Case Study 9-5: Protecting AToM Pseudowires with MPLS Traffic Engineering Fast Reroute MPLS traffic engineering automatically establishes and maintains LSPs across the MPLS core network using RSVP. Such LSPs are created based on the resource constraints that are configured and available network resources, such as bandwidth. IGP routing protocols such as IS-IS or OSPF announce available network resources using traffic engineering protocol extensions along with link state advertisements throughout the network.In any network, links, routers, or both can fail because of unexpected events. Network operators include this factor their network planning by having redundant links and routers at the physical or logical locations where the failures are most likely to happen. When such failure conditions occur, routers within the network might temporarily have inconsistent routing information. They might need to exchange routing updates and come up with a new, consistent view of the network. This process is known as network convergence. During network convergence, routing loops and black holes can cause packet loss. The longer the convergence takes, the larger the amount of packet loss.The convergence time includes the amount of time for an adjacent router to detect the link (or router) failure. It also includes the amount of time for this router to distribute the information to all other routers and for all other routers to recalculate routes in the forwarding tables. Detecting a link failure requires physical and link layerspecific mechanisms. MPLS traffic engineering does not have a way to reduce the amount of time to detect failures. However, it can reduce the time required to distribute the failure information and update the forwarding tables by using MPLS traffic engineering fast rerouting capability.Prior to a failure, fast reroute calculates and establishes a protection traffic engineering tunnel around the link or node that is deemed vulnerable. Upon detecting such a failure, the backup tunnel takes over packet forwarding immediately. Rerouting typically takes less than 50 ms upon failure detection, and packet loss is kept minimal.Before you enable fast reroute for an AToM pseudowire, you need to configure an MPLS traffic engineering tunnel as the preferred path, as shown in the previous case study. Then at the ingress PE where the traffic engineering tunnel headend is, you can use fast reroute options to configure a backup traffic engineering tunnel to protect the primary traffic engineering tunnel.In Case Study 9-4: Configuring a Preferred Path Using MPLS Traffic Engineering Tunnels."
Figure 9-4. Protect AToM Pseudowire with Fast Reroute Case Study 9-4. The following steps describe how to enable fast reroute on the primary traffic engineering tunnel.
Step 1. | Add an explicit path on PE1 that originates from the PE, traverses through P2, and ends at P1. PE1(config)#ip explicit-path name P2-P1 enable PE1(cfg-ip-expl-path)#next-address 10.23.12.2 Explicit Path name P2-P1: 1: next-address 10.23.12.2 PE1(cfg-ip-expl-path)#next-address 10.33.23.1 Explicit Path name P2-P1: 1: next-address 10.23.12.2 2: next-address 10.33.23.1
| Step 2. | Provision a backup traffic engineering tunnel with the explicit path configured in Step 1. Note that the tailend of this backup tunnel is P1, and its IP address is 10.1.2.1. PE1(config)#interface Tunnel100 PE1(config-if)#ip unnumbered Loopback0 PE1(config-if)#tunnel destination 10.1.2.1 PE1(config-if)#tunnel mode mpls traffic-eng PE1(config-if)#tunnel mpls traffic-eng priority 7 7 PE1(config-if)#tunnel mpls traffic-eng bandwidth 1000 PE1(config-if)#tunnel mpls traffic-eng path-option 1 explicit name P2-P1
| Step 3. | Configure the primary traffic engineering tunnel with fast reroute protection. The initial tunnel interface configuration is as follows: PE1#show running-config interface Tunnel1 Building configuration... Current configuration : 274 bytes ! interface Tunnel1 ip unnumbered Loopback0 no ip directed-broadcast tunnel destination 10.1.1.2 tunnel mode mpls traffic-eng tunnel mpls traffic-eng priority 7 7 tunnel mpls traffic-eng bandwidth 1000 tunnel mpls traffic-eng path-option 1 explicit name P1-PE2 end PE1#config t Enter configuration commands, one per line. End with CNTL/Z. PE1(config)#interface Tunnel1 PE1(config-if)#tunnel mpls traffic-eng fast-reroute
| Step 4. | Configure the protected link to use the backup tunnel. The interface that connects to the protected link on PE1 is Serial3/0. PE1(config)#interface Serial3/0 PE1(config-if)#mpls traffic-eng backup-path Tunnel100
| Step 5. | Verify that the primary tunnel is protected by fast reroute and the backup tunnel is ready under normal conditions. Use the show mpls traffic-eng tunnels protection and show mpls interfaces commands. PE1#show mpls traffic-eng tunnels protection PE1_t1 LSP Head, Tunnel1, Admin: up, Oper: up Src 10.1.1.1, Dest 10.1.1.2, Instance 31 Fast Reroute Protection: Requested Outbound: FRR Ready Backup Tu100 to LSP nhop Tu100: out i/f: Et1/0, label: 16 LSP signalling info: Original: out i/f: Se3/0, label: 16, nhop: 10.23.11.2 With FRR: out i/f: Tu100, label: 16 LSP bw: 1000 kbps, Backup level: any-unlim, type: any pool PE1_t2 LSP Head, Tunnel2, Admin: up, Oper: up Src 10.1.1.1, Dest 10.1.1.2, Instance 18 Fast Reroute Protection: None PE1_t100 LSP Head, Tunnel100, Admin: up, Oper: up Src 10.1.1.1, Dest 10.1.2.1, Instance 18 Fast Reroute Protection: None PE1#show mpls interfaces Tunnel1 detail Interface Tunnel1: MPLS TE Tunnel Head IP labeling not enabled LSP Tunnel labeling not enabled BGP labeling not enabled MPLS not operational Fast Switching Vectors: IP to MPLS Fast Switching Vector MPLS Disabled MTU = 1496 Tun hd Untagged 0 Tu1 point2point MAC/Encaps=4/8, MRU=1500, Tag Stack{16}, via Se3/0 0F008847 00010000 No output feature configured Fast Reroute Protection via {Tu100, outgoing label 16}
Notice that the fast reroute status for the primary tunnel is ready. This means that the backup tunnel is operational and ready to protect the primary tunnel. | Step 6. | Verify the status of AToM pseudowire with VC ID 200, which traverses the primary tunnel under normal conditions. Label 16 is the traffic engineering tunnel label. PE1#show mpls l2transport vc 200 detail Local interface: Et0/0.2 up, line protocol up, Eth VLAN 200 up Destination address: 10.1.1.2, VC ID: 200, VC status: up Preferred path: Tunnel1, active Default path: disabled Tunnel label: 3, next hop point2point Output interface: Tu1, imposed label stack {16 24} Create time: 01:14:59, last status change time: 01:11:17 Signaling protocol: LDP, peer 10.1.1.2:0 up MPLS VC labels: local 17, remote 24 Group ID: local 0, remote 0 MTU: local 1500, remote 1500 Remote interface description: Sequencing: receive disabled, send disabled VC statistics: packet totals: receive 101, send 101 byte totals: receive 31270, send 29960 packet drops: receive 0, send 5
| Step 7. | To verify the effectiveness of the fast reroute capability, introduce a link failure and use the show mpls traffic-eng tunnels protection and show mpls l2transport vc commands to examine the fast reroute status and pseudowire information. PE1#show mpls traffic-eng tunnels protection PE1_t1 LSP Head, Tunnel1, Admin: up, Oper: up Src 10.1.1.1, Dest 10.1.1.2, Instance 124 Fast Reroute Protection: Requested Outbound: FRR Active Backup Tu100 to LSP nhop Tu100: out i/f: Et1/0, label: 16 LSP signalling info: Original: out i/f: Se3/0, label: 16, nhop: 10.1.2.1 With FRR: out i/f: Tu100, label: 16 LSP bw: 1000 kbps, Backup level: any-unlim, type: any pool PE1_t2 LSP Head, Tunnel2, Admin: up, Oper: up Src 10.1.1.1, Dest 10.1.1.2, Instance 18 Fast Reroute Protection: None PE1_t100 LSP Head, Tunnel100, Admin: up, Oper: up Src 10.1.1.1, Dest 10.1.2.1, Instance 19 Fast Reroute Protection: None PE1#show mpls l2transport vc 200 detail Local interface: Et0/0.2 up, line protocol up, Eth VLAN 200 up Destination address: 10.1.1.2, VC ID: 200, VC status: up Preferred path: Tunnel1, active Default path: disabled Tunnel label: 16, next hop point2point Output interface: Tu100, imposed label stack {16 16 24} Create time: 01:17:49, last status change time: 01:14:07 Signaling protocol: LDP, peer 10.1.1.2:0 up MPLS VC labels: local 17, remote 24 Group ID: local 0, remote 0 MTU: local 1500, remote 1500 Remote interface description: Sequencing: receive disabled, send disabled VC statistics: packet totals: receive 111, send 114 byte totals: receive 33316, send 32384 packet drops: receive 0, send 5
Notice that the fast reroute status has changed from ready to active. The output interface for the pseudowire has switched from Tunnel1 to Tunnel100, and the label stack has become {16 16 24}. The top label 16 is the backup tunnel label so that pseudowire packets can be forwarded to the tailend router P1 through the backup traffic engineering tunnel. The second label 16 is the primary tunnel label that P1 assigns. The last label 24 is the VC label for the pseudowire. |
The configuration on PE1 after finishing these steps is shown in Example 9-19.
Example 9-19. Configuration for MPLS Fast RerouteProtected Pseudowire
hostname PE1 ! ip cef mpls label protocol ldp mpls ldp router-id Loopback0 mpls traffic-eng tunnels pseudowire-class PE1-P1-PE2 encapsulation mpls preferred-path interface Tunnel1 disable-fallback ! pseudowire-class High_Bandwidth encapsulation mpls preferred-path interface Tunnel2 ! interface Loopback0 ip address 10.1.1.1 255.255.255.255 ! interface Tunnel1 ip unnumbered Loopback0 tunnel destination 10.1.1.2 tunnel mode mpls traffic-eng tunnel mpls traffic-eng priority 7 7 tunnel mpls traffic-eng bandwidth 1000 tunnel mpls traffic-eng path-option 1 explicit name P1-PE2 tunnel mpls traffic-eng fast-reroute ! interface Tunnel2 ip unnumbered Loopback0 tunnel destination 10.1.1.2 tunnel mode mpls traffic-eng tunnel mpls traffic-eng priority 7 7 tunnel mpls traffic-eng bandwidth 5000 tunnel mpls traffic-eng path-option 1 dynamic ! interface Tunnel100 ip unnumbered Loopback0 no ip directed-broadcast tunnel destination 10.1.2.1 tunnel mode mpls traffic-eng tunnel mpls traffic-eng priority 7 7 tunnel mpls traffic-eng bandwidth 1000 tunnel mpls traffic-eng path-option 1 explicit name P2-P1 ! interface Ethernet0/0 no ip address ! interface Ethernet0/0.1 encapsulation dot1Q 100 xconnect 10.1.1.2 100 encapsulation mpls ! interface Ethernet0/0.2 encapsulation dot1Q 200 xconnect 10.1.1.2 200 pw-class PE1-P1-PE2 ! interface Ethernet0/0.3 encapsulation dot1Q 300 xconnect 10.1.1.2 300 pw-class High_Bandwidth ! interface Ethernet1/0 ip address 10.23.12.1 255.255.255.0 mpls ip mpls traffic-eng tunnels ip rsvp bandwidth 8000 ! interface Serial3/0 ip address 10.23.11.1 255.255.255.0 mpls ip mpls traffic-eng tunnels mpls traffic-eng backup-path Tunnel100 ip rsvp bandwidth 1200 ! router ospf 1 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 0 network 10.1.1.1 0.0.0.0 area 0 network 10.23.11.0 0.0.0.255 area 0 network 10.23.12.0 0.0.0.255 area 0 ! ip explicit-path name P1-PE2 enable next-address 10.23.11.2 next-address 10.23.21.2 ! ip explicit-path name P2-P1 enable next-address 10.23.12.2 next-address 10.33.23.1
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