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Pseudowire Label Switch Path Load Sharing doesn't work.

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TitlePseudowire Label Switch Path Load Sharing doesn't work.
Symptoms
When LSP load sharing is enabled, traffic is not being load shared between LSPs:
X670G2-48X[L5:U32].13 # show mpls statistics l2vpn
 
L2VPN Name
  Peer IP/LSP    Flags            RxPackets              RxBytes            TxPackets              TxBytes
----------------------------------------------------------------------------------------------------------
VPLS_VPN       
  10.0.0.35          U                    0                    0            224353666          19294415276
    LSP1             +                                                      224353666          19294415276
    LSP2             +                                                              0                    0
    LSP3             +                                                              0                    0
    LSP4             +                                                              0                    0
 
 
Flags: (U) Up, (D) Down, (R) Ready, (S) Signaling, (+) In-use, (-) Not In-use
 
X670G2-48X[L5:U32].13 # show mpls rsvp-te lsp 
Ingress LSP Name Path Name        Destination     Next Hop I/F     UpTm Flags   
---------------- ---------------- --------------- ---------------- ---- --------
LSP1             lsp-path         10.0.0.35       v3233              7m UEP--OIV
LSP2             lsp-path         10.0.0.35       v3233              7m UEP--OIV
LSP3             lsp-path         10.0.0.35       v3233              7m UEP--OIV
LSP4             lsp-path         10.0.0.35       v3233              7m UEP--OIV
 
Egress LSP Name  Source IP       Destination     Prev Hop I/F     UpTm
---------------- --------------- --------------- ---------------- ----
LSP3             10.0.0.35       10.0.0.32       v3233              7m
LSP2             10.0.0.35       10.0.0.32       v3233              7m
LSP4             10.0.0.35       10.0.0.32       v3233              7m
LSP1             10.0.0.35       10.0.0.32       v3233              7m
 
Flags: (U) Up, (E) Enabled, (P) Primary LSP, (S) Secondary LSP,
       (F) FRR Primary LSP, (R) Redundant Paths, (B) Bandwidth Requested,
       (O) ERO Specified, (I) IP Traffic Allowed, (V) VPN Traffic Allowed,
       (v) VPN Assigned Traffic Allowed
 
 
Summary of RSVP-TE LSPs
    Ingress LSPs (Enabled/Disabled)               : 4 (4/0)
    Ingress LSPs with no configured path          : 0
    Ingress LSP Paths (Up/Down)                   : 4 (4/0)
    Detour LSP Paths (Up/Down)                    : 0 (0/0)
    Transit LSPs                                  : 0
    Egress LSPs                                   : 4
 
X670G2-48X[L5:U32].14 # show vpls "VPLS_VPN" 
L2VPN Name      VPN ID Flags   Services Name   Peer IP         State Flags 
--------------- ------ ------- --------------- --------------- ----- -------
VPLS_VPN        111    EAX--L- v1000           10.0.0.35       Up    C--NV-L
 
 
 
VPN Flags:  (E) Admin Enabled, (A) Oper Enabled, (I) Include Tag,
            (X) Exclude Tag, (T) Ethertype Configured,
            (V) VCCV HC Enabled, (W) VPN Type VPWS, (L) VPN Type VPLS,
            (M) CFM MIP Configured
Peer Flags: (C) Core Peer, (S) Spoke Peer, (A) Active Core,
            (p) Configured Primary Core, (s) Configured Secondary Core, 
            (N) Named LSP Configured, (V) VCCV HC Capabilities Negotiated, 
            (F) VCCV HC Failed, (L) LDP Signaled, (T) Static (Not Signaled)
Environment
  • EXOS 15.4 and higher
  • EXOS platforms with support of L2VPN LSP sharing
  • L2VPN LSP sharing feature
Cause
One of possible reasons could be that traffic which should be load shared is a BUM (broadcast, unknown unicast, multicast) traffic.
Resolution
One of limitations of Pseudowire Label Switch Path Load Sharing is that ECMP is not supported for flood traffic (unknown unicast, multicast, broadcast). These packets will only go over one LSP. To overcome this limitation switch should learn destination addresses to reduce amount of unknown unicast traffic and provide better load sharing across LSPs:
X670G2-48X[L5:U32].2 # show mpls statistics l2vpn
L2VPN Name
  Peer IP/LSP    Flags            RxPackets              RxBytes            TxPackets              TxBytes
----------------------------------------------------------------------------------------------------------
VPLS_VPN
  10.0.0.35          U                17368               561612                60166              5414940
    LSP1             +                                                          14157              1274130
    LSP2             +                                                          21236              1911240
    LSP3             +                                                          10617               955530
    LSP4             +                                                          14156              1274040
 
Flags: (U) Up, (D) Down, (R) Ready, (S) Signaling, (+) In-use, (-) Not In-use
X670G2-48X[L5:U32].3 #
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