#2886 Overflow causes malfunction when reporting HCInOctets on interface.

[Hans-Henrik Stærfeldt]

Overflow causes malfunction when reporting transferred bytes on interface.
We are transferring a lot of data to a host, and we want to use SNMP to monitor it as well.

OS: Ubuntu 18.04 (64 bit)

>uname -a
Linux loxodonta 4.15.0-33-generic #36-Ubuntu SMP Wed Aug 15 16:00:05 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

/etc/snmp/snmpd.conf:

agentAddress  udp:127.0.0.1:161
rocommunity  mycomunity 10.0.0.0/8
syslocation "Here"
syscontact "me <me@example.com>"

>snmpd --version
NET-SNMP version:  5.7.3
Web:               http://www.net-snmp.org/
Email:             net-snmp-coders@lists.sourceforge.net

Reproduce:
Install and set up snmpd
service start snmpd (works)
transfer several terrabytes data over the net

Observed problem. SNMP times out with no response

>snmpwalk -c mycomunity -v 2c 127.0.0.1
Timeout: No Response from 127.0.0.1

root@loxodonta:~# service snmpd status
● snmpd.service - Simple Network Management Protocol (SNMP) Daemon.
   Loaded: loaded (/lib/systemd/system/snmpd.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2018-09-18 11:06:27 UTC; 55min ago
  Process: 28499 ExecStartPre=/bin/mkdir -p /var/run/agentx (code=exited, status=0/SUCCESS)
 Main PID: 28507 (snmpd)
    Tasks: 1 (limit: 4915)
   CGroup: /system.slice/snmpd.service
           └─28507 /usr/sbin/snmpd -Lsd -Lf /dev/null -u Debian-snmp -g Debian-snmp -I -smux mteTrigger mteTriggerConf -f

Sep 18 11:06:27 loxodonta systemd[1]: Starting Simple Network Management Protocol (SNMP) Daemon....
Sep 18 11:06:27 loxodonta systemd[1]: Started Simple Network Management Protocol (SNMP) Daemon..
Sep 18 11:06:27 loxodonta snmpd[28507]: NET-SNMP version 5.7.3
Sep 18 11:08:27 loxodonta snmpd[28507]: Error expanding HCInOctets to 64bits in ipSystemStatsTable.ipv4
root@loxodonta:~# ifconfig
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.4.2.8  netmask 255.255.255.0  broadcast 10.4.2.255
        inet6 fe80::d294:66ff:fe7a:c5f5  prefixlen 64  scopeid 0x20<link>
        ether d0:94:66:7a:c5:f5  txqueuelen 1000  (Ethernet)
        RX packets 25497378464  bytes 38533039501515 (38.5 TB)
        RX errors 0  dropped 164903  overruns 0  frame 0
        TX packets 6420986229  bytes 746780703952 (746.7 GB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 17  

eno2: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether d0:94:66:7a:c5:f6  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 18  

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 19351193  bytes 2175412969 (2.1 GB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 19351193  bytes 2175412969 (2.1 GB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Possible problem:
Network Interface has transferred 38533039501515 bytes (it really has) and its too big a number.