🗒️ Parham Notes

Network Namespace

Nov 20, 20242 min read

I want to experiment with Network Namespaces on Linux. First enable routing:

sysctl -w net.ipv4.ip_forward=1

Then create a network namespace named net1:

sudo ip netns add net1

Create veth with two ends veth0 and veth1, and put veth1 into net1 namespace:

sudo ip link add veth0 type veth peer name veth1
 
sudo ip link set veth1 netns net1

Set IP address for veth1 and bring it up:

sudo ip -n net1 addr add 192.168.1.101/24 dev veth1
sudo ip -n net1 link set dev veth1 up
 
sudo ip -n net1 link set lo up

Info

The -n option is short for ip netns exec

sudo ip -n net1 addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host proto kernel_lo
       valid_lft forever preferred_lft forever
6: veth1@if7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 8a:c4:62:3e:2d:23 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 192.168.1.101/24 scope global veth1
       valid_lft forever preferred_lft forever
    inet6 fe80::88c4:62ff:fe3e:2d23/64 scope link proto kernel_ll
       valid_lft forever preferred_lft forever

Then set IP address for veth0 (which is attached to the root namespace) and bring it up:

sudo ip addr add 192.168.1.100/24 dev veth1
sudo ip link set dev veth0 up

Then you can ping the other end and also ping IP addresses that are accessible on the root namespace.

# ping the other side
sudo ip netns exec net1 ping 192.168.1.100
# ping an address that is accessible from the other side (?)
# no, it is not going to work, because the destination have no idea about 192.168.1.x
# range. SNAT (source NAT) is the answer!
sudo ip netns exec net1 ping 192.168.73.1

Let’s do it with iptables:

sudo iptables -A FORWARD -j ACCEPT
sudo iptables -t nat -s 192.168.1.0/24 -A POSTROUTING -j MASQUERADE
Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
MASQUERADE  all  --  10.254.1.0/24        anywhere
MASQUERADE  all  --  192.168.1.0/24       anywhere

sudo ip netns exec net1 mtr -rn 192.168.73.1
Start: 2024-11-12T20:10:32+0000
HOST: death-star                  Loss%   Snt   Last   Avg  Best  Wrst StDev
  1.|-- 192.168.1.100              0.0%    10    0.0   0.1   0.0   0.1   0.0
  2.|-- 192.168.73.1               0.0%    10    1.2   1.5   1.0   3.6   0.8

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