ip link add veth0 type veth peer name veth0 netns sip
ip link set veth0 up
ip netns exec sip ip link set veth0 up
ip addr add 172.25.136.1/24 dev veth0
ip netns exec sip ip addr add 172.25.136.2/24 dev veth0
ip route add 192.168.136.0/24 via 172.25.36.1
ip netns exec sip ip route add 192.168.100.0/24 via 172.25.36.2
iptables -A FORWARD -s 192.168.136.0/24 -d 192.168.100.0/24 -j ACCEPT
ip netns exec sip iptables -A FORWARD -s 192.168.100.0/24 -d 192.168.136.0/24 -j ACCEPT
ip netns exec sip echo 1 > /proc/sys/net/ipv4/ip_forward