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• What does this UDP Packet mean ?

  - by asksuperuser

  I'm total newbie at tcp/ip and I was experimenting with Wireshark. What this mean: 1824 578.194204 xxx.xxx.xxx.xxx yyy.yyy.yyy.yyy UDP Source port: 17500 Destination port: 17500 In data I can see that my user pc name is sent (happily it's a generic name): does this mean someone is trying to hack my pc ?

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• How to know the source of certain TCP traffic on AIX

  - by A.Rashad

  We have two AIX boxes, one for production system and another for testing. both systems are running ATM machine switches, where the ATM device is connected via TCP socket. we had an issue on production system where the machine would power off or get disconnected but the netstat -na | grep <IP of machine > would still mention that the socket is up when simulated that case on the UAT environment, the problem did not happen, where the socket would terminate in 3 to 5 minutes. when sniffed on the traffic between the machine and ATM we found that no traffic takes place on production while there is some sort of heartbeat on UAT. but it is not initiated by the application. $>tcpdump | grep -v "10.2.2.71" | grep -v "HSRP" | grep "10.3.1.30" tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on en6, link-type 1, capture size 96 bytes 09:08:13.323421 IP server073.afs3-callback > 10.3.1.30.impera: . 278204201:278204202(1) ack 3307884029 win 164 09:08:13.335334 IP 10.3.1.30.impera > server073.afs3-callback: . ack 1 win 64180 09:08:23.425771 IP 10.3.1.30.impera > server073.afs3-callback: . 1:2(1) ack 1 win 64180 09:08:23.425789 IP server073.afs3-callback > 10.3.1.30.impera: . ack 2 win 65535 09:09:13.628985 IP server073.afs3-callback > 10.3.1.30.impera: . 0:1(1) ack 1 win 164 09:09:13.633900 IP 10.3.1.30.impera > server073.afs3-callback: . ack 1 win 64180 09:09:23.373634 IP 10.3.1.30.impera > server073.afs3-callback: . 1:2(1) ack 1 win 64180 09:09:23.373647 IP server073.afs3-callback > 10.3.1.30.impera: . ack 2 win 65535 while on production, that traffic is not there. we want to know where this traffic is initiated from to implement on production to sense disconnection our comms parameters are: tcp_keepcnt = 2 tcp_keepidle = 100 tcp_keepinit = 150 tcp_keepintvl = 150 tcp_finwait2 = 1200 can anyone help?

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• Too many connectons to 212.192.255.240

  - by Castor

  Recently, my Internet slowed down drastically. I downloaded a tool to see the TCP/IP connections from my Vista computer. I found out that a lot TCP/IP connections are being connected to 212.192.255.240 through SVCHost. It seems that it is trying to connect to different ports. I think that my computer is being infected with some kind of malware etc. But I am not sure how to get rid of it. I did a little bit of research on this IP but found nothing. Any suggestions are highly apprecitated.

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• How to get a service to listen on port 80 on Windows Server 2003

  - by Miky D

  I've coded a custom windows service that listens on TCP port 80 but when I try to install it on a Windows Server 2003 machine it fails to start because some other service is already listening on that port. So far I've disabled the IIS Admin service and the HTTP SSL service but no luck. When I run netstat -a -n -o | findstr 0.0:80 it gives me the process id 4 as the culprit, but when I look at the running processes that process id points to the "System" process. What can I do to get the System process to stop listening on port 80 and get my service to listen instead? P.S. I should point out that the service runs fine if I install it on my Windows XP or Windows 7 development boxes. Also, I should specify that this has nothing to do with it being a service. I've tried starting a regular application that attempts to bind to port 80 on the Windows Server 2003 with the same outcome - it fails because another application is already bound to that port.

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• Wrong DNS for just one site on development machine

  - by Patrick

  www.superyoink.de is my clients' website. I can access it from any machine except my development one. If I ping it on my development machine, I get 80.67.28.107 - this is wrong. My laptop, next to me, is able to resolve it correctly. I have tried putting correct address into hosts like so: 93.187.232.191 www.superyoink.de Still resolves to wrong address. I can enter bogus DNS server addresses so nothing works. But www.superyoink.de still resolves to 80.67.28.107. Rebooted, did ipconfig /flushdns nothing seems to work. I run 32 bit Vista. My impression is that it has stored the wrong dns resolution somewhere and is not even trying the DNS servers. But where? Help please!

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• Is there a tool to modify HTTP packet on the fly?

  - by http

  Wireshark is good, but it doesn't allow you to change the content of the packet. Is there a tool to do this job?

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• What does this TCP Packet mean ?

  - by asksuperuser

  I'm total newbie at tcp/ip and I was experimenting with Wireshark. What this mean: 1824 578.194204 xxx.xxx.xxx.xxx yyy.yyy.yyy.yyy UDP Source port: 17500 Destination port: 17500 In data I can see that my user pc name is sent (happily it's a generic name): does this mean someone is trying to hack my pc ?

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• Just one client bound to address and port: does it make a difference broadcast versus unicast in terms of overhead?

  - by chrisapotek

  Scenario: I am implementing failed over for a network node, so my idea is to make the master node listens on a broadcast ip address and port. If the master node fails, another failover node will start listening on this broadcast address (and port) and take over. Question: My concern is that I will be using a broadcast IP address just for a single node: the master. The failover node only binds if the master fails, in other words, almost never. In terms of network/traffic overhead, is it bad to talk to a single node through a broadcast address or the network somehow is smart enough to know that nobody else is listening to this broadcast address and kind of treat it as a unicast in terms of overhead? My concern is that I will be flooding my network with packets from this broadcast address even thought I am just really talking to a single node (the master). But I can't use unicast because the failover node has to be able to pick up the master stream quickly and transparently in case it fails.

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• Can I make TCP/IP session to run less than 60 seconds?

  - by par

  Our server is overloaded with TCP/IP sessions, we have 1200 - 1500 of them. Most of them are hanging in TIME_OUT state. It turns out that a connection in TIME_OUT state occupies a socket until 60 second time-out is elapsed. The problem is that the server gets unresponsive and many clients are not getting served. I have made a simple test: download an XML file from the server with Internet Explorer 8.0 The download finishes in a fraction of second. But then I see that the TCP/IP connection is hanging in TIME_OUT state for 60 seconds. Is there any way to get rid of TIME_OUT waiting or make it less to free the socket for new connections? I understand why TCP/IP connection enters TIME_OUT state, but I don't understand why Internet Explorer does not close the connection after the XML file download is over. The details. Our server runs web service written in Perl (mod-perl). The service provides weather data to clients. Client is a Flash appication (actually Flash ActiveX control embedded in Windows application). OS: Ubuntu Apache "Keep Alive" option is set to 0

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• AFP / Apple Filling Protocol aka Netatalk access over Internet

  - by PJJ

  I got a simple cloud server and thought it would be nice to have mac native afp Volumes accesss. Installed Netatalk and this seems to work pretty nice. No sensitive data or something but I don't like to wake up someday and have my www docs rm-rfed by some kid h4x0r. Q1: Is afp encrypted? Q2: How can I make it (semi)secure? Q3: Does VPN makes sense for this? Q4: What would you do to get afp working over net? Opening any service meant for Lan only is a basic flaw, i know - but me be ignorant about it. According to Apple Dev only the authentication is encrypted or am I mssing something?

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• How can I verify the integrity of a WAN connection?

  - by Nic Waller

  We have two scanners in our branch office which upload images to the head office via FTP. In the last week, both scanners have started delivering a lot of corrupted images. I suspect that the problem may be with the WAN link, and that TCP might not be detecting/correcting all errors. Is there any software for Windows that allows me to test the integrity of the connection by sending packets with an embedded CRC?

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• How is the MTU is 65535 in UDP but ethernet does not allow frame size more than 1500 bytes

  - by nikku

  I am using a fast ethernet of 100 Mbps, whose frame size is less than 1500 bytes (1472 bytes for payload as per my textbook). In that, I was able to send and receive a UDP packet of message size 65507 bytes, which means the packet size was 65507 + 20 (IP Header) + 8 (UDP Header) = 65535. If the frame's payload size itself is maximum of 1472 bytes (as per my textbook), how can the packet size of IP be greater than that which here is 65535? I used sender code as char buffer[100000]; for (int i = 1; i < 100000; i++) { int len = send (socket_id, buffer, i); printf("%d\n", len); } Receiver code as while (len = recv (socket_id, buffer, 100000)) { printf("%d\n". len); } I observed that send returns -1 on i > 65507 and recv prints or receives a packet of maximum of length 65507.

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• how to reinstall the TCP IP protocol driver on windows 7 ?

  - by Revolter

  how to reinstall the tcp/ip protocol driver on windows7 ?

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• Issues regarding internet connectivity

  - by andySF

  Hello. My problem started when Yahoo Messenger stopped connecting. I've tried to see if Internet Explorer was working but will not load any page. The diagnostics of Internet Explorer says that is something wrong with my dns(using just ip of google or yahoo or my local webserver was not working). I use Windows 7 and at the moment i've had Internet Explorer 8 and after a lot of failing updates to ie9 I've successfully install the Romanian version of IE9(now i have ie8 after a system restore). Then I installed the service pack 1. I've done a lot of things and I will try to enumerate them, but my problem persists. Settings from Yahoo Messenger and Internet Explorer are OK. I've try to reset winsock and ip from netsh. I've scanned my pc with spybot, mallwarebytes, Trojan Remover(simplysup), Loaris Trojan Remover, Avast, Nod32, Kaspersky, Bitdefender,alot of registry cleaner including CCleaner and maybe others that I cannot remember now. I reset the registry permissions using subinacl. At a moment my files permissions was set jut to "trusted installer" and I've put the permission back to files and folders using the model of other windows 7 machine. I have try so many things that now i'm stuck in a loop using different security tools to check for problems. Oh, and my virtual machines are working just fine.(I'm using VirtualBox) Please Help. PS, Reinstalling Windows is not an option. Thank you!

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• network will not work properly after having run TCP optimizer, but safe mode settings work perfectly. how to restore?

  - by michele

  I was experiencing some issues with my connection while playing online and I tried to optimize it by running TCP optimizer on my PC (Windows 7 64bit professional). I thought maybe the situation could improve. but it didn't. actually, I now get an extremely slow page loading time, probably due to a very low RWIN value of 1024. I understand that Windows 7 has a system to automatically adjust the RWIN value when needed. The setting from netsh is "normal" so I guess something else must be wrong. I tried every automatic tool out there to restore Windows' default values, but I had no success. I currently have what should be labeled as "default values" for everything TCP Optimizer initially changed, but the problem persists. The thing is, I just found out that running Windows in safe mode SOLVES the problem completely. The problem is that as soon as I reboot, I get the same issue all over again. So my question is: is there a way to use SAFE MODE network settings in NORMAL mode?

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• How does IPv4 Subnetting Work?

  - by Kyle Brandt

  This is a Canonical Question about IPv4 Subnets How does Subnetting Work, and How do you do it by hand or in your head? Can someone explain both conceptually and with several examples? Server Fault gets lots of subnetting homework questions, so we could use an answer to point them to on Server Fault itself. What is classless routing and why is class-based routing obsolete? If I have a network, how do I figure out how to split it up? If I am given a netmask, how do I know what the network Range is for it? Sometimes there is a slash followed by a number, what is that number? Sometimes there is a subnet mask, but also a wildcard mask, they seem like the same thing but they are different? Someone mentioned something about knowing binary for this? What is NAT (Network Address Translation).

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• Latency in TCP/IP-over-Ethernet networks

  - by aix

  What resources (books, Web pages etc) exist out there that: explain the causes of latency in TCP/IP-over-Ethernet networks; mention tools for looking out for things that cause latency (e.g. certain entries in netstat -s); suggest ways to tweak the Linux TCP stack to reduce TCP latency (Nagle, socket buffers etc). The closest I am aware of is this document, but it's rather brief. Alternatively, you're welcome to answer the above questions directly.

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• How to detect Internet Connection Sharing thru sniffing ?

  - by blez

  I'm sniffing my current connection, but I have second computer linked to mine with ICS. And my app makes no difference between the two. How can I detect the second one and filter it?

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• Is Winpcap able to capture all packets going through a Gigabit NIC without missing any packets?

  - by Patrick L

  I want to use Winpcap to capture all network packets going through a Gigabit NIC of a server. Assuming that I am able to utilize the network link up to 100%, the maximum network speed is 1000Mbps. If we exclude the TCP/IP headers, the maximum TCP data rate should be roughly 940Mbps. Let's say I send a 1GB file through the NIC at 940Mbps using TCP destination port 6000. I use Winpcap to capture all network packets going through the NIC and then dump it to a pcap file. If I use Wireshark to analyze the pcap file and then check the sum of packet size for all network packets sent to TCP port 6000, am I able to get exactly 1GB from the pcap file? Thanks.

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• Recommendation for a non-standard SSL port

  - by onurs

  Hey guys, On our server I have a single IP, and need to host 2 different SSL sites. Sites have different owners so have different SSL certificates, and can't share the same certificate with SAN. So as a last resort I have modified the web application to give the ability to use a specified port for secure pages. For its simple look I used port 200. However I'm worried about some visitors may be unable to see the site because of their firewalls / proxies blocking the port for ssl connections. I heard some people were unable to see the website, a home user and someone from an enterprise company, don't know if this was the reason. So, any recommendations for a non-standard SSL port number (443 is used by the other site) which may work for visitors better than port 200 ? Like 8080 or 8443 perhaps? Thanks!

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• What is the maximum number of TCP connections I can have in Windows Server 2008?

  - by evilfred

  I would like to have as many connections (single connections from many different clients) as humanly possible in a server running on Windows Server 2008, in order to support a Comet-style application. The application is written in C#. The connections will not be chatty, they just need to be open (and stay open). Buying boatloads of memory and fast CPUs are not a problem. As far as I can tell, I will be limited to 65k simultaneous open connections per NIC - the maximum number of ports. Is this accurate? Or can I go beyond 65k connections / NIC somehow? It seems like there are server products for Linux at least that support hundreds of thousands of connections. How do they do this?

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• is possible just deny download from TCP/IP?

  - by Kerberos

  Hi all! I want to deny my internet connection's download properties for all port. I mean i want to make just upload. is it possible? Thank you very much for your help, already now.

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• TCP Windows Size vs Socket Buffer Size on Windows

  - by Patrick L

  I am new to Windows networking. When people talk about TCP tuning on Windows platform, they always mention about TCP Window Size. I am wondering whether Windows uses the concept of "Socket Buffer Size"? On Windows XP, the TCP window size is fixed. We can set it using the TCPWindowSize registry value. How about Socket Buffer Size? How can we set Socket Buffer size on Windows? Can we set it to a value different from TCP window size?

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• Windows Server 2008 R2 DNS Server not working?

  - by wolfvilleian

  I have a server running Windows Server 2008 R2 hosting a DNS server, exchange 2010 and is a domain controller. One computer on the network (and domain) can ping the server 25% of the time, also when I try to ping it's own hostname it also does not work. However another computer that is on the domain can ping it fine, and another computer on the network but not domain can ping fine as well. The computer that cannot ping the server is setup to use the DNS server running on the server only (secondary dns points to nothing) and it will resolve the hostname of the server to the external IP not internal when the other two computers correctly resolve the internal All 3 computers and server are connected directly into the same switch. Does anyone have any ideas on how to fix this? Thanks

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• Solaris TCP/IP performance tuning

  - by Andy Faibishenko

  I am trying to tune a high message traffic system running on Solaris. The architecture is a large number (600) of clients which connect via TCP to a big Solaris server and then send/receive relatively small messages (.5 to 1K payload) at high rates. The goal is to minimize the latency of each message processed. I suspect that the TCP stack of the server is getting overwhelmed by all the traffic. What are some commands/metrics that I can use to confirm this, and in case this is true, what is the best way to alleviate this bottleneck? PS I posted this on StackOverflow originally. One person suggested snoop and dtrace. dtrace seems pretty general - are there any additional pointers on how to use it to diagnose TCP issues?

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