Discussion between VaTo and Barmar

Feeds

21:33

Q: I can't ping to a local IP of server A from server B creating a static route.

I’m trying to create a static route between two servers, server A and server B, I created the static route from server B to server A so I could ping to a docker container in server A. Server A details: 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN link/loopback 00:0...

Barmar

Did you add a route on server A so it knows how to reply?

VaTo

I didn't add any route on server A. Could you please explain more on what you are saying? Thank you!

Barmar

Communication is a two-way problem. Just because B knows the route to A, it doesn't mean that A knows the route to B. So A can't reply to the pings.

VaTo

Are you saying that I need to add a new route from A to B or open ports in the firewall?

Barmar

You need a route from A to B. And you have to allow ICMP through the firewall (there are no ports for ICMP).

VaTo

21:33

I did this on my server A> sudo iptables -A INPUT -p icmp -i eth0 -j ACCEPT and still is not getting any response back when pinging.

Barmar

Did you add the route? Or does its default route point to the appropriate router already?

VaTo

You mean the route I already created in server B? Yes it's already there.

Barmar

No, the route in A that I keep asking about. Ping is 2 way. B sends a message to A, then A has to send a response to B. If A doesn't have a route to B, it can't send the response.

VaTo

Hello

Barmar

VaTo

21:33

I hope you don't mind moving this discussion here

Barmar

no problem

VaTo

and thank you for your help by the way

so now I'm thinking in how I can add the route in server A to Server B, I just thought I had to do it in only one way.

Barmar

The same way you added the route in B.

VaTo

ok let me check

Barmar

ip route add 172.31.0.0/24 via 172.17.x.x dev eth0

where 172.17.x.x is the address of the router that connects the two networks.

VaTo

21:36

the router? that would be the same ip as Server B

so same ip where I'm executing this command

Barmar

Ahh, I didn't look at your details close enough.

So 172.17 and 172.31 aren't really different networks, one of them is a virtual network in the docker container

VaTo

yes

it's a local ip to the server A

and I'm trying to see that IP from the server B, but Server A and server B are on the same network

Barmar

Maybe this is a docker issue, I'm not familiar with it.

VaTo

well, I took docker as an example

I don't really care about that

I'm studying to create static routes

Barmar

But if you weren't using docker you'd have real networks, so the two servers wouldn't both have 172.31 addresses.

VaTo

21:40

and that's what I thought would be a good exercise

I think then the problem is in the /24

Barmar

In the normal case each server just has an address on one network, and there's a router in between that has interfaces on each network. Docker makes it more confusing.

VaTo

how can I cover 172.x.x.x?

is that /40?

sorry, I really don't know networks that well

Barmar

That's /8

But /20 should cover both 172.31.124 and 172.31.126

VaTo

it seems like with /24 I'm only covering 172. 17.x.x

Barmar

You're talking about the route from B. That's fine.

VaTo

21:42

oh ok that's not the issue then?

Barmar

/24 covers all of 172.17.0.x

VaTo

I would like to cover 172.x.x.x

sudo ip route add 172.0.0.0/8 via 172.31.124.249 dev eth0

so this would do it?

Barmar

That's not a good idea, since that includes many public networks.

VaTo

that's ok, I would like to just test it and delete it

Barmar

The private address range is 172.16.x.x - 172.31.x.x, which is 172.16.0.0/12

But if you want to do that, it's /8

VaTo

21:48

how can I add a route?

sorry, delete

Barmar

But I really think the problem has something to do with the docker virtualization, not the route from B to A.

The Server A details you posted, are they of the real machine or the docker container?

VaTo

well, if that is the problem, do you have any other way that I can test if my setup is working?

Server A and B are VMs

Barmar

So you have virtual machines, and then you're running docker inside one of the VMs?

VaTo

the only docker container I have is the ip 172.17.x.x

correct

as you can see in the post under Server A details

Barmar

If you want to simulate a real network, create 3 VMs, no docker. Server A on 172.17, Server B on 172.31, and routerC with interfaces on both networks.

VaTo

21:53

so two interfaces for routerc?

Barmar

right

VaTo

damn, I don't think I can do that

it's pretty limited

I can't even change the ip of the VMs

but I think I understand what is going on

Barmar

Sorry, assumed you had more flexibility. I suggest you look into what's going on in docker's networking setup. I don't know enough about docker to tell you what to look for.

It might just need some kind of default gateway.

good luck with the rest

VaTo

ok thank you Bamar

Barmar

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