Description

This KB explains the root cause and solution of the multiple MAC addresses learned by EX4400 mge ports due to a bad cable connection.

Symptoms

​​​​​​The customer has an ex4400-48mp VC where due to a bad cable connection they learn multiple Mac addresses. The port has ARUBA AP MODEL: 535 connected, the connection negotiates at 100M full. The issue was identified as Bad FCS frames not dropped by the mge ports on ex4400 which results in multiple Mac addresses being learned due to incoming corrupt packets (suspecting source mac address fields getting changed). No such issue is seen on gig ports.
 
  • Multiple Mac addresses are learned on an access port due to bad incoming frames:
switch1> show ethernet-switching table interface mge-4/0/46

MAC database for interface mge-4/0/46

MAC database for interface mge-4/0/46.0

MAC flags (S - static MAC, D - dynamic MAC, L - locally learned, P - Persistent static, C - Control MAC

SE - statistics enabled, NM - non configured MAC, R - remote PE MAC, O - ovsdb MAC)

Ethernet switching table : 6 entries, 6 learned

Routing instance : default-switch

Vlan MAC MAC Age Logical NH RTR

name address flags interface Index ID

wap-mgmt400 80:61:c0:c3:d7:92 D - mge-4/0/46.0 0 0

wap-mgmt400 d0:61:c0:ca:d7:92 D - mge-4/0/46.0 0 0

wap-mgmt400 f0:61:70:c7:d7:92 D - mge-4/0/46.0 0 0

wap-mgmt400 f0:61:c0:ca:56:92 D - mge-4/0/46.0 0 0

wap-mgmt400 f0:61:c0:ca:d7:92 D - mge-4/0/46.0 0 0

wap-mgmt400 f0:6f:c0:ca:d7:92 D - mge-4/0/46.0 0 0

 
 
  • No input framing errors are seen,No CRC/Align errors are seen.Ideally, bad FCS frames should be dropped by the device. But we do not see it below:
switch1> show interfaces mge-4/0/46 extensive | match error

Link-level type: Ethernet, MTU: 1514, LAN-PHY mode, Link-mode: Full-duplex, Speed: 10Gbps, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None,

Input errors:

Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0, L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0

Output errors:

Carrier transitions: 0, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0, MTU errors: 0, Resource errors: 0

Bit errors 0

Errored blocks 0

Ethernet FEC statistics Errors

FEC Corrected Errors 0

FEC Uncorrected Errors 0

FEC Corrected Errors Rate 0

FEC Uncorrected Errors Rate 0

CRC/Align errors 0 0

FIFO errors 0 0

Solution

Bad FCS frames are not dropped and framing errors are not incrementing on mge ports on receiving bad/corrupted packets due to the layer 1 issue (bad cabling/bad port etc.)
 

It is identified as a bug and the fix has been tested and provided in PR - 1756745 [Confidential] - [Hardening:EX4400MP]: FCS error packets not dropped on mge ports, packets forwarded.

 

Resolved-In:

junos:22.2R3-S2

junos:22.3R2-S2

junos:22.4R3

junos:23.1R2

junos:23.2R2

junos:23.3R1

junos:23.3R2

junos:23.4R1


On the fix image, if we receive a bad FCS frame it will be dropped and we will see it under framing errors:

switch1> show interfaces mge-4/0/46 extensive | match error

 Link-level type: Ethernet, MTU: 1514, LAN-PHY mode, Link-mode: Full-duplex, Speed: Auto, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None,

 Input errors:

   Errors: 198, Drops: 0, Framing errors: 198, Runts: 0, Policed discards: 0, L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0

 Output errors:

   Carrier transitions: 0, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0, MTU errors: 0, Resource errors: 0

   Bit errors                            0

   Errored blocks                        0

 Ethernet FEC statistics             Errors

   FEC Corrected Errors                   0

   FEC Uncorrected Errors                 0

   FEC Corrected Errors Rate              0

   FEC Uncorrected Errors Rate            0

   CRC/Align errors                      198               0

   FIFO errors                             0               0

Modification History

2023-09-12: <initial publication>