I recently did a post showing that in order to signal an RSVP-TE signalled path accross an ISP core, you could do this even if all the routers were not in the same OSPF area or IS-IS level. You do of course lose complete end to end information which means things like link affinities cease to work.
You can also signal an RSVP-TE LSP over a link that isn’t even running an IGP.
This is the topology:
R1 and R2 are running OSPF with each other. R3 and R4 are running OSPF with each other. R2 and R3 are not running OSPF over their directly attached link. Let’s configure R1’s RSVP-TE tunnel to R4.
mpls traffic-eng tunnels ! interface Loopback0 ip address 188.8.131.52 255.255.255.255 ip ospf 1 area 0 ! interface Tunnel4 ip unnumbered Loopback0 tunnel mode mpls traffic-eng tunnel destination 184.108.40.206 tunnel mpls traffic-eng autoroute destination tunnel mpls traffic-eng path-option 5 explicit name TO-R4 ! interface FastEthernet0/0 ip address 10.10.12.1 255.255.255.0 ip ospf 1 area 0 mpls traffic-eng tunnels ! router ospf 1 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 0 ! ! ip explicit-path name TO-R4 enable next-address loose 220.127.116.11 next-address loose 18.104.22.168 next-address loose 22.214.171.124
R4 has similar config, but on the other side.
To confirm, there is no adjacency or static routes between R2 and R3:
R2#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 126.96.36.199 1 FULL/BDR 00:00:34 10.0.12.1 FastEthernet1/0 R2#sh ip route ospf | beg Gate Gateway of last resort is not set 188.8.131.52/32 is subnetted, 1 subnets O 184.108.40.206 [110/2] via 10.0.12.1, 00:10:35, FastEthernet1/0 R2#sh ip route 220.127.116.11 % Network not in table
We need to ensure R2 knows how to signal an RSVP tunnel to 18.104.22.168, even though it has no information about that destination in it’s IGP.
mpls traffic-eng tunnels ! interface Loopback0 ip address 22.214.171.124 255.255.255.255 ip ospf 1 area 0 ! interface FastEthernet1/0 ip address 126.96.36.199 255.255.255.0 mpls traffic-eng tunnels mpls traffic-eng passive-interface nbr-te-id 188.8.131.52 nbr-if-addr 184.108.40.206 ! router ospf 1 router-id 220.127.116.11 log-adjacency-changes mpls traffic-eng router-id Loopback0 mpls traffic-eng area 0
This allows R2 to know that node 18.104.22.168 is actually on the other side of the link with R3’s interface address. This will allow R2 to send the RSVP-TE reservation off to R3, even though there is no IGP running between them:
R1#sh mpls traffic-eng tunnels P2P TUNNELS/LSPs: Name: R1_t4 (Tunnel4) Destination: 22.214.171.124 Status: Admin: up Oper: up Path: valid Signalling: connected path option 5, type explicit TO-R4 (Basis for Setup, path weight 1) Config Parameters: Bandwidth: 0 kbps (Global) Priority: 7 7 Affinity: 0x0/0xFFFF Metric Type: TE (default) AutoRoute announce: disabled LockDown: disabled Loadshare: 0 bw-based AutoRoute destination: enabled auto-bw: disabled Active Path Option Parameters: State: explicit path option 5 is active BandwidthOverride: disabled LockDown: disabled Verbatim: disabled InLabel : - OutLabel : FastEthernet0/0, 17 Next Hop : 10.0.12.2 RSVP Signalling Info: Src 126.96.36.199, Dst 188.8.131.52, Tun_Id 4, Tun_Instance 27 RSVP Path Info: My Address: 10.0.12.1 Explicit Route: 10.0.12.2 184.108.40.206 220.127.116.11* 18.104.22.168* Record Route: Tspec: ave rate=0 kbits, burst=1000 bytes, peak rate=0 kbits RSVP Resv Info: Record Route: 22.214.171.124 126.96.36.199 188.8.131.52 Fspec: ave rate=0 kbits, burst=1000 bytes, peak rate=0 kbits History: Tunnel: Time since created: 11 minutes, 53 seconds Time since path change: 7 minutes, 37 seconds Number of LSP IDs (Tun_Instances) used: 27 Current LSP: [ID: 27] Uptime: 7 minutes, 37 seconds Prior LSP: [ID: 26] ID: path option unknown Removal Trigger: path error
The tunnel is now up. This means I’ll be able to trace to 184.108.40.206 over the non IGP-enabled link:
R1#traceroute 220.127.116.11 so lo0 Type escape sequence to abort. Tracing the route to 18.104.22.168 1 10.0.12.2 [MPLS: Label 17 Exp 0] 12 msec 12 msec 12 msec 2 22.214.171.124 [MPLS: Label 17 Exp 0] 12 msec 12 msec 8 msec 3 126.96.36.199 8 msec * 20 msec
This could be handy if you wanted to signal and end-to-end LSP with another provider. Far more likely you’ll be running BGP+Label over that type of link though.