TCP stands for Transmission Control Protocol and is one of the core protocols of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP.

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CirrOS server has ports filtered; its IP address pings but from a different IP address in the echo

nmap to a CirrOS server shows that ports 22 and 135 are filtered. On the CirrOS server, I can ssh to 127.0.0.1. I've noticed that pings to the CirrOS server return from an IP address different from ...
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1answer
1k views

How to reset a tcp connection immediately on both ends on a certain condition using linux netfilter/iptables?

Dear Serverfault community, I have the following problem: I need to reset (disconnect) tcp connections on both network sides immediately if a certain string is encountered in the packet data. I don't ...
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19 views

CentOS appliance becomes unresponsive with lot of outgoing http connections [on hold]

I have an ESXi VM running CentOS-7. My application is deployed inside a tomcat instance running on this server. The application periodically makes 1200 "outgoing" http connections every 15secs. I am ...
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1answer
20 views

Why is the same socket in TIME_WAIT many times?

I have read other threads regarding sockets in TIME_WAIT, but I am clearly still missing something. Below is a few lines from a "netstat -an". How could it get into this situation? If I understood ...
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3answers
1k views

Linux: Invalid TCP Flags

It is often recommended in tutorials and books to filter invalid TCP flags with iptables. I wonder if those aren't already filtered by the kernel itself or the iptables state module. Does anyone have ...
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1answer
2k views

option http-server-close on HAProxy haproxy-1.5-dev19 will result in Connection: close header sent in response

I basically have the following issue: whenever I add option http-server-close to the haproxy config (either in frontend or backend section), haproxy will send a Connection: close header in the ...
3
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1answer
40 views

notify when a TCP port start listening

I need to be notified exactly when an application start LISTENING on any/specified TCP port. is there anything like configuring an application to log this event using a library in any programming ...
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1answer
1k views

why 5 rx queues per NIC

On my office server, the output of cat /proc/interrupts displays one tx queue and 5 rx queues. Is this due to NIC hardware capabilities or can you configure multiple receive ring buffers in linux per ...
3
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4answers
3k views

Need help troubleshooting intermittant TCP timeout in HAProxy

I have an application where the client connects to a server via a simple TCP based protocol over TLS/SSL. In development, this has worked great for many months while we were building our application ...
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1answer
1k views

How to increase nginx connections

I am facing the problem of nginx max connection issues. I am not able to increase max active connections(520) made by nginx. Some time it is using whole writing (516) operation connections. and due to ...
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0answers
13 views

Should I change the value of TcpTimedWaitDelay after increasing the MaxUserPort's value?

I have Apache running on Windows 2008 R2. I had an issue where my Windows Server is reaching maxing outbound TCP connection which caused many connections to be interrupted and my application started ...
38
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8answers
11k views

Windows TCP Window Scaling Hitting plateau too early

Scenario: We have a number of Windows clients regularly uploading large files (FTP/SVN/HTTP PUT/SCP) to Linux servers that are ~100-160ms away. We have 1Gbit/s synchronous bandwidth at the office and ...
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1answer
50 views

Configure Squid Proxy Server to use TCP for DNS lookups? [closed]

Is there a way to configure squid 3.5.1 to use TCP for DNS lookups? I've setup up the proxy server to use TCP for lookups by adding "options tcp" to my /etc/resolv.conf, but squid seems to be doing ...
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1answer
30 views

Server 2012 R2 TCP Timestamps

We will be having some penetration testing performed shortly and looking to clean up a few things. One of these is TCP timstamps in Windows. A simiple NMAP scan shows me a guess of the TCP timestamp ...
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0answers
41 views

tcp previous segment not captured when NAT

I have a client request web service on a server behide NAT. My client IP is 10.54.10.193 NAT address: 10.54.28.183 Server address: 62.209.39.203 When client request web service on server we have TCP ...
9
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3answers
208 views

How does server-side `TIME_WAIT` really work?

I know there are quite a few SE questions on this, and I believe I read as many of them as it matters before coming to this point. By "server-side TIME_WAIT" I mean the state of a server-side socket ...
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2answers
3k views

TCP port numbers reused and TCP Retransmission

Facing issues due to TCP Port Reuse and Retransmission for HTTP traffic. My deployment is as follows: enter image description here I have a squid proxy installed on a unix machine which is sending ...
2
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3answers
318 views

Why does TCP Reno cut the congestion window in half when I get duplicate ACKs?

I'm having a hard time understanding this conceptually. Why does TCP Reno cut its congestion window in half when it detects triple duplicate ACKs and cuts its window to 1 segment when it times out? ...
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3answers
7k views

What are the ramifications of setting tcp_tw_recycle/reuse to 1?

I set both tcp_tw_recycle/reuse to 1 in my configuration file. What are the ramifications of doing this? If a tcp socket is re-used, does that pose a security risk? i.e. 2 different connections both ...
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1answer
56 views

Packets being routed to the wrong IP

Looked around, can't find a similar issue anywhere... I have been having some very strange and hard to explain problems on my network lately, and in my efforts to find the cause, I came across an ...
74
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7answers
102k views

How to forcibly close a socket in TIME_WAIT?

I run a particular program on linux which sometimes crashes. If you open it quickly after that, it listens on socket 49201 instead of 49200 as it did the first time. netstat reveals that 49200 is in ...
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1answer
25 views

Send proper UUID over tcp

I have a small ingest TCP server that should accept a device UUID as a first message, which is only 16 bytes. I'd like to test this manually from terminal, but sending a string won't work, since it ...
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1answer
27 views

Is “keeping alive connections” the smartest approach to access devices behind a router? [closed]

The problem I'm developing an IOT device that will connect to a common Wifi router. As you know in order to make this device publicly accessible from WAN you'll have to do some ports forwarding or ...
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2answers
25 views

Keeping TCP connections alive to track which clients are online

I am developing an application where a server needs to stay in touch with lots of simple IoT devices. Nearly no information exchange is needed between the server and each device, but devices need to ...
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1answer
1k views

How to force use of tcp instead of udp for rpcbind?

I'm trying to use tcp/111 for rpcbind under Debian Wheezy instead of udp/111. The portmap in Squeeze uses tcp/111 without any special configuration, but Wheezy fails. Even numerous sites (as well as ...
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33 views

Inconsistency in TCP and HTTP connection management

I observe following scenario in WireShark: The problem I see here is that after receiving [FIN, ACK] from server (4090) and acknowledging it (4092), http client attempts to send another HTTP ...
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0answers
18 views

What exactly constitutes a bad TCP segment?

What constitutes a bad segment as in bad segments received in the netstat output below? I would think a TCP header's checksum could do it, but are there other things? If a segment arrives after its ...
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2answers
736 views

How to edit TCP window size from iptables?

There is TCPMSS target to edit MSS value of connections (including forwarded). How to edit window size (for example, cap to some maximum value) by iptables rule? Expecting something like iptables ...
2
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1answer
44 views

(Completely) randomize IP addresses in PCAP file

I have several PCAP files which contain network traffic. To perform some experiments for a network experiment, I need real data with completely randomized IP addresses. I am well aware about the ...
2
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2answers
919 views

Troubleshooting High TCP Retransmit Rate

I've been attempting to troubleshoot a network issue that presents with very high rate of TCP retransmits. 36 samples (taken with Wireshark 1.10.8 running on 32-bit Windows 7) totaling a little over ...
3
votes
1answer
1k views

How to achieve multiple NFS/TCP connections to the same server?

I'm trying to maximize the NFS/TCP bandwidth between a Linux client and a single NFS server over a 10Gbps link. Although each NFS mount has its own device (major/minor), everything comes down to a ...
9
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1answer
172 views

SynProxy can not return syn ack packets with asymmetric dual bridge topology

I have a asymmetric dual bridge topology as shown below when i connect from 172.16.11.5 and 172.16.10.6 with ssh but i can not connect because of SynProxy. ------- ...
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1answer
54 views

Nginx Configuration:504 Gateway Time-out error

We are using Nginx as a Load balancer. Nginx having IP address of :10.110.0.200 and address of host machines are 10.110.3.20|10.110.3.21 this is the configuration file: upstream test1 { server ...
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1answer
51 views

Is it possible to run 2 concurrent tcpdump with different options?

I need to run 2 concurrent tcpdump commands with different arguments/options. Why ? Because we wrote some long long scripts compatible with following options : tcpdump -ixenbr0 -s 400 -n -A 'port sip ...
2
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3answers
4k views

Monitor loopback traffic (monitor MS TCP Loopback inteface traffic) with Microsoft Network Monitor 3.4 - possible?

I've downloaded NM 3.4 from microsoft.com and it appears that the software doesn't capture traffic on MS TCP Loopback interface. When I ping 127.0.0.1 address, NM shows no packets flowing. I've tried ...
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3answers
4k views

Configuring keepalives with TOAD client communication

I have a scenario where long-idle sessions of TOADSoft client communication with the Oracle server seem to be torn down as they timeout on an intermediate state-full firewall. These sessions could ...
17
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4answers
33k views
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1answer
82 views

Millions of TCP FIN-ACK retransmissions blocking traffic on my desktop machine

In a few minutes I have received about 7 millions(!) FIN-ACK packets from IP address that belongs to Google 74.125.133.188 what totally blocked network traffic on my desktop(!) machine. Other ...
3
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0answers
76 views

Does Fast Retransmit and Retransmission Timer work at the same time?

When Fast Retransmit is implemented, if I received packet 1, then I will send an ACK that says I need packet 2, and then if I received packet 3, I will send a duplicate ACK that says that I need ...
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11 views

Why is server refusing new connections?

One of our proprietary closed source server applications sometimes stops accepting new connection from remote nodes on its server port. Remote nodes that are already connected work fine. Any new ...
2
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1answer
768 views

Disable kernel processing of TCP packets for raw socket

I'm working on a TCP/IP implementation, for an embedded device, that I want to test from a Linux user space process using raw sockets. raw(7) says that Raw sockets may tap all IP protocols in ...
29
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5answers
39k views

How passively monitor for tcp packet loss? (Linux)

How can I passively monitor the packet loss on TCP connections to/from my machine? Basically, I'd like a tool that sits in the background and watches TCP ack/nak/re-transmits to generate a report on ...
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3answers
1k views

Windows Server 2008 - unable to bind any TCP port

OS: Win Server 2008 RC2 Windows firewall on (no effect when off) I have suddenly been plagued by an issue in which I cannot find any similar ones with a search. I am running about 20 game servers ...
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0answers
18 views

Can I use MS Host Integration Server to connect to an IBM without using SNA

I'm sorry, this will represent a lot of information, but I'd like to avoid some of the back and forth I'm having with various forums trying to resolve this issue. So please, bear with me. I've taken ...
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0answers
17 views

What technology do data center use to guarantee low RTT?

I was reading about data-center-tcp DCTCP and the paper was talking about the low retransmission timer (RTT) of about 250µs, but didn't state how that is being done. Somewhere else I read that DCTCP ...
6
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4answers
490 views

Why is my web server dropping connections with a TCP reset at high load?

I have a small VPS setup with nginx. I want to squeeze as much performance as possible out of it, so I've been experimenting with optimization and load testing. I'm using Blitz.io to do load testing ...
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1answer
44 views

Does ColdFusion use TCP Ports?

I am trying to access a link on our network. Whenever I try, the page times out. I have discovered that this link is a Adobe ColdFusion web page. Does ColdFusion use a TCP port other than port 80? I ...
9
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3answers
849 views

How does Intel AMT (Active Management Technology) not interfere with the TCP/IP host stack?

The Intel dev kit I've been using includes a remote management feature (also see the Ubuntu man page here) which allows remote reboots in case the operating system hangs. It has the capability of ...
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1answer
149 views

Slow Upload to IIS Server

I have a Windows 2012 R2 Server running on an Amazon EC2 instance with IIS 8.5. It hosts a web application, and a custom WebDAV server that interacts with the same database as the web application. I ...
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38 views

better alternative for tcp_syncookies in linux

In an effort to prevent DDOS attacks I followed suggestions to leave /proc/sys/net/ipv4/tcp_syncookies value set to 1 in my linux box to enable TCP syncookies. However, when I look at this URL: ...