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iBGP session flapping due to 'Malformed Attribute List' after upgrade to NI 6.3

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TitleiBGP session flapping due to 'Malformed Attribute List' after upgrade to NI 6.3
Symptoms
  • iBGP session flapping due to 'Malformed Attribute List' after upgrade to NI 6.3
    Nov 28 08:24:44:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:24:43:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Malformed Attribute List)
    Nov 28 08:24:40:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:24:37:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Malformed Attribute List)
    Nov 28 08:24:26:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:24:06:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Unrecognized Well-known Attribute)
    Nov 28 08:23:27:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:23:17:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Malformed Attribute List)
    Nov 28 08:23:02:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:23:00:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Malformed Attribute List)
    Nov 28 08:22:57:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:22:52:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Malformed Attribute List)
    Nov 28 08:22:44:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:22:40:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Malformed Attribute List)
    Nov 28 08:22:33:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:22:09:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Unrecognized Well-known Attribute)
    Nov 28 08:21:20:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
    Nov 28 08:21:10:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 DOWN (Rcv Notification:Malformed Attribute List)
    Nov 28 08:20:47:N:BGP: Peer (VRF: default-vrf) 10.123.123.23 UP (ESTABLISHED)
Environment
  • MLX Series
  • CER/CES
  • Netiron OS 6.3
  • iBGP
  • DEFECT000667280
Cause
BGP receives NLRI along path attributes from an eBGP peer (RIB-IN-PEER) and stores the NLRI and path attributes (including unrecognized attributes) in BGP RIB-IN. While sending the NLRI out to an iBGP peer (RIB-OUT-PEER), BGP has to advertise all path-attributes(both recognized and un-recognized). These attributes are encoded into the update message one after the other. BGP large-community attributes are encoded (if present) just before encoding un-recognized attribute.
Hence, BGP generates malformed updates whenever unknown attributes are present, irrespective of whether large-community attributes are present or absent in BGP advertisements.
Resolution
  • Workaround
    1. Look for 'Malformed" BGP packets on the peer router side and identify the prefixes with 'Malformed Attribute List' by debugging BGP updates
    2. Define a BGP prefix-list filter to filter out these prefixes on the inbound side from where the prefixes are learned from
  • Fix
    1. Upgrade to NI 6.3a or any release that has the fix for DEFECT000667280
Additional notes
  • Topology
    R1--eBGP--R2--iBGP--R3

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