[j-nsp] LSP ECMP selection process - forwarding table

[Martyniak Lukasz]

Hi All 

I have a question about LSP next-hop selection process. I need to know is it possible to influence the selection of a LSP (prioritise it somehow) when i have multiple ECMP LSP installed int forwarding table. I would like to always use a LSP-A as a selected (e.g. to-r1) the other should be used when the to-r1 is gone. It is important to have all of the next hops in the forwarding table. (They don’t have to be ECMP until both next hops will be in the forwarding table)

The scenario is :
Single router with an LSP to 3 other routers (same cost of LSP e.g metric 10) and “install active” prefix on this LSP 

set protocols mpls label-switched-path to-r4 metric 10
set protocols mpls label-switched-path to-r4 install 0.0.0.0/0 active
set protocols mpls label-switched-path to-r3 metric 10
set protocols mpls label-switched-path to-r3 install 0.0.0.0/0 active  
set protocols mpls label-switched-path to-r2 metric 10
set protocols mpls label-switched-path to-r2 install 0.0.0.0/0 active
set protocols mpls label-switched-path to-r1 metric 10
set protocols mpls label-switched-path to-r1 install 0.0.0.0/0 active

Than i have 

0.0.0.0/0          *[RSVP/7/1] 21:25:21, metric 10
                    > to 10.20.21.4 via ge-0/0/0.2021, label-switched-path to-r2
                      to 10.20.21.2 via ge-0/0/0.2021, label-switched-path to-r4
                      to 10.20.55.2 via ge-0/0/0.2055, label-switched-path to-r3
                      to 10.30.8.2 via ge-0/0/3.1310, label-switched-path to-r1



Looks like it is selected in random way

0.0.0.0/0 (2 entries, 1 announced)
        State: <FlashAll>
        *RSVP   Preference: 7/1
                Next hop type: Router, Next hop index: 0
                Address: 0xce2eb70
                Next-hop reference count: 2
                Next hop: 10.20.21.4 via ge-0/0/0.2021 weight 0x1, selected
                Label-switched-path to-r2
                Label operation: Push 300160
                Label TTL action: prop-ttl
                Load balance label: Label 300160: None; 
                Label element ptr: 0xb3978a0
                Label parent element ptr: 0x0
                Label element references: 3
                Label element child references: 0
                Label element lsp id: 21
                Session Id: 0x0
                Next hop: 10.20.21.2 via ge-0/0/0.2021 weight 0x1
                Label-switched-path to-r4
                Label operation: Push 300064
                Label TTL action: prop-ttl
                Load balance label: Label 300064: None; 
                Label element ptr: 0xb397b40
                Label parent element ptr: 0x0
                Label element references: 3
                Label element child references: 0
                Label element lsp id: 23
                Session Id: 0x0
                Next hop: 10.20.55.2 via ge-0/0/0.2055 weight 0x1
                Label-switched-path to-r3
                Label operation: Push 559840
                Label TTL action: prop-ttl
                Load balance label: Label 559840: None; 
                Label element ptr: 0xb396b80
                Label parent element ptr: 0x0
                Label element references: 3
                Label element child references: 0
                Label element lsp id: 24
                Session Id: 0x0


 run show route forwarding-table destination 0/0    
Routing table: default.inet
Internet:
Destination        Type RtRef Next hop           Type Index    NhRef Netif
default            user     0                    ulst  1048591     2
                              50:0:0:1f:0:2     Push 300160      629     2 ge-0/0/0.2021
                              50:0:0:1e:0:2     Push 300064      630     2 ge-0/0/0.2021
                              50:0:0:20:0:2     Push 559840      641     2 ge-0/0/0.2055
                              50:0:0:1a:0:5     Push 300256      627     2 ge-0/0/3.1310