I have an application that is very simple. It sends out UDP packets to a client somewhere else on the network.
The host computer is 192.168.11.66 (Windows 10), the client device is 192.168.11.65 (proprietary device).
The host pc cannot see the client device, however I know that it is on and listening to traffic. When I send UDP packets from the host, I use Wireshark and I do not see the packets being sent out. Instead I see messages from ARP trying to locate the client. I assume because ARP is unsuccessful, the host cancels the sending of the packets.
If I change the destination address of the packets to a broadcast address, all of the packets get sent and I see everything on Wireshark. I need to be able to specify the IP address of the client and have Windows send the packets regardless of whether or not it thinks the client device is on the network or not. The client device looks for UDP traffic specifically addressed to itself and the client device has no way of making itself visible on the network.
Does anyone know how to work around this?
Thank you #Remy: instead to create your own ARP record manually. – Remy Lebeau
I did not realize that I could create manual entries in the ARP. I need to read more about ARP. Adding a manual entry solved my issue. I found that you could do it using ASP -s, or add neighbor using NETSH .
Thanks!
I'm using BOOST-ASIO for a simple echo client-server (there is a separate link for the client and server). When I try to run the server I use this async_tcp_echo_server 4000. For the client I use blocking_tcp_echo_client #.#.#.# 4000 (with #.#.#.# as the ip address). I'm on XP-SP3 with my computer connected to my wireless dsl modem using a usb card. After a few seconds on the client side I get this error:
Exception: connect: A connection attempt failed because the connected party did
not properly respond after a period of time, or established connection failed be
cause connected host has failed to respond
Any ideas what it could be? I turned off my firewall including the windows firewall and still I get no response. Could my port be in the incorrect range? Do I need to include a computer name to specify the machine on the network( there are other machines on the network sometimes active)? I did try running this on another computer directly connected to the dsl modem and same issue. I did ping my address and that did work for 4/4 packets.
It could be a variety of issues. Thus, it can be worthwhile to use lower level networking tools, such as netcat to serve a port on the server, and try connecting with netcat from the client side. This can help simplify the problem by removing any potential problems introduced by an application's network programming code. If the problem is identified as being a network issue, then there are a few things to check:
Verify firewall exceptions on the server.
Verify firewall exceptions in the server's network gateway.
If the server and client are on different networks, with the client trying to connect to the server's external IP, then verify that the server's gateway knows what traffic to route to the server. This may require setting up rules, such as port forwarding, in the routing device.
If the server and client are on the same network, but the client is trying to connect to the server through the network's external IP, then verify that the gateway supports looping back internal traffic destined to the external IP.
Use a network analyzer tool, such as Wireshark, to verify that the time to live field in the packets is high enough that it will not be discarded.
you could try
$ telnet server-ip 4000
from your client and see if it is possible to establish the tcp connection.
I am working on a project that involves a usb device, through which we will receive ip packets from a remote pc. We assign the remote pc its IP Address. I have been experimenting with sending raw ip packets via several methods:
1 - raw sockets: ping works fine, problems sending tcp
2 - tun/tap W32: I managed to get this working enough to send pings out and get pings back to the phy ethernet device, but could not read them using ReadFile(...) on the driver guid.
3 - winpcap: ping works, out going tcp shows up on wireshark(so I assume it is leaving the pc), but i never get an ack to my syn. Im also worried that if I did get an ack the windows TCP stack would send a rst.
Our goal is to be a transparent pass through from the client pc to the network.
Client <-wrapped ip packet-> [device] <-wrapped ip packet-> WinPC <- IP -> IpNetwork
Its possible that im going about this wrong, seems like this should be easier.
I realize that windows is prob not the ideal OS for this, however I have no control over the OS.
thanks in advance
Fixed my issue with TCP Syn packets not getting acked, turns out I forgot to include the pseudo-header when calculating the TCP header checksum. Now it looks like the tcp handshake completes, so im calling this problem solved. If anyone feels like recomending a better way to accomplish this, feel free to reply. For now looks like we will use the winpcap method.
Update:
For this to work without windows constantly RST'ing tcp connections, you have to enable internet connection sharing(ICS) on the adapter you are sending packets out of. Other than that this ended up working for us.
I'm trying to see the results of an incoming ping on a target windows machine. This is needed to verify that the ping, which is running in a background thread, is being sent from the originator.
I have tried netstat to no avail. Are there any other approaches I could try?
Thanks.
Ping is an ICMP packet and doesn't create a TCP connection (hence you won't see it in netstat). On Linux, I'd add a rule to the firewall.
The most simple solution for your case might be to open a connection and close it. That will add it to the output of netstat with WAIT_CLOSE.
As Aaron Digulla already noted, ping is ICMP. This also means the originator even less trustable then with TCP; there's no SYN/ACK handshake. You just get an IP packet on your host, and you have to trust the header fields. Anyone can spoof those header fields, with almost no restrictions (It might be a bit challenging to get an IP claiming to come from 127.0.0.1 past a router)
Therefore, ICMP is not suitabel for verification tasks. You need a challenge/response protocol. TCP works reasoanbly well as long as you can trust the network but not necessarily all hosts on it (a reasonable assumption for the Internet. Not strong enough for financial transactions, which is why they use SSL)
I often run into problems where I can't get something to connect to something else. I usually forget to check something obvious. Can you help with:
A tip/technique for diagnosing a connection issue
The name of a tool or application that can help (and the situation in which it's useful)
I know the question is a little non-specific, but hopefully the answers can form a useful starting point for anybody who's stuck trying to get computers/programs talking to each other.
Please can you give one answer per answer so the best ones can be voted up.
Simple checks to run when debugging network problems:
Has each machine got an IP address, Go to command prompt and run ipconfig. Key things to check here are the interfaces and ensuring the appropriate ones have IP addresses.
Check both machines IP addresses are in the same range and subnet if you are running it on an internal or Virtual network.
Try pinging each machine from the other to see if they can communicate with each other. Note that some firewalls will block ping requests.
If Pinging fails then check to see if firewalls are active. If the communication is within a 'safe' internal network then try disabling the firewalls and re-pinging.
If the connections are over a wireless network then check signal strength.
If pinging fails and you are connecting through several networks then try running a tracert to see at which will may show you where on the network the connection is failing.
If you are able to ping but not connect then check firewall settings and network connection settings. Windows 2000+ has the capability of setting port an ip access on a connection properties.
Try drawing a network diagram of the connections to help in visualising the problem.
If you are connecting through routers, firewalls and loadbalancers then check that all devices are not tied to any specific ip addresses and that the IP address redirection (if in place) is correct. Also check any NAT logs to see if connections are being received and properly re-directed.
Wireshark
Latest versions of ProcMon
netstat
Wireshark www.wireshark.org
Wireshark is a network protocol analyzer for Unix and Windows.
Features:
Deep inspection of hundreds of protocols, with more being added all the time
Live capture and offline analysis
Standard three-pane packet browser
Multi-platform: Runs on Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and many others
Captured network data can be browsed via a GUI, or via the TTY-mode TShark utility
The most powerful display filters in the industry
Rich VoIP analysis
Read/write many different capture file formats: tcpdump (libpcap), Catapult DCT2000, Cisco Secure IDS iplog, Microsoft Network Monitor, Network General Sniffer® (compressed and uncompressed), Sniffer® Pro, and NetXray®, Network Instruments Observer, Novell LANalyzer, RADCOM WAN/LAN Analyzer, Shomiti/Finisar Surveyor, Tektronix K12xx, Visual Networks Visual UpTime, WildPackets EtherPeek/TokenPeek/AiroPeek, and many others
Capture files compressed with gzip can be decompressed on the fly
Live data can be read from Ethernet, IEEE 802.11, PPP/HDLC, ATM, Bluetooth, USB, Token Ring, Frame Relay, FDDI, and others (depending on your platfrom)
Decryption support for many protocols, including IPsec, ISAKMP, Kerberos, SNMPv3, SSL/TLS, WEP, and WPA/WPA2
Coloring rules can be applied to the packet list for quick, intuitive analysis
Output can be exported to XML, PostScript®, CSV, or plain text.
work the OSI model from the bottom up
Physical (Do you have a network adapter/connection)
Link layer (arp, ethernet port blocked by network team (I've seen this where locked down environments see two MAC addresses coming from one workstation port and shut down the port)
Network layer (ipconfig, tracert, ping,)
Do you have a network address (DHCP, fixed)
Are you on a proper subnet/have routing between subnets
Is something in the middle blocking you
firewalls, routing tables
When in doubt, check to see if the windows firewall is messing with your communications. 8 times out of 10, it's at fault.
Using tracert is a good start to see how far along the chain you are getting.
For virtual machines it's usally a good idea to make sure you have the loopback adapter set correctly in the Host os.
Most frequently used tool is the ping. It can be used both to test your connection and the availability of a target
Second tool is the tracert if you want to see where the packets get lost.
For more advanced debugging I use the following tools: nmap, wireshark, etc.
Windows has a netstat utility which is pretty similar to the Unix netstat and can do a number of different things that might help you solve network issues.
Random example:
netstat -r displays routing information
netstat /? for usage information
Since you said you're using 2 virtual machines I would hazard a guess that both machines are setup in a NAT configuration (rather than a unique network device) -- In the NAT configuration, neither machine would (typically) be able to ping the other.
If you're familiar with the command line, you can try the "netstat" command.
You can also try "arp -a" to list all the IP/MAC addresses known to your PC.
The "tracert [ip address]" command will show you how many gateways/routers your packets jump through on their way to their destination. (This is probably not helpful if both machines are on the same network, though.)
And don't forget to check your Windows firewall settings.
Otherwise, if you want to get down and dirty, you can try the packet sniffer known as Wireshark: http://www.wireshark.org/ (aka. Ethereal)
Pull the network cable out
If you can get some communications to a device (eg a ping), but can't get your program to talk to a service on the computer. Then, try pulling the network cable out and see if the ping stops. This will verify you're communicating with the computer you really think you are.
On windows i user PortQueryUI : http://www.microsoft.com/en-us/download/details.aspx?id=24009
DNS activity: Portable DNS Cache and Firewall;
General network activity: Wireshark, Network Monitor;
Windows utilities: ping, netstat, nslookup.
You need to be use the process of elimination, for example if you can ping the ip address but not the hostname then there's DNS issues. If you can ping the system but not connect to a share etc.
DNS out of sync
If you're using a virtual machine and you perform a roll-back on it, then it could become out of sync with the DNS (Domain name server). Try to remove and re-add the machine to the domain, or if you've got access to the DNS machine, then get it to flush its cache.