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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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
26 views

TCP - MSS option and different payload

This is a tcpdump from servers side. In line 1 i see MSS=1400. Why server sent in line 6 a packet of 4230 bytes when client want max 1400?
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36 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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7answers
1k views

Why is it good practice to compare checksums when downloading a file?

Websites which supply ISO files for download will often give the md5 checksums of those files, which we can use to confirm that the file has downloaded correctly, and has not been corrupted. Why is ...
7
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2answers
145 views

Extreme UDP packet loss at 300Mbit (14%), but TCP > 800Mbit w/o retransmits

I have a linux box I use as the iperf3 client, testing 2 identically equipped Windows 2012 R2 server boxes with Broadcom BCM5721, 1Gb adapters (2 ports, but only 1 used for the test). All machines are ...
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0answers
24 views

How to enable SYN Cookies on Debian 7.5? [migrated]

How do I enable SYN Cookies on Debian 7.5? nano /etc/sysctl.conf #net.ipv4.tcp_syncookies = 1 remove here the # sysctl -p service network restart Is that the correct way? Or what must I look ...
2
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1answer
50 views

Outgoing packet has NATed src address

Configuration/Topology: There are 3 machines hadoop2 | hadoop | driver eth0 10.10.15.3 | eth0 10.10.15.2 | tap0 192.168.0.199 ...
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1answer
35 views

No response to TCP SYN packet when padding is not 0's or F's

I have this client which initiates a 3 way handshake with a SYN packet but there is no SYN ACK response. We figured out that it was because the client did not pad the end of the TCP headers with 0's ...
0
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1answer
13 views

Upgrading Web Application's Systems' Kernels for IW10 & other related improvements - upgrade all machines? LB first? Most important?

Stackers - We're making the push to upgrade the systems for our web app to take advantage of the various TCP improvements becoming more readily available (e.g. ...
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0answers
56 views

Nginx TCP Fast Open Issue

I have configured Nginx and Apache on one of my servers. The nginx server listens on port 80 and Apache on port 81. Nginx works as a reverse proxy. In nginx I configured TCP Fast Open: server { ...
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0answers
27 views

What happens if a machine gets a SYN/ACK packet without sending initial SYN packet?

I'm thinking of a situation where an attacker manipulates a SYN packet that was sent from A's source IP address to B. The server will receive the packet and think it's a legitimate packet, and send a ...
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0answers
59 views

TCP/UDP traffic forwarding to a different IP

I have the following configuration. Several remote clients are sending some data packet via TCP and/or UDP to a legacy server beyond an ADSL router. The router has a static public IP and forward ...
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0answers
7 views

How to make TCPFlow to not store package body?

Is it possible to configure tcpflow to store only package headers without package body? My log simply explodes in production.
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0answers
33 views

haproxy get ssl interrupt error, how haproxy tell server to close ssl or tcp?

I use haproxy 1.5 and a windows server build site. my site work under the https protocol, so for haproxy I use tcp mode since I think the ssl can not work on http mode. my problem is the ssl ...
0
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0answers
23 views

Can I use a domain name for a TCP process hosted in IIS?

I'm trying to set up a WCF service hosted in IIS 7.5, with TCP bindings. I also need to use a SSL certificate for security. From what I have read, I can add net.tcp as a binding type. However when I ...
0
votes
1answer
26 views

ssh tunneling lmgrd port what I've missed?

I've got 2 machines: one local , one flexserver I'd like to do a ssh connection for forwarding the TCP port of the flexserver. On the flexserver, lmutil lmstat -c 5280@localhost is working fine So I ...
0
votes
1answer
36 views

How to ping a host with different MTU size to simulate icmpv6 packet too big scenario?

As the Title states,I want to check whether my host will actually send a ICMPv6 packet too big if i send a packet with beyond the defined MTU size.I don't have a cisco router(extended ping) to try out ...
0
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0answers
122 views

massive amount of CLOSE_WAIT due nginx (lsof)

My VPS keeps hanging up every 5 days. I can see that the nginx worker processes are eating up my memory over time. I think this is due the massive amount of CLOSE_WAIT's open. When I type LSOF, I get ...
6
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1answer
212 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 ...
1
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1answer
122 views

Squid3 CONNECT imap.gmail.com:993 TCP_DENIED:NONE

I have the following configuration under squid.conf. However, when my Blackberry email client attempts to fetch new emails, etc. Squid access log show the following error: imap.gmail.com "CONNECT ...
1
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1answer
27 views

Does TCP's MSS hide a mismatched intra-LAN MTU?

I'm trying to understand how mismatched MTUs behave in a network. Suppose two hosts are able to talk to each other through an Ethernet-based network. The network and host A are configured for jumbo ...
3
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1answer
127 views

Common back pressure strategies for services under sustained high load

I'm wondering what are the common backpressure strategies people use for their web services? Imagine your service operates under heavy load, and at some point the load reaches 120% of your capacity. ...
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0answers
68 views

Azure intermittent outbound connection failure to EC2 [closed]

I have three Linux VMs (Ubuntu 14.04) running in a vnet, like this: Host Internal IP External IP prod1 10.0.1.1 104.45.234.56 <---\__ load balanced prod2 ...
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1answer
54 views

Forwarding ports and traffic to VPN tunnel

I've installed OpenVPN on my VPS. I have one question: how to forward traffic going to that VPS to go to VPN tunnel created with my local PC. I will use TCP connection. The whole traffic will be like ...
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3answers
242 views

How can one redirect to a new host all traffic destined for an old host?

We're moving a bunch of services, say from 1.2.3.4 to 5.6.7.8. In order to test that the new services are correctly configured, we'd like to redirect (to the new host) all traffic destined for the ...
1
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0answers
43 views

Why is SQL Server using all ephemeral ports connecting to itself and causing TIME_WAITs?

I've got an AWS server with Windows 2008 R2, SQL Server 2012, and Tomcat 7. When I run netstat -ano the screen is flooded with TIME_WAIT. I posted the output in a Gist. When I run CurrPorts, filter ...
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votes
1answer
64 views

How to artificially open many tcp connection on a host (testing)? [closed]

I'm trying to build a test setup which test my server's performance under high load. In order to do that I want to open thousands of tcp connection. The problem is that I only have two hosts, one is ...
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votes
1answer
83 views

IIS listening 127.0.0.1 instead 0.0.0.0

I configure binding on my IIS 7 server like: ip address: All Unassigned port: 8080 but in netstat -aon command see only 127.0.0.1:8080 instead 0.0.0.0:8080(which I would like) (0.0.0.0:8080 is ...
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0answers
52 views

After sending Duplicate ack by the server, it stop responding [closed]

My TCP client communicates with multiple 3rd TCP servers. However one particular server produces duplicate ack and stop responding in the specific time only. That particular server is OK other time. I ...
6
votes
2answers
160 views

TCP acks are paused, then resumed, then paused again. Why?

I would like some help finding the reason for the reduced data transfer rate in my application. I have 12 embedded systems and a Linux server. The embedded systems send data to the server over TCP on ...
1
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2answers
75 views

is it normal for NGINX to accumulate connections in writing state?

This is a graph showing connection count from nginx's stab_status, the drops in graph are server restarts done manually. I find this behaviour strange, looks like some leakage. I think there are ...
0
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1answer
32 views

TCP ACK Window shrinking

(Note: I am not a networking engineer) We are sending files to an outside vendor and getting random timeouts on different services. It seems that we are getting timeouts most often on larger files. We ...
0
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1answer
44 views

what could cause a not so busy redis server to close connection?

We have 17k tcp connection in CLOSING state on redis server. My understanding is that only client would initiate closing a connection, not from a redis server. So I should see 0 connection in CLOSING ...
0
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0answers
44 views

TCP connections drop off after initial build up

A bizarre problem on a production setup. Scenario 1) A server listens on a particular port. 2) There are potentially thousands of TCP connection requests. 3) About 200-300 TCP connections reach ...
0
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1answer
99 views

Windows Server 2012, application needs administrative access to open port

How can I grant an application access to listen on one particular port, without running it as Administrator or disabling UAC? Per policy, had to transition from an old server (Windows Server 2003) to ...
1
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0answers
13 views

How do I cap each individual tcp stream, to a fixed maximum rate?

I've read but not in depth all the various traffic shaping docs and seen the long question on HSFC scheduling Does anyone really understand how HFSC scheduling in Linux/BSD works? looked at the ...
0
votes
1answer
68 views

A LOT of connections from my external IP address to my web server

I installed Nagios recently on a Debian machine running an Apache web server among other things. The thing is that lately, Nagios tells me that the HTTP service is failing intermittently and it seems ...
1
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0answers
95 views

TCP High Send-q coupled with FIN_WAIT1 status

I'm having a problem with one of my webservers, which is taking minutes to completely render a web page. I had a look at the TCP connection and noticed that I have a very high value in the send-q ...
4
votes
4answers
1k views

Is there a way to see what is actually filtering TCP port communication?

nmap -p 7000-7020 10.1.1.1 Will output all the filtered ports Starting Nmap 6.40 ( http://nmap.org ) at 2015-03-04 12:18 EET Nmap scan report for 10.1.1.1 Host is up (0.00091s latency). PORT ...
0
votes
1answer
93 views

How do I open specific ports on Linux (an AWS instance of RHEL v. 7)?

I'm using RedHat version 7. My AWS instances are in a security group with ample permissions for inbound connectivity. I can do Yum updates. The servers can ping each other. I can transfer files ...
0
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0answers
38 views

TCP forwarding IIS

i have a server, let's call it: GATEWAY-SERVER (GS). On GS i installed a custom build TCP proxy/forwarder. This tool accepts connection TCP level and formulates a new request towards a TARGETSERVER ...
2
votes
1answer
76 views

How to filter for the most common problems with tcpdump/tshark

I am currently using the following command in Linux to get specifics on network problems. tshark -r file.pcap -q -z io,stat,1,\ "COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission",\ ...
0
votes
1answer
16 views

Windows Server 2008 sending regular TCP DNS requests to Forwarders

Our organization's primary DNS server is a Windows Server 2008 which two Forwarders set. I happened to notice on our firewall that this server is sending out regular TCP requests to the Forwarders in ...
3
votes
1answer
171 views

(Why) does FreeBSD 'net.inet.tcp.always_keepalive' violate RFC1122?

While working on a server application that runs on FreeBSD and uses TCP, I noticed that TCP keepalive probes get sent even though my application explicitly disables SO_KEEPALIVE on TCP sockets. ...
0
votes
1answer
40 views

length of Tcp segment exceed MSS

I find a weird behavior in my Linux system, when I curling a web page, the received TCP segments are significant larger THAN the MSS. here is the output of tcpdump: 00:00:00.000000 IP ...
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296 views

tcp connection reset [RST, ACK]

getting this errors looks like server is restating the connection because of some packet loss any possible suggestion's to figure out this 37713 591.925575000 ...
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0answers
184 views

Cisco ASA firewall blocking requests to internally hosted DNS server

I have a DNS server behind a Cisco ASA firewall. The Cisco firewall is performing NAT. When inside the network, I can NSLOOKUP directly to the server. When the client is external, requests time out. ...
0
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1answer
79 views

how to determine client side or server side retransmission from a pcap

I am trying to get some clarification on something I read here: how to calculate packet loss from a binary TCPDUMP file The first answer says that the sequence number will be the same from client to ...
0
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1answer
68 views

server is not responding on SYN packets

On the attached tcp dump, the first two SYN packets (#21800 and 21801) came to the server, however SYN ACK was sent for the second SYN. Is that correct behaviour? My understanding is that the client ...
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votes
1answer
64 views

How to redirect all incoming packets to sniffer in Linux using iptables?

I need to redirect all incoming tcp packets from eth0 to current host (change ip address from 1.1.1.1 to 1.1.1.2) and outgoing tcp packets from sniffer from eth1 to another host(from 2.2.2.2 to ...