sflow issue observed with lower MTU - EX4300 virtual-chassis

The next-hop interface towards collector is set to MTU 1280.

# run show interfaces ge-0/0/9 | grep mtu
Link-level type: Ethernet, MTU: 1280, LAN-PHY mode, Link-mode: Full-duplex,
Protocol inet, MTU: 1266

tcpdump on server:

# tcpdump -i ens160f0 -vv 'port 4739'
tcpdump: listening on ens160f0, link-type EN10MB (Ethernet), capture size 262144 bytes
11:41:27.748069 IP (tos 0x0, ttl 255, id 65358, offset 0, flags [+], proto UDP (17), length 1260)
10.233.32.1.64865 > 192.192.1.1.4739: UDP, bad length 1324 > 1232
11:41:27.748176 IP (tos 0x0, ttl 255, id 65359, offset 0, flags [+], proto UDP (17), length 1260)
10.233.32.1.64865 > 192.192.1.1.4739: UDP, bad length 1260 > 1232
11:41:27.765084 IP (tos 0x0, ttl 255, id 65360, offset 0, flags [+], proto UDP (17), length 1260)
10.233.32.1.64865 > 192.192.1.1.4739: UDP, bad length 1284 > 1232
11:41:27.766550 IP (tos 0x0, ttl 255, id 65361, offset 0, flags [+], proto UDP (17), length 1260)
10.233.32.1.64865 > 192.192.1.1.4739: UDP, bad length 1252 > 1232
11:41:27.766609 IP (tos 0x0, ttl 255, id 65362, offset 0, flags [+], proto UDP (17), length 1260)
10.233.32.1.64865 > 192.192.1.1.4739: UDP, bad length 1324 > 1232
11:41:27.847790 IP (tos 0x0, ttl 255, id 65363, offset 0, flags [+], proto UDP (17), length 1260)
10.233.32.1.64865 > 192.192.1.1.4739: UDP, bad length 1324 > 1232

It appears the switch is trying to pack upto 1324 bytes of UDP payload and requires a minimum inet mtu of 1352. Interestingly there was no fragment after the first packet.

So after setting the mtu to 1366:

# run show interfaces ge-0/0/9 | grep mtu
Link-level type: Ethernet, MTU: 1366, LAN-PHY mode, Link-mode: Full-duplex,
Protocol inet, MTU: 1352

# tcpdump -i ens160f0 -vv 'port 4739'
tcpdump: listening on ens160f0, link-type EN10MB (Ethernet), capture size 262144 bytes
11:42:42.444032 IP (tos 0x0, ttl 255, id 3395, offset 0, flags [none], proto UDP (17), length 1352)
10.233.32.1.64865 > 192.192.1.1.4739: [udp sum ok] UDP, length 1324
11:42:42.444269 IP (tos 0x0, ttl 255, id 3396, offset 0, flags [none], proto UDP (17), length 1352)
10.233.32.1.64865 > 192.192.1.1.4739: [udp sum ok] UDP, length 1324
11:42:42.444326 IP (tos 0x0, ttl 255, id 3397, offset 0, flags [none], proto UDP (17), length 1296)
10.233.32.1.64865 > 192.192.1.1.4739: [udp sum ok] UDP, length 1268
11:42:42.513998 IP (tos 0x0, ttl 255, id 3398, offset 0, flags [none], proto UDP (17), length 1348)
10.233.32.1.64865 > 192.192.1.1.4739: [udp sum ok] UDP, length 1320
11:42:42.514479 IP (tos 0x0, ttl 255, id 3399, offset 0, flags [none], proto UDP (17), length 1352)
10.233.32.1.64865 > 192.192.1.1.4739: [udp sum ok] UDP, length 1324
11:42:42.545967 IP (tos 0x0, ttl 255, id 3400, offset 0, flags [none], proto UDP (17), length 1352)
10.233.32.1.64865 > 192.192.1.1.4739: [udp sum ok] UDP, length 1324

Is the switch ignoring its outgoing interface's mtu? 

regards,

Krish