This KB explains why below syslog message is seen, and how to identify the source of the packet with invalid id.

May 6 14:30:03 2024 re0.MX fpc9 PPMAN_CFM_SLM: SLM: SLM dropped due to invalid id.

Here MX is a acting as reflector to receive iterators SLM to respond with SLR PDU. Above syslog message indicates SLM received from remote CFM peer contains invalid test id and is getting dropped.

To identify the source of problematic CFM neighbor:

1-log into the CFM neighbor that generates SLM packet as probe/iteartor and check SLM/SLR statistics mismatch

2-Perform packet-via-dmem capture on MX and identify the SLM packet with test id 0

Hint- to capture SLM packet, find out the maintenance-domain level configured on MX, here maintenance domain is configured with 3, so 0110 is used , capture pattern is 0x89026037

Sample packet:

a8 d0 e5 09 8f c4 

84 c8 07 41 7f 84 89 02 

60 37 00 10 00 0a 00 00 

00 00 00 00 0c 83 9d 03 

00 00 00 00 03 00 42 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 00 00 00 00 00 00 

00 00 

•  Frame 1: 120 bytes on wire (960 bits), 120 bytes captured (960 bits)
• Ethernet II, Src: AdvaOpti_41:7f:84 (84:c8:07:41:7f:84), Dst: JuniperN_09:8f:c4 (a8:d0:e5:09:8f:c4)
• CFM EOAM 802.1ag/ITU Protocol, Type Synthetic Loss Message (SLM)
  • 011. .... = CFM MD Level: 3
  • ...0 0000 = CFM Version: 0
  • CFM OpCode: Synthetic Loss Message (SLM) (55)
• CFM SLM PDU
  • Flags: 0x00
  • First TLV Offset: 16
  • ...0 0000 0000 1010 = Source MEP ID: 10
  • ...0 0000 0000 0000 = Responder MEP ID: 0
  • TestID: 00000000 >>>>>>>>>>>>>>>>>>>>>>>>
  • TxFcF: 209952003
  • TxFcB: 0
• CFM TLVs
  • TLV: Data TLV (t=3,l=66)
  • TLV: End TLV (t=0,l=0)