Sets up IP subnets over a single Ethernet broadcast domain formed by a Linux bridge.

net_lab_l3_to_l2_mapping.sh

#!/usr/bin/env bash

set -euo pipefail

create_bridge() {
    local nsname="$1"
    local ifname="$2"

    echo "Creating bridge ${nsname}/${ifname}"

    ip netns add ${nsname}
    ip netns exec ${nsname} ip link set lo up
    ip netns exec ${nsname} ip link add ${ifname} type bridge
    ip netns exec ${nsname} ip link set ${ifname} up
}

create_end_host() {
    local host_nsname="$1"
    local peer1_ifname="$2a"
    local peer2_ifname="$2b"
    local peer1_ifaddr="$3"
    local bridge_nsname="$4"
    local bridge_ifname="$5"

    echo "Creating end host ${host_nsname} ${peer1_ifaddr} connected to ${bridge_nsname}/${bridge_ifname} bridge"

    # Create end host network namespace.
    ip netns add ${host_nsname}
    ip netns exec ${host_nsname} ip link set lo up

    # Create a veth pair connecting end host and bridge namespaces.
    ip link add ${peer1_ifname} netns ${host_nsname} type veth peer \
                ${peer2_ifname} netns ${bridge_nsname}
    ip netns exec ${host_nsname} ip link set ${peer1_ifname} up
    ip netns exec ${bridge_nsname} ip link set ${peer2_ifname} up

    # Setting host's IP address.
    ip netns exec ${host_nsname} ip addr add ${peer1_ifaddr} dev ${peer1_ifname}

    # Attach peer2 interface to the bridge.
    ip netns exec ${bridge_nsname} ip link set ${peer2_ifname} master ${bridge_ifname}
}


# ---=== Scenario 1: 1:1 mapping ===---

setup__one_to_one_mapping() {
    create_bridge netns_br0 br0

    create_end_host netns_veth0 veth0 '192.168.0.5/24' netns_br0 br0
    create_end_host netns_veth1 veth1 '192.168.0.6/24' netns_br0 br0
    create_end_host netns_veth2 veth2 '192.168.0.7/24' netns_br0 br0
}

teardown__one_to_one_mapping() {
    ip netns delete netns_br0
    ip netns delete netns_veth0
    ip netns delete netns_veth1
    ip netns delete netns_veth2
}

# ---=== Scenario 2: 1:N mapping ===---

setup__one_to_many_mapping() {
    create_bridge netns_br0 br0

    # Subnet 1
    create_end_host netns_veth0 veth0 192.168.0.5/24 netns_br0 br0
    create_end_host netns_veth1 veth1 192.168.0.6/24 netns_br0 br0
    create_end_host netns_veth2 veth2 192.168.0.7/24 netns_br0 br0

    # Subnet 2
    create_end_host netns_veth3 veth3 192.168.1.5/24 netns_br0 br0
    create_end_host netns_veth4 veth4 192.168.1.6/24 netns_br0 br0
    create_end_host netns_veth5 veth5 192.168.1.7/24 netns_br0 br0
}

teardown__one_to_many_mapping() {
    ip netns delete netns_br0
    ip netns delete netns_veth0
    ip netns delete netns_veth1
    ip netns delete netns_veth2
    ip netns delete netns_veth3
    ip netns delete netns_veth4
    ip netns delete netns_veth5
}