Routing

SPRING: MPLS Traffic Engineering for SR LSP routes

  • 1.  SPRING: MPLS Traffic Engineering for SR LSP routes

    Posted 05-14-2021 08:11

    Hello friends,

    I am using Juniper vmx with Junos version 19.4R3.11. I am stuck with a problem related to SR LSPs and MPLS Traffic Engineering.

    I configured non-colored SR LSPs, which are documented here - Understanding Non-Colored Segment Routing LSPs . According to the document, the SPRING routes for non colored SR LSPs are inserted into inet.3. I verified that too. Refer below -

    user@router> show route 10.66.3.162
    
    inet.0: 34 destinations, 34 routes (34 active, 0 holddown, 0 hidden)
    @ = Routing Use Only, # = Forwarding Use Only
    + = Active Route, - = Last Active, * = Both
    
    10.66.3.162/32     *[IS-IS/18] 06:12:01, metric 20
                        >  to 10.153.161.1 via ge-0/0/1.0
    
    inet.3: 8 destinations, 9 routes (8 active, 0 holddown, 0 hidden)
    + = Active Route, - = Last Active, * = Both
    
    10.66.3.162/32     *[SPRING-TE/8] 06:12:01, metric 1, metric2 20
                           to 10.153.161.1 via ge-0/0/1.0, Push 16162, Push 16011(top)
                        >  to 10.153.161.1 via ge-0/0/1.0, Push 16162
                        [L-ISIS/14] 06:12:01, metric 20
                        >  to 10.153.161.1 via ge-0/0/1.0, Push 16162
    
    user@router>


    Now, as inet.3 table is used only for BGP next-hop resolution, the SPRING-TE route will be available for use only by BGP traffic and services which use BGP (MPLS VPN, EVPN). So far, the behavior is similar to RSVP-TE tunnels. Now, for RSVP tunnels, we can use various mpls traffic-engineering configurations to make all traffic use the tunnel instead of BGP traffic. The mpls traffic-engineering configurations are documented here - MPLS Traffic Engineering Configuration. For a simple example, if I set the below configuration -

    set protocols mpls traffic-engineering bgp-igp


    After setting this configuration, the traffic-engineering routes (RSVP-TE or SPRING-TE) should be usable by both IGP and BGP traffic, and all the traffic-engineering routes should be moved to inet.0 table. But it does no happen for the SPRING-TE routes. Refer below -

    user@router> show route 10.66.3.162
    
    inet.0: 34 destinations, 42 routes (34 active, 0 holddown, 0 hidden)
    @ = Routing Use Only, # = Forwarding Use Only
    + = Active Route, - = Last Active, * = Both
    
    10.66.3.162/32     *[L-ISIS/14] 00:00:06, metric 20
                        >  to 10.153.161.1 via ge-0/0/1.0, Push 16162
                        [IS-IS/18] 00:00:06, metric 20
                        >  to 10.153.161.1 via ge-0/0/1.0
    
    inet.3: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden)
    + = Active Route, - = Last Active, * = Both
    
    10.66.3.162/32     *[SPRING-TE/8] 00:00:06, metric 1, metric2 20
                           to 10.153.161.1 via ge-0/0/1.0, Push 16162, Push 16011(top)
                        >  to 10.153.161.1 via ge-0/0/1.0, Push 16162
    
    user@router>


    Note that the L-ISIS (ISIS-SR, kind of a replacement for LDP) routes do move to inet.0, but SPRING-ROUTES do not move. I have tried all the mpls traffic-engineering configurations (bgp-igp, bgp-igp both ribs, bgp-igp both ribs mpls-forwarding),  but the SPRING-TE routes do not move into inet.0. I also tried traceroute and found that forwarding does not use the SPRING-TE route with labels, but uses unlabled IGP route.

    So, is there no way to allow non colored SR LSP routes to be used for forwarding non BGP traffic, or is the support added in a newer version ?



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    Vaibhav Lohani
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