I am splitting an application into a tray application and a Windows Service and I want to use TCP to communicate between the two*. They will both be running on the same machine.
My question is do firewalls block TCP communication between applications running on the same machine? I want to know whether firewalls are something I need to worry about when testing.
(*note that I want to use TCP instead of named pipes for communication because the apps might one day run on separate computers but that will be far in the future)
The primary objective of the firewall is to control the incoming and the outgoing network traffic! Firewall's are designed to work on IP or PORT basis.
So yes, it is 100% capable of blocking connection on same machine.(I guess you are using Class A IP [127.x.y.x] address used mainly for loopback testing and interprocess communication on the local computer).
Some firewall are preconfigured not to block local machine connection while other are configured to block them. But either way a firewall can be configured to allow/deny such connection.
Related
I am using a Juniper firewall device that our incoming internet connection receives, then a switch that connects a bunch of servers that is connected to the firewall.
For some reason, some of the traffic between the hosts connected to the switch are showing up as sessions on the Juniper firewall. The hosts are using the same network address. I thought the traffic should be strictly going through the switch to other host, not out to the firewall and then back to the switch then the host.
I created a test environment, with a small switch, and the traffic between the hosts did not show up on the firewall sessions.
Is there anything particular to the Cisco SG200-50 that would cause traffic bound from one port to another, same network address, to be sent out to the firewall before switching the traffic to the other port?
The switch will not be looking at the layer-3 packet, it only delivers known unicasts to the port where the destination MAC address is located. It will flood unknown unicasts and broadcasts to all switch ports, including the router. To the switch, the router is just another host.
I have seen this when one or more hosts have either an incorrect mask or an incorrect gateway configured.
On the linux network socket server machine, what happens when all network ports are allocated for clients? If it happens, the connection request from clients are denied, or delayed? If that's right, is it right to think that one linux machine can serve at most the number of open ports simultaneously? (under assumption that all other resources are enough)
If that's right, is it right to think that one linux machine can serve at most the number of open ports simultaneously?
No, the port is not the limiting factor here. TCP connected socket is actually a quintuple (src_port, src_address, dest_port, dest_address, protocol).
So, for every server listening on one port, every client will be able to make whatever is set in ip_local_port_range connections using the same protocol.
However, you can work around this - if you have more IP addresses (you could use IP aliasing for this, even if you don't have more than one interface), or if your server is listening on more than one port, the number of possible connections goes up.
Resources:
http://vincent.bernat.im/en/blog/2014-tcp-time-wait-state-linux.html
I am trying to find somw Windows based tools that can help me validate TCP and UDP connection on remote machines.
My Problem (just one use case):
At work, I manage many clustered servers that I run load tests against. In order to get a rich test, I use Jmeter-Plugins which provides a Server agent that opens a TCP socket on port 4444 on a target remote machine: http://code.google.com/p/jmeter-plugins/wiki/PerfMonAgent
There are many times when I setup a new load test farm, that either the network, or the server configuration, or the ServerAgent itself can have issues and thus not allowing a Load test client to access that TCP connection.
The issue I have is that I dont know what part of the system is broken.
What I think I need:
I would like to know how I can open a TCP (not HTTP with cUrl), connection to a remote server to validate that the network allows the connection, as well as the Server firewall allows the given TCP connection to be accessed remotely.
What I have looked:
These are some of the tools I have looked at so far:
Nmap http://nmap.org
Ncat http://sourceforge.net/projects/nmap-ncat/
TCP/IP Builder http://www.drk.com.ar
Zenmap 6.01 and nmap might do the job I want, but some machines where not accessible to Zenmap when I know 100% that the server was accessible via HTTP, so that was strange.
I have looked at many tools and either they:
Dont allow remote connections
Dont seem to want to connect to a TCP socket
Or I dont understand the tools to accomplish the validation I stated above.
I would greatly appreciate all comment and suggestions to help with this re-occurring problem I face.
Mick,
Firebind.com can do what you'd like to do. Firebind is an Internet based server that can listen on any of the 65535 UDP or TCP ports. It uses a java based client to send traffic to and from the server from your machine.
Carl
www.firebind.com
If I create a c++ server/client application, the port I used to communicate does it need to be open on the router of the server and client machine
Or what other approach could I take? the client computer needs to receive information from the server but I am not able to have any ports opened because it is on a school network....
[edit]
Hmm My setup is a php page running on a server say when I press hello, the server makes a ssh connection through php and sends shell commands to the machine. The server is running off of a school server which I do have ssh access to and run all my things from there. The client computer will be my pc running off of the school wifi which is not connected to the server. The server will try to make a ssh connection to the public ip of my computer running off of the school wifi(no ports open/can ssh out but no ssh in). Will these methods you mention make this possible, in particular the connect.c since I can't run putty off of the server, and the connect.c I could call from the php.
The choice of language is highly irrelevant here.
There don't need to be ports 'open' on any router, unless your traffic must pass through it. On normal peer hosts in the same network (or subnet) there would hardly be any firewall policy, not even in schools.
Technically it is possible for the switch to block peer-2-peer traffic (meaning traffic not destined to the outgoing gateway), but that is not very usual.
Of course, if the school doesn't allow outbound (WAN) traffic on most ports, tough luck, and they're absolutely right :)
You can look at
ssh (with tunnels -L, -D and -R options, perhaps -o GatewayPorts on)
stunnel
connect.c
http-tunnel
All very readily googled
To establish a TCP/IP connection, only the server port needs to be accessible by the client. The connection is full-duplex, therefore data can flow from the client to the server and vice-versa.
If you are using UDP for your application, which is a connection-less protocol, what happens depends heavily on the firewall or router and whether it performs connection tracking for your service or not.
Unless you provide some additional information on your service and the network setup on both the client and the server side, we cannot provide more concrete information.
I have a local server written in C++ listening to inbound TCP connects using plain socket ::accept() and UDP recvfrom(). I have two problems with this that I wish to solve:
Can I programatically make Windows let me open the accept socket without it automatically being blocked by the Windows (software) firewall?
Are there any ports I can use that will allow my packets to pass through both Windows firewall and external firewall? Port 80 is often taken by things like Skype, but are there others? Will most external firewalls typically by default allow incoming UDP and TCP connects on port 80?
Thanks!
In general, network routers need Port Forwardng enabled for the listening port, and firewalls need the listening port opened. If you are using a uPNP-enabled firewall/router, then you can dynamically set up those settings programmmably via the uPNP API. But more times than not, uPNP is either disabled or unavailable, requiring manual settings by the firewll/router admin.