ERS 8600 jumbo frames unresponsive

[gmolenkamp]

I am trying to debug a pathmtu issue between servers attached to an ERS8600 using the tracepath tool and I notice that the ERS 8600 running v7.1.3.1, will not get an icmp reply from an ers interface when the server has an mtu greater than 1500, but th server will get a reply from the ers when the server has an mtu of 1500.

from a tcpdump at mtu=1500

10:28:51.466895 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto UDP (17), length 1500)
server.site.45283 > gateway.site.44444: UDP, length 1472
10:28:51.467574 IP (tos 0x40, ttl 64, id 28848, offset 0, flags [DF], proto ICMP (1), length 56)
gateway.site > server.site: ICMP gateway.site udp port 44444 unreachable, length 36
IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto UDP (17), length 1500
server.site.45283 > gateway.site.44444: [no cksum] UDP, length 1472

from a tcpdump at mtu=9000

10:45:50.403026 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto UDP (17), length 9000)
server.site.39851 > gateway.site.44446: UDP, length 8972
this repeats

I know the 9k frames are traversing the ERS8600 as I can sniff the traffic on the next hop, but its unexpected that the router is not responding directly.

Is this a know bug/limitation?