Validates the VLAN configuration on an interface by creating a tagged subinterface, assigning the next available address, and sending a ping to the provided gateway IP address.

vlan-check.sh

#!/usr/bin/env bash

# vlan-check.sh
#
# Validates the VLAN configuration on an interface
# by creating a tagged subinterface, assigning the
# next available address, and sending a ping to the
# provided gateway IP address.
#
# Supports Ubuntu and RHEL/CentOS. I think.
#

if [[ ( $# -ne 3 ) && ( $# -ne 4 ) ]]; then
    echo "usage: ${0} <interface> <vlan-id> <gateway-ip/cidr> [ip]" 1>&2
    echo "   ex: ${0} eth0 10 192.168.1.1/24" 1>&2
    exit 2
fi

# Bash string manipulations Cliffs Notes
#
# ${string%substring}
# Deletes shortest match of $substring from back of $string.
#
# ${string#substring}
# Deletes shortest match of $substring from front of $string.
#
# To delete the longest match, use the symbol twice, e.g.:
#
# ${string##substring}
#
# http://tldp.org/LDP/abs/html/string-manipulation.html
#
INTERFACE="$1"
VLAN="$2"
GATEWAY_IP="${3%/*}"
CIDR="/${3##*/}"
VLAN_INTERFACE_IP="$4"

ADD="vconfig add"
REMOVE="vconfig rem"

get_distro() {
    if [[ -f "/etc/redhat-release" ]]; then
        DISTRO="rhel"
    elif [[ -f "/etc/debian_version" ]]; then
        DISTRO="ubuntu"
    else
        echo "Unrecognized distribution. Aborting."
        exit 2
    fi
}

is_ubuntu() {
    [[ "$DISTRO" == "ubuntu" ]]
}

save_result() {
    "$@"
    RESULT=$?
}

clean_up() {
    if [[ -n "${VLAN_TAGGED_INTERFACE}" ]]; then
        ${REMOVE} ${VLAN_TAGGED_INTERFACE} &> /dev/null
    fi
}

trap clean_up EXIT

get_distro

# Install dependencies
if is_ubuntu; then
    apt-get update > /dev/null
    apt-get install -qy vlan > /dev/null
else
    yum install -q -y vconfig > /dev/null
fi

modprobe 8021q

# Create tagged subinterface
${ADD} ${INTERFACE} ${VLAN}
VLAN_TAGGED_INTERFACE="${INTERFACE}.${VLAN}"
ifconfig ${VLAN_TAGGED_INTERFACE} up

if [[ -z "$VLAN_INTERFACE_IP" ]]; then
    # Find IP address by incrementing the last octect of the
    # gateway's IP address. It's ghetto but it works.
    FIRST_THREE_OCTETS="${GATEWAY_IP%.*}"
    LAST_OCTET=$((${GATEWAY_IP##*.} + 1))

    while ping -c 1 ${FIRST_THREE_OCTETS}.${LAST_OCTET} > /dev/null; do
        LAST_OCTET=$((LAST_OCTET + 1))
    done

    VLAN_INTERFACE_IP="${FIRST_THREE_OCTETS}.${LAST_OCTET}"
fi

ip a a ${VLAN_INTERFACE_IP}${CIDR} dev ${VLAN_TAGGED_INTERFACE}

save_result ping -c 1 -I ${VLAN_TAGGED_INTERFACE} ${GATEWAY_IP}

if [[ ${RESULT} -eq 0 ]]; then
    echo -e "\e[1;32mSUCCESS\e[0m"
else
    echo -e "\e[1;31mFAILURE\e[0m"
fi

exit ${RESULT}