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Common Configuration MistakesBy now, you should understand how to configure MPLS TE. Although a basic MPLS TE configuration is simple, there are lots of things to type, and it's easy to get one or two things wrong. This section presents problems that can arise from common configuration mistakes. Portions of the configuration are highlighted to call your attention to potential problem areas. MPLS TE configuration can be divided into two parts:
Common Configuration on All MPLS TE RoutersCommon configuration has three parts:
Global ConfigurationTwo commands are required on LSRs that are participating in MPLS TE: ip cef {distributed} mpls traffic-eng tunnels These commands, and the effects of not having them, are covered in the following two sections. ip cef {distributed} CommandThe ip cef command configures CEF forwarding on the LSR. Some platforms, such as the 7500 or 12000 series of routers, use distributed forwarding line cards, and as such, should be configured with ip cef distributed. If the LSR is a 12000 series router, CEF is the only forwarding mechanism. CEF is also the default forwarding method in Cisco IOS Software Release 12.0 and later, so ip cef {distributed} might not show up in your configuration. By and large, you should be running CEF on every device in your network. MPLS TE tunnels don't come up if you don't have CEF enabled on your router. Example 11-2 shows the MPLS Traffic Engineering state when CEF is turned on. Example 11-2 MPLS TE Tunnels State When CEF Is Enabled7200a#show mpls traffic-eng tunnels brief Signalling Summary: LSP Tunnels Process: running RSVP Process: running Forwarding: enabled Periodic reoptimization: every 3600 seconds, next in 3134 seconds Periodic FRR Promotion: every 300 seconds, next in 134 seconds Periodic auto-bw collection: disabled TUNNEL NAME DESTINATION UP IF DOWN IF STATE/PROT Primary tunnel 7200a->12008a... 12.12.12.12 - PO3/0 up/up Displayed 1 (of 1) heads, 0 (of 0) midpoints, 0 (of 0) tails As you can see from the highlighted text in Example 11-2, the primary tunnel is up/up, and forwarding is enabled. Example 11-3 shows what you see when CEF is disabled. Example 11-3 MPLS TE Tunnels State After CEF Is Disabled7200a#configure terminal Enter configuration commands, one per line. End with CNTL/Z. 7200a(config)#no ip cef 7200a(config)#end 00:27:50: %SYS-5-CONFIG_I: Configured from console by console 00:28:01: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel1, changed state to down 7200a#show mpls traffic-eng tunnels brief Signalling Summary: LSP Tunnels Process: running RSVP Process: running Forwarding: disabled Periodic reoptimization: every 3600 seconds, next in 2025 seconds Periodic FRR Promotion: every 300 seconds, next in 225 seconds Periodic auto-bw collection: disabled TUNNEL NAME DESTINATION UP IF DOWN IF STATE/PROT Primary tunnel 7200a->12008a... 12.12.12.12 - unknown up/down Displayed 1 (of 1) heads, 0 (of 0) midpoints, 0 (of 0) tails As you can see from Example 11-3, tunnel1 goes down immediately after CEF is disabled. The forwarding state is disabled, and the primary tunnel is up/down. You can use show ip cef summary to check if CEF is enabled on your router. Example 11-4 shows the output of show ip cef summary when CEF is turned on. Example 11-4 show ip cef summary When CEF Is Turned Onmpls-7200a#show ip cef summary IP CEF with switching (Table Version 631), flags=0x0, bits=8 51 routes, 0 reresolve, 0 unresolved (0 old, 0 new), peak 2 51 leaves, 52 nodes, 61808 bytes, 235 inserts, 184 invalidations 3 load sharing elements, 1032 bytes, 3 references universal per-destination load sharing algorithm, id B7E4AF56 2(1) CEF resets, 268 revisions of existing leaves 405 in-place/0 aborted modifications Resolution Timer: Exponential (currently 1s, peak 1s) refcounts: 13711 leaf, 13568 node Table epoch: 0 (51 entries at this epoch) Adjacency Table has 9 adjacencies Example 11-5 shows the output of show ip cef summary when CEF is turned off. Example 11-5 show ip cef summary When CEF Is Turned Offmpls-7200a#show ip cef summary IP CEF without switching (Table Version 563), flags=0x0, bits=8 0 routes, 0 reresolve, 0 unresolved (0 old, 0 new), peak 1 0 leaves, 0 nodes, 0 bytes, 175 inserts, 175 invalidations 0 load sharing elements, 0 bytes, 0 references universal per-destination load sharing algorithm, id B7E4AF56 2(1) CEF resets, 258 revisions of existing leaves 397 in-place/0 aborted modifications Resolution Timer: Exponential (currently 1s, peak 1s) refcounts: 0 leaf, 0 node Table epoch: 0 %CEF not running As you can see, when CEF is not running, this is indicated in a few places. mpls traffic-eng tunnels CommandConfiguring mpls traffic-eng tunnels at the global level starts various internal subsystems that comprise MPLS TE. They are collectively referred to as the LSP Tunnels Process. Example 11-6 shows what the LSP Tunnels Process state looks like when you have the mpls traffic-eng tunnels command on the router at the global level. Example 11-6 LSP Tunnels Process State When mpls traffic-eng tunnels Is Configured at the Global Level7200a#show mpls traffic-eng tunnels brief | include Process Signalling Summary: LSP Tunnels Process: running RSVP Process: running As you can see from the highlighted text in Example 11-6, the LSP Tunnels Process shows running. Example 11-7 shows what you see if mpls traffic-eng tunnels is not configured at the global level. Example 11-7 LSP Tunnels Process State When mpls traffic-eng tunnels Is Not Configured at the Global Level7200a#configure terminal Enter configuration commands, one per line. End with CNTL/Z. 7200a(config)#no mpls traffic-eng tunnels 7200a(config)#end 00:49:32: %SYS-5-CONFIG_I: Configured from console by console 00:49:51: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel1, changed state to down 7200a#show mpls traffic-eng tunnels brief | include Process LSP Tunnels Process: not running, disabled RSVP Process: running As you might expect, tunnel1 goes down, and the LSP tunnels process shows not running, disabled. Interface-Level ConfigurationThe following two interface-level commands are required for MPLS TE: mpls traffic-eng tunnels ip rsvp bandwidth {bandwidth}[{bandwidth}] [sub-pool bandwidth] NOTE Configuring ip rsvp bandwidth is not strictly necessary, because you can build an MPLS TE network entirely out of zero-bandwidth tunnels (those that don't have any bandwidth requirements) if you want to. However, reserving bandwidth is such a common use of MPLS TE that bandwidth configuration is essentially mandatory. If you know you don't need to advertise any reservable bandwidth, you can disregard the ip rsvp bandwidth command. For all nonzero-bandwidth tunnels, you need to configure the ip rsvp bandwidth statement on each MPLS TE interface. In addition, the configured bandwidth needs to be large enough to satisfy the bandwidth requested by the primary tunnel if you want the primary tunnel to choose this interface. The mpls traffic-eng tunnels command has to be configured on both sides of a link at the interface level. Failure to do so results in the link not being flooded in the IGP, which causes Path Computation's (PCALC's) bidirectionality check to fail, and the link in question will never be used for any TE tunnels in either direction. Omitting either of these two configurations at the interface level will make the link unavailable to headends when they do their CSPF computation. This could have two undesirable results:
The way 7200a has been configured (see Example 11-1), it falls into the second category, because it has a second path option—path option 6 configured under the tunnel1 interface. If you remove the mpls traffic-eng tunnels command on interface POS1/1 of 12008c, as shown in Figure 11-2, 7200a reroutes the primary tunnel. Figure 11-2. Removing mpls traffic-eng tunnels from Interface POS1/1 on 12008c
This is demonstrated in the following four steps. First, debug mpls traffic-eng tunnels events detail is enabled on the headend, as shown in Example 11-8. You can see what happens in Example 11-10. Example 11-8 Turning on debug mpls traffic-eng tunnels events detail on 7200a
7200a#debug mpls traffic-eng tunnels events detail
MPLS traffic-eng tunnels system events debugging is on (detailed)
Next, mpls traffic-eng tunnels is removed from interface POS1/1 on 12008c, as shown in Example 11-9. Example 11-9 Removing mpls traffic-eng tunnels on Interface POS1/1 on 12008c12008c#configure terminal 12008c(config)#interface pos 1/1 12008c(config-if)#no mpls traffic-eng tunnels 7200a realizes that the link is no longer in the TE database, and then 7200a falls back to the next configured path option, rerouting the LSP, as shown in Example 11-10. Example 11-10 Output of debug mpls traffic-eng tunnel events detail Shows the Tunnel Being Rerouted*Apr 3 21:52:46.382: LSP-TUNNEL: received event: TPDB--link down [10.0.5.11 -> 10.0.5.5] *Apr 3 21:52:46.382: LSP-TUNNEL: posting action(s) to all-tunnels: *Apr 3 21:52:46.382: verify all LSPs *Apr 3 21:52:46.382: LSP-TUNNEL: scheduling pending actions on all-tunnels *Apr 3 21:52:46.386: LSP-TUNNEL: receiving LSA change events for node 11.11.11. 11 (0.0.0.0, ospf 100 area 0) *Apr 3 21:52:46.386: LSP-TUNNEL: received event: TPDB--link bw chg [10.0.17.11 -> 10.0.17.12] *Apr 3 21:52:46.386: LSP-TUNNEL: posting action(s) to all-tunnels: *Apr 3 21:52:46.386: LSP path lookup *Apr 3 21:52:46.386: LSP-TUNNEL: processing actions list... *Apr 3 21:52:46.386: LSP-TUNNEL: applying actions to all-tunnels, as follows: *Apr 3 21:52:46.386: verify all LSPs, LSP path lookup *Apr 3 21:52:46.386: LSP-TUNNEL: done COMPLETE processing of actions list As you can see from the highlighted output of Example 11-11, the primary tunnel now uses path option 6 (dynamic), and the ERO has changed from what you saw in Example 11-1. Example 11-11 Primary Tunnel Is Now Dynamic Path Option 6 After the Reroute7200a#show mpls traffic tunnels tunnel1 Name: Primary tunnel 7200a->12008a->12... (Tunnel1) Destination: 12.12.12.12 Status: Admin: up Oper: up Path: valid Signalling: connected path option 6, type dynamic (Basis for Setup, path weight 4) path option 5, type explicit primary Config Parameters: Bandwidth: 100 kbps (Global) Priority: 7 7 Affinity: 0x0/0xFFFF Metric Type: TE (default) AutoRoute: enabled LockDown: disabled Loadshare: 100 bw-based auto-bw: disabled InLabel : - OutLabel : POS3/0, 12325 RSVP Signalling Info: Src 4.4.4.4, Dst 12.12.12.12, Tun_Id 1, Tun_Instance 53 RSVP Path Info: My Address: 4.4.4.4 Explicit Route: 10.0.3.5 10.0.13.16 10.0.7.11 10.0.17.12 12.12.12.12 Record Route: NONE Routing Protocol ConfigurationFor all LSRs participating in MPLS TE, you also need to configure your IGP:
Table 11-1 shows the potential problems that arise from misconfiguring these commands.
Headend ConfigurationAs you know by now, a TE tunnel is configured at the headend LSR only. Example 11-12 shows the configuration for Tunnel1 in the sample network. The most important TE commands are highlighted. Example 11-12 Headend Tunnel Configuration on 7200a7200a#show running-config interface tunnel 1 Building configuration... Current configuration : 425 bytes ! interface Tunnel1 description Primary tunnel 7200a->12008a->12008c->7200c ip unnumbered Loopback0 no ip directed-broadcast tunnel destination 12.12.12.12 tunnel mode mpls traffic-eng tunnel mpls traffic-eng autoroute announce tunnel mpls traffic-eng priority 7 7 tunnel mpls traffic-eng bandwidth 100 tunnel mpls traffic-eng path-option 5 explicit name primary tunnel mpls traffic-eng path-option 6 dynamic end 7200a#show ip explicit-paths name primary PATH primary (strict source route, path complete, generation 6) 1: next-address 10.0.3.5 2: next-address 10.0.5.11 3: next-address 10.0.17.12 4: next-address 12.12.12.12 Table 11-2 lists the effects of misconfiguring the highlighted commands in Example 11-12.
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