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Question on EVPN Type 3 Route

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  • 1.  Question on EVPN Type 3 Route

     
    Posted 05-15-2021 13:46

    Hi.

     

    Here is an EVPN Type 3 route advertised by a VXLAN VTEP:

     

    user@S1> show route advertising-protocol bgp 4.4.4.4 match-prefix 3* detail

    bgp.evpn.0: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden)

    * 3:1.1.1.1:1::5010::1.1.1.1/248 IM (1 entry, 1 announced)

    BGP group overlay type Internal

         Route Distinguisher: 1.1.1.1:1

         Route Label: 5010

         PMSI: Flags 0x0: Label 5010: Type INGRESS-REPLICATION 1.1.1.1

         Nexthop: Self

         Localpref: 100

         AS path: [100] I

         Communities: target:100:5010

                      encapsulation:vxlan(0x8)

                      PMSI: Flags 0x0:

                            Label 313

                            Type INGRESS-REPLICATION

                            1.1.1.1

     

     

    What is the MPLS label 313 used for?

     

    Many thanks,

    Deepak


    Juniper Business Use Only



  • 2.  RE: Question on EVPN Type 3 Route
    Best Answer

     
    Posted 05-17-2021 09:34
    Hi, 

    Not sure what is the use of that label or its significance.
    It's certainly not exchanged as part of BGP updates between EVPN neighbors as not seen in packet capture.
    However, looks like it's derived from the VNID, last 4 HEX omitting the last one, effectively 3 HEX.

    vnid in decimal: 5010
    vnid in HEX: 1392
    
    Label value in HEX: 139
    Label value in Dec: 313​


    This appears to be consistent across different VNIDs:

    vnid in decimal: 5201/5202/5216/5232
    vnid in HEX: 1451/1452/1460/1470
    
    Label value in HEX: 145/145/146/147
    Label value in Dec: 325/325/326/327


    BGP Type 3 received:

    > show route receive-protocol bgp 192.168.1.2 match-prefix 3* detail | match "3:|Label"
    * 3:192.168.1.2:1::5201::192.168.1.2/248 IM (1 entry, 0 announced)
    PMSI: Flags 0x0: Label 325: Type INGRESS-REPLICATION 192.168.1.2
    * 3:192.168.1.2:1::5202::192.168.1.2/248 IM (1 entry, 0 announced)
    PMSI: Flags 0x0: Label 325: Type INGRESS-REPLICATION 192.168.1.2
    * 3:192.168.1.2:1::5216::192.168.1.2/248 IM (1 entry, 0 announced)
    PMSI: Flags 0x0: Label 326: Type INGRESS-REPLICATION 192.168.1.2
    * 3:192.168.1.2:1::5232::192.168.1.2/248 IM (1 entry, 0 announced)
    PMSI: Flags 0x0: Label 327: Type INGRESS-REPLICATION 192.168.1.2


    From packet capture, there is no exchange of this value (326 in this case for vnid 5216) in PMSI_TUNNEL_ATTRIBUTE:

            Path Attribute - PMSI_TUNNEL_ATTRIBUTE
                Flags: 0xc0, Optional, Transitive, Complete
                Type Code: PMSI_TUNNEL_ATTRIBUTE (22)
                Length: 9
                Flags: 0
                Tunnel Type: Ingress Replication (6)
                VNI: 5216
                Tunnel ID: tunnel end point -> 192.168.1.2
                    Tunnel type ingress replication IP end point: 192.168.1.2


    Not sure if this is intentional or possibly a bug.

    Cheers,



    ------------------------------
    Ashvin
    ------------------------------



  • 3.  RE: Question on EVPN Type 3 Route

     
    Posted 05-22-2021 02:00
    Thank you Ashvin for your answer. Much appreciate your test results.

    At least I know that the value is not that important. 

    --Deepak