This article describes the default behavior of loose EROs (Explicit Route Objects) when used to form RSVP signaled LSPs.

Topology:

192.168.0.1     192.168.0.2        192.168.0.3          192.168.0.4        192.168.0.6

 R1--------------R2-------------------R3--------------------R4--------------R6
     10.10.10.0/30     10.20.20.0/30     |  10.30.30.0/30  |         10.60.60.0/30       
                                         |                 |
                                         |                 |  
                                         |                 |
                                         |---------R5------|
                                             192.168.0.5

• If the loop-back IP address is given as a loose ERO, the computed ERO will show only the physical path that it traversed.
• Additionally, each physical hop that is traversed will be shown as a strict ERO under computed ERO. This behaviour is expected with CSPF enabled LSPs.

  [edit protocols mpls]
  lab:R1# show
  label-switched-path LSP-1 {
      from 192.168.0.1;
      to 192.168.0.6;
      primary LSP-1-P;
  }
  path LSP-1-P {
      192.168.0.3 loose;
      192.168.0.5 loose;
  }
  interface all;
  

Only ERO's that  are defined as strict, that too every physical hop that was traversed when forming a traffic-engineered LSP, will be shown as strict under computed ERO in the output of show mpls lsp extensive .

The same is not true with loosely defined ERO's; even though a provision has been made to show loosely defined ERO's, as per the following output:

Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 5)

[edit]

lab:R1# run show mpls lsp extensive
Ingress LSP: 1 sessions

192.168.0.6
From: 192.168.0.1, State: Up, ActiveRoute: 0, LSPname: LSP-1
ActivePath: LSP-1-P (primary)
LSPtype: Static Configured
LoadBalance: Random
Encoding type: Packet, Switching type: Packet, GPID: IPv4
*Primary LSP-1-P State: Up
Priorities: 7 0
SmartOptimizeTimer: 180
Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 5)
10.10.10.2 S 10.20.20.2 S 10.40.40.2 S 10.50.50.2 S 10.60.60.2 S
Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt 20=Node-ID):
10.10.10.2 10.20.20.2 10.40.40.2 10.50.50.2 10.60.60.230 Jun 16 19:01:39.596 Selected as active path
29 Jun 16 19:01:39.596 Record Route: 10.10.10.2 10.20.20.2 10.40.40.2 10.50.50.2 10.60.60.2
28 Jun 16 19:01:39.594 Up
27 Jun 16 19:01:39.478 Originate Call

This is expected behavior; irrespective of the Junos version being used. This is strictly with respect to the traffic-engineered LSP's.

Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 5)
10.10.10.2 S 10.20.20.2 S 10.40.40.2 S 10.50.50.2 S 10.60.60.2 S
Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt 20=Node-ID):
10.10.10.2 10.20.20.2 10.40.40.2 10.50.50.2 10.60.60.2


lab:R1# run traceroute mpls rsvp LSP-1
Probe options: retries 3, exp 7

ttl Label Protocol Address Previous Hop Probe Status
1 299824 RSVP-TE 10.10.10.2 (null) Success
2 299824 RSVP-TE 10.20.20.2 10.10.10.2 Success
3 299776 RSVP-TE 10.40.40.2 10.20.20.2 Success
4 299824 RSVP-TE 10.50.50.2 10.40.40.2 Success
5 3 RSVP-TE 10.60.60.2 10.50.50.2 Egress

Path 1 via xe-1/2/0.10 destination 127.0.0.64

2022-11-17: Updated non-compliant IP addresses to RFC standards