IBM Switch 6 MPLS User Manual

Specialized Models User Guide  
6
MPLS Model User Guide  
6 MPLS Model User Guide  
Multi-Protocol Label Switching (MPLS) is a multi-layer switching technology that  
uses labels to determine how packets are forwarded through a network. The  
first part of this document describes key features of the MPLS specialized model  
and the second part focuses on procedures for configuring MPLS in your  
network model.  
Model Features  
This section contains a list of the main features available in the Multi-Protocol  
Label Switching model:  
• The MPLS model captures the following protocol behavior:  
Table 6-1 MPLS Model Features  
Feature  
Description  
• LSPs can be created manually or  
automatically from traffic conversation  
pairs.  
LSP (Label Switched Path) configuration  
• LSPs are easily reused in other scenarios  
or projects by using the LSP import and  
export features.  
• Both dynamic and static LSPs are created  
using the path object.  
• DiffServ extensions, as defined in  
RFC-2475, are provided.  
Differential Services (DiffServ)  
• The model enables you to perform QoS  
(quality of service) analyses by accounting  
for different types of service.  
Traffic Engineering  
Traffic engineered routes are computed  
using Constrained Shortest Path First  
(CSPF) with OSPF or IS-IS routing protocols.  
End of Table 6-1  
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Node Models  
The MPLS model suite supports workstation, server, router, and link models  
from the standard model library. The LER (Label Edge Router) and LSR (Label  
Switching Router) node models in the MPLS object palette are preconfigured to  
support MPLS. However, you can configure any of the router models in the  
standard model library to model LERs and LSRs.  
Figure 6-1 MPLS Object Palette  
Model Attributes  
Global MPLS attributes, which are used to configure network-wide MPLS  
parameters, are grouped in the MPLS configuration object. Router-specific  
MPLS attributes are grouped in the MPLS Parameters attribute on each router.  
MPLS Configuration Object Attributes  
Some of the important MPLS configuration object attributes are described  
below.  
FEC Specifications This attribute specifies the Forwarding Equivalence  
Class (FEC) parameters used by MPLS in the network. FECs classify and  
group packets so that all packets in a group are forwarded the same way.  
FECs are based on any of the IP header fields—ToS, Protocol, Source  
Address Range, Destination Address Range, Source Port, and Destination  
Port can all be used to define a FEC. Figure 6-2 Specifying FEC Attributes  
on page SPM-6-4 shows the attribute sequence for defining an FEC.  
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Figure 6-2 Specifying FEC Attributes  
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The FEC Details Table helps define the FEC through a set of match rules,  
which are combinations of TCP, UDP, and IP header fields. FECs are  
determined by taking a logical AND of the column settings in a row and by  
taking a logical OR of each of the rows. In other words, for a packet to qualify  
for a particular FEC, the IP header fields must satisfy every condition of at  
least one row of the defined FEC. For example, a FEC that consists only of  
email and ftp traffic would be specified as shown in Figure 6-3.  
Figure 6-3 FEC Details for E-mail and FTP Traffic  
Therefore, if the IP header of a packet contained either email or FTP, it would  
qualify for the FEC defined in Figure 6-3, and would be sent over the  
corresponding LSP.  
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LSP Specification File This attribute indicates whether the network LSPs  
should be configured according to the text file specified. You can update the  
text file by clicking OK in the LSP Browser. Updating the file recreates the file  
based on the current network LSP settings, including LSPs that might not  
have been in the original file (such as those created manually).  
Traffic Trunk Profiles This attribute specifies out-of-profile actions and  
traffic classes for traffic trunks in the network. Traffic trunks capture traffic  
characteristics such as peak rate, average rate, and average burst size. The  
default Trunk Details setting configures a trunk with a value of  
32,000 bits/sec for maximum and average bit rate and 32,000 bits for  
maximum burst size.  
Figure 6-4 Specifying Traffic Trunk Profiles  
EXP <--> Drop Precedence and EXP <--> PHB These attributes specify  
how EXP bits in the MPLS shim header are translated into diffserv  
information at each LSR. For E-LSPs, LSRs determine Per Hop Behavior  
(PHB), while on L-LSPs, they determine Drop Precedence. Use the default  
setting unless you are analyzing the effects of QoS.  
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Figure 6-5 Mapping EXP Bits to Drop Precedence and PHB  
Router Attributes  
Some of the important MPLS Parameters attributes set on routers are described  
below.  
Traffic Mapping Configuration  
This attribute specifies bindings between FECs and LSPs. Each row of the  
Traffic Mapping Configuration table specifies a distinct traffic engineering (TE)  
binding. Each TE binding specifies the FEC, traffic trunk, and LSP that is applied  
to the label of the incoming packet.  
Only previously defined values appear in the attribute pull-down lists. If no  
values appear in the attribute pull-down lists, verify that you have defined the  
FECs and traffic trunks in the MPLS Configuration object, and that the LSPs  
appear in the network path browser.  
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When an unlabeled packet arrives at an ingress LER, the following sequence  
occurs to determine the correct label for the packet:  
1) The TE binding is selected based on the packet FEC and the incoming  
interface.  
2) The packet is checked to make sure that its traffic characteristics conform  
to those specified for the TE binding’s traffic trunk.  
3) The packet is labeled for and sent through the primary LSP specified for the  
TE binding.  
Figure 6-6 Configuring TE Bindings  
\
This weight attribute  
configuration uses LER2-LER5  
75% of the time and LER2-site9  
25% of the time.  
EXP <--> Drop Precedence and EXP <--> PHB These attributes specify  
which mappings, defined in the MPLS configuration object, are used by the  
router.  
LDP Parameters—specifies Label Distribution Protocol parameters used by  
the LSR. LDP Parameters is a compound attribute, composed of the  
following sub-attributes:  
Discovery Configuration—specifies Hello message parameters  
needed to learn of neighboring routers  
Session Configuration—specifies Keep-alive message parameters  
used to establish LDP sessions  
Recovery Configuration—specifies how node and link failures are  
detected  
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Figure 6-7 Configuring LDP Parameters  
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Simulation Attributes  
The following simulation attributes are available (Configure/Run Discrete Event  
Simulation dialog box) when using the MPLS model suite.  
CR-LDP Routing—specifies if CR-LDP routing uses CSPF or conventional  
IGP to determine routes in loosely defined LSPs. The default value is IGP.  
CSPF Retry Timer—specifies how long an ingress LER waits after detecting  
a node or link failure before rerouting an LSP that traverses the failed node  
or link. The default value for this attribute is 45 seconds.  
LDP Discovery End Time—specifies when LDP discovery ends. After this  
time, no more LDP discovery packets are sent through the network. This  
value should occur after the network reaches a final, constant state in the  
simulation since no network topology or device status changes are reflected  
in the LDP routing tables after LDP Discovery End Time.  
LDP Discovery Start Time—specifies when LDP starts sending discovery  
packets through the network. Set this attribute to a value other than Do Not  
Start to enable LDP.  
LSP Signaling Protocol—specifies whether dynamic LSPs are signaled  
using CR-LDP (constraint-based routed LDP) or RSVP. The default value is  
CR-LDP.  
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LSP Attributes  
Some of the important LSP attributes are described below. Most of these  
attributes can also be configured in the LSP browser, which is described in the  
next section.  
Figure 6-8 Configuring an LSP’s Attributes  
Directionality—specifies if an LSP is unidirectional or bidirectional. Dynamic  
LSPs are always unidirectional.  
LSP Type—specifies whether the LSP is of type E-LSP or L-LSP. For  
E-LSP, three experimental bits in the shim header carry the Diff-Serv  
information. This provides eight different types of service (TOS) per LSP. For  
L-LSP, TOS information is contained in the MPLS label and all packets  
traversing the link are treated equally.  
Path Details—specifies which packets use the LSP and defines how  
packets are forwarded through the LSP. This attribute is automatically  
configured for dynamic LSPs. To configure this attribute for static LSPs,  
select Update LSP Details from the Protocols > MPLS menu.  
Figure 6-9 Path Details for a Static LSP  
Recovery Parameters—specifies recovery parameters that are used to  
reroute traffic on this LSP if there is a link or node failure along the LSP.  
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Figure 6-10 Recovery Parameters Configuration  
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Setup Parameters—specifies the duration of the LSP.  
Figure 6-11 Setup Parameters Configuration  
TE Parameters—specifies the traffic engineering constraints used by  
CR-LDP to find a route through the network. CR-LDP uses Constrained  
Routing to find the route that is the best fit for the specified constraints. This  
attribute applies to dynamic LSPs only. Make sure you account for network  
bandwidth availability when configuring static LSPs.  
Figure 6-12 TE Parameters Configuration  
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LSP Browser  
After you create the LSPs in the network, you may want to edit or view the  
default settings. You do this in the LSP browser, which you can access from the  
Protocols > MPLS > Browse/Edit LSP Information... menu item. The browser  
enables you to  
• Set the hop type of LERs  
• Set the start and end times for the LSP  
• Set threshold values for bandwidth, delay, and hop counts in the LSP  
• Hide some or all of the LSPs from view in the Project Editor workspace  
• Export LSP configuration details to a file  
Figure 6-13 Using the LSP Browser  
These attributes set the  
LSP’s Path Details and  
This column indicates if the  
attribute values shown are  
Setup, TE, and Recovery  
from the GUI or the LSP  
Parameters attributes.  
specification file.  
Clicking OK saves the current settings in  
Clicking here toggles the display  
the LSP specification file or creates this  
settings—the workspace is immediately  
file if one does not yet exist.  
refreshed to show or hide the LSPs.  
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Available Statistics  
To analyze MPLS performance, you can collect path statistics on end-to-end  
delay, utilization, and the amount of traffic on the LSP. These statistics can be  
collected on a per-flow or per LSP basis, where flows are individual flows of  
traffic within an LSP.  
Figure 6-14 Selecting Statistics to Collect  
When analyzing your MPLS network, you may also want to look at the routes  
used for the LSPs. You can do this by selecting the Protocols > MPLS >  
Display LSP Routes... menu item.  
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Configuring MPLS in a Network  
Configuring MPLS in a network is a three-step process. Before you can run a  
simulation using MPLS, you must  
1) Create LSPs in the network topology  
2) Create FECs and traffic trunks in the MPLS Configuration object  
3) Configure LERs to direct packets into the appropriate LSPs  
After this basic configuration is in place, you can add QoS/differentiated  
services (DiffServ) constraints or traffic shaping parameters.  
Creating LSPs  
After you create your network topology, you can add LSPs to the network. There  
are three methods of adding LSPs to your network:  
• From traffic conversation pairs  
• By drawing the LSPs in the Project Editor workspace  
• From text files  
The Update LSP Details operation creates traffic profiles and forward  
equivalence classes (FECs) for the LSPs, which you can modify later as you  
fine-tune your model.  
The model supports both static and dynamic LSPs using the strict and loose  
path objects in OPNET. To create LSPs, use the standard procedure for  
creating paths as described in the Building Models chapter of the User Guide  
manual (Guru product documentation) or the Communication Mechanisms  
chapter of the Modeling Concepts manual (Modeler documentation).  
You can create dynamic LSPs automatically using the Create LSPs From Traffic  
Conversation Pairs utility or manually using the standard procedure for creating  
path objects.  
The Create LSPs From Traffic Conversation Pairs utility creates LSPs quickly  
based on some or all of the traffic conversation pairs in the network.  
Procedure 6-1 Creating Dynamic LSPs from Demands  
1 From the Protocols > MPLS menu, choose Configure LSPs from Demands.  
The Assign IP Addresses dialog box appears.  
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2 If you have not assigned IP addresses to all connected interfaces in the network,  
click the “Perform Auto-Assignment” button. Otherwise, click the “Skip  
Auto-Assignment” button.  
The MPLS Configuration dialog box opens.  
This box shows all the traffic pairs configured in the network with suggested  
configuration for LSP configuration.  
3 In the MPLS LSP Configuration dialog box, specify which traffic conversation pairs  
should not generate LSPs by changing their Create LSP? fields to “No”.  
4 Verify that the LSP configuration is correct for each LSP you would like to create.  
5 Click the Export To Network button to create the LSPs in the network.  
The LSPs appear in the network  
End of Procedure 6-1  
To create dynamic LSPs manually, you must specify the end points (ingress and  
egress LERs) of the LSP. You can also specify one or more intermediate routers  
or links along the path. When a specific link is selected for the LSP path, that  
hop is marked as strict and the LSP is always set up through that link. Use this  
method to indicate that certain routers or links must be used when routing  
packets in an LSP. If a node or link on a dynamic LSP’s route fails, the ingress  
LER automatically tries to find an alternate route. However, if the failed link or  
node is marked as strict, the entire LSP fails and the ingress LER diverts  
packets to the backup LSP, if one exists.  
Procedure 6-2 Creating Dynamic LSPs Manually  
1 Click on the MPLS_E-LSP_DYNAMIC object in the MPLS object palette.  
2 In the project workspace, click on the LSP’s ingress LER.  
3 If the LSP must use certain routers or links, click on the intermediate routers or links  
that must be used. Be sure to click on the objects in the same order that they occur  
in the LSP.  
4 Click on the LSP’s egress LER.  
5 Double-click in the project workspace to finish drawing the LSP.  
6 If you are finished creating dynamic LSPs, right-click in the project workspace and  
select Abort Path Definition to exit path definition mode. Otherwise, draw the next  
dynamic LSP.  
End of Procedure 6-2  
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Constrained OSPF (CSPF) is used to implement constraint-based routing of  
LSPs. You can configure dynamic LSPs to use constraint-based routing in the  
LSP’s TE Parameters attribute by setting the Bandwidth, Delay, and Hop Count  
constraints. When using TE constraints, the model must be configured to use  
(CSPF) as follows:  
• The CR-LDP simulation attribute must be set to CSPF  
• The IP routing protocol must be set to OSPF (You can set the dynamic  
routing protocol to OSPF using the IP Dynamic Routing Protocol simulation  
attribute.)  
With static LSPs, you can specify the exact route used by the LSP. Static LSPs  
allow more routing control, but offer less resiliency to node and link failures. For  
this reason, you should always specify at least one backup route when  
configuring static LSPs in your network.  
Procedure 6-3 Creating Static LSPs  
1 Click on the MPLS_E-LSP_STATIC object in the MPLS object palette.  
2 In the project workspace, click on the LSP’s ingress LER.  
3 Click on the next link or router in the LSPs route.  
The tooltips indicate which links and routers can be added to the route. Hold the  
cursor over a link or router for details about adding it to the LSP.  
4 Continue clicking on each link or router in the route until all have been added.  
5 Right-click in the project workspace and select Finish Path Definition to finish  
drawing the LSP.  
6 If you are finished creating static LSPs, right-click in the project workspace and  
select Abort Path Definition. Otherwise, draw the next static LSP.  
7 From the Protocols > MPLS menu, choose Update LSP Details to configure label  
switching information on the LSP(s).  
End of Procedure 6-3  
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Creating FECs and Traffic Trunks  
The traffic engineering bindings that govern how packets are labeled and  
forwarded in a network use FECs and traffic trunks to classify packets. All of the  
FECs and traffic trunks in a network are defined in the MPLS configuration  
object.  
Procedure 6-4 Creating FECs  
1 Place an MPLS configuration object in the project workspace and open its  
Attributes dialog box.  
2 Double-click on the value for FEC Specifications.  
The FEC Specifications Table appears.  
3 Change the Rows value to the number of FECs you want to create.  
4 For each FEC, assign a name, then double-click in the Details column to describe  
the FEC.  
End of Procedure 6-4  
To work correctly, the model requires that you set up at least one default traffic  
trunk. Additional trunks can be used to handle prioritized flows.  
Procedure 6-5 Creating a Default Traffic Trunk  
1 Place an MPLS configuration object in the project workspace and open its  
Attributes dialog box.  
2 Double-click on the value for Traffic Trunk Profiles.  
The Traffic Trunk Profiles Table appears.  
3 Change the Rows value to 1.  
4 Specify a name for the trunk, such as Default Traffic Trunk.  
5 Leave the Trunk Details attribute as “Default”.  
End of Procedure 6-5  
This procedure can be modified to set up separate trunks for traffic of different  
priorities. To do this, double-click on the Trunk Details attribute and specify the  
appropriate values for each traffic trunk.  
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Creating TE Bindings on LERs  
After you create the LSPs, FECs, and traffic trunks, you can create TE bindings  
that govern which packets are sent to which LSPs. You do this in the LER’s  
MPLS Parameters Traffic Mapping Configuration attribute.  
Procedure 6-6 Creating a TE Binding  
1 Open the LER’s Traffic Mapping Configuration attribute dialog box (MPLS  
Parameters Traffic Mapping Configuration).  
2 Add a row to the table.  
3 Click in the “Interface In” column and specify which interfaces the binding applies  
to in the Interface Binding Specification table. To select an interface, click in the  
Apply Binding column for that interface to toggle the value to “Yes.”  
The interface(s) you selected appear in the Traffic Mapping Configuration dialog  
box. Note that the interface number for higher layers corresponds to the router’s  
loopback interface.  
4 Select a FEC for the binding from the FEC pull-down menu.  
5 Select a traffic trunk for the binding from the Traffic Trunk pull-down menu.  
6 Click in the LSP column to specify the primary and backup LSPs.  
End of Procedure 6-6  
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Exporting LSP Configuration Details for Use in Other Scenarios  
You can reuse LSPs that you have configured elsewhere by exporting the LSP  
configuration details to an ASCII file and using this file to create LSPs in the  
network.  
Procedure 6-7 Exporting LSP Configuration to an ASCII File  
1 From the Protocols > MPLS menu, choose Browse/Edit LSP Information....  
The LSP Browser appears.  
2 Click Export to export the LSP configuration for all LSPs to a file.  
The Output File Name dialog box appears.  
3 Specify a name for the file.  
4 Click OK to perform the export.  
The file is saved in the primary models directory.  
5 Click Cancel to close the LSP Browser.  
End of Procedure 6-7  
The exported file contains the attribute settings of all LSPs in the network. You  
can use the file as is in other scenarios, or you can modify the file to add,  
remove, or change LSPs. Notice that the LSP configuration file closely  
resembles the Path Details table for each LSP.  
Procedure 6-8 Using an LSP Configuration File in a Scenario  
1 Open the MPLS Configuration object’s Attributes dialog box.  
2 Select the LSP configuration file you wish to import from the LSP Specification File  
pull-down menu.  
3 Click OK to close the Attributes dialog box.  
The LSPs are added to the scenario. By default, LSPs from files are not  
displayed in the network. To display these LSPs, open the LSP browser and set  
their Display attributes to Yes.  
End of Procedure 6-8  
If you are using an LSP configuration file in your network, any changes to LSPs  
that you make in the LSP browser are subsequently written to the configuration  
file when you click OK to close the browser.  
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Applying QoS to an MPLS Network Model  
Differential Services (DiffServ) extensions can be used to apply  
quality-of-service constraints to your MPLS network model. To do this, you must  
configure QoS do the following:  
• Specify traffic classes in the MPLS configuration object  
• Adjust DSCP settings in the QoS configuration object  
• Configure queuing schemes and profiles on the affected routers  
To use different traffic classes in your MPLS network, you must first specify  
separate traffic trunks for the different classes in the MPLS configuration object.  
To do this, use Procedure 6-5 on page SPM-6-16 to create a default traffic  
trunk. However, instead of setting the Trunk Details attribute to Default,  
double-click to set the traffic profile, out-of-profile actions, and traffic class of  
each trunk.  
To configure quality-of-service parameters, edit the Priority Queuing Profiles ➥  
DSCP Based attribute in the QoS configuration object.  
Finally, you must configure the affected routers to use the correct queueing  
scheme and queuing profile.  
Procedure 6-9 Configuring the Queuing Stream and Profile of a Router  
1 Set the Queuing Scheme attribute (IP Routing Parameters Interface  
Information QoS Information)  
2 Set the Queuing Profile attribute to DSCP Based.  
End of Procedure 6-9  
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If you change the queuing scheme later, make sure you reset the queuing profile  
because the order of these steps is important.  
Figure 6-15 Configuring QoS on an LER  
Always set the Queuing  
Scheme before setting  
the Queuing Profile.  
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MPLS Menu Operations  
The Protocols > MPLS menu enables you to configure, edit, and display MPLS  
features in the network topology. With the MPLS menu operations, you to  
streamline the MPLS configuration process. Table 6-3 lists the operations  
available from the Project Editor’s Protocols > MPLS menu.  
Table 6-3 MPLS Menu Summary  
Menu Item  
Description  
Update LSP Details  
Updates all static LSPs with label switching  
information.  
Configure LSPs from Demands  
Browse/Edit LSP Information...  
Import LSP Information...  
Display LSP Routes...  
Creates dynamic LSPs between all traffic flows.  
Opens the LSP browser.  
Imports LSP information from files.  
Displays the routes chosen by CR-LDP. Does not  
display link statistic information.  
Hide all LSP Routes...  
Show All LSPs  
Hides LSP route display.  
Displays hidden LSPs in the workspace. This  
operation does not display LSPs which are configured  
only in the LSP configuration file. To display those  
LSPs, use the display functions in the LSP browser.  
Hide All LSPs  
Clear All LSPs  
Hides LSPs displayed in the project workspace from  
view.  
Deletes all LSPs in the network and resets the traffic  
mapping configuration.  
Deploy MPLS VPNs  
Configure Interface Status  
Enables/disables MPLS protocol status on either  
selected or all routers.  
Model User Guide  
Opens this document.  
End of Table 6-3  
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Information for OPNET Modeler Users  
The rest of this document contains information for model developers (such as  
OPNET Modeler users). The following sections describe the topics necessary  
for understanding the internal details of and interfacing to the MPLS model.  
Model Architecture  
Each node that can use MPLS has an IP module, which contains a dispatcher  
process that spawns MPLS processes. The following table lists the process  
models used by the MPLS model.  
Table 6-4 MPLS Process Models  
Process model  
Description  
mpls_mgr  
One instance of this process is spawned by ip_dispatch on  
each MPLS enabled node in the network. It represents the  
forwarding component of MPLS and the forwarding control  
plane.  
When the IP module of an LSR receives labeled packets or  
packets with matching FEC descriptions, it performs no IP  
processing on the packet. Instead, the packet is re-directed to  
the mpls_mgr process for MPLS forwarding.  
mpls_mgr uses ILM (incoming label map) and FTN (FEC to  
NHLFE maps) to forward packets.  
mpls_ldp_mgr  
Implements the LDP control plane in the LDP module of all  
routers. This process is the dispatcher for the  
mpls_discovery_mgr, mpls_session_mgr, and mpls_lsp_mgr  
processes.  
mpls_discovery_mgr  
mpls_session_mgr  
Sends periodic broadcast hello messages over UDP to  
discover MPLS-enabled neighbor routers.  
Negotiates, opens, and maintains TCP sessions to neighboring  
LDP routers. The TCP sessions are used to exchange label  
maps. This process is based on RFC 3036.  
mpls_lsp_mgr  
Controls the exchange-to-label mappings between LDP peers.  
Communication with LDP peers occurs through the session  
established by the mpls_session_mgr process. This process is  
based on RFC 3036.  
End of Table 6-4  
SPM-6-22  
Modeler/Release 10.0  
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