiers/virtual circuit identifiers
(VPIs/VCIs) for labels. Depending on its configuration, an LDP platform may support zero, one, or
more interface-specific label spaces.
• Platform-wide—An LDP platform supports a single platform-wide label space for use by interfaces that
can share the same labels. For Cisco platforms, all interface types, except LC-ATM, use the platform-wide
label space.
LDP uses a 6-byte quantity called an LDP Identifier (or LDP ID) to name label spaces. The LDP ID is made
up of the following components:
• The first four bytes, called the LPD router ID, identify the label switch router (LSR) that owns the label
space.
• The last two bytes, called the local label space ID, identify the label space within the LSR. For the
platform-wide label space, the last two bytes of the LDP ID are always both 0.
The LDP ID takes the following form:
<LDP router ID> : <local label space ID>
The following are examples of LPD IDs:
• 172.16.0.0:0
• 192.168.0.0:3
The device determines the LDP router ID as follows, if the mpls ldp router-id command is not executed,
1 The device examines the IP addresses of all operational interfaces.
2 If these IP addresses include loopback interface addresses, the device selects the largest loopback address
as the LDP router ID.
3 Otherwise, the device selects the largest IP address pertaining to an operational interface as the LDP router
ID.
The normal (default) method for determining the LDP router ID may result in a router ID that is not usable
in certain situations. For example, the device might select an IP address as the LDP router ID that the routing
protocol cannot advertise to a neighboring device. The mpls ldp router-id command allows you to specify
the IP address of an interface as the LDP router ID. Make sure the specified interface is operational so that
its IP address can be used as the LDP router ID.
When you issue the mpls ldp router-id command without the force keyword, the device select selects the
IP address of the specified interface (provided that the interface is operational) the next time it is necessary
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MPLS Label Distribution Protocol
How to Configure MPLS Label Distribution Protocol
to select an LDP router ID, which is typically the next time the interface is shut down or the address is
configured.
When you issue the mpls ldp router-id command with the force keyword, the effect of the mpls ldp router-id
command depends on the current state of the specified interface:
• If the interface is up (operational) and if its IP address is not currently the LDP router ID, the LDP router
ID changes to the IP address of the interface. This forced change in the LDP router ID tears down any
existing LDP sessions, releases label bindings learned via the LDP sessions, and interrupts MPLS
forwarding activity associated with the bindings.
• If the interface is down (not operational) when the mpls ldp router-id interface force command is
issued, when the interface transitions to up, the LDP router ID changes to the IP address of the interface.
This forced change in the LDP router ID tears down any existing LDP sessions, releases label bindings
learned via the LDP sessions, and interrupts MPLS forwarding activity associated with the bindings.
How to Configure MPLS Label Distribution Protocol
Enabling Directly Connected LDP Sessions
This procedure explains how to configure Multiprotocol Label Switching (MPLS) Label Distribution Protocol
(LDP) sessions between two directly connected devices.
SUMMARY STEPS
1. enable
2. configure terminal
3. mpls ip
4. mpls label protocol [ldp | tdp | both]
5. interface type number
6. mpls ip
7. exit
8. exit
9. show mpls interfaces [interface] [detail]
10. show mpls ldp discovery [all | vrf vpn-name] [detail]
11. show mpls ldp neighbor [[vrf vpn-name] [address | interface] [detail] | all]
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
Example:
• Enter your password if prompted.
Device> enable
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Enabling Directly Connected LDP Sessions
Step 2
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Device# configure terminal
Step 3
Configures MPLS hop-by-hop forwarding globally.
mpls ip
• The mpls ip command is enabled by default; you do not
have to specify this command.
Example:
Device(config)# mpls ip
Step 4
• Globally enabling MPLS forwarding does not enable it on
the device interfaces. You must enable MPLS forwarding on
the interfaces as well as for the device.
mpls label protocol [ldp | tdp | both]
Configures the use of LDP on all interfaces.
• The keywords that are available depend on the hardware
platform.
Example:
Device(config)# mpls label protocol ldp
Step 5
interface type number
• If you set all interfaces globally to LDP, you can override
specific interfaces with either the tdp or both keyword by
specifying the command in interface configuration mode.
Specifies the interface to be configured and enters interface
configuration mode.
Example:
Device(config)# interface fastethernet
0/3/0
Step 6
mpls ip
Example:
Configures MPLS hop-by-hop forwarding on the interface.
• You must enable MPLS forwarding on the interfaces as well
as for the device.
Device(config-if)# mpls ip
Step 7
exit
Exits interface configuration mode and enters global configuration
mode.
Example:
Device(config-if)# exit
Step 8
exit
Exits global configuration mode and enters privileged EXEC mode.
Example:
Device(config)# exit
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Enabling Directly Connected LDP Sessions
Step 9
Command or Action
Purpose
show mpls interfaces [interface] [detail]
Verifies that the interfaces have been configured to use LDP.
Example:
Device# show mpls interfaces
Step 10
show mpls ldp discovery [all | vrf vpn-name]
[detail]
Verifies that the interface is up and is sending Discovery Hello
messages.
Example:
Device# show mpls ldp discovery
Step 11
show mpls ldp neighbor [[vrf vpn-name]
[address | interface] [detail] | all]
Displays the status of LDP sessions.
Example:
Device# show mpls ldp neighbor
Examples
The following show mpls interfaces command verifies that interfaces FastEthernet 0/3/0 and 0/3/1 have been
configured to use LDP:
Device# show mpls interfaces
Interface
IP
FastEthernet0/3/0
Yes (ldp)
FastEthernet0/3/1
Yes
Tunnel
No
No
BGP Static Operational
No No
Yes
No No
Yes
The following show mpls ldp discovery command verifies that the interface is up and is sending LDP
Discovery Hello messages (as opposed to TDP Hello messages):
Device# show mpls ldp discovery
Local LDP Identifier:
172.16.12.1:0
Discovery Sources:
Interfaces:
FastEthernet0/3/0 (ldp): xmit
The following example shows that the LDP session between devices was successfully established:
Device# show mpls ldp neighbor
Peer LDP Ident: 10.1.1.2:0; Local LDP Ident 10.1.1.1:0
TCP connection: 10.1.1.2.18 - 10.1.1.1.66
State: Oper; Msgs sent/rcvd: 12/11; Downstream
Up time: 00:00:10
LDP discovery sources:
FastEthernet0/1/0, Src IP addr: 10.20.10.2
Addresses bound to peer LDP Ident:
10.1.1.2
10.20.20.1
10.20.10.2
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MPLS Label Distribution Protocol
Establishing Nondirectly Connected MPLS LDP Sessions
Establishing Nondirectly Connected MPLS LDP Sessions
This section explains how to configure nondirectly connected MPLS Label Distribution Protocol (LDP)
sessions, which enable you to establish an LDP session between devices that are not directly connected.
Before You Begin
• Multiprotocol Label Switching (MPLS) requires Cisco Express Forwarding.
• You must configure the devices at both ends of the tunnel to be active or enable one device to be passive
with the mpls ldp discovery targeted-hello accept command.
SUMMARY STEPS
1. enable
2. configure terminal
3. mpls ip
4. mpls label protocol [ldp | tdp | both]
5. interface tunnel number
6. tunnel destination ip-address
7. mpls ip
8. exit
9. exit
10. show mpls ldp discovery [all | vrf vpn-name] [detail]
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
Example:
• Enter your password if prompted.
Device> enable
Step 2
configure terminal
Enters global configuration mode.
Example:
Device# configure terminal
Step 3
mpls ip
Example:
Device(config)# mpls ip
Configures MPLS hop-by-hop forwarding globally.
• The mpls ip command is enabled by default; you do not have
to specify this command.
• Globally enabling MPLS forwarding does not enable it on the
device interfaces. You must enable MPLS forwarding on the
interfaces as well as for the device.
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Establishing Nondirectly Connected MPLS LDP Sessions
Step 4
Command or Action
Purpose
mpls label protocol [ldp | tdp | both]
Configures the use of LDP on all interfaces.
Example:
Device(config)# mpls label protocol ldp
Step 5
interface tunnel number
• The keywords that are available depend on the hardware
platform.
• If you set all interfaces globally to LDP, you can override
specific interfaces with either the tdp or both keyword by
specifying the command in interface configuration mode.
Configures a tunnel interface and enters interface configuration mode.
Example:
Device(config)# interface tunnel 1
Step 6
tunnel destination ip-address
Assigns an IP address to the tunnel interface.
Example:
Device(config-if)# tunnel destination
172.16.1.1
Step 7
mpls ip
Example:
Configures MPLS hop-by-hop forwarding on the interface.
• You must enable MPLS forwarding on the interfaces as well
as for the device.
Device(config-if)# mpls ip
Step 8
exit
Exits interface configuration mode and enters global configuration
mode.
Example:
Device(config-if)# exit
Step 9
exit
Exits global configuration mode and enters privileged EXEC mode.
Example:
Device(config)# exit
Step 10
show mpls ldp discovery [all | vrf vpn-name] Verifies that the interface is up and is sending Discovery Hello
messages.
[detail]
Example:
Device# show mpls ldp discovery
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MPLS Label Distribution Protocol
Saving Configurations MPLS Tag Switching Commands
Examples
The following example shows the output of the show mpls ldp discovery command for a nondirectly connected
LDP session:
Device# show mpls ldp discovery
Local LDP Identifier:
172.16.0.0:0
Discovery Sources:
Interfaces:
POS1/2/0 (ldp): xmit/recv
LDP Id: 172.31.255.255:0
Tunnel1 (ldp): Targeted -> 192.168.255.255
Targeted Hellos:
172.16.0.0 -> 192.168.255.255 (ldp): active, xmit/recv
LDP Id: 192.168.255.255:0
172.16.0.0 -> 192.168.0.0 (ldp): passive, xmit/recv
LDP Id: 192.168.0.0:0
This command output indicates that:
• The local label switch router (LSR) (172.16.0.0) sent LDP link Hello messages on interface POS1/2/0
and discovered neighbor 172.31.255.255.
• The local LSR sent LDP targeted Hello messages associated with interface Tunnel1 to target
192.168.255.255. The LSR was configured to use LDP.
• The local LSR is active for targeted discovery activity with 192.168.255.255; this means that the targeted
Hello messages it sends to 192.168.255.255 carry a response request. The local LSR was configured to
have an LDP session with the nondirectly connected LSR 192.168.255.255.
• The local LSR is not passive from the discovery activity with 192.168.255.255 for one of the following
reasons:
• The targeted Hello messages it receives from 192.168.255.255 do not carry a response request.
• The local LSR has not been configured to respond to such requests.
• The local LSR sent Tag Distribution Protocol (TDP) directed Hello messages to the target LSR
192.168.0.0. This LSR uses TDP because the Hello messages received from the target LSR 192.168.0.0
were TDP directed Hello messages.
• The local LSR is passive in discovery activity with LSR 192.168.0.0. This means that the directed Hello
messages it receives from LSR 192.168.0.0 carry a response request and that the local LSR has been
configured with the mpls ldp discovery targeted-hello accept command to respond to such requests
from LSR 192.168.0.0.
• The local LSR is not active in discovery activity with LSR 192.168.0.0, because no application that
requires an LDP session with LSR 192.168.0.0 has been configured on the local LSR.
Saving Configurations MPLS Tag Switching Commands
In releases prior to Cisco IOS Release 12.4(2)T, some Multiprotocol Label Switching (MPLS) commands
had both a tag-switching version and an MPLS version. For example, the two commands tag-switching ip
and mpls ip were the same. To support backward compatibility, the tag-switching form of the command was
written to the saved configuration.
Starting in Cisco IOS Release 12.4(2)T, the MPLS form of the command is written to the saved configuration.
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MPLS Label Distribution Protocol
Specifying the LDP Router ID
For example, if an ATM interface is configured using the following commands, which have both a tag-switching
form and an MPLS form:
Device(config)# interface ATM 3/0
Device(config-if)# ip unnumbered Loopback0
Device(config-if)# tag-switching ip
Device(config-if)# mpls label protocol ldp
After you enter these commands and save this configuration or display the running configuration with the
show running-config command, the commands saved or displayed appear as follows:
interface ATM 3/0
ip unnumbered Loopback0
mpls ip
mpls label protocol ldp
Specifying the LDP Router ID
The mpls ldp router-id command allows you to establish the IP address of an interface as the LDP router
ID.
The following steps describe the normal process for determining the LDP router ID:
1 The device considers all the IP addresses of all operational interfaces.
2 If these addresses include loopback interface addresses, the device selects the largest loopback address.
Configuring a loopback address helps ensure a stable LDP ID for the device, because the state of loopback
addresses does not change. However, configuring a loopback interface and IP address on each device is
not required.
The loopback IP address does not become the router ID of the local LDP ID under the following circumstances:
•
• If the loopback interface has been explicitly shut down.
• If the mpls ldp router-id command specifies that a different interface should be used as the LDP
router ID.
If you use a loopback interface, make sure that the IP address for the loopback interface is configured with a
/32 network mask. In addition, make sure that the routing protocol in use is configured to advertise the
corresponding /32 network.
1 Otherwise, the device selects the largest interface address.
The device might select a router ID that is not usable in certain situations. For example, the device might
select an IP address that the routing protocol cannot advertise to a neighboring device.
The device implements the router ID the next time it is necessary to select an LDP router ID. The effect of
the command is delayed until the next time it is necessary to select an LDP router ID, which is typically the
next time the interface is shut down or the address is deconfigured.
If you use the force keyword with the mpls ldp router-id command, the router ID takes effect more quickly.
However, implementing the router ID depends on the current state of the specified interface:
• If the interface is up (operational) and its IP address is not currently the LDP router ID, the LDP router
ID is forcibly changed to the IP address of the interface. This forced change in the LDP router ID tears
down any existing LDP sessions, releases label bindings learned via the LDP sessions, and interrupts
Multiprotocol Label Switching (MPLS) forwarding activity associated with the bindings.
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Specifying the LDP Router ID
• If the interface is down, the LDP router ID is forcibly changed to the IP address of the interface when
the interface transitions to up. This forced change in the LDP router ID tears down any existing LDP
sessions, releases label bindings learned via the LDP sessions, and interrupts MPLS forwarding activity
associated with the bindings.
Before You Begin
Make sure the specified interface is operational before assigning it as the Label Distribution Protocol (LDP)
router ID.
SUMMARY STEPS
1. enable
2. configure terminal
3. mpls ip
4. mpls label protocol [ldp | tdp | both]
5. mpls ldp router-id interface [force]
6. exit
7. show mpls ldp discovery [all | detail | vrf vpn-name]
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
• Enter your password if prompted.
Example:
Device> enable
Step 2
Enters global configuration mode.
configure terminal
Example:
Device# configure terminal
Step 3
Configures MPLS hop-by-hop forwarding globally.
mpls ip
• The mpls ip command is enabled by default; you do not have
to specify this command.
Example:
Device(config)# mpls ip
Step 4
• Globally enabling MPLS forwarding does not enable it on the
device interfaces. You must enable MPLS forwarding on the
interfaces as well as for the device.
mpls label protocol [ldp | tdp | both]
Configures the use of LDP on all interfaces.
• The keywords that are available depend on the hardware
platform.
Example:
Device(config)# mpls label protocol ldp
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Preserving QoS Settings with MPLS LDP Explicit Null
Command or Action
Purpose
• If you set all interfaces globally to LDP, you can override
specific interfaces with either the tdp or both keyword by
specifying the command in interface configuration mode.
Step 5
mpls ldp router-id interface [force]
Specifies the preferred interface for determining the LDP router ID.
Example:
Device(config)# mpls ldp router-id pos
2/0/0
Step 6
Exits global configuration mode and enters privileged EXEC mode.
exit
Example:
Device(config)# exit
Step 7
show mpls ldp discovery [all | detail | vrf
vpn-name]
Displays the LDP identifier for the local device.
Example:
Device# show mpls ldp discovery
Example
The following example assigns interface pos 2/0/0 as the LDP router ID:
Device> enable
Device# configure terminal
Device(config)# mpls ip
Device(config)# mpls label protocol ldp
Device(config)# mpls ldp router-id pos 2/0/0 force
The following example displays the LDP router ID (10.15.15.15):
Device# show mpls ldp discovery
Local LDP Identifier:
10.15.15.15:0
Discovery Sources:
Interfaces:
FastEthernet0/3/0 (ldp): xmit/recv
LDP Id: 10.14.14.14:0
Preserving QoS Settings with MPLS LDP Explicit Null
Normally, the Label Distribution Protocol (LDP) advertises an Implicit Null label for directly connected
routes. The Implicit Null label causes the second last (penultimate) label switched router (LSR) to remove
the Multiprotocol Label Switching (MPLS) header from the packet. In this case, the penultimate LSR and the
last LSR do not have access to the quality of service (QoS) values that the packet carried before the MPLS
header was removed. To preserve the QoS values, you can configure the LSR to advertise an explicit NULL
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MPLS Label Distribution Protocol
Preserving QoS Settings with MPLS LDP Explicit Null
label (a label value of zero). The LSR at the penultimate hop forwards MPLS packets with a NULL label
instead of forwarding IP packets.
An explicit NULL label is not needed when the penultimate hop receives MPLS packets with a label stack
that contains at least two labels and penultimate hop popping is performed. In that case, the inner label
can still carry the QoS value needed by the penultimate and edge LSR to implement their QoS policy.
Note
When you issue the mpls ldp explicit-null command, Explicit Null is advertised in place of Implicit Null for
directly connected prefixes.
SUMMARY STEPS
1. enable
2. configure terminal
3. mpls ip
4. mpls label protocol [ldp | tdp | both]
5. interface type number
6. mpls ip
7. exit
8. mpls ldp explicit-null [for prefix-acl | to peer-acl | for prefix-acl to peer-acl]
9. exit
10. show mpls forwarding-table [network {mask | length} | labels label [-label] | interface interface | next-hop
address | lsp-tunnel [tunnel-id]] [vrf vpn-name [detail]
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
Example:
• Enter your password if prompted.
Device> enable
Step 2
configure terminal
Enters global configuration mode.
Example:
Device# configure terminal
Step 3
mpls ip
Example:
Device(config)# mpls ip
Configures MPLS hop-by-hop forwarding globally.
• The mpls ip command is enabled by default; you do not have
to specify this command.
• Globally enabling MPLS forwarding does not enable it on
the device interfaces. You must enable MPLS forwarding on
the interfaces as well as for the device.
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Preserving QoS Settings with MPLS LDP Explicit Null
Step 4
Command or Action
Purpose
mpls label protocol [ldp | tdp | both]
Configures the use of LDP on all interfaces.
Example:
Device(config)# mpls label protocol ldp
Step 5
interface type number
• The keywords that are available depend on the hardware
platform.
• If you set all interfaces globally to LDP, you can override
specific interfaces with either the tdp or both keyword by
specifying the command in interface configuration mode.
Specifies the interface to be configured and enters interface
configuration mode.
Example:
Device(config)# interface atm 2/2/0
Step 6
mpls ip
Example:
Configures MPLS hop-by-hop forwarding on the interface.
• You must enable MPLS forwarding on the interfaces as well
as for the device.
Device(config-if)# mpls ip
Step 7
exit
Exits interface configuration mode and enters global configuration
mode.
Example:
Device(config-if)# exit
Step 8
mpls ldp explicit-null [for prefix-acl | to peer-acl Advertises an Explicit Null label in situations where it would
normally advertise an Implicit Null label.
| for prefix-acl to peer-acl]
Example:
Device(config)# mpls ldp explicit-null
Step 9
exit
Exits global configuration mode and enter privileged EXEC mode.
Example:
Device(config)# exit
Step 10
show mpls forwarding-table [network {mask | Verifies that MPLS packets are forwarded with an explicit-null
length} | labels label [-label] | interface interface label (value of 0).
| next-hop address | lsp-tunnel [tunnel-id]] [vrf
vpn-name [detail]
Example:
Device# show mpls forwarding-table
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Preserving QoS Settings with MPLS LDP Explicit Null
Examples
Enabling explicit-null on an egress LSR causes that LSR to advertise the explicit-null label to all adjacent
MPLS devices.
Device# configure terminal
Device(config)# mpls ldp explicit-null
If you issue the show mpls forwarding-table command on an adjacent device, the output shows that MPLS
packets are forwarded with an explicit-null label (value of 0). In the following example, the second column
shows that entries have outgoing labels of 0, where once they were marked “Pop label”.
Device# show mpls forwarding-table
Local
label
19
22
23
24
25
26
27
28
Outgoing
Prefix
label or VC or Tunnel Id
Pop tag
10.12.12.12/32
0
10.14.14.14/32
0
172.24.24.24/32
0
192.168.0.0/8
0
10.15.15.15/32
0
172.16.0.0/8
25
10.16.16.16/32
0
10.34.34.34/32
Bytes label Outgoing
switched
interface
0
Fa2/1/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
Next Hop
172.16.0.1
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.22
192.168.0.2
Enabling explicit-null and specifying the for keyword with a standard access control list (ACL) changes all
adjacent MPLS devices' tables to swap an explicit-null label for only those entries specified in the access-list.
In the following example, an access-list is created that contains the 10.24.24.24/32 entry. Explicit null is
configured and the access list is specified.
Device# configure terminal
Device(config)# mpls label protocol ldp
Device(config)# access-list 24 permit host 10.24.24.24
Device(config)# mpls ldp explicit-null for 24
If you issue the show mpls forwarding-table command on an adjacent device, the output shows that the only
the outgoing labels for the addresses specified (172.24.24.24/32) change from Pop label to 0. All other Pop
label outgoing labels remain the same.
Device# show mpls forwarding-table
Local
label
19
22
23
24
25
26
27
28
Outgoing
Prefix
label or VC or Tunnel Id
Pop tag
10.12.12.12/32
0
10.14.14.14/32
0
172.24.24.24/32
0
192.168.0.0/8
0
10.15.15.15/32
0
172.16.0.0/8
25
10.16.16.16/32
0
10.34.34.34/32
Bytes label Outgoing
switched
interface
0
Fa2/1/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
Next Hop
172.16.0.1
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.22
192.168.0.2
Enabling explicit null and adding theto keyword and an access list enables you to advertise explicit-null labels
to only those adjacent devices specified in the access-list. To advertise explicit-null to a particular device, you
must specify the device's LDP ID in the access-list.
In the following example, an access-list contains the 10.15.15.15/32 entry, which is the LDP ID of an adjacent
MPLS device. The device that is configured with explicit null advertises explicit-null labels only to that
adjacent device.
Device# show mpls ldp discovery
Local LDP Identifier:
10.15.15.15:0
Discovery Sources:
Interfaces:
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FastEthernet2/0/0(ldp): xmit/recv
TDP Id: 10.14.14.14:0
Device# configure terminal
Device(config)# mpls label protocol ldp
Device(config)# access-list 15 permit host 10.15.15.15
Device(config)# mpls ldp explicit-null to 15
If you issue the show mpls forwarding-table command, the output shows that explicit null labels are going
only to the device specified in the access list.
Device# show mpls forwarding-table
Local
label
19
22
23
24
25
26
27
28
Outgoing
Prefix
label or VC or Tunnel Id
Pop tag
10.12.12.12/32
0
10.14.14.14/32
0
172.24.24.24/32
0
192.168.0.0/8
0
10.15.15.15/32
0
172.16.0.0/8
25
10.16.16.16/32
0
10.34.34.34/32
Bytes label Outgoing
switched
interface
0
Fa2/1/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
0
Fa2/0/0
Next Hop
172.16.0.1
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.2
192.168.0.22
192.168.0.2
Enabling explicit-null with both the for and to keywords enables you to specify which routes to advertise
with explicit-null labels and to which adjacent devices to advertise these explicit-null labels.
Device# show access 15
Standard IP access list 15
permit 10.15.15.15 (7 matches)
Device# show access 24
Standard IP access list 24
permit 10.24.24.24 (11 matches)
Device# configure terminal
Device(config)# mpls label protocol ldp
Device(config)# mpls ldp explicit-null for 24 to 15
If you issue the show mpls forwarding-table command, the output shows that it receives explicit null labels
for 10.24.24.24/32.
Device# show mpls forwarding-table
Local
label
17
20
21
22
23
25
27
28
29
Outgoing
Prefix
label or VC or Tunnel Id
0 <--10.24.24.24/32
Pop tag
172.16.0.0/8
20
10.12.12.12/32
16
10.0.0.0/8
21
10.13.13.13/32
Pop tag
10.14.14.14/32
Pop tag
192.168.0.0/8
25
10.16.16.16/32
Pop tag
192.168.34.34/32
Bytes label Outgoing
switched
interface
0
Fe2/0/0
0
Fe2/0/0
0
Fe2/0/0
0
Fe2/0/0
0
Fe2/0/0
0
Fe2/0/0
0
Fe2/0/0
0
Fe2/0/0
0
Fe2/0/0
Next Hop
172.16.0.1
172.16.0.1
172.16.0.1
172.16.0.1
172.16.0.1
172.16.0.1
172.16.0.1
172.16.0.1
172.16.0.1
Protecting Data Between LDP Peers with MD5 Authentication
You can enable authentication between two Label Distribution Protocol (LDP) peers, which verifies each
segment sent on the TCP connection between the peers. You must configure authentication on both LDP peers
using the same password; otherwise, the peer session is not established.
Authentication uses the Message Digest 5 (MD5) algorithm to verify the integrity of the communication and
authenticate the origin of the message.
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Protecting Data Between LDP Peers with MD5 Authentication
To enable authentication, issue the mpls ldp neighbor password command. This causes the device to generate
an MD5 digest for every segment sent on the TCP connection and check the MD5 digest for every segment
received from the TCP connection.
When you configure a password for an LDP neighbor, the device tears down existing LDP sessions and
establishes new sessions with the neighbor.
If a device has a password configured for a neighbor, but the neighboring device does not have a password
configured, a message such as the following appears on the console who has a password configured while the
two devices attempt to establish an LDP session. The LDP session is not established.
%TCP-6-BADAUTH: No MD5 digest from [peer's IP address](11003) to [local device's IP address](646)
Similarly, if the two devices have different passwords configured, a message such as the following appears
on the console. The LDP session is not established.
%TCP-6-BADAUTH: Invalid MD5 digest from [peer's IP address](11004) to [local device's IP address](646)
SUMMARY STEPS
1. enable
2. configure terminal
3. mpls ip
4. mpls label protocol [ldp | tdp | both]
5. mpls ldp neighbor [vrf vpn-name] ip-address [password [0-7] password-string]
6. exit
7. show mpls ldp neighbor [[vrf vpn-name] [address | interface] [detail] | all]
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
Example:
• Enter your password if prompted.
Device> enable
Step 2
configure terminal
Enters global configuration mode.
Example:
Device# configure terminal
Step 3
mpls ip
Example:
Device(config)# mpls ip
Configures MPLS hop-by-hop forwarding globally.
• The mpls ip command is enabled by default; you do not have
to specify this command.
• Globally enabling MPLS forwarding does not enable it on the
device interfaces. You must enable MPLS forwarding on the
interfaces as well as for the device.
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Protecting Data Between LDP Peers with MD5 Authentication
Step 4
Command or Action
Purpose
mpls label protocol [ldp | tdp | both]
Configures the use of LDP on all interfaces.
Example:
Device(config)# mpls label protocol ldp
Step 5
• The keywords that are available depend on the hardware
platform.
• If you set all interfaces globally to LDP, you can override
specific interfaces with either the tdp or both keyword by
specifying the command in interface configuration mode.
mpls ldp neighbor [vrf vpn-name] ip-address Specifies authentication between two LDP peers.
[password [0-7] password-string]
Example:
Device(config)# mpls ldp neighbor
172.27.0.15 password onethirty9
Step 6
Exits global configuration mode and enters privileged EXEC mode.
exit
Example:
Device(config)# exit
Step 7
show mpls ldp neighbor [[vrf vpn-name]
[address | interface] [detail] | all]
Example:
Displays the status of LDP sessions.
If the passwords have been set on both LDP peers and the passwords
match, the show mpls ldp neighbor command displays that the LDP
session was successfully established.
Device# show mpls ldp neighbor detail
Examples
The following example configures a device with the password cisco:
Device> enable
Device# configure terminal
Device(config)# mpls ip
Device(config)# mpls label protocol ldp
Device(config)# mpls ldp neighbor 10.1.1.1 password cisco
Device(config)# exit
The following example shows that the LDP session between devices was successfully established:
Device# show mpls ldp neighbor
Peer LDP Ident: 10.1.1.2:0; Local LDP Ident 10.1.1.1:0
TCP connection: 10.1.1.2.11118 - 10.1.1.1.646
State: Oper; Msgs sent/rcvd: 12/11; Downstream
Up time: 00:00:10
LDP discovery sources:
FastEthernet1/0/0, Src IP addr: 10.20.10.2
Addresses bound to peer LDP Ident:
10.1.1.2
10.20.20.1
10.20.10.2
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Configuration Examples for MPLS Label Distribution Protocol
The following show mpls ldp neighbor detail command shows that MD5 is used for the LDP session.
Device# show mpls ldp neighbor 10.0.0.21 detail
Peer LDP Ident: 10.0.0.21:0; Local LDP Ident 10.0.0.22:0
TCP connection: 10.0.0.21.646 - 10.0.0.22.14709; MD5 on
State: Oper; Msgs sent/rcvd: 1020/1019; Downstream; Last TIB rev sent 2034
Up time: 00:00:39; UID: 3; Peer Id 1;
LDP discovery sources:
FastEthernet1/1/0; Src IP addr: 172.16.1.1
holdtime: 15000 ms, hello interval: 5000 ms
Addresses bound to peer LDP Ident:
10.0.0.21
10.0.38.28
10.88.88.2
172.16.0.1
172.16.1.1
Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab
Configuration Examples for MPLS Label Distribution Protocol
Example: Configuring Directly Connected MPLS LDP Sessions
The figure below shows a sample network for configuring directly connected Label Distribution Protocol
(LDP) sessions.
This example configures the following:
• Multiprotocol Label Switching (MPLS) hop-by-hop forwarding for the POS links between Device 1
and Device 2 and between Device 1 and Device 3.
• LDP for label distribution between Device 1 and Device 2.
• LDP for label distribution between Device 1 and Device 3.
• A loopback interface and IP address for each LSR that can be used as the LDP router ID.
Figure 1: Configuration of MPLS LDP
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Example: Configuring Directly Connected MPLS LDP Sessions
Note
The configuration examples below show only the commands related to configuring LDP for Device 1,
Device 2, and Device 3 in the sample network shown in the figure above.
Device 1 Configuration
ip cef distributed
interface Loopback0
ip address 172.16.0.11 255.255.255.255
!
interface POS0/3/0
ip address 10.0.0.44 255.0.0.0
mpls ip
mpls label protocol ldp
!
interface POS1/3/0
ip address 192.168.0.44 255.0.0.0
mpls ip
mpls label protocol ldp
!Assumes R1 supports distributed CEF
!Loopback interface for LDP ID.
!Enable hop-by-hop MPLS forwarding
!Enable hop-by-hop MPLS forwarding
Device 2 Configuration
ip cef distributed
!
interface Loopback0
ip address 172.16.0.22 255.255.255.255
!
interface POS2/0/0
ip address 10.0.0.33 255.0.0.0
mpls ip
mpls label protocol ldp
!Assumes R2 supports distributed CEF
!Loopback interface for LDP ID.
!Enable hop-by-hop MPLS forwarding
Device 3 Configuration
ip cef
!
interface Loopback0
ip address 172.16.0.33 255.255.255.255
!
interface POS1/0/0
ip address 192.168.0.55 255.0.0.0
mpls ip
mpls label protocol ldp
!Assumes R3 does not support dCEF
!Loopback interface for LDP ID.
!Enable hop-by-hop MPLS forwarding
The LDP configuration for Device 1 uses the mpls label protocol ldp command in interface configuration
mode. To specify LDP for all interfaces, use the mpls label protocol ldp command in global configuration
mode without any interface mpls label protocol commands.
The configuration of Device 2 also uses the mpls label protocol ldp command in interface configuration
mode. To specify LDP for all interfaces, use the mpls label protocol ldp command in global configuration
mode without any interface mpls label protocol commands.
Configuring the mpls ip command on an interface triggers the transmission of discovery Hello messages for
the interface.
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MPLS Label Distribution Protocol
Example: Establishing Nondirectly Connected MPLS LDP Sessions
Example: Establishing Nondirectly Connected MPLS LDP Sessions
The following examples illustrate the configuration of platforms for Multiprotocol Label Switching (MPLS)
Label Distribution Protocol (LDP) nondirectly connected sessions using the sample network shown in the
figure below. Note that Devices 1, 4, 5, and 6 in this sample network are not directly connected to each other.
Figure 2: Sample Network for Configuring LDP for Targeted Sessions
The configuration example shows the following:
• Targeted sessions between Devices 1 and 4 use LDP. Devices 1 and 4 are both active.
• Targeted sessions between Devices 1 and 6 use LDP. Device 1 is active and Device 6 is passive.
• Targeted sessions between Devices 1 and 5 use LDP. Device 5 is active.
These examples assume that the active ends of the nondirectly connected sessions are associated with tunnel
interfaces, such as MPLS traffic engineering tunnels. They show only the commands related to configuring
LDP targeted sessions. The examples do not show configuration of the applications that initiate the targeted
sessions.
Device 1 Configuration
Tunnel interfaces Tunnel14 and Tunnel16 specify LDP for targeted sessions associated with these interfaces.
The targeted session for Device 5 requires LDP. The mpls label protocol ldp command in global configuration
mode makes it unnecessary to explicitly specify LDP as part of the configuration from the Tunnel14 and
Tunnel16.
ip cef distributed
!Device1 supports distributed CEF
mpls label protocol ldp
!Use LDP for all interfaces
interface Loopback0
!Loopback interface for LDP ID.
ip address 10.25.0.11 255.255.255.255
interface Tunnel14
!Tunnel to Device 4 requiring label distribution
tunnel destination 10.11.0.4 !Tunnel endpoint is Device 4
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Additional References
mpls ip
interface Tunnel15
tunnel destination 10.11.0.5
mpls label protocol ldp
mpls ip
interface Tunnel16
tunnel destination 10.11.0.6
mpls ip
!Enable hop-by-hop forwarding on the interface
!Tunnel to Device 5 requiring label distribution
!Tunnel endpoint is Device 5
!Use LDP for session with Device 5
!Enable hop-by-hop forwarding on the interface
!Tunnel to Device 6 requiring label distribution
!Tunnel endpoint is Device 6
!Enable hop-by-hop forwarding on the interface
Device 4 Configuration
The mpls label protocol ldp command in global configuration mode makes it unnecessary to explicitly specify
LDP as part of the configuration for the Tunnel41 targeted session with Device 1.
ip cef distributed
!Device 4 supports distributed CEF
mpls label protocol ldp
!Use LDP for all interfaces
interface Loopback0
!Loopback interface for LDP ID.
ip address 10.25.0.44 255.255.255.255
interface Tunnel41
!Tunnel to Device 1 requiring label distribution
tunnel destination 10.11.0.1 !Tunnel endpoint is Device 1
mpls ip
!Enable hop-by-hop forwarding on the interface
Device 5 Configuration
Device 5 uses LDP for all targeted sessions. Therefore, its configuration includes the mpls label protocol
ldp command.
ip cef
!Device 5 supports CEF
mpls label protocol ldp
!Use LDP for all interfaces
interface Loopback0
!Loopback interface for LDP ID.
ip address 10.25.0.55 255.255.255.255
interface Tunnel51
!Tunnel to Device 1 requiring label distribution
tunnel destination 10.11.0.1 !Tunnel endpoint is Device 1
mpls ip
!Enable hop-by-hop forwarding on the interface
Device 6 Configuration
By default, a device cannot be a passive neighbor in targeted sessions. Therefore, Device 1, Device 4, and
Device 5 are active neighbors in any targeted sessions. The mpls ldp discovery targeted-hello accept
command permits Device 6 to be a passive target in targeted sessions with Device 1. Device 6 can also be an
active neighbor in targeted sessions, although the example does not include such a configuration.
ip cef distributed
!Device 6 supports distributed CEF
interface Loopback0
!Loopback interface for LDP ID.
ip address 10.25.0.66 255.255.255.255
mpls ldp discovery targeted-hellos accept from LDP_SOURCES
!Respond to requests for targeted hellos
!from sources permitted by acl LDP_SOURCES
ip access-list standard LDP_SOURCES
!Define acl for targeted hello sources.
permit 10.11.0.1
!Accept targeted hello request from Device 1.
deny any
!Deny requests from other sources.
Additional References
Related Documents
Related Topic
Document Title
Cisco IOS commands
Cisco IOS Master Command List, All Releases
MPLS Label Distribution Protocol Configuration Guide, Cisco IOS Release 15S
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MPLS Label Distribution Protocol
Additional References
Related Topic
Document Title
MPLS commands
Cisco IOS Multiprotocol Label Switching Command
Reference
Configures LDP on every interface associated with
a specified IGP instance.
“MPLS LDP Autoconfiguration” module in the MPLS
Label Distribution Protocol Configuration Guide
Ensures that LDP is fully established before the IGP “MPLS LDP IGP Synchronization” module in the
path is used for switching.
MPLS Label Distribution Protocol Configuration
Guide
Allows ACLs to control the label bindings that an
LSR accepts from its peer LSRs.
“MPLS LDP Inbound Label Binding Filtering”
module in the MPLS Label Distribution Protocol
Configuration Guide
Enables standard, SNMP-based network management “MPLS Label Distribution Protocol MIB Version 8
of the label switching features.
Upgrade” module in the MPLS Embedded
Management and MIBs Configuration Guide
MIBs
MIB
MIBs Link
• MPLS Label Distribution Protocol MIB
(draft-ietf-mpls-ldp-mib-08.txt)
To locate and download MIBs for selected platforms,
Cisco software releases, and feature sets, use Cisco
MIB Locator found at the following URL:
• SNMP-VACM-MIB The View-based Access
Control Model (ACM) MIB for SNMP
http://www.cisco.com/go/mib
RFCs
RFC
Title
RFC 3036
LDP Specification
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Feature Information for MPLS Label Distribution Protocol
Technical Assistance
Description
Link
The Cisco Support and Documentation website
http://www.cisco.com/cisco/web/support/index.html
provides online resources to download documentation,
software, and tools. Use these resources to install and
configure the software and to troubleshoot and resolve
technical issues with Cisco products and technologies.
Access to most tools on the Cisco Support and
Documentation website requires a Cisco.com user ID
and password.
Feature Information for MPLS Label Distribution Protocol
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.
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Feature Information for MPLS Label Distribution Protocol
Table 2: Feature Information for MPLS Label Distribution Protocol
Feature Name
Releases
Feature Information
MPLS Label Distribution Protocol 12.0(10)ST
12.0(14)ST
12.1(2)T
12.1(8a)E
12.2(2)T
12.2(4)T
12.2(8)T
12.0(21)ST
12.0(22)S
12.0(23)S
12.2(13)T
12.4(3)
12.4(5)
Cisco IOS XE Release 2.1
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Feature Information for MPLS Label Distribution Protocol
Feature Name
Releases
Feature Information
MPLS Label Distribution Protocol
(LDP) enables peer label switch
routers (LSRs) in an Multiprotocol
Label Switching (MPLS) network
to exchange label binding
information for supporting
hop-by-hop forwarding in an
MPLS network. This module
explains the concepts related to
MPLS LDP and describes how to
configure MPLS LDP in a network.
This feature was introduced in
Cisco IOS Release 12.0(10)ST,
incorporating a new set of MPLS
CLI commands implemented for
use with Cisco devices. The CLI
commands in this release reflected
MPLS command syntax and
terminology, thus facilitating the
orderly transition from a network
using the Tag Distribution Protocol
(TDP) to one using the LDP.
In Cisco IOS Release 12.0(14)ST,
several new MPLS CLI commands
were introduced. Support for
MPLS VPNs was added by means
of a new vrf vpn-name keyword
and argument in certain existing
commands, and other commands
were modified to ensure consistent
interpretation of associated
prefix-access-list arguments by
Cisco software.
In Cisco IOS 12.1(2)T, this feature
was integrated into this release.
Also, the debug mpls atm-ldp api,
debug mpls atm-ldp routes, and
debug mpls atm-ldp states
commands were modified.
This feature was integrated into
Cisco IOS Release 12.1(8a)E.
This feature was integrated into
Cisco IOS Release 12.2(2)T.
The following commands were
introduced or modified by this
feature: mpls label protocol
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Feature Information for MPLS Label Distribution Protocol
Feature Name
Releases
Feature Information
(global configuration), mpls ldp
router-id
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Feature Information for MPLS Label Distribution Protocol
Feature Name
Releases
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Feature Information
MPLS Label Distribution Protocol
Feature Information for MPLS Label Distribution Protocol
Feature Name
Releases
Feature Information
In Cisco IOS Release 12.2(4)T,
support was added for Cisco MGX
8850 and MGX 8950 switches
equipped with a Cisco MGX
RPM-PR card, and the VPI range
in the show mpls atm-ldp
bindings and show mpls ip
binding commands was changed
to 4095.
In Cisco IOS Release 12.2(8)T, the
debug mpls atm-ldp failure
command was introduced.
In Cisco IOS Release 12.0(21)ST,
the mpls ldp neighbor
implicit-withdraw command was
introduced.
This feature was integrated into
Cisco IOS Release 12.0(22)S. The
mpls ldp neighbor
targeted-session command and the
interface keyword for the mpls
ldp advertise-labels command
were added.
This feature was integrated into
Cisco IOS Release 12.0(23)S.
Default values for the mpls ldp
discovery command holdtime
and interval keywords were
changed.
This feature was integrated into
Cisco IOS Release 12.2(13)T.
In Cisco IOS Release 12.4(3), the
default MPLS label distribution
protocol changed from TDP to
LDP. If no protocol is explicitly
configured by the mpls label
protocol command, LDP is the
default label distribution protocol.
See the mpls label protocol
(global configuration) command
for more information.
Also in Cisco IOS Release 12.4(3),
LDP configuration commands are
saved by using the MPLS form of
the command rather than the
tag-switching form. Previously,
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Feature Information for MPLS Label Distribution Protocol
Feature Name
Releases
Feature Information
commands were saved by using the
tag-switching form of the
command, for backward
compatibility.
In Cisco IOS Release 12.4(5), the
vrf vrf-name keyword and
argument was added for the mpls
ldp router-id command to allow
you to associate the LDP router ID
with a nondefault VRF.
In Cisco IOS XE Release 2.1, this
feature was implemented on the
Cisco ASR 1000 Series
Aggregation Services Router.
The following commands were
introduced or modified: debug
mpls atm-ldp failure, mpls label
protocol (global configuration),
mpls ldp advertise-labels, mpls
ldp discovery, mpls ldp neighbor
implicit-withdraw, mpls ldp
neighbor targeted-session, mpls
ldp router-id.
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