TCP and IP are two important protocols used in networking today. Due to their importance, the Internet Protocol Suite is also commonly known as "TCP/IP"

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How to fix “TCP/IP has reached the security limit…” event message

I get the following warning as a System event: "TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts." on o box running Win XP SP3. How can I fix this issue? ...
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Backups take so long that the firewall closes the connection

A bit of a mashup of systems here, so bear with me. Essentially, I'm having some trouble using the Backup Exec agent for Oracle, while trying to backup a remote Linux server. The BE agent appears to ...
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Why ARP request is unicast?

I have a wireshark capture that indicating a unicast ARP request from source to destination. As per my understanding ARP requests (including gratutious ARP) use broadcast. In what case the ...
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How do I fake dropped packets (or actually make them fail)?

Background One of our clients suffers from an intermittant problem with their internet where it will drop packets when a user downloads a large file (their IT is looking into the problem). I have ...
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Why does the TCP Chimney Offload feature on some ethernet cards fail to pass some network packets to the OS?

In http://support.microsoft.com/kb/942861 Microsoft reports that in some situations Microsoft SQL Server experiences network issues due to the network card having a TCP Chimney Offload turned on. I ...
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Networking security and TCP/IP internals books/sites

I am searching for good books and articles about TCP/IP, mainly the security aspects of TCP/IP protocols. I have TCP/IP Illustrated and the TCP Guide, but they kinda lack on description of 'classic' ...
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Where did TCP/IP Filtering go in Windows Server 2008?

I'm configuring our new Windows Server 2008 machine. In Windows Server 2003 we would enable TCP/IP Filtering on our network cards to only allow traffic on specific ports to get through. This was ...
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How Can I Harden the TCP/IP Stack in Windows Server 2008? [duplicate]

I would like to make sure that my Windows 2008 servers are hardened against DDOS attacks. There is a Microsoft Technet article on Hardening the TCP/IP stack, but it was last revised in January 2006. ...
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UNC Path fails by IP “no network provider accepted the given network path”, but works using hostname

I have an unusual problem with a Windows Server 2003 (Standard x86) box. It appears the machine will not accept connections to its shares (locally and from other domain member servers) by using its ...
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How do I apply multiple subnets to a server with one NIC?

I am trying to route multiple IPs through one physical NIC on my dedicated server for use with Proxmox KVM VMs. I have a dedicated server which is currently running Debian 4.4.5-8 with 3 available ip ...
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Rapidly changing public IP addresses on certain networks?

I run/develop an online game where many of our users are in southeast asia. I recently went to southeast asia and made an alarming discovery. Anywhere I got internet access, whether it was via 3G, a ...
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509 views

Behaviour of solaris tcp stack with relatively high RTT and bursty traffic

I have an application that is distributing data from New York to Tokyo over TCP running Solaris 10. Mean throughput is < 1Mbps, peak throughput can reach 20-30Mbps for seconds at a time though ...
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120 views

TCP works for a while, then fails, why?

This comes from an implementation of OpenStack, and we have a fix, but I don't understand why we need this fix. My machine has an ip of 192.168.20.45 My default gateway (pfsense) has an ip of ...
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729 views

Where are my TIME_WAITs on Mac OS X?

No TIME_WAITs on Mac OS X Normally, when a TCP connection is closed, the socket on the side where close() is called first is left in the TIME_WAIT state. When one of the peers is a Mac OS X (Lion) ...
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TCP Windows Size vs Socket Buffer Size on Windows

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 ...
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TCP Sessions and IP Changes

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 ...
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IP address used by nslookup and ping is different

I have a web server hosted in the network. It has a domain name registered. However, I also host a DNS server for the LAN. So, when someone wants to access the web server, it would check the DNS ...
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288 views

Which route when there are two physical connections?

I'm a developer, not an admin, so apologies in advance. In a small office I have two Windows Server 2008 boxes connected to a 100mbps router, which is fine for day to day running. I'm looking to ...
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ESXi network setup for isolated internal virtual machines

Using ESXi v5.1 and vSphere, my networking is setup like so: One standard Switch: vSwitch0 vSwitch0 has one uplink physical adapter (Internet connected) vSwitch0 VM Network has 3 virtual machines ...
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Determining cause of TCP/IP connect issue without traceroute

I'm trying to connect from a company network to a host (via HTTPS), but my attempts fail with timeout. I can resolve the host. I know the host is up. I know there is a firewall filtering by incoming ...
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Practical Anycast

I've read How can I send visitors to the closest server using DNS? post, but there's still some thing, on a practical level that I don't understand. Say I have two servers. One in NY another in ...
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248 views

List of IPs that are not in DNS

What's the easiest way to get a list of windows desktops that are on a subnet but do not have names listed in the dns server?
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When a server IP changes, do exising TCP (e.g. http/mysql) connections remain running

We have some PHP-FPM servers and when they need a database connection, they connect to an HAProxy server which selects them a database server to use and the connection opens. When we then want to ...
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187 views

Given a 100mbit connection, what is your max downstream speed?

I'm a (very) junior sysadmin and was asked this question on an interview. The answer was 96mbit/s. I know this is related to network overhead but I cannot find any good information on why this ...
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Can a TIME_WAIT connection be restored?

Is it possible to restore a connection that is in state TIME_WAIT? If not, I use raw packets (forgering the source), is it possible? (Please understand that I do not intend to do bad things, it's ...
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wireshark http POST

I would like to have a http POST request method CAPTURE filter. I know it is easy to do it by display filter http.request.method==POST but I need tcpdump compatible. I wrote tcp dst port 80 and ...
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custom route not working on windows

My windows laptop is directly connected to 192.168.1.0/24 (wireless lan). I access 10.21.0.0/16 though a router that is connected to both networks. The routing works fine with this configuration. I ...
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How is the MTU is 65535 in UDP but ethernet does not allow frame size more than 1500 bytes

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 ...
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IIS7 hundreds of connections in CLOSE_WAIT

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 ...
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Is it possible to configure Nginx to send TCP keepalive?

On TCP connections held by NGinx, can it be configured to send TCP Keepalive (Not HTTP KeepAlive!)
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What are good and bad jitter times for a LAN

Ive just ran jperf (frontend to iperf) on our network between 2 workstations, its recorded jitter between 0.033ms and 0.048ms. Is this good or bad? Are there more variables that i would need to ...
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Iproute2 tools vs conntrack tools

I have a linux box which is setup as firewall/gateway for the network. Was just wondering why ss and other iproute2 tools show much less than iptables conntrack. Is it because the router function is ...
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How to get a service to listen on port 80 on Windows Server 2003

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 ...
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Using IP alias and route to visit a site through assigned IP address

I want to visit a site through assigned IP address. I run the following commands: ifconfig eth0:1 [ip address] route add -host [the target host ip] dev eth0:1 gw [gateway] This works fine on ...
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Can you use WMI to determine if a connection gets its DNS servers from DHCP?

The DNS server search order for a network interface can be read from Win32_NetworkAdapterConfiguration like this in Powershell, or programmatically using .Net ManagementObjects: > $NICs = ...
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once in a while windows / .net application ignores the tcp fin flag

i've run into a network problem which i cannot solve. on a few computers running windows 8.1 and communicating with linux http server tcp connections dangle on the windows side instead of being ...
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TCP Congestion Window on Windows Server 2003

After reading this blog post by Ben Strong, I started looking on the internet for information on how the Initial Window size could be manipulated on Microsoft Windows Server 2003 (R2, 64bit in case it ...
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Restricting ssh tunnel port access by group

My understanding is when creating an ssh tunnel to a remote machine, the ports become open on that machine for anyone to use and connect back to my local box (not just the user who opened the tunnel). ...
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1answer
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Machine cannot communicate on local network any more

I have a machine that has a problem I've never seen and cannot understand. The machine is a Dell laptop with Windows 7 Ultimate. The user tried to do something fancy with this machine (bridging the ...
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Solaris TCP stack tuning

We have a large web project (about 2-3k requests per second), using haproxy (http://haproxy.1wt.eu/) as a frontend and load balancer between the java application servers. The frontend (haproxy) is ...
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How to increase MTU size on Linux 2.6?

How to increase MTU size on Linux 2.6? Is such a thing possible? If yes, which files (in /etc or elsewhere) must one edit?
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Windows 7 DHCP Default Gateway not Overridden by manual Default Gateway

We have recently installed Windows 7 for student computers. All student computers must be routed through our content filter which is located at 192.168.0.63. This was done in WinXP by adding a Default ...
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LVS Configuration issue (Using piranha Tool)

I have configured LVS on cent os using piranha tool .I am using vip of internal n/w as gateway for real server we have two NIC one having exteranl Ip and other for internal n/w which is on ...
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different ACK behaviors (slowing down throughput?)

I'm running netio (http://freshmeat.net/projects/netio/) on one machine (opensolaris) and contacting two different Linux machines (both on 2.6.18-128.el5 ), machine A and machine B. Machine A has a ...
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If I make a request to my server's IP address, will it be the same as using 127.0.0.1, or slower?

I have application servers with memcached running on them. What will happen if I make a request to memcached on 10.243.98.5, which just happens to be the originating server? Will it use the same ...
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Sporatic Connection issues connecting to SQL 2005 - Named Pipes vs TCP/IP issue?

We have a production website that is experiencing periodic connection errors to our SQL 2005 server, several times a day during peak usage: An error has occurred while establishing a connection ...
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Maximum number of TCP clients in Windows 7?

I am running client load testing software for my server from a Windows 7 Enterprise box. The client box is able to get up to 16346 TCP connections out, and then it starts giving the error “An ...
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TCP/IP Stack in Windows Server 2008 vs Windows 7 Ultimate

Does anyone know the details as to the differences between the TCP/IP stack in Windows Server 2008 (Standard) vs Windows 7 Ultimate? This question pertains to TCP/IP ONLY. I know that Windows 7 and ...
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How to make Windows honour an ICMP Connection Refused message after a TCP connection attempt

We have a tool which is used to manage a server process remotely over TCP. One of the tools features is to check if the server is running by attempting to connect to the server in a loop for a given ...
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How to debug why WAN TCP/IP throughput is lower than expected?

I'm trying to figure out why tcp/ip throughput between two hosts I control is much lower than expected. Host A: internet connectivity provided by Comcast (Residential) in Boston Metro -- can ...