Re: [gentoo-user] iproute2 reference

[Grant Taylor]

It helps if I actually add the foot note.

On 06/10/2018 10:38 AM, Grant Taylor wrote:
> I will say that you'll likely need other systems [1] to test things like
> tunnels to / between.

[1] You can easily have one machine be multiple systems via Network 
Namespaces.

I routinely use Network Namespaces to mess with networking in my 
virtualization lab.  Think of Network Namespaces as micro TCP/IP stacks 
in the Linux kernel.  Each can be configured completely independent of 
the others.

I was using Network Namespaces about 12 hours ago to test what I 
determined was a bug in VirtualBox.  (KVM didn't exhibit the same behavior.)

I used the "ip" command to create a pair of vEth (virtual Ethernet) links:

    ip link add veth0 type veth peer name veth1
    ip link add veth2 type veth peer name veth3

I then created a new Network Namespace:

    ip netns add myNetNS

Then I moved two of the vEth interfaces to the vEth links into myNetNS.

    ip link set veth1 netns myNetNS
    ip link set veth3 netns myNetNS

Then I brought all the interfaces up:

    ip link set veth0 up
    ip link set veth2 up
    ip netns exec myNetNS ip link set veth1 up
    ip netns exec myNetNS ip link set veth3 up

Then I bound IPs to three of the vEth interfaces:

    ip addr add 192.0.2.1/24 dev veth0
    ip netns exec myNetNS ip addr add 192.0.2.254/24 dev veth1
    ip netns exec myNetNS ip addr add 198.51.100.254/24 dev veth3

Then I added a route to my workstation (main / default / nameless NetNS) 
to point to the remote 198.51.100.0/24 network:

    ip route add 198.51.100.0/24 via 192.0.2.254

That gave me what I needed to continue troubleshooting my VirtualBox 
issue.  I was able to have both VBox and KVM glom onto the veth2 
interface and put the guest at 198.51.100.1/24 IP address using 
198.51.100.254 as it's default gateway.

This meant that I had a micro routed connection from my workstation 
(main / default / nameless NetNS) to the VM that I was testing.

I do things like this weekly.  Almost all of the configuration uses the 
"ip" command.  IMHO the biggest issue is that you have to understand 
what you want to do and then translate it to the proper ip commands to 
do it.  You need that high level blueprint (if you will) so that you can 
then implement it with the "ip" command.  This is why you need at least 
a basic understanding of networking to fully take advantage of the "ip" 
command.



-- 
Grant. . . .
unix || die