#!/bin/bash

# https://ixnfo.com/en/snmp-oid-and-mib-for-interfaces.html
# https://oidref.com/1.3.6.1.2.1.2.2.1
# https://bestmonitoringtools.com/mibdb/mibdb_search.php?mib=IF-MIB

RESULTS=(OK WARNING CRITICAL UNKNOWN)

readonly MIB_IFOPERSTATUS="1.3.6.1.2.1.2.2.1.8"
readonly MIB_ALIAS="1.3.6.1.2.1.31.1.1.1.18"
readonly MIB_NAME="1.3.6.1.2.1.31.1.1.1.1"
readonly MIB_IN="1.3.6.1.2.1.31.1.1.1.6"
readonly MIB_OUT="1.3.6.1.2.1.31.1.1.1.10"
readonly MIB_ERR_IN="1.3.6.1.2.1.2.2.1.14"
readonly MIB_ERR_OUT="1.3.6.1.2.1.2.2.1.20"

perror() {
	echo "$@"
} >&2

fail() {
	local RET=$1
	shift
	perror "$@"
	exit $RET
}

result() {
	local RET=$1
	shift
	echo -n "SNMP IF ${RESULTS[$RET]}: $@"
	perfdata
	exit $RET
}

walk() {
	snmpwalk $AUTH "$HOSTNAME" "$1"
	return $?
}

extract_val()  {
	sed -n 's/.*=\(.*\)/\1/p' | sed -n 's/.*:\s*\(.*\)/\1/p'  | tr -d "\"'"
}

perfdata() {
	[ $GENPERFDATA -eq 0 ] && return

	echo -n "| "
	echo -n "in=$INOCTETS "
	echo -n "out=$OUTOCTETS "
	echo -n "in_err=$INERRORS "
	echo -n "out_err=$OUTERRORS "
	echo
}

GENPERFDATA=0

while getopts ":H:c:i:u:p:" opt; do
	case $opt in
		H)
			HOSTNAME="$OPTARG"
			;;
		c)
			COMMUNITY="$OPTARG"
			;;
		i)
			INTERFACE="$OPTARG"
			;;
		u)
			SNMP_USER="$OPTARG"
			;;
		p)
			SNMP_PW="$OPTARG"
			;;
		:)
			fail 3 "$OPTARG requires Argument."
			;;
		*)
			fail 3 "Invalid option $OPTARG"
	esac
done

AUTH=""
if [ -n "$COMMUNITY" ]; then
	AUTH="-c $COMMUNITY -v 2c"
elif [ -n "$SNMP_USER" ] && [ -n "$SNMP_PW" ]; then
	AUTH="-v 3 -u $SNMP_USER -A $SNMP_PW -l authNoPriv"
else
	result 3 "No or insufficient authentication info provided"
fi

SNMPWALK_RESULT=$(walk "$MIB_IFOPERSTATUS.$INTERFACE"; exit $?)
RET=$?

[ $RET -ne 0 ] && result 3 "snmpwalk failed with code $RET: $SNMPWALK_RESULT"
[ -z "$SNMPWALK_RESULT" ] && result 2 "No matching entry found."

GENPERFDATA=1

NAME=$(walk "$MIB_NAME.$INTERFACE" | extract_val)
ALIAS=$(walk "$MIB_ALIAS.$INTERFACE" | extract_val)

COMPLETE_NAME="$NAME"
if [ -n "$ALIAS" ]; then COMPLETE_NAME+=" ($ALIAS)"; fi

INOCTETS=$(walk "$MIB_IN.$INTERFACE" | extract_val)
OUTOCTETS=$(walk "$MIB_OUT.$INTERFACE" | extract_val)

INERRORS=$(walk "$MIB_ERR_IN.$INTERFACE" | extract_val)
OUTERRORS=$(walk "$MIB_ERR_OUT.$INTERFACE" | extract_val)

extract_val <<< "$SNMPWALK_RESULT" | grep "up\|1" > /dev/null && result 0 "$COMPLETE_NAME is up."

result 2 "$COMPLETE_NAME $INTERFACE is not up: $SNMPWALK_RESULT"