Layer: SNMP & Protocols

The plumbing under monitoring: SNMP versions, MIBs, OIDs, counters and traps, plus syslog, ICMP, flow export and time sync.

SNMP ports 161 and 162: firewall rules that let polling and traps through

Which SNMP port listens where, which way the packets flow, and the exact iptables, nftables, ufw and firewalld rules for polling and traps.

October 26, 2026Gail Rutherford

Netmask, wildcard, total and usable addresses for every prefix from /8 to /32, plus the block-size trick, /31 and /32 links and the private ranges.

October 23, 2026Gail Rutherford

SNMP says the link is full. Flow data says who filled it. NetFlow, IPFIX and sFlow compared, plus the sampling math that keeps you honest.

October 21, 2026Gail Rutherford

The snmpwalk lines for v2c and v3 you will actually type, what each part of the output means, and the errors that stop a walk cold.

One rsyslog server, one folder per device, logs you can grep at 2 a.m. Formats, severities, device settings, rotation and clocks for a small network.

November 12, 2024Gail Rutherford

What ifHCInOctets, ifInErrors and ifOutDiscards really count, how a rate is computed, and the worked math behind a graph that lies after a wrap.

January 16, 2024Gail Rutherford

Community strings, USM users, GETBULK and 64-bit counters: what each SNMP version changed, and when v2c is still a fair choice.