Troubleshooting Idrops

[Rob Belics]

I have a VPS server running FreeBSD 10.3-RELEASE-p4 and nginx. It contains
three very low volume web sites that have been up for about three years. I
was tinkering with TLS and SSL ciphers by eliminating TLSv1 and TLSv1.1
with different ciphers when I noticed my daily "Network interface status"
report one morning saying I was getting Idrops of 48665.

Network interface status:
Name    Mtu Network       Address              Ipkts Ierrs Idrop    Opkts
Oerrs  Coll  Drop
em0    1500 <Link#1>      xx:xx:3c:cd:7e:c7 225569570     0 48665
923463     0     0     0
em0       - xxxx::xxx:3cf fe80::216:3cff:fe        0     -     -
4     -     -     -
em0       - 107.xxx.xx.xx mysite1.co    94833     -     -        0
-     -     -
em0       - 107.xxx.xx.0  mysite2.co   479981     -     -   920067
-     -     -
lo0   16384 <Link#2>                             783     0     0
783     0     0     0
lo0       - ::1           ::1                      0     -     -
0     -     -     -
lo0       - xxxx::1%lo0   xxxx::1%lo0              0     -     -
0     -     -     -
lo0       - your-net      localhost              783     -     -
783     -     -     -

I reverted my TLS/SSL changes but, the next day, that exact same number of
Idrops happened and continued for a couple of days afterwards. I just don't
know what I could have done to cause this and am looking for
troubleshooting help since it's been so long since I've had to deal with
this and forgotten nearly everything. All the sites seem to function
normally and I should note that, besides the nginx server, there are also
two nodejs servers listening via proxy. I do nothing with IPv6.

Here is part of vmstat -z where I notice FAILs:

ITEM                   SIZE  LIMIT     USED     FREE      REQ FAIL SLEEP

UMA Hash:               128,      0,       5,      26,       7,   0,   0
4 Bucket:                16,      0,       8,     496,   21344,   0,   0
6 Bucket:                24,      0,       0,     336,     121,   0,   0
8 Bucket:                32,      0,       2,     376,    1600,   0,   0
12 Bucket:               48,      0,       0,       0,   97831,   0,   0
16 Bucket:               64,      0,      12,     303,    9585,   8,   0
32 Bucket:              128,      0,      14,     389,   46423,   0,   0
64 Bucket:              256,      0,      20,     235,   48362,   0,   0
128 Bucket:             512,      0,      19,     101,   23133,   0,   0

mbuf_packet:            256,  30975,     256,     253,455561904,97330,   0
mbuf:                   256,  30975,       2,     254, 2124523,   0,   0
mbuf_cluster:          2048,   4840,     509,       3,   17874,194660,   2
mbuf_jumbo_page:       4096,   2419,       0,       2,   10659,   0,   0
mbuf_jumbo_9k:         9216,    716,       0,       0,       0,   0,   0
mbuf_jumbo_16k:       16384,    403,       0,       0,       0,   0,   0
mbuf_ext_refcnt:          4,      0,       0,       0,       0,   0,   0

256 Bucket:            1024,      0,      27,      45,   56839,5856,   0
vmem btag:               28,      0,    6648,    1848,   68924,  58,   0

I ran netstat -s and can post that here if it's OK for something that big
or if someone wants something specific from that.

In addition, what can I do to see these drops without having to wait till
the next day for the report? I know I can do netstat -i but that contains
drops for the current day.