juniper weird IPv6 error ICMPs

[Philip Homburg]

Playing with traceroute I noticed that juniper routers send error ICMPs
with weird sizes. Did anyone else notice this as well, I can't remember
seeing it mentioned anywhere.

Here is some tcpdump output:
11:51:14.691810 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has fe80::13:0:0:1, length 32
11:51:14.694750 IP6 2001:67c:2e8:13::3 > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, neighbor advertisement, tgt is fe80::13:0:0:1, length 32
11:51:14.694781 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 1, length 1308
11:51:14.697665 IP6 2001:67c:2e8:13::3 > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 989
11:51:14.708090 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 2, length 1308
11:51:14.710634 IP6 2001:67c:2e8:13::3 > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 989
11:51:14.721396 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 3, length 1308
11:51:14.728065 IP6 2001:67c:2e8:13::3 > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 989
11:51:14.739038 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 4, length 1308
11:51:14.741656 IP6 ams-ix.sara.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 989
11:51:14.752068 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 5, length 1308
11:51:14.754816 IP6 ams-ix.sara.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 989
11:51:14.766003 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 6, length 1308
11:51:14.770292 IP6 ams-ix.sara.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 989
11:51:14.780776 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 7, length 1308
11:51:14.784750 IP6 0.ae4.xr3.3d12.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 990
11:51:14.795372 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 8, length 1308
11:51:14.798701 IP6 0.ae4.xr3.3d12.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 990
11:51:14.809910 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 9, length 1308
11:51:14.812934 IP6 0.ae4.xr3.3d12.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 990
11:51:14.823234 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 10, length 1308
11:51:14.828122 IP6 0.ae0.dr12.d12.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 993
11:51:14.838781 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 11, length 1308
11:51:14.842716 IP6 0.ae0.dr12.d12.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 993
11:51:14.853966 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 12, length 1308
11:51:14.857645 IP6 0.ae0.dr12.d12.xs4all.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 993
11:51:14.868309 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 13, length 1308
11:51:14.889053 IP6 stereo6.hq.phicoh.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 1240
11:51:14.899403 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 14, length 1308
11:51:14.920754 IP6 stereo6.hq.phicoh.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 1240
11:51:14.931113 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 15, length 1308
11:51:14.951985 IP6 stereo6.hq.phicoh.net > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, time exceeded in-transit for 2001:980:1284:10:2a0:c9ff:fe9f:17a9, length 1240
11:51:14.962779 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 16, length 1308
11:51:14.983705 IP6 2001:980:1284:10:2a0:c9ff:fe9f:17a9 > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, echo reply, seq 16, length 1308
11:51:14.994245 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 17, length 1308
11:51:15.014929 IP6 2001:980:1284:10:2a0:c9ff:fe9f:17a9 > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, echo reply, seq 17, length 1308
11:51:15.025703 IP6 2001:67c:2e8:13:21c:42ff:fe9f:b8b3 > 2001:980:1284:10:2a0:c9ff:fe9f:17a9: ICMP6, echo request, seq 18, length 1308
11:51:15.046708 IP6 2001:980:1284:10:2a0:c9ff:fe9f:17a9 > 2001:67c:2e8:13:21c:42ff:fe9f:b8b3: ICMP6, echo reply, seq 18, length 1308

As far as I know, the routers 2001:67c:2e8:13::3, ams-ix.sara.xs4all.net,
0.ae4.xr3.3d12.xs4all.net and 0.ae0.dr12.d12.xs4all.net are Juniper.

This seems to violate a MUST in RFC 4443:
In Section 2.4:
   (c) Every ICMPv6 error message (type < 128) MUST include as much of
       the IPv6 offending (invoking) packet (the packet that caused the
       error) as possible without making the error message packet exceed
       the minimum IPv6 MTU [IPv6].

And I'm really curious how to got sizes like 989, 990, 993