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  • HTTP, TCP, UDP and connectionless

    - by user132199
    I am a bit confused with HTTP lately. Some facts are that TCP can operate connection orientated or connectionless this I understand. TCP though is connection-oriented while UDP is connectionless which is used when the message itself can be fit into a single message. Question: If HTTP uses TCP, and TCP provides reliable conjnections for multiple message excahnge, and HTTP is said to be connectionless then how is this possible? TCP is connection-oriented? So how is HTTP connectionless????

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  • Is there a limit to how many sites can be hosted on a single IP address when using HTTP Host Headers on Windows 2008?

    - by Kev
    For reasons that are lost in the mists of time, our older Windows (2000, 2003) servers have been configured with a "Administrative" IP address and three further "Hosting" IP addresses. There are also additional IP's for sites with SSL certificates. The "Administrative" IP address is where all our internal provisioning, monitoring and other such apps are bound to. We lock this down and don't permit access to it from the outside world (other than over our VPN). The three "Hosting" IP addresses are used for IIS website hosting (in conjunction with host headers). Historically, new site IP address allocations have been rotated through these three IP addresses. I'm not really sure why. I'm building a new batch of servers and I'm considering just having a single hosting IP address. Our servers can host up to 1200 sites on a single machine. Is there a technical limit to the number of IIS sites that can bind to a single IP address? Our Linux platform seems to do just fine with just a single shared IP + host headers. I initially thought this might be an SEO thing, but given that IPv4 address space conservation is paramount I hardly think Google or other search engines could reasonably penalise site rankings just because hundreds of sites hang off the same IP.

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  • Why would you use IPv6 internally?

    - by KCotreau
    Of course, I realize the need to go to IPv6 out on the open Internet since we are running out of addresses, but I really don't understand why there is any need to use it on an internal network. I have done zero with IPv6, so I also wonder: Won't modern firewalls do NAT between internal IPv4 addresses, and external IPv6 addresses? I was just wondering since I have seen so many people struggling with IPv6 questions here, and wonder why bother?

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  • One Windows Domain workstation can ping gateway but gets no internet access

    - by dindeman
    One of the (Windows XP SP3) workstations of our Windows Domain could not access internet anymore, this problem suddenly happened overnight. The domain controllers (there are three of them) are all running Windows Server 2008. First I compared the output of ipconfig /all on the faulty workstation with the output of a working workstation and it was just fine as it had always been. In particular the default gateway was correct and always remained pingable from the faulty workstation. I guessed that something was wrong with the DHCP service and I restarted the DHCP server service on all of our three DCs as well as the DHCP client service on the faulty workstation. This didn't solve the issue. I then thought of renewing the DHCP lease with ipconfig /release and ipconfig /renew and here is my first question: why did this never work? The same IP address (192.168.0.45) kept being assigned despite all my attempts to renew it (note that all our workstation are getting their TCP/IP automatically.) Even by leaving the domain and changing the computer name the same address was yet again obtained... Anyway I then proceeded to switch the TCP/IP configuration for that machine manually to another free valid IP address (192.168.0.41)... and then the internet access came back! I then cleared any traces of the previous IP in the DHCP leases list and in the DNS tables of our DCs and, after setting back the TCP/IP configuration to 'automatic', finally, the new lease would be granted (192.168.0.41) alongside with the internet access. My second question: what went suddenly wrong with the original IP address?

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  • TCP/IP communication between Hyper-V host and guests

    - by Tedd Hansen
    This may be a simple one. :) I have a simple Hyper-V setup with a few guest os running. The host has 1 physical network adapter with a static IP assigned to it. The guests have network adapters assigned to "Internet" (Hyper-V network) which is bound to the physical host network adapter (Hyper-V "External" connection type). I am not able to communicate (ping or anything else) between guests and host. I've checked firewall and it seems fine (ports open from anywhere still don't work). I'm trying to communicate with the hosts IP assigned to the same physical interface that the guests are sharing. Guests can communicate between them just fine. I can't seem to find any relevant setting (I might just be missing it). So my questions: How do I fix it so host and guests can communicate?

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  • What would cause my SendMail server not to acknowledge receiving a TCP Sequence?

    - by Mike B
    My TCP/IP Stack knowledge is a little rusty so please bear with me.... I have a CentOS 5.7 server with SendMail and am having seeing intermittent timeout issues sending email (particularly larger email) to other remote domains. It doesn't happen with all attachments or recipient domains. Just some. After some extended troubleshooting, I think I've narrowed it down to TCP Sequences not being acknowledged. Here's a breakdown of the TCP session from a packet capture I collected directly on my MTA (fooMTA): Packet 1 - 11: Standard TCP handshake followed by initial SMTP conversation. No errors. Packet #12 Recipient MTA: TCP sequence 231. Ack 91. Packet #13 FooMTA: TCP sequence 91. Ack 305. Packet #14 FooMTA: TCP sequence 1115. Ack 305. Packet #15 Recipient MTA: TCP sequence 305. Ack 2495. Packet #16 FooMTA: TCP sequence 2495. Ack 305. Packet #17 FooMTA: TCP sequence 5255. Ack 305. Packet #18: Recipient MTA: TCP sequence 305. Ack 5255. Packet #19: FooMTA: TCP sequence 6635. Ack 305. Packet #20: FooMTA: TCP sequence 8015. Ack 305. Packet #21: Recipient MTA: TCP Sequence 305. Ack 8015. Packet #22: FooMTA: TCP Sequence 10775. Ack 305. Packet #23: FooMTA: TCP Sequence 13535. Ack 305. Packet #24: Recipient MTA: TCP sequence 305. Ack 10775 Packet #25: FooMTA: TCP Sequence 14915. Ack 305 It keeps going like this with my server still thinking it hasn’t received sequence 305… in response the remote side eventually retransmits its prior data thinking that it never arrived. Eventually the gap gets so large that no new data is sent and the remote MTA keeps retransmitting old stuff. This contributes to an exponential backoff and eventually the remote side gives up. What’s strange to me is that I see the “missing” TCP sequence (305 in this case) arriving back to my server (via a packet capture collected directly from fooMTA) So I don’t get why my server keeps asking for it. Could this be firewall related? What would be the next step in troubleshooting?

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  • Why is a network ID not needed to connect to an IP address?

    - by baddogai
    I know how IP basically works, and knows that an IP address composed of a network ID portion and a host ID portion, but when I type a IP address, say 8.8.8.8 into the web browser, I didn't supply any subnet mask information. So, how does the browser know where the dividing line is between the network ID and host ID? Since 8.8.8.8 may mean 8.8.8.8/8, 8.8.8.8/24 etc. In a nutshell, the IP address I supplied is ambiguous.

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  • switch OFF syn cookies

    - by Nick
    We have several servers they have public IP's, but work together (one is with Load Balancer, orther with Apache Web server, other with MySQL and so on. Most of the ports are fire-walled, so only "local" servers can be connect there. However ALL servers have some ports that must be publicly open. We have SYN Cookies enabled and from time to time we got: possible SYN flooding on port 8080. Sending cookies. Port 8080 is not public. How we can switch OFF SYN Cookies for some ports (e.g. 8080, 3306 etc) or from some sources (e.g. our servers), but in same time SYN Cookies to be switched ON for all other ports, e.g. port 80. We found this similar problem, except our servers are with public IP's: SYN cookies on internal machines

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  • Why can't I ping a PC on my home network?

    - by AngryHacker
    Whenever I try to ping another box on my home network, it pings the wrong ip address: C:\Users\Papa>ping macmini Pinging macmini.belkin [208.68.143.55] with 32 bytes of data: Reply from 208.68.143.55: bytes=32 time=50ms TTL=110 As you can see it always appends belkin to anything I try to ping. So I hit up ipconfig and belkin happens to be Connection-specific DNS Suffix: Wireless LAN adapter Wireless Network Connection: Connection-specific DNS Suffix . : belkin IPv4 Address. . . . . . . . . . . : 192.168.2.7 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.2.1 My setup is all DHCP, so I am not sure where belkin is coming from. I looked through all the networking stuff, as you can see below: Bottom line: how do I fix this?

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  • connections in FIN_WAIT and CLOSE_WAIT state

    - by Raj
    I would like to elaborate the setup so You guys can understand the question and answer more accurately. I have HAProxy as load-balancer, 4 webservers (apache 2.2.3) and one database server (MySQL 5). I am monitoring these servers by nagios. I have disabled the keepalive on apache as we have only 8GB of memory. Now what happens whenever I receive alerts for high memory and cpu utilization, I have observed that the connections from apache to database server hang in established mode (keepalive with timeout value of 7200) and at other side means connections between haproxy and apache shows status as FIN_WAIT on haproxy server and CLOSE_WAIT at apache side. I also see the huge memory swapping and apache taking the most of the memory. I did strace on apache process and did not find any information. strace gets attached to apache process but did not produce any output. The processlist on Mysql server show s those processes in sleep mode. The application on webserver is Magento a php application. if you need further information please let me know. Thanks.

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  • Access Windows from Mac via Remote Dekstop Connection using hostname

    - by stevekuo
    I'm using Snow Leopard with Remote Desktop Connection attempting to access a Windows XP machine on a home network. If I specify the Windows PC's hostname it won't connect. Only by specifying the IP address does it connect. It's the same issue when trying to ping the Windows machine - IP address works, hostname doesn't. Both machines are on the same subnet connecting with a wireless router. Is there way to get OSX to resolve the Windows PC by its hostname?

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  • IIS7 houndreds of connections in CLOSE_WAIT

    - by rjlopes
    I have a .Net application on my IIS7 server it was working fine until I had to move it to another server. I moved the exact same code to the new server and I noticed that after some hours the website stopped responding to remote requests but if I did remote desktop to the server it responded to the request done to localhost. If I stop the website and the application pool it started working fine again. I was able to track the problem to hundreds of requests left in CLOSE_WAIT state to the http port that are never closed (I waited a few hours and they remain the same). Any ideias?

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  • Looking for an open source real-time network analysis program

    - by JrSysAdmin
    Can somebody recommend an open source real-time network analysis program? What I'm looking for the program to do is display a graph of bandwidth usage by IP within our internal network that can quickly be viewed any time we need to (typically when we want to quickly find out who is utilizing high amounts of bandwidth and slowing down the network). We ideally simply want to hook up a monitor on the wall of our server room to a system whose NIC will be in permissive mode to log all network activity in a visual manner which can easily be seen and running 24/7. Prefer open source as I do not have a budget for this project and prefer open source projects in general. I'd also prefer for this to be available for CentOS but any linux distro or Windows OS would be acceptable. Thanks!

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  • Host data transfer limit calculations and network protocol headers

    - by UpTheCreek
    OK, this might be a really stupid question, but... I'm building a web app that utilises websockets. There's fairly rapid messaging going on, so I've been taking a look at the network traffic with wireshark, to see if there's any way of reducing the amount of data we are sending over the wire, and hence costs. A typical message has approx 150 byte data payload, and according to wireshark the lower layer stuff takes up about: Ethernet: 14 bytes IP: 20 Bytes TCP: 20 Bytes My question is, are these network headers included in data transfer calculations? What about TCP ACK messages? (another 54 bytes according to wireshark) This may seem petty, but because we have so much messaging going on, and because the payload is a similar size to these headers, it's significant.

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  • TCP Sessions and IP Changes

    - by Kyle Brandt
    What happens to a TCP session when the IP of a client changes? I did a simple test of having netcat listen on a port, and connecting to that port from a client machine. I then changed the IP of the client while that nc session was open and sent some data, no data was received by server after changing the IP. I know they are different layers, but does TCP use IPs for part of how it distinguishes sessions? Does my example not work because of how the application handles it, or is this not working because of something happening at TCP/IP/Ethernet layers? Does this depend on the OS implementation? ( I am most interested in Linux at the moment)

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  • What is "Disable class based route addition" good for?

    - by JRoppert
    In the advanced TCP/IP settings of a VPN connection, i found a checkbox labeled with "Disable class based route addition". The checkbox is only enabled as long as "Use default gateway on remote network" is switched off. What is "Disable class based route addition" good for? Detailed instructions to find the settings: Open Properties of VPN connection Go to Networking tab Open Properties of "Internet Protocol Version 4 (TCP/IPv4)" (and/or TCP/IPv6) Click "Advanced..." Button Change to "IP Settings" tab Here you can find the checkboxes mentioned above

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  • Disable Network settings (TCP/IP & DNS) on Windows 7 Ultimate

    - by TiD91
    i also read this discussion here How to disable Tcp/Ip settings in windows 7 via GPO? about what i want to do but i still have problems. So here i am: i have a desktop pc with two accounts, both with Administrative rights. One is used by the entire my family, in particular by my brother. The problem is that i set some DNS and IP configurations to let be possible the VNC connection from remote. Now i would like to disable the network settings (TCP/IP and DNS) to prohibit my brother to change it preventing me to connect to it. So how can i do this? I set the policies from GPO but i still can change these settings from his account. Here's a pic of Registry Keys: http://imageshack.us/a/img339/3310/famigliapc2012092017274.png what didn't i do? Thanks in advance for your help. Rub|TiD

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  • Why won't sql server express 2008 service restart after I enable TCP/IP Protocol?

    - by John
    Whenever I enable TCP/IP connections on my SQL Server Express 2008 database server running on Windows XP SP3, I cannot restart the service, it simply states "The request failed or did respond in a timely fashion". Any suggestions of what I may have configured incorrectly? [update] Here is the applicable part of the Error Log: MSSQL$SQLEXPRESS Server failed to list on 'any' 3060. Error: 0x2747. To proceed, notify you system administrator. MSSQL$SQLEXPRESS TDSSNIClient initialization failed with error 0x2747, status code 0xa. Reason: Unable to initialize the TCP/IP listener. An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full. MSSQL$SQLEXPRESS TDSSNIClient initialization failed with error 0x2747, status code 0x1. Reason: Initialization failed with an infrastructure error. Check for previous errors. An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full. MSSQL$SQLEXPRESS Could not start the network library because of an internal error in the network library. To determine the cause, review the errors immediately preceding this one in the error log. MSSQL$SQLEXPRESS SQL Server could not spawn FRunCM thread. Check the SQL Server error log and the Windows event logs for information about possible related problems.

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  • How does the internet protocol handle network card numbers?

    - by Giorgio
    I know that data packets sent over the internet carry the source and destination IP address, so that the protocol can route the data to the correct destination and keep track of the source address of the packet. But what about the network card address? As far as I know, each network card has a unique identification number. Is this also transmitted with a TCP/IP packet? And when a packet is received at its destination, how is the IP address mapped to a network card number? In other words. On the sender part: does the sender store the sender network card number in the IP packets that it is sending? On the receiver part: which component maps the IP address to the receiver's network card number when a packet is received? E.g., in a home network, does the modem / router map the destination IP address of an incoming packet to a network card number and deliver the packet directly to that network card? A link to documentation on these topics would be of great help.

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  • Too Many ESTABLISHED connection from a single IP address in Apache

    - by ananthan
    netstat -ntp |grep 80 shows too many ESTABLISHED connection from single IP address. Around 300 of them and it is not an attack and user is using a 2G connection to access Apache. This is the case with other 2G connections also. As a result of this Apache is running out of children. Earlier it was showing too many close_wait and after enabling tcp_tw_reuse and tcp_tw-recycle there is not much close_wait but the number of ESTABLISHED connections increased. We are using Ubuntu 11.04 having 48 GB ram keepalive On keepalive timeout 10 max clients 800 max-request-perchild 4000 timeout 300 I have set syn_ack to 1 and syn_retries to 2. On wifi there is no such issue. Connections are closing properly, but with 2G connections Apache is running out of children and too many ESTABLISHED connection. also i have tried setting timeout from default 300 to 30,but since our project is image hosting for mobile phones,clients couldn't upload images properly as they are getting frequent time out.Also there were a lot of 408 messages so changed it to the default 300

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  • Role of OSI layers when we open a url in browser?

    - by user2715898
    I have searched on this topic a lot but I am not able to understand how and where OSI layers (Application, Presentation, Session, Transport, Network, Datalink, Physical) come into picture in the whole process of opening a webpage in browser. I have read this - http://stackoverflow.com/questions/2092527/what-happens-when-you-type-in-a-url-in-browser?lq=1 and I know all the functions of all the layers that are there in OSI model. Also, do we use OSI model or TCP/IP in the whole process? Basically I am having problem linking all the things together. And please forgive me if there are resources out there that explain this concept. You can definitely point to them.

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  • How come ftp protocol produces transmission errors sometimes if the data is using TCP, which is checksummed?

    - by Cray
    Every once in a while, downloading (especially large) files through ftp will produce errors. I am guessing that's also partly the reason why all major sites are publishing external checksums along with their downloads. How is this possible if ftp goes through TCP, which has checksum inbuilt and resends data if it is transmitted corruptly? One could argue that this is due to the short length of the CRC in the TCP protocol (which is 16bit I think, or something like that), and the collisions are simply happening too often. but 1) for this to be true, not only must there be a CRC collision, but also the random network error must modify both the CRC in the packet, and the packet itself so that the CRC will be valid for the new packet... Even with 16 bitCRC, is that so likely? 2) There are seemingly not many errors in, say, browsing the web which also goes through TCPIP.

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