MPLS-TE explicit vs. dynamic

Using the same topology and configuration from the previous MPLS-TEbasic configuration lab

As you may recall I have configured the path R3->R6->R7 with RSVP bandwidth of 50Kbps while the path R3->R4->R5->R7 has been configured with 100Kbps, and because the MPLS-TE tunnel has a constrain which required a 100Kbps path this path wasn’t valid and both tunnels were going through R3->R4->R5->R7 path.

So now I configured path R3->R6->R7 with 100Kbps, what will happen to the tunnels?

R3#sh mpls traffic-eng tunnels         Name: R3_t37                              (Tunnel37) Destination: 7.7.7.7   Status:     Admin: up         Oper: up     Path: valid       Signalling: connected     path option 1, type dynamic (Basis for Setup, path weight 3)   Config Parameters:     Bandwidth: 100      kbps (Global)  Priority: 0  0   Affinity: 0x0/0xFFFF     Metric Type: TE (default)     AutoRoute:  enabled   LockDown: disabled  Loadshare: 100      bw-based     auto-bw: disabled   Active Path Option Parameters:     State: dynamic path option 1 is active     BandwidthOverride: disabled  LockDown: disabled  Verbatim: disabled   InLabel  :  -   OutLabel : FastEthernet2/0, 24   RSVP Signalling Info:        Src 3.3.3.3, Dst 7.7.7.7, Tun_Id 37, Tun_Instance 1     RSVP Path Info:       My Address: 10.1.34.3         Explicit Route: 10.1.34.4 10.1.45.4 10.1.45.5 10.1.57.5                       10.1.57.7 7.7.7.7       Record   Route:   NONE       Tspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits     RSVP Resv Info:       Record   Route:   NONE       Fspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits   History:     Tunnel:       Time since created: 1 hours, 41 minutes       Time since path change: 1 hours, 41 minutes       Number of LSP IDs (Tun_Instances) used: 1     Current LSP:       Uptime: 1 hours, 41 minutes LSP Tunnel R7_t37 is signalled, connection is up   InLabel  : FastEthernet2/0, implicit-null   OutLabel :  -   RSVP Signalling Info:        Src 7.7.7.7, Dst 3.3.3.3, Tun_Id 37, Tun_Instance 1     RSVP Path Info:       My Address: 3.3.3.3         Explicit Route:  NONE       Record   Route:   NONE       Tspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits     RSVP Resv Info:       Record   Route:   NONE       Fspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits R3#sh mpls traffic-eng tunnels summary Signalling Summary:     LSP Tunnels Process:            running     Passive LSP Listener:           running     RSVP Process:                   running     Forwarding:                     enabled     Head: 1 interfaces, 1 active signalling attempts, 1 established           1 activations, 0 deactivations           0 SSO recovery attempts, 0 SSO recovered     Midpoints: 0, Tails: 1     Periodic reoptimization:        every 3600 seconds, next in 64 seconds     Periodic FRR Promotion:         Not Running     Periodic auto-bw collection:    every 300 seconds, next in 64 seconds

You can see that tunnel re-optimization occurs once in every 1 hour so only after that period of time the tunnel will recalculate the LSP and choose best new one:

R3#sh mpls traffic-eng tunnels         Name: R3_t37                              (Tunnel37) Destination: 7.7.7.7   Status:     Admin: up         Oper: up     Path: valid       Signalling: connected     path option 1, type dynamic (Basis for Setup, path weight 2)   Config Parameters:     Bandwidth: 100      kbps (Global)  Priority: 0  0   Affinity: 0x0/0xFFFF     Metric Type: TE (default)     AutoRoute:  enabled   LockDown: disabled  Loadshare: 100      bw-based     auto-bw: disabled   Active Path Option Parameters:     State: dynamic path option 1 is active     BandwidthOverride: disabled  LockDown: disabled  Verbatim: disabled   InLabel  :  -   OutLabel : FastEthernet2/1, 20   RSVP Signalling Info:        Src 3.3.3.3, Dst 7.7.7.7, Tun_Id 37, Tun_Instance 3     RSVP Path Info:       My Address: 10.1.36.3          Explicit Route: 10.1.36.6 10.1.67.6 10.1.67.7 7.7.7.7       Record   Route:   NONE       Tspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits     RSVP Resv Info:       Record   Route:   NONE       Fspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits   History:     Tunnel:       Time since created: 1 hours, 51 minutes       Time since path change: 8 minutes, 7 seconds       Number of LSP IDs (Tun_Instances) used: 3     Current LSP:       Uptime: 8 minutes, 10 seconds       Selection: reoptimization     Prior LSP:       ID: path option 1 [1]       Removal Trigger: reoptimization completed LSP Tunnel R7_t37 is signalled, connection is up   InLabel  : FastEthernet2/1, implicit-null   OutLabel :  -   RSVP Signalling Info:        Src 7.7.7.7, Dst 3.3.3.3, Tun_Id 37, Tun_Instance 3     RSVP Path Info:       My Address: 3.3.3.3         Explicit Route:  NONE       Record   Route:   NONE       Tspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits     RSVP Resv Info:       Record   Route:   NONE       Fspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits

We can set the re-optimization period by issue the following command:

R3(config)#mpls traffic-eng reoptimize timers frequency 60

Or initiate a re-optimization manually by issuing the command in privilege mode:

R3#mpls traffic-eng reoptimize tunnel 37

Now both tunnels, tunnel 37 and tunnel 73 are going in the same LSP through R3->R6->R7, but what if I want to do load balance between both (physical) paths?

Let’s configure an explicit path for tunnel 37 on R3:

ip explicit-path name TUN37-PATH   next-address 10.1.34.4   next-address 10.1.45.5   next-address 10.1.57.7 ! interface tunnel 37   tunnel mpls traffic-eng path-option 1 explicit name TUN37-PATH

By this I have instructed explicitly, to tunnel 37, the path it should go to the tailend – R7.

Now let’s look and tunnel 37 path:

R3#show mpls traffic-eng tunnels tunnel 37 Name: R3_t37                              (Tunnel37) Destination: 7.7.7.7   Status:     Admin: up         Oper: up     Path: valid       Signalling: connected     path option 1, type explicit TUN37-PATH (Basis for Setup, path weight 3)   Config Parameters:     Bandwidth: 100      kbps (Global)  Priority: 0  0   Affinity: 0x0/0xFFFF     Metric Type: TE (default)     AutoRoute:  enabled   LockDown: disabled  Loadshare: 100      bw-based     auto-bw: disabled   Active Path Option Parameters:     State: explicit path option 1 is active     BandwidthOverride: disabled  LockDown: disabled  Verbatim: disabled   InLabel  :  -   OutLabel : FastEthernet2/0, 23   RSVP Signalling Info:        Src 3.3.3.3, Dst 7.7.7.7, Tun_Id 37, Tun_Instance 114     RSVP Path Info:       My Address: 10.1.34.3         Explicit Route: 10.1.34.4 10.1.45.4 10.1.45.5 10.1.57.5                       10.1.57.7 7.7.7.7       Record   Route:   NONE       Tspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits     RSVP Resv Info:       Record   Route:   NONE       Fspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits   Shortest Unconstrained Path Info:     Path Weight: 2 (TE)     Explicit Route: 10.1.36.3 10.1.36.6 10.1.67.6 10.1.67.7                     7.7.7.7   History:     Tunnel:       Time since created: 3 hours, 50 minutes       Time since path change: 6 minutes, 40 seconds       Number of LSP IDs (Tun_Instances) used: 114     Current LSP:       Uptime: 6 minutes, 40 seconds     Prior LSP:       ID: path option 1 [3]       Removal Trigger: configuration changed

And verify the tunnel path and reachability:

R3#ping mpls traffic-eng tunnel 37                      Sending 5, 100-byte MPLS Echos to Tunnel37,      timeout is 2 seconds, send interval is 0 msec: Codes: '!' - success, 'Q' - request not sent, '.' - timeout,   'L' - labeled output interface, 'B' - unlabeled output interface,   'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch,   'M' - malformed request, 'm' - unsupported tlvs, 'N' - no label entry,   'P' - no rx intf label prot, 'p' - premature termination of LSP,   'R' - transit router, 'I' - unknown upstream index,   'X' - unknown return code, 'x' - return code 0 Type escape sequence to abort. !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 72/87/112 ms R3#traceroute mpls traffic-eng tunnel 37 Tracing MPLS TE Label Switched Path on Tunnel37, timeout is 2 seconds Codes: '!' - success, 'Q' - request not sent, '.' - timeout,   'L' - labeled output interface, 'B' - unlabeled output interface,   'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch,   'M' - malformed request, 'm' - unsupported tlvs, 'N' - no label entry,   'P' - no rx intf label prot, 'p' - premature termination of LSP,   'R' - transit router, 'I' - unknown upstream index,   'X' - unknown return code, 'x' - return code 0 Type escape sequence to abort.   0 10.1.34.3 MRU 1500 [Labels: 23 Exp: 0] L 1 10.1.34.4 MRU 1500 [Labels: 23 Exp: 0] 88 ms L 2 10.1.45.5 MRU 1504 [Labels: implicit-null Exp: 0] 60 ms ! 3 10.1.57.7 84 ms

Now we have two tunnels, 37 and 73, where 37 goes through R3->R4->R5->R7 using explicit path while 73 goes through R3->R6->R7 using dynamic path. Looking on the routing table of R3 toward R7:

R3#sh ip route 7.7.7.7 Routing entry for 7.7.7.7/32   Known via "ospf 1", distance 110, metric 3, type intra area   Last update from 7.7.7.7 on Tunnel37, 04:00:35 ago   Routing Descriptor Blocks:   * 7.7.7.7, from 7.7.7.7, 04:00:35 ago, via Tunnel37       Route metric is 3, traffic share count is 1     7.7.7.7, from 7.7.7.7, 04:00:35 ago, via Tunnel73       Route metric is 3, traffic share count is 1

We can see that tunnel 37 is the best route and that’s because of the tunnel priority:

R3#sh running-config interface tunnel 37 Building configuration... Current configuration : 323 bytes ! interface Tunnel37  ip unnumbered Loopback0  mpls ip  tunnel destination 7.7.7.7  tunnel mode mpls traffic-eng  tunnel mpls traffic-eng autoroute announce  tunnel mpls traffic-eng priority 0 0  tunnel mpls traffic-eng bandwidth 100  tunnel mpls traffic-eng path-option 1 explicit name TUN37-PATH  no routing dynamic end R3#sh running-config interface tunnel 73 Building configuration... Current configuration : 332 bytes ! interface Tunnel73  ip unnumbered Loopback0  mpls traffic-eng tunnels  mpls ip  tunnel destination 7.7.7.7  tunnel mode mpls traffic-eng  tunnel mpls traffic-eng autoroute announce  tunnel mpls traffic-eng priority 1 1  tunnel mpls traffic-eng bandwidth 100  tunnel mpls traffic-eng path-option 1 dynamic  no routing dynamic end

We can change the priority between the tunnels to choose the preferred tunnel to use, remember lower is better.

R3(config)#interface tunnel 37 R3(config-if)#tunnel mpls traffic-eng priority 2 2

And the result:

R3#sh ip route 7.7.7.7 Routing entry for 7.7.7.7/32   Known via "ospf 1", distance 110, metric 3, type intra area   Last update from 7.7.7.7 on Tunnel73, 00:01:13 ago   Routing Descriptor Blocks:   * 7.7.7.7, from 7.7.7.7, 00:01:13 ago, via Tunnel73       Route metric is 3, traffic share count is 1     7.7.7.7, from 7.7.7.7, 00:01:13 ago, via Tunnel37       Route metric is 3, traffic share count is 1

Don’t forget that the tunnels are unidirectional so we need to change the same on R7 else we will have asymmetric route.