Basic MPLS Configuration
“DATA NETWORK” FOR JTOs PH-II : MPLS_Configuration
Basic MPLS Configuration In the first chapter, you were introduced to the MPLS forwarding model in which labels are used to forward packets for a certain destination network. You were also provided details on frame- and cell-mode MPLS operation. In this chapter, the following topics are covered: •
Frame-mode MPLS configuration and verification - Basic frame-mode MPLS configuration and verification - Frame-mode MPLS over RFC 2684 (obsoletes RFC 1483) routed PVC
•
Cell-mode MPLS over ATM configuration and verification - Basic cell-mode MPLS configuration and verification - Configuring cell-mode MPLS with and without virtual circuit merge (VCmerge) - MPLS over VP tunnels configuration and verification - Configuring MPLS over ATM using BPX ATM switch and 7200 as label switch controller (LSC)
Frame-Mode MPLS Configuration and Verification In frame mode, MPLS uses a 32-bit label that is inserted between the Layer 2 and Layer 3 headers. Layer 2 encapsulations like HDLC, PPP, Frame Relay, and Ethernet are frame-based except for ATM, which can operate either in frame mode or cell mode. Basic Frame-Mode MPLS Overview, Configuration, and Verification Figure 2-1 shows a frame-based MPLS provider network providing MPLS services to sites belonging to Customer A. The frame-based provider's network consists of routers R1, R2, R3, and R4. R1 and R4 function as Edge Label Switch Routers (LSRs) while R2 and R3 serve as LSRs.
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“DATA NETWORK” FOR JTOs PH-II : MPLS_Configuration
Figure 2-1. Frame-Mode MPLS Provider Network [View full size image]
Figure 2-2 illustrates the configuration flowchart to implement frame-mode MPLS on the provider network shown in Figure 2-1. The configuration flowchart assumes that IP addresses are preconfigured where required. Figure 2-2. Frame-Mode MPLS Configuration Flowchart [View full size image]
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“DATA NETWORK” FOR JTOs PH-II : MPLS_Configuration
Basic Frame-Mode MPLS Configuration Steps The steps to configure frame-mode MPLS are based on the configuration flowchart outlined in Figure 2-2. Ensure that IP addresses are configured prior to following these steps: Step 1.
Enable CEF—CEF is an essential component for label switching and is responsible for imposition and disposition of labels in an MPLS network. Configure CEF globally on routers R1, R2, R3, and R4 by issuing the ip cef [distributed] command. Ensure that CEF is not disabled on the interface. If disabled, enable CEF on the interface by issuing ip route-cache cef in interface mode. Use the distributed keyword in the global configuration mode for Cisco platform capable of distributed CEF switching. Example 21 highlights the configuration to enable CEF on R2. Similarly enable CEF on R1, R3, and R4. Example 2-1. Enable CEF R2(config)#ip cef distributed R2(config)#do show running-config interface s0/0 | include cef no ip route-cache cef R2(config)#interface s0/0 R2(config-if)#ip route-cache cef
Step 2.
Configure IGP routing protocol—Configure the IGP routing protocol; in this case, OSPF. Enable the interfaces on R1, R2, R3, and R4 that are part of the provider network in OSPF using network ip-address wild-card-mask area area-id command under the OSPF routing process. Example 2-2 highlights the OSPF configuration on R2. Similarly configure OSPF on R1, R3, and R4. Example 2-2. Configure IGP Routing Protocol on R2 R2(config)#router ospf 100 R2(config)#network 10.10.10.0 0.0.0.255 area 0 Enabling the label distribution protocol is an optional step. TDP is deprecated, and by default, LDP is the label distribution protocol. The command mpls label protocol {ldp | tdp} is configured only if LDP is not the default label distribution protocol or if you are reverting from LDP to TDP protocol or vice versa. The command can be configured in the global as well as in the interface configuration mode. The interface configuration
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“DATA NETWORK” FOR JTOs PH-II : MPLS_Configuration command will, however, override the global configuration. Step 3.
Assign LDP router ID—LDP uses the highest IP address on a loopback interface as the LDP router ID. If there is no loopback address defined, the highest IP address on the router becomes the LDP router ID. To force an interface to be an LDP router ID, mpls ldp router-id interface-type number command can be used. The loopback interface address is recommended because it always remains up. Configure the loopback 0 interface on the R2 router to be the LDP router ID as shown in Example 23. Repeat the configuration on R1, R3, and R4, assigning the local loopback interface as LDP router-id. Example 2-3. Assign LDP Router ID R2(config)#mpls ldp router-id loopback 0
Step 4.
Enable IPv4 MPLS or label forwarding on the interface—Example 2-4 demonstrates the step to enable MPLS forwarding on the interface. Example 2-4. Enable MPLS Forwarding R2(config)#interface serial 0/0 R2(config-if)#mpls ip R2(config)#interface serial 0/1 R2(config-if)#mpls ip
Verification of Basic Frame-Mode MPLS Operation The steps to verify the frame-mode MPLS operation are as follows. All verification steps were performed on Router R2. Outputs of the commands have been truncated for brevity, and only pertinent lines are depicted:
Step 1. Example 2-5 verifies whether CEF is globally enabled or disabled on the router by issuing the sh cef command. As shown in Example 2-5, CEF is disabled on R2. Example 2-5 shows if CEF is e on the router interfaces. Example 2-5. CEF Verification R2#show ip cef %CEF not running Prefix
Next Hop
Interface
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“DATA NETWORK” FOR JTOs PH-II : MPLS_Configuration R2#show cef interface serial 0/0 Serial0/0 is up (if_number 5) (Output truncated) IP CEF switching enabled IP CEF Fast switching turbo vector (Output Truncated)
_________________________________________________________________ R2#show cef interface serial 0/1 Serial0/1 is up (if_number 6) (Output Truncated) IP CEF switching enabled IP CEF Fast switching turbo vector
Step 2. Verify MPLS forwarding is enabled on the interfaces by issuing the show mpls interfaces com Example 2-6 shows that MPLS is enabled on the serial interfaces. The IP column depicts Yes if I switching is enabled on the interface. The Tunnel column is Yes if LSP tunnel labeling (discusse in Chapter 9, "MPLS Traffic Engineering") is enabled on the interface, and the Operational col Yes if packets are labeled on the interface. Example 2-6. MPLS Forwarding Verification R2#show mpls interfaces Interface
IP
Tunnel
Operational
Serial0/0
Yes (ldp)
No
Yes
Serial0/1
Yes (ldp)
No
Yes
Step 3. Verify the status of the Label Distribution Protocol (LDP) discovery process by issuing show mp discovery. This command displays neighbor discovery information for LDP and shows the inte over which the LDP discovery process is running. Example 2-7 shows that R2 has discovered tw neighbors, 10.10.10.101 (R1) and 10.10.10.103 (R3). The xmit/recv field indicates that the inter transmitting and receiving LDP discovery Hello packets. Example 2-7. LDP Discovery Verification R2#show mpls ldp discovery
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“DATA NETWORK” FOR JTOs PH-II : MPLS_Configuration Local LDP Identifier: 10.10.10.102:0 Discovery Sources: Interfaces: Serial0/0 (ldp): xmit/recv LDP Id: 10.10.10.101:0 Serial0/1 (ldp): xmit/recv LDP Id: 10.10.10.103:0
Step 4. Issue show mpls ldp neighbor to verify the status of the LDP neighbor sessions. Example 2-8 that the LDP session between R2 and R1 (10.10.10.101), as well as between R2 and R3 (10.10.10 is operational. Downstream indicates that the downstream method of label distribution is being us this LDP session in which the LSR advertises all of its locally assigned (incoming) labels to it peer (subject to any configured access list restrictions). Example 2-8. LDP Neighbor Verification R2#show mpls ldp neighbor
Peer LDP Ident: 10.10.10.101:0; Local LDP Ident 10.10.10.102: TCP connection: 10.10.10.101.646 - 10.10.10.102.11012 State: Oper; PIEs sent/rcvd: 26611/26601; Downstream Up time: 2w2d LDP discovery sources: Serial0/0, Src IP addr: 10.10.10.1 Addresses bound to peer LDP Ident: 10.10.10.101 10.10.10.1
Peer LDP Ident: 10.10.10.103:0; Local LDP Ident 10.10.10.102: TCP connection: 10.10.10.103.11002 - 10.10.10.102.646 State: Oper; Msgs sent/rcvd: 2374/2374; Downstream Up time: 1d10h
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“DATA NETWORK” FOR JTOs PH-II : MPLS_Configuration LDP discovery sources: Serial0/1, Src IP addr: 10.10.10.6 Addresses bound to peer LDP Ident: 10.10.10.6
10.10.10.103
10.10.10.9
Control and Data Plane Forwarding in Basic Frame-Mode MPLS Figure 2-3 shows the control and data plane forwarding operation in frame-mode MPLS. Figure 2-3. Frame-Mode MPLS Control and Data Plane Operation [View full size image]
Control Plane Operation in Basic Frame-Mode MPLS Figure 2-3 shows the control plane operation for prefix 10.10.10.101/32 from R1 to R4. The following steps are performed in the label propagation process for prefix 10.10.10.101/32: Step 1.
Example 2-9 shows that R1 sends an implicit null or the POP label to R2. A value of 3 represents the implicit-null label. R1 propagates the implicit-null label to its penultimate Router R2, which performs the POP function in the data forwarding from R4 to 10.10.10.101/32. If R1 propagates an explicitnull label, the upstream LSR R2 does not POP the label but assigns a label value of 0 and sends a labeled packet to R2. Example 2-9. MPLS Label Bindings on R1 R1#show mpls ldp bindings
