Networking :: Server Stuck On Recvfrom And Client Waits On Receive
Apr 1, 2010
I have a problem with a simple client/server socket program. the connection is done through 2 connections a udp connection and a tcp connection. the flow is that the client sends a udp packet to the server and the server returns it through a tcp connection. this is done in a loop. my code works fine on an ubuntu server, when I try to use it on redhat it sometimes get stuck. the server is stuck on recvfrom and the client waits on the recv. if i add a delay in the server or run the client through strace everything works fine.
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May 25, 2011
Mu understanding of RFC 1122 (Fast Retransmit) is that upon receipt of the 3rd duplicate ACK, the sender should react by starting to retransmit the lost packets.
In my case, looking at the Wireshark trace, I see the sender receiving hundreds of DUP ACKS from the receiver and doing nothing about it until 200 ms pass by. Only then does the sender finally starts to retransmit. That's killing performance.
The sender is running Red Hat 5.3 (which is Linux 2.6.18). Is this an indication that the sender does not support Fast Retransmit? Is there a config param that I need to turn on?
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Apr 7, 2010
I am contemplating the use of DHCP options as a way of passing host-specific information to hosts that are booting disklessly from a network server. My intention is to have the DHCP client request certain options, and use the reply to configure the diskless hosts accordingly. The theory and rules behind all of this seem well documented on web sites such as die.net. However, the practical application of the protocol seems to be a lot less clear. What I am looking for is an explanation of what (existing, I hope) tool(s) are used, and how they are applied so that I can grab information from the DHCP server, and use it in userspace scripts or other programs. Specifically, my intention is to use a locally defined option that would give a host-specific directory name or filesystem to use by the diskless host to obtain host-specific applications and configuration data.
So far, all of the DHCP client documentation I've found relates to the usual function of assigning IPs, etc. I've looked at dhclient-script on a Redhat system and can't figure out the relationship between it and the dhclient program. Clearly, the script is invoked somehow by dhclient, but I don't understand where the transfer of data received from the server gets into the script. Does dhclient just create a list of exported environment variables the child script then gets access too? What are the rules for how variables are created and what variables are created?
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May 18, 2010
I have installed a working DNS server on my home network. I have an unique server, devoted to dns, gateway, storage which runs opensuse 11.0 (I known that it is rather old). Two new clients require DHCP. I have installed, using yast, a very simple DHCP server, according to the following config:
option domain-name "XXX.XXX";
option domain-name-servers 192.168.0.1;
option routers 192.168.0.1;
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(I have tried to add "ddns-update-style none", and to remove the ntp-servers option, since my server is not a time server, without success). Unfortunately, even if the client (a mac running OSX 10.4) receives a right IP and gateway address, it displays neither dns server address nor default domain name. The same mac, on my office network (not managed by me), receives everything.
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Jan 15, 2009
I ran a yum update this morning on my Fedora 10 box (i386), which updated the 'nfs-utils' package from 1.1.4-4.fc10 to 1.1.4-6.fc10. Before the update I was able to connect to the fedora NFS exports just fine from my Macbook Pro running latest version of Leopard on a simple home network. After the update, when I try to connect to the NFS export it waits for a while at leopard's "Connecting to Server" dialog box, and after about a minute I get a message saying "Could not connect to the server because the name or password is not correct" (though my UID's are the same on both systems). My /etc/exports and /etc/sysconfig/nfs files were unchanged by the update. I tried restarting the nfs services as well as shutting down iptables and setting SELinux to permissive, etc. with no success.
I get the following in /var/log/messages (192.168.1.102 is the address of my macbook):
I was able to download the RPM for the older version of nfs-utils and then do a 'yum localinstall' to revert to the older version. This fixed my issues completely and my setup works as it did before. However I am curious to know why the latest version of nfs-utils breaks my setup, and whether it is a problem with my setup or if I should just wait for the next version to come out and see if the same thing happens.
Here is my /etc/exports file. If I understand this correctly it should allow connections from anyone with an IP address on my local network.
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Mar 6, 2010
I have a directory that contains a bunch of sound directories containing WAV files.I want to make a script that plays one, waits 500ms, plays one, waits, etc.i tried cat `find . -name *.wav && sleep 1` > /dev/dsp.It plays them but with no delay between.
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Apr 12, 2011
I have a very basic install of dovecot and postfix on the latest version of Ubuntu server. This is an internal only email server with internal only DNS. I can send email via clients and check said emails via the command line when logged in as the appropriate user. I cannot for the life of me check said emails via SquirrelMail on the server nor using IMAP clients. I have no idea where to look and I can't find a basic tutorial for the life of me. Where should I start?
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Oct 2, 2010
I want to setup an email client in order to send/receive emails, but since i am experiencing some issues with my ISP, i decided to setup an SMTP server with Postfix on my machine.The problem is that i can receive emails but i can not send.I read almost every thread in here refering to Postfix, but i could not find the problem on my configuration.So here it is..
Code:
# See /usr/share/postfix/main.cf.dist for a commented, more complete version
# Debian specific: Specifying a file name will cause the first
[code]....
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Apr 13, 2010
Running Ubuntu Hardy and just installed synergy through apt get However each time I try to run the clinet all I get is - tried hostname etc and all fail - is there anything im missing
synergyc -f 192.168.1.50 INFO: synergyc.cpp,716: Synergy client 1.3.1 on Linux 2.6.24-23-generic #1 SMP Wed Apr 1 21:47:28 UTC 2009 i686 DEBUG: CXWindowsScreen.cpp,840: XOpenDisplay(":0.0") No protocol specified
WARNING: synergyc.cpp,337: cannot open secondary screen: unable to open screen DEBUG: synergyc.cpp,237: retry in 60 seconds
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Oct 4, 2009
It's been awhile since I posted anything which is a good sign my install has been working well and I have been able to handle most everything. However, I'm not able to handle this issue. I recently installed F11 and everything went well. But, when trying to see my other computers on the local network, I cannot. I receive this error message: Unable to mount location Failed to receive shared list from server. I understand the message as it is obvious, but do not know how to fix it.
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Mar 1, 2010
I'm using at struct sockaddr_in to receive multicast data sent out from another machine. When I print out the source address using inet_ntoa it gives me the source address of the PC that sent the data. This is ok but I would like to know if there is a way of getting the multicast address that the data was 'sent to'. I know I can see the multicast address in tcpdump being directed to my PC but I would like to be able to display the multicast address too? Is this possible or does the sockaddr_in give me the source address of the packet not the multicast address that the packet was sent to?
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Jul 25, 2011
I have a socket library that I tinker with from time to time. Lately, I decided to expand it to support IPv6.
One of the issues I am having is sending data, using sendto(). When the server receives data from a client, using recvfrom(), it does not retain the sockaddr_in information, but instead provides the callee the IPv6 address and port number from where the data originated. See here:
Code:
int
UDPSocket::recv(char* buffer, size_t bufferLen, std::string& sourceAddr, unsigned short& sourcePort)
{
sockaddr_in sin;
socklen_t sinLen = sizeof(sin);
[Code]....
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Jun 11, 2011
I configured openLdap in RHEL5 on virtual achines,everything is working fine, I created a user called ldapuser,in LDAP server and i created a home directory for ldapuser in my LDAP client, now i can able to login to the both Server and client with ldapuser account....
Now here what am expecting is i want to export my server's home directory to the client, i dont want to create home directories manually in the client machine, i googled about that, and it can be done through autofs.....
what need to be done on the client and server side.
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Nov 27, 2010
I have 2 ethernet cards but when I look at the Network configuration in "Hardware Tab" I have another acx wireless network. How to delete that because In my system Idon't have wireless card..probably installed before but want delete it now.
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then windows can ping server and resolve ip address and browsing Internet but can't ping [URL]... result is Request time out. ICMP already enabled in iptables.
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Dec 18, 2010
I have a server with Fedora 13 with which I would like to get NFS working. I have looked up multiple howto's and tutorials, but I'm having a problem not addressed by any of them.Official how-to, another how-to, and another how-to.I have verified that nfs-utils, nfs-utils-lib, portmap, and system-config-nfs are installed and running. I have verified that I have, in fact, shared the directory that I want to share, and that the proper permissions are set.
I had to go through some gyrations to get the Belkin wireless N router to allow my server to have a static IP. However, I can ping the server from the nfs client (a toshiba satellite running mint 8), and vice versa. I have (for now) disabled firewalls on both computers. I think I have disabled SELinux on Fedora 13 (for now).When I attempt to connect to the server from the client, the output looks like this:Quote:
aragorn ~ # mount -v 192.168.2.101:/test /home/kelev/test/
mount: no type was given - I'll assume nfs because of the colon
mount.nfs: timeout set for Sat Dec 18 12:21:09 2010
[code]....
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Nov 14, 2010
I have a wireless router situated in another room. I am able to access this router (and consequently the internet) through a Windows laptop that has a wireless card in it. However, my other laptop that has Ubuntu 10.10 installed on it, doesn't seem to have a wireless card in it, and I have confirmed this by running the commands
Code:
lspci
and
Code:
iwlist scan
I briefly was able to share a folder in my Windows machine, and access it through my Ubuntu machine, after connecting both laptops with a cross-over cable. However, I can't even ping the Windows machine from my Ubuntu machine anymore, after trying to configure the IP addresses. I think I screwed it up.
Also, although this is not an Ubuntu issue, I have a weird Windows problem, where I can't access the Internet when both wireless and wired ethernet controllers are active at the same time. It would be a bonus if you could solve this problem too for me. I was surfing online for a solution to this problem for quite some time, but I was unable to comprehensively understand and implement what I browsed through. Also, some of the guides, like for example, that on configuring Samba, seem to be outdated, as the terminal tells me something like the package (that was required to be installed by the guides through sudo apt-get install) has been superceded. Hence I post here for clear, concise and easy-to-understand help from you gurus. It would be great if I could achieve the end result of being able to access the internet on my Ubuntu machine (through the Windows one).
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Apr 19, 2010
I'm trying to synchronize a client with an ntpdate server. The ntp.conf file from the server has the following lines: # /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for
driftfile /var/lib/ntp/ntp.drift
# Enable this if you want statistics to be logged.
#statsdir /var/log/ntpstats/
statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
[Code]...
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Jul 5, 2009
How I am configure DNS Client and server in Redhat Linux 4 in my lab.I have total 5 computers and they are Lan connected.I want to make one of them server and the others are client.
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Jun 16, 2010
I'm trying to setup a linux box to act as just a DNS server. Its something I'd like to use just for WAN type requests and leave other domain related things to the Server running WIndows.At this point on my Linux box, I can run queries and nslookups from it. I can not however, from a Windows box, run a NSLOOKUP command from the Linux box which is telling me to check the permissions from Linux to enable that for the clients. It's enabled.From a C: I type in nslookup - *ip of Linux box* and it tells me -- Can't find server name for address.
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Feb 4, 2010
Running Linux Fedora 10 on an Intel Core 2 Duo PC. Runs great. We are trying establish VPN between a client and server on the same LAN. The network is a standard fast ethernet, run great. We are trying to install OpenVPN server, but having a little difficulty. Key and certificate builds seem to execute without a problem. But when we try to start the service we get [FAILED]. I've attached a copy of our procedure.
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May 7, 2010
Is it possible for a client to "export" or "send" it's /dev/cdrom0 to a server via SSH? I have managed to st up a connection with Xserver so I can see the servers gnome interface in my ubuntu client.
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Oct 20, 2010
Can we create both server and client on the same system. I want to know whether it can be used on the same system.
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Feb 16, 2009
in my office all users connect to internet via VPN.in our office there is one special server that we want when users connected via VPN,users can not connect to the special server and when users are not connect to via VPN can connect to that server.
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Apr 12, 2010
We have a problem with tcp link.
Os version: linux 2.6.9
Client will connect 2 tcp links to server.
One link is ok but another can't.
From tcpdump, we see:
1. client SYN-----> server
2. server SYN/ACK---> client
3. client ACK ----> server
4. client data ----> server
5. client retransmit data some times ----> server
6. server SYN/ACK ----> client (weird, it look like server miss the step 3)
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Oct 26, 2010
I have an Ubuntu server that is currently running Ubuntu 8.10. I was thinking of making it a VPN server for my iPhone and also for my laptop whenever I'm outside and need to access internet over insecure wireless networks. Now that part should be easy I found several guides on how to configure OpenVPN server, as well as enabling clients on iPhone, and OSX.
However, the things is that my server is currently a OpenVPN client also, I have a paid tunnel set up to bypass my ISP blocking incoming traffic on various ports. Is it possible to keep this setting but still enabling a VPN server? Essentially causing traffic from my external device to go in through my tunnel to the VPN server, and then out through the external VPN provider.
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Jan 26, 2011
I'm currently successfully using the Terminal Server Client to connect to an SBS 2003 server at a remote location. I've been trying to figure out if it's possible to connect to any of the XP machines on the LAN behind it. I currently have to use RWW in IE on a VirtualBox XP machine to do that, and I'd love to be able to get rid of VirtualBox completely.
The server has 2 NICs, one connected to the internet, and the other connected to the LAN. There is only one public IP. The computer I'd most like to connect to has a static, private IP. Anybody done anything like this or have any thoughts on how to get it to work?
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Aug 24, 2010
I am facing connection refused error 111 in TCP client server program, in android native code which in C , but if code is in JAVA it works fine, but i want to continue in C only, in manifest file i have given permission and ip, port is correct .What am doing wrong?? or is their any network setting?? am using UBUNTU 10.04and If both client server Linux pc it works fine. only if android emulator becomes client then am getting connection refused
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Sep 5, 2010
I have about 5 computers on my network that get their internet connection from a Linux NAT server.
192.168.12.02 is a Linux server that has a NAT set up to share the internet connection.
192.168.12.03 is a download server that is almost always downloading
192.168.12.05 - 192.168.12.20 is assigned by DHCP to users.
I want to make it so that the download server runs at full speed but is throttled only when someone from the user IP addresses range tries to use the NAT server.I think I'm looking for some way to set the download server's packets to have a lower priority than the client's packets. Is there a way to set this in the Linux server?
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Mar 7, 2011
Was trying to understand the behavior of TCP when the server becomes unreachable . For this I am using vsftpd and the default linux ftp client to check the behavior.I was trying the following things. Was Trying to download a file from an FTP server using the FTP client as anonymous user. While the file is getting downloaded, I removed the network cable from the FTP server to understand the behavior of TCP when the server becomes unreachable.
As per the functionality of TCP/IP , when the server becomes unreachable for whatever reason , the client tries retransmitting the data till it can send the data or it timeouts. But in my above experiment using FTP , I can see that the FTP client is not trying to retransmit data at all . This I came to know using by sniffing FTP traffic at the client side. Is this expected or default FTP client available in Linux does not obey TCP/IP functionality properly ?
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Sep 12, 2009
I have one Windows-XP on Machin 1 and one Linux on Machine 2. I want make Linux machine as CVS server and Windows Xp as CVS client. How to setup CVS Server in Fedora-11 machine and CVS client in Windows Xp?
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