RSVP-TE LSPs without IGP

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.

R1:

mpls traffic-eng tunnels
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
ip ospf 1 area 0
!
interface Tunnel4
ip unnumbered Loopback0
tunnel mode mpls traffic-eng
tunnel destination 4.4.4.4
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 2.2.2.2
next-address loose 3.3.3.3
next-address loose 4.4.4.4

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
1.1.1.1           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

1.0.0.0/32 is subnetted, 1 subnets
O        1.1.1.1 [110/2] via 10.0.12.1, 00:10:35, FastEthernet1/0

R2#sh ip route 3.3.3.3
% Network not in table

We need to ensure R2 knows how to signal an RSVP tunnel to 3.3.3.3, even though it has no information about that destination in it’s IGP.

R2:

mpls traffic-eng tunnels
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
ip ospf 1 area 0
!
interface FastEthernet1/0
ip address 20.0.23.2 255.255.255.0
mpls traffic-eng tunnels
mpls traffic-eng passive-interface nbr-te-id 3.3.3.3 nbr-if-addr 20.0.23.3
!
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
mpls traffic-eng router-id Loopback0
mpls traffic-eng area 0

This allows R2 to know that node 3.3.3.3 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: 4.4.4.4
  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 1.1.1.1, Dst 4.4.4.4, Tun_Id 4, Tun_Instance 27
    RSVP Path Info:
      My Address: 10.0.12.1
      Explicit Route: 10.0.12.2 2.2.2.2 3.3.3.3* 4.4.4.4*
      Record   Route:
      Tspec: ave rate=0 kbits, burst=1000 bytes, peak rate=0 kbits
    RSVP Resv Info:
      Record   Route:  20.0.23.2 20.0.34.3 20.0.34.4
      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 4.4.4.4 over the non IGP-enabled link:

R1#traceroute 4.4.4.4 so lo0

Type escape sequence to abort.
Tracing the route to 4.4.4.4

  1 10.0.12.2 [MPLS: Label 17 Exp 0] 12 msec 12 msec 12 msec
  2 20.0.23.3 [MPLS: Label 17 Exp 0] 12 msec 12 msec 8 msec
  3 20.0.34.4 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.

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