Windows Server 2008 R2, fully patched and updated.
I have 4 static IPs on a dedicated server. I will refer to them as follows:
x.x.x.x
y.y.y.y
z.z.z.z
a.a.a.a
x.x.x.x is the default external and internal IP address of the server.
All external IPs are the same as the internal IPs, all running on the same NIC.
x.x.x.x and y.y.y.y were running on port 80 for HTTP through IIS, with different host headers handling the destinations. That worked perfectly.
I recently added two new IP addresses, z.z.z.z and a.a.a.a for a different application that uses two ports, but we want external port 80 traffic to translate to the internal ports it is using.
We want incoming traffic to work as follows:
Incoming traffic on x.x.x.x:80 map to x.x.x.x:8080
Incoming traffic on y.y.y.y:80 map to y.y.y.y:8080
Incoming traffic on z.z.z.z:80 map to y.y.y.y:8088
Incoming traffic on a.a.a.a:80 map to y.y.y.y:8089
We changed the binding in IIS to only listen on the specific IPs and internal ports so that port 80 was only being listened to by netsh portproxy.
We have been able to accomplish this with 4 separate netsh portproxy rules and everything works great. All traffic to the two HTTP IPs works fine, and the traffic for the other two IPs to the other two internal ports get routed properly as well.
The problem is that everything works as expected, but occasionally something hangs, usually around 4 PM EST, and the websites are no longer available. There are no application pool or website crashes. Just ports no longer routing.
When it hangs the easiest fix is to run "portproxy reset" and re-create the portproxy rules through a batch file and everything works again.
I guess my question is if there is some kind of idle timeout built into netsh portproxy or possibly some type of buffer overrun protection.
Not a single log shows any faults.
The application pools in IIS were adjusted to recycle at shorter intervals (30 minutes) to prevent any long running worker processes in case that was the issue. Same result.
I can easily create a Windows service to check the port status at a very short interval and reset the specific portproxy rule, but this is not ideal, as there is still the potential for packet loss and unavailability of the services (even if for only a few seconds) requiring the HTTP requests to be re-sent.
Again, I should reiterate that everything works great until a certain point in the day, and that this has absolutely nothing to do with the Windows Firewall, as we get the exact same results with it on or off. There are no apparent DDoS or other types of attacks either. All separate websites and other applications still run on their internal ports when the portproxy hangs (i.e. accessing http://example.com:8080 still works without issue).
The point of failure is the netsh portproxy.
Has anyone experienced similar issues? I am considering adding a Fortinet hardware firewall that has this functionality built in, but I am wondering if that will handle it any better than what is already in place.
Related
Followed this tutorial to setup two ec2 instances: 12 . Creation of two EC2 instances and how to establish ping communication - YouTube
The only difference is I used a linux image.
I setup a simple python http server on a machine (on port 8000). But I cannot access this from my other machine; whenever I curl, the program kind of waits. (It might eventually timeout but I wasn't patient enough to witness that).
However, the workaround, I figured, was that you have to add a port rule via the security group. I do not like this option since it means that that port (for the machine that hosts the web server) can be accessed via the internet.
I was looking for an experience similar to what people usually have at home with their routers; machines connected to the same home router can reach out to other machines on any port (provided the destination machine has some service hosted on that port).
What is the solution to achieve something like this when working with ec2?
The instance is open to the internet because you are allowing access from '0.0.0.0/0' (anywhere) in the inbound rule of the security group.
If you want to the communication to be allowed only between the instances and not from the public internet. You can achieve that by assigning the same security group to both the instances and modifying the inbound rule in the security group to allow all traffic or ICMP traffic sourced from security group itself.
You can read more about it here:
AWS Reference
I am attempting to spin up an application that listens on a port and responds to HTTP requests. I am on a Windows 8 machine connecting through a Netgear router that provides port forwarding. I have:
modified my DNS zone file of one of my domains to point to the IP address that is assigned to my cable modem
Added a port-forwarding rule to my router that sends requests to port 8080 to port 8081 on my computer
Opened port 8081 on my Windows Firewall
Executed netsh http add urlact http://+:8081/ user=Everyone listen=yes as administrator
Started up my app which uses the simple webserver solution found at http://codehosting.net/blog/BlogEngine/post/Simple-C-Web-Server.aspx which uses an HttpListener object with a prefix of http://+:8081/.
From any machine on my local network, I can browse to http://home.example.com:8080/blah/blah and everything works great. Whenever I attempt the same URL from a machine connected elsewhere on the Internet, the connection times out. I have tried using the IP address instead the domain name, and have tried disabling my Windows Firewall (temporarily), still with no luck.
I'm sure this is more of a network setup issue than a code issue, but I thought I would ask anyway to see if there is anything I can do. Sorry for the spaces in the urls above. This is my first post to SO, and I apparently don't have enough of a reputation to post more than a single link.
By "elsewhere on the Internet", I am assuming you are attempting to access it from a different ISP.
The thing about some ISPs is that unless you are paying for a "business class" connection, they will do all sorts of tricks to ensure that you remain a "consumer". What you need is an unNATed static IP address.
By this I mean that the IP address that you may have at your home may not be accessible to the outside world because the ISP is actually NATing (or other) that address to you. This is a fairly common practice because of limited IP4 addresses. If you really want a service accessible via the WWW, I would suggest moving your product to a VPN, or at least a commodity hosting provider.
Edit: Try a VPN service like Hamachi
I need to find the port number of a server, I have the host name and the IP address.
Is this possible?
I need this as when I try to connect to this server through putty its throwing a Network error:Connection refused error, which may be because of the wrong port number
So you are looking for the port number the ssh server on that system listens on. Usually that is port 22 (well known ssh port), but you are right, this can be changed in the ssh server configuration. If so there are two possibilities yo have:
ask the administrator of the ssh server for the port number
make a network scan of the server which shows up all open ports. Note however that this can be regarded as offensive behavior and may be blocked in mid way.
But most likely you are facing another problem: some firewall blocking your requests or the ssh server not listening to request from outside at all.
And a side note: a server is a service, often listening on a port, you can interact with it typically by "speaking" a specific protocol. A system might refer to a computer running software, typically reachable via network these days. Many servers can be operated on a system. A system can be identified by its ip address. Many people confuse this and speak of a "server" when referring to such a "system" which is simply wrong and creates confusion from a technical point of view.
Based on my understanding, port numbers are just like telephone extensions. Just as a business telephone switchboard can use a main phone number and assign each employee an extension number (like x100, x101, etc.), so a computer has a main address and a set of port numbers to handle incoming and outgoing connections.
But the question is:
On what basis is a port number assigned? A process or an application?
Based on my experience with firewall, I usually open a port for a specific application. So port number should be assigned on an application's basis. But what if there're multiple instances of the same application running on a single machine. Each of the instances uses the same port number. So if a message is arrived at that port number, how could the system tell which instance should the message go?
And another question also related to port.
If a web server is setup to listen on port 80, client browser should always contact the 80 port. I am not sure if the following illustration of the communication between a web browser and the web server is correct.
Client Browser sent request to Server, the message should contain info like this:
To: < ServerAddress:80 >
From: < ClientAddress:XXX >
Server sent reponse to Client Browser like this:
To: < ClientAddress:XXX >
From: < ServerAddress:80 >
So the question is, will the server pick other port numbers for sending messages to client? Because I think a single 80 port doesn't look enough.
Add - 1 - 21:16 2010/12/19
In my above post, the word "application" represents a static program file that the system knows. Multiple instnaces of this application could be launched, which are multiple "processes"
Each client connection will be represented by a socket on the server. Sockets are uniquely represented by the combination of the following 4 pieces of information:
Peer IP address
Peer port
Local IP address
Local port
The client chooses a random port, so if there are multiple connections from one client to the same server/port, the connections will still differ by the client's port.
If there are multiple web server applications running on the same server, they will have to listen on different ports or the server will need to have multiple IP addresses.
On a computer, only one process can be listening on a specific port number. For example, if an Apache process is listening on port 80, no other application can also listen on port 80.
Apache usually pre-forks several processes, only one of those is listening on port 80. The job of that process is to hand over the processing for any connection to one of the pool of other Apache processes as quickly and efficiently as it can.
Each of many concurrent connections to port 80 is distinguished by it's source IP-address and by the source TCP port number (which the client computer chooses randomly from the set not in use).
(Edit)
I was pretty sure that webservers have one process (or thread) listening which accepts incoming connections and passes corresponding filehandles to the worker processes (or threads). EJP advises that this is not so.
Apache seems to have several different multi-processing modules that affect how it spreads the load of responding to multiple concurrent requests. For example: MPM Prefork and MPM Worker
Jeff Pozkaner wrote an overview of HTTP server design that I found interesting:
The basic operation of a web server is to accept a request and send back a response. The first web servers were probably written to do exactly that. Their users no doubt noticed very quickly that while the server was sending a response to someone else, they couldn't get their own requests serviced. There would have been long annoying pauses.
The second generation of web servers addressed this problem by forking off a child process for each request. …
A slight variant of this type of server uses "lightweight processes" or "threads" instead of full-blown Unix processes. …
The third generation of servers is called "pre-forking". Instead of starting a new subprocess for each request, they have a pool of subprocesses that they keep around and re-use. …
The fourth generation. One process only. No non-portable threads/LWPs. Sends multiple files concurrently using non-blocking I/O, calling select()/poll()/kqueue() to tell which ones are ready for more data. …
Network stack distinguishes TCP connections by triple <source IP,source port,destination port>, so knowing client address and port is enough to work correctly.
What is the application, if it is not a process? In firewalls you open ports for executables. It may be considered as an application, and it is a process when it is running.
Multiple listeners cannot listen to the same port. The same process can listen to multiple ports.
Ports are assigned to the listeners. Depending on the firewall (and its configuration) you can allow the process (executable) to listen several ports, or to create several exceptions for the same process listening to multiple ports.
I'm not sure what you mean by the difference between a "process" and an "application". Everything is just code executing on your box.
Anyway, a process/application will listen/bind to whatever port number the authors of the application have configured. By convention, many port numbers are reserved for particular types of application - that is applications which communicate using a particular protocol. So for example web servers which use HTTP typically run on port 80. SMTP servers run on port 22. HTTPS is 443 and so on.
Of course you can configure your web server (e.g apache httpd) to run on whatever port you like - but your client needs to know else it will assume port 80.
Two processes/applications may not bind to the same port. If you try to start another process/application on a port already in use you'll get an error: cannot bind to port or something to that effect.
will the server pick other port
numbers for sending messages to
client?
No. All the accepted sockets use the same server-side port number as the original listening socket. The identifying tuple mentioned above disambiguates this so as to make each connection unique.
In short: How to reliably discover a server running somewhere on a (presumably multi-segmented) local area network with zero client configuration
My client application has to locate the server application without knowing the server IP address. It has to work on a local LAN that may be split into segments with hubs or other switching devices.
I already have a working solution, but it is a bit cumbersome to get it working on multi-segment networks. It works as follows:
When the client starts up, it sends UDP broadcasts on its own network segment. If the server is running on the same segment, it works without any issues - the server responds with the appropriate messages.
If the server and client are running on networks separated by a hub / switch that won't forward UDP (the most likely case), then I have a server instance running on each segment, and they forward client requests to each other via TCP - but I need to configure this for the server instances (simple, but still a pain for tech support.) This is the main problem that I need to address. There are sites where we have hundreds of clients running on 5 or 6 separate segments.
The problems I'm facing:
1. Although my application installer enables the appropriate ports on the firewall, sometimes I come across situations where this doesn't seem to happen correctly.
2. Having to run multiple server instances (and therefore configure and maintain them) on hub/switched networks that won't forward UDP
Finally I need a solution that will work without maintenance on a minimal Windows network (XP / 2000 / Vista) that probably doesn't have Active Directory or other lookup services configured.
I don't want to tag on any runtime stuff for this - should be able to do it with plain VC++ or Delphi.
What approaches do commercial apps usually take? I know that SQL Server uses a combination of broadcast and NetBEUI calls (I may be wrong about this).
Thanks in advance.
You have a few terminology issues:
Where you say "network segment" you appear to mean "IP subnet". Devices on the same network segment can see the same IP broadcasts.
Where you say "hub/switch" you appear mean "IP router".
Where you say "won't forward UDP", the problem is actually "won't forward IP broadcasts".
Once we get past that, you have a few options:
Your servers could register themselves under a well-known name in DNS, if you have a DNS server that allows dynamic DNS updates. You should probably use a SRV record as specified in RFC2782. The clients then do a DNS lookup to find the server(s).
You could statically assign your server(s) well-known names in the organisation's DNS, perhaps with a SRV record as with the previous option.
Your servers could join an IP multicast group, if your routers support IP multicast. The clients then send their initial discovery request as a UDP packet to the (pre-ordained) multicast address.
If you have domain server, I would go with small service on it. You can connect with other services to it and use it as distribution point.
Why domain server? It is relatively easy to find it's name (DsGetDcName).
Other choices would include DHCP server, DNS server or something of that kind that needs to be filled by maintenance staff anyhow.