Symptom
After creating/deleting interface vlan on N9K we see MTU mis-programming on all interfaces.
Conditions
[+] N9K
[+] All interfaces on the switch should be configured with high MTU (for example 9216)
[+] Creating and deleting interface vlan with MTU other than the one specified earlier
Workaround
[+]Flap the interface by shut/no shut
Further Problem Description
[+] Normal packets with default size will not be impacted.
[+] ELAM for packets with high MTU, we see the packet getting dropped
BIGSKY ELAM REPORT SUMMARY
slot - 1, asic - 0, slice - 2
============================
Incoming Interface: Eth1/4
Src Idx : 0xd, Src BD : 4108
Outgoing Interface Info: dmod 1, dpid 172
Dst Idx : 0x9, Dst BD : 4107
Packet Type: IPv4
Sup hit: 1, Sup Idx: 3049
Outer Dst IPv4 address: 10.254.2.75
Outer Src IPv4 address: 10.254.2.70
Ver = 4, DSCP = 0, Don't Fragment = 0
Proto = 17, TTL = 255, More Fragments = 0
Hdr len = 20, Pkt len = 8078, Checksum = 0x2c28
Inner Payload
Type: IPv4
Inner Dst IPv4 address: 10.17.21.14
Inner Src IPv4 address: 10.17.21.17
L4 Protocol : 17
L4 info not available
Drop Info:
----------
LUA:
LUB:
LUC:
LUD:
IP_MTU_CHECK_FAIILURE <<<<<<<<
Final Drops:
[+] Consistency checker will fail for MTU:
PINE01# show consistency-checker l3-interface all
L3 LIF Checks: for physical interfaces L3 Vlan, CML Flags, IPv4 Enable, VRFid check, MTU check, MTU check for L3VNI/L2VNI and for Sub-interface, IPv4 Enable, VRFid check, MTU check
Consistency Check passed for Vlan351
Consistency Check passed for Vlan352
Consistency Check passed for Vlan353
Error: Hw Mtu 1500 L3 mtu 9216
Consistency Check Failed for Vlan2250
Error: Hw Mtu 1500 L3 mtu 9216
Consistency Check Failed for Ethernet1/1
Interface Ethernet1/2 is link state down
Error: Hw Mtu 1500 L3 mtu 9216
Consistency Check Failed for Ethernet1/3
Error: Hw Mtu 1500 L3 mtu 9216
Consistency Check Failed for Ethernet1/4
