Hello,
MTU on all interfaces is > 9000 bytes. Here is the debug result when I am pinging from the server via gre tunnel MX960 router with 1470 bytes:
mtu exceeded - its increasing on each packet
# show jnh exceptions-trace
[Jan 23 20:30:01.891] [241572] jnh_exception_packet_trace:1800 ###############
[Jan 23 20:30:01.891] [241573] jnh_exception_packet_trace:1805 [iif:334,code/info:149 D(mtu exceeded)/0x5ea,score:(0x1),ptype:2/0,orig_ptype:2,offset:60,orig_offset:60,len:1558,l2iif:328,oif:337,BD 3,l2-off=180388627013,token=2791800 ]
[Jan 23 20:30:01.891] [241574] jnh_exception_packet_trace:1829 0x00: 20 01 95 00 5e a0 01 4e 2a 3c 06 16 80 01 48 20
[Jan 23 20:30:01.891] [241575] jnh_exception_packet_trace:1829 0x10: 3c 00 03 40 02 00 00 02 45 00 00 00 00 15 10 08
[Jan 23 20:30:01.891] [241576] jnh_exception_packet_trace:1829 0x20: 81 f4 89 15 f3 28 c0 da fa 28 a5 81 00 01 fa 08
[Jan 23 20:30:01.891] [241577] jnh_exception_packet_trace:1829 0x30: 00 45 00 06 04 6d 00 00 00 3f 2f f5 0b b9 cd d0
[Jan 23 20:30:01.891] [241578] jnh_exception_packet_trace:1829 0x40: 12 b9 cd d0 11 00 00 65 58 00 25 90 a2 80 ab 28
[Jan 23 20:30:01.892] [241579] jnh_exception_packet_trace:1829 0x50: c0 da fa 2f f0 81 00 0b c1 08 00 45 00 05 da 6c
[Jan 23 20:30:01.892] [241580] jnh_exception_packet_trace:1829 0x60: ff 40 00 40 01 98 20 5b 84 3c 01 5b 84 3c fa 00
[Jan 23 20:30:01.892] [241581] jnh_exception_packet_trace:1829 0x70: 00 6b 66 0c 21 00 55 10 f5 29 5e 00 00 00 00 bc
iif:334 is the gre tunnel - Logical interface gr-0/0/0.0 (Index 334) (SNMP ifIndex 621)
show interfaces gr-0/0/0
Physical interface: gr-0/0/0, Enabled, Physical link is Up
Interface index: 140, SNMP ifIndex: 566
Description: S3C-TEST
Type: GRE, Link-level type: GRE, MTU: Unlimited, Speed: 10000mbps
Device flags : Present Running
Interface flags: Point-To-Point SNMP-Traps
Input rate : 43096 bps (69 pps)
Output rate : 23664 bps (6 pps)
Logical interface gr-0/0/0.0 (Index 334) (SNMP ifIndex 621)
Flags: Up Point-To-Point SNMP-Traps Reassemble-Pkts 0x0 IP-Header xx.xx.xx.xx:xx.xx.xx.xx:47::64:0000000000000000 Encapsulation: L2-over-GRE
Copy-tos-to-outer-ip-header: Off, Copy-tos-to-outer-ip-header-transit: Off
Gre keepalives configured: Off, Gre keepalives adjacency state: down
Input packets : 131830202
Output packets: 2781297
Protocol bridge, MTU: Unlimited
Flags: Trunk-Mode