cheap network emulation with Linux network namespaces

iptablesnet.sh

#!/bin/bash

# emulate a 3 nodes network using Linux network namespaces
# n1 -- r0 -- n2

set -x

# cleanup
ip netns del n1
ip netns del r0
ip netns del n2
ip link del veth1
ip link del veth2
ip link del veth3
ip link del veth4

set -e

# create 3 namespaces corresponding to the three nodes
ip netns add n1
ip netns add r0
ip netns add n2

# create a veth between n1 and r0
ip link add veth1 type veth peer name veth2
ip link set veth1 netns n1
ip link set veth2 netns r0

# create a veth between r0 and n2
ip link add veth3 type veth peer name veth4
ip link set veth3 netns r0
ip link set veth4 netns n2

# configure n1
ip netns exec n1 ip link set lo up
ip netns exec n1 ip addr add 10.0.0.1/24 dev veth1
ip netns exec n1 ip link set veth1 up
ip netns exec n1 ip route add default via 10.0.0.2

# configure r0
ip netns exec r0 ip link set lo up
ip netns exec r0 ip addr add 10.0.0.2/24 dev veth2
ip netns exec r0 ip link set veth2 up
ip netns exec r0 ip addr add 10.0.1.2/24 dev veth3
ip netns exec r0 ip link set veth3 up

# configure n2
ip netns exec n2 ip link set lo up
ip netns exec n2 ip addr add 10.0.1.1/24 dev veth4
ip netns exec n2 ip link set veth4 up
ip netns exec n2 ip route add default via 10.0.1.2

# ip netns list
# ip netns exec <node name> bash

# ping from n1 to r0
ip netns exec n1 ping -c 3 10.0.0.2

# ping from r0 to n1
ip netns exec r0 ping -c 3 10.0.0.1

# ping from r0 to n2
ip netns exec r0 ping -c 3 10.0.1.1

# ping from n2 to r0
ip netns exec n2 ping -c 3 10.0.1.2

# enable forwarding on r0
echo 1 | ip netns exec r0 tee /proc/sys/net/ipv4/ip_forward

# ping from n1 to n2
ip netns exec n1 ping -c 3 10.0.1.1

The same with single subnet and bridge: https://gist.github.com/kotovalexarian/0194cb801ca4fa9ab77c9f4a2104f4ef