Unable to connect to a service hosted on a certain port

[Anju Gopinath]

Hi,

I am unable to connect to a service hosted on a certain port.

Detailed scenario:

Node A is on cluster A

Node B is on cluster B

Node B runs a service on port 7777.

Node A is not able to connect to port 7777 .

Node A is able to connect to the same service on a different server (not in cloudlab).

[Mike Hibler]

Can you point us to the status page of an experiment where you are having
this problem?

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[Anju Gopinath]

CloudLab - Experiment Status

specifically the node clnodevm164-1

[Mike Hibler]

Try a different port. You might be running into an internal proxy service
that runs on the VM host and uses port 7777.

> cloudlab-users/7348a732-e6a7-4b29-b5ea-6cedafd8032bn%40googlegroups.com.

[Anju Gopinath]

That did not work either.

[Mike Hibler]

Need a URL for the experiment status page.

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[Anju Gopinath]

Server -----------------------------------------------

Service I am trying to connect to is on :  

CloudLab - Experiment Status

node : pcvm431-1

Client-------------------------------------------------------

Node from where I am trying to connect:

CloudLab - Experiment Status

node :  aptvm163-1

command I execute : nohup sudo ./client -c 10000000 -p 7777 172.19.31.1 & ( here, 172.19.31.1  is what I get when I execute ifconfig on pcvm431-1 (node mentioned above under 'Server'))

error  I get : 172.19.31.1(port 7777) failed 

I have checked that traceroute on the ip 172.19.31.1 gives results.

Should I add a specific path ? because telnet command from the client fails

"

anjug@node-0-0:~$ telnet 172.19.31.1 7777
Trying 172.19.31.1...
telnet: Unable to connect to remote host: No route to host

[Anju Gopinath]

Actually, traceroute also has issues:

anjug@node-0-0:~$ traceroute 172.19.31.1
traceroute to 172.19.31.1 (172.19.31.1), 30 hops max, 60 byte packets
 1  apt163.apt.emulab.net (128.110.96.163)  0.315 ms  0.262 ms  0.133 ms
 2  apt163.apt.emulab.net (128.110.96.163)  3063.397 ms !H  3063.280 ms !H  3063.166 ms !H

[Mike Hibler]

Oh, didn't know you were trying to communicate between VMs on different
clusters. That is not going to work. If you are using the default "private"
(172.16.x.x) control net addresses, those are only routed within a cluster.
You would have to use routable IPs on your VMs (see
https://www.cloudlab.us/p/PortalProfiles/routable-ip
for an example), but each cluster has a very limited number of these dynamic
IPs (less than 100 typically) so you are not going to achieve any scale.

What are you trying to achieve by doing this cross-cluster? Large scale?

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[Anju Gopinath]

We want a few VMs or even pcs to act as a server (even one VM or node will do). So, we just need very few ips (one ip address if we only get one server).

Then, we want to sent and receive TCP packets from this server VMs. (say from clients)

I want these clients to be on VMs on different clusters for geographical diversity since that is a requirement for our experiments.

I did try it with the profile you mentioned (routable-ip) and also single-pc. And I opted for routable ip in the advanced settings (when you try to instantiate the profile).

I got the same error there also - connect to port 7777 failed.

[Anju Gopinath]

So, 1 server and several clients (say 400 clients - or 400 VMs)

[Anju Gopinath]

So, earlier, I have been able to send and receive TCP packets from Cloudlab clients/VMs when connected to an external pc acting as a server.

I am facing the issue when trying to set up a server also on a Cloudlab VM/pc. 

I am not sure what I am missing. 

[Mike Hibler]

Okay, I kinda confused things there. The physical VM host machines will NAT
for their VMs (I had forgotten that). So you should be able to initiate
traffic from the VMs to a server that has a routable IP address. But you
cannot initiate a connection to a server VM with an unroutable IP address...
unless that server VM is on the same cluster. Confusing, yes.

What should work is to have your server always be a VM with a routable IP
or have it be a physical host (which do all have routable IPs). You still
won't be able to initiate connections from the server back to the clients,
it can just reply to client requests that have NATed addresses/ports.

There are still going to be ports, like 7777, that are used for VM/host
communication and won't work.

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