Linked Questions

1 vote
0 answers
171 views

Server does not respond to SYN [duplicate]

When I launch an FTP transfer from a client machine, it fails because it cannot connect to the server. With tcpdump I can see that the client sends a SYN to the server, and I can also see that the ...
Baroudi Safwen's user avatar
7 votes
1 answer
16k views

Outbound Packets Dropping / Timeouts - Only with Azure

I have an issue with packets dropping to a third party data center in Florida, USA. The issue only occurs on Azure Virtual Machines, no matter which data center the VM is in. I've done the same tests ...
Andrew Bucklin's user avatar
2 votes
2 answers
7k views

many different TCP timestamps through NAT device cause server to drop packets (PAWS)

Various workstations behind the client side Network Address Translation (NAT) firewall are sending timestamp information on the TCP packet to our server. The packets from many workstations arrive ...
user93453's user avatar
9 votes
1 answer
5k views

No response to some SYN packets when timestamps are enabled

I have a TCP server listening on a machine ("the server") running Ubuntu 12.04.3 (kernel 3.8.0-31-generic). It receives connections from 2 different client machines. Machine A is running Ubuntu 12.04....
user133831's user avatar
0 votes
1 answer
7k views

No SYN-ACK Packet from server

I have two servers and I used my own embedded system with LwIP to do connection to these server. My embedded system with LwIP is the client and I have server1 and server2. I connected to server1 and ...
Sue Koh's user avatar
2 votes
2 answers
9k views

kernel reported iSCSI connection 1:0 error (1022-Invalid or unknown error code) state (3) Fed 25/VessRaid/rsnapshot

We run rsnapshot (rsync) and use ionice & nice. Towards the end of the backup memory usage explodes and the below iSCSI errors start appearing. This is a Dell PowerEdge 1850 running Fedora 25 with ...
RobbieTheK's user avatar
1 vote
1 answer
6k views

Is it fine to turn off tcp window scaling and tcp timestamps on server?

Our application is running on Amazon server and we were continuously facing the issue related to tcp handshaking. Sometimes we were not able to connect to our application or telnet on port 80 of our ...
Sidd's user avatar
  • 11
0 votes
1 answer
4k views

Linux server failing to send SYN/ACK after receiving SYN remotely, works locally

Problem: A server process can be accessed by a device on the LAN or by the server itself, but it cannot be accessed outside the LAN (port forwarding is configured correctly as the server does receive ...
Lynxy's user avatar
  • 21
1 vote
1 answer
4k views

Why does my linux box fail to send SYN/ACK until after eight SYNs have arrived?

Two people are using different PCs behind the same NAT box. They are regularly accessing the same website, hosted elsewhere. Intermittently, one of them sees the website take several minutes to load. ...
SteveRawlinson's user avatar
1 vote
1 answer
2k 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 ...
sidorvm's user avatar
  • 11
2 votes
1 answer
2k views

Linux clients can't connect, server and TCP Windows Size / Timestamps issue

We have a problem that a number of clients (all linux Ubuntu) are sometimes not able to connect to a remote server over SSH. If the problem occurs, Windows clients don't have that problem and can ...
Tom Cannaerts's user avatar
0 votes
1 answer
1k views

Linux servers sometimes doesn't answer TCP connections or very delayed

I have Linux server (Ubuntu 16.04) where every serverce seems to be fine, except that it sometimes answers TCP connection very slowly (eg. 10 -20 sec) or not at all. The server is not under load and ...
Gene Vincent's user avatar
0 votes
0 answers
605 views

"Filtered" port when accessing server

I'm having periodic trouble accessing one of my DigitalOcean servers from Azure machines. I have isolated a test that - I believe - demonstrates the issue and captured a tcpdump from the server for ...
Charles Offenbacher's user avatar
1 vote
1 answer
412 views

Weird AWS EC2 accessibility problems - Ubuntu, nginx, iPad

I would not say that I am a total newbie to server administration but obviously I have missed some key moment here... Problem: Connectivity to the server lost (like lockout via firewall on the server)...
Didzis's user avatar
  • 121
1 vote
0 answers
97 views

Troubleshooting steps when the server not responding to some SYNs

What are the troubleshooting steps that I can take if I see that my Linux server does not respond to some of the SYNs that are being sent to it? (I know this from PCAPs that I recorded on my server) I ...
Hillel Schattner's user avatar