Linux Networking refers to any networking function performed by a server running Linux. A Linux server operating as a router or firewall are the most common applications.

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Reduce ACK frequency

Good morning, I understand the basics of the ACK response including SACK settings, receiver windows and congestion windows. I wondered is it possible for the server to tell the client the maximum ...
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19 views

Listening to all IPv6 Addresses? [duplicate]

I have a Server that has a /64 IPv6 block assigned to it (fully routed to the Server according to the network technician). Is there a possibility to have the Server listen on the entire IPv6 block? (I ...
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18 views

dns server ip address is not written into resolv.conf

linux mint 17.3 i have to manually write "nameserver 8.8.8.8" in /etc/resolv.conf on every reboot, it also gets stuck with message "waiting for network" where i press "ESC" button to skip that and ...
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1answer
17 views

smb prompting me for root password?

I issued the command: sudo smbclient -L //serverXYZ to list the shares on a remote Windows server on the network and Ubuntu system asked me first for my password (I am a sudoer), then it asked ...
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5 views

Connecting 2 servers with QLogic BCM57810

I'm experimenting with different ways of connecting 2 servers together I already have 2 Qlogic BCM57810 and Avago AFBR-709SMZ along with some fiber patch leads. This is my first time playing around ...
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1answer
39 views

UDP multicast send/receive: Routing or socat issues?

I'm using 'socat' on Linux Centos 7 to diagnose some problems. Server and clients are all linux centos7, they all have multiple interfaces. Server 10.1.1.1 is on Switch 1, 10.1.1.2 is on Switch 2. ...
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13 views

Maximizing file sharing speed to macs from linux

I am trying to set up a very high performance linux-based NAS to replace older iSCSI and eSATA drobos around the office. I’m trying to find the best open tools for running a high performance mac ...
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17 views

SSH connections via pivot [closed]

I'm searching for way to make next environment: I have a lot of network managed by ssh. I need to install one linux server and every ssh connection to any network device should go via tunnel through ...
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1answer
24 views

Forward port and keep source IP

I have a system with a static IP address running several LXC containers. I can communicate with the containers over an interface as it would be a physical machine. One of this containers is a postfix ...
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17 views

how to make a console server using a VM [closed]

i have a headless server and a windows 10 PC, I want to connect to the console of the headless linux server. so i found this cheapest solution: https://help.ubuntu.com/community/SerialConsoleHowto ...
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31 views

How to forward traffic from A to B on the default gateway for sniff? [closed]

I have the following devices: A laptop (192.168.1.128) A Linux box (192.168.1.156) A router running OpenWRT(also the default gateway for the LAN) (192.168.1.1) Now I want to achieve the following: ...
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1answer
99 views

When wouldn't an ARP reply be generated?

Summary of the problem: a ping from client does not go to rpi1, its ARP call is not answerd at srv. host0and tap0 are bridged by br0. vpninand lan0 are two independent interfaces. All traffic ...
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39 views

My CGI program written in C langauge on Linux gets download instead of execution from HTML [closed]

I am Embedded Software Engineer, I am new to Embedded Web Server programming, I wrote the HTML code which is simple form as the code shown below : <form action="/cgi-bin/gpio.cgi" method="post">...
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1answer
17 views

Ubuntu 12.04 server cannot access anything outside

My Ubuntu 12.04 server was working fine a few days ago. But today I couldn't access anything outside. And i cannot ssh to my server neither. I am directly plugged into the console through my vps ...
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1answer
66 views

tcp source port is not randomly

When we trying to get a file from a web-server, sometimes access is not possible. After checking the communication with tcpdump, we saw that the Source-machine is randomly choosing a source-port for ...
2
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1answer
16 views

Ubuntu VMware (Windows Host) - Apache only routeable by LocalHost

I am a Windows based, python developer, who is currently working with configuring his first linux VM. I am able to get the VM set up, with internet access. I can apt-get with no issues. After ...
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13 views

Configuring Bidirectional Host Based Authentication in SSH [closed]

I have 3 servers (Ruby, Sapphire, Onyx) that I have been trying to setup passwordless (host based) authentication between for all users. I've configured the machines to use host based authentication ...
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15 views

Iptables don't load balance

I have consulted multiple tutorials to achieve load balancing over two internet connections. However, all traffic continues to get routed over the default route with the lowest metric, and I can't ...
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25 views

Can't open some websites in linux

I have a machine with debian jessie 8.3.0 on it that i use as a hotspot service (coova chilli, free radius) at my work office and is behind a pfsense firewall. but after 3 days ago, i cant browse some ...
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11 views

How to redirect traffic every time when service hostapd is started?

I have been using iptables to redirect all traffic to remote host on port 80 towards my local proxy 127.0.0.1:8080 for testing. I used iptables -n nat -L to check if iptables is set. sudo iptables -t ...
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2answers
80 views

Martian sources from my public IP

These days I get some Martian packets in the kern.log: Jul 7 02:28:20 box14932 kernel: [789192.798073] IPv4: martian source XXX.XXX.XXX.XXX from 10.91.12.01, on dev eth1 Jul 7 02:28:20 box14932 ...
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1answer
17 views

Sending shutdown messages to all clients from server

I'm trying to find a way to broadcast a shutdown message to all the users on clients connected to my centos server. The wall command sends only to users logged into the server and not to clients .I ...
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1answer
43 views

Small LAN Linux fileserver and network design

We have a small LAN with a couple dozen desktop client PC's and one fileserver. Our goal is to enable the client PC's to have all storage on the fileserver and for file I/O operations to feel as if ...
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33 views

cpu load and nfs performance

I have an issue about nfs performance. The server is connected via an ISCSI connection TO a SAN. I have sometimes and more and more often load picks and client freezes. I added RAM and try to ...
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1answer
58 views

How to use native ipv6 together with 6to4? I got lost packets

I've found that I can't run native IPV6 interface (at eth0) with 6to4 tunnel (at tun6to4) together. Here's my setup (/etc/network/interfaces/): auto eth0 auto bond0 iface eth0 inet static ...
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1answer
27 views

Subnet cannot access internet on CentOS 7 with VMWare

Using VMWare Pro, I have two nodes with Centos 7 installed - one connected to my router with two network cards. The other is another node I want to connect to the internet on a different subnet. It ...
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1answer
27 views

PostgreSQL not listening on local eth1 after reboot

I have a server with 2 networking interfaces - global on eth0, and local on eth1 with IP like 10.181.xx.xx. Running Ubuntu 16.04. I set up PostgreSQL to listen on this local address, so another ...
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1answer
59 views

How to figure out why my NAT-box sends TCP RST packets?

TL;DR: I see that an ubuntu (which I have an absolute control of) host sends a packet under certain circumstances. How to find the application/kernel module responsible for that packet? I am ...
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1answer
14 views

Centos 6 Require Password to Enable NIC

We are using a dedicated NIC as a port forward target to allow support access to port 22 on a CentOS 6 machine. I would like to prevent the NIC from being enabled without a password. I know I could ...
2
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1answer
82 views

dhcp server gives “no free leases” error although there should be available IPs

We have a small HPC cluster of about 40 machines running Rocks Linux Distro 6.2 (based on Centos 6.6). I have been trying to add 6 more machines to the system in the last few days. The first 3 were ...
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1answer
30 views

Difference between vlan and ip aliasing from user perspective

I was reading information about vlanand how to manage it on GNU/Linux. Whenever I needed to add a second network to the same physical NIC I would do ifconfig eth0:test 192.168.66.1 and with it I ...
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1answer
45 views

Can't access apache webserver remotely after connecting to VPN

I have an apache webserver installed on my pc whcih works as expected untill I connect to my VPN service provider (Private Internet Access) using their software. Once connected I'm no longer able to ...
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32 views

How to upgrade Ubuntu to 16.04 LTS and not lose network access

When I upgraded one of my servers to 16.04 LTS I had to adjust network configuration (I use interfaces file) and use the new network interface name. I was lucky that the server runs in a VM and I ...
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1answer
50 views

DH GEX group out of range

I'm having a sudden issue SSHing into my server: ssh -v --@-- OpenSSH_7.2p2 Ubuntu-4ubuntu1, OpenSSL 1.0.2g-fips 1 Mar 2016 debug1: Reading configuration data /home/paul/.ssh/config debug1: Reading ...
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19 views

How can I make Kickstart chose which build to run, depending on the subnet of the client?

I have 2 possible subnets that systems could be built in using Kickstart, with the subnet of the client directing which build should occur. How could I go about this? I have tried the following %...
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1answer
148 views

CentOS 7 connectivity issues

I have a second CentOS 7 box that's having a lot of trouble connecting. Basically, we were running WHMCS, but a domain lookup kept failing. So the issue is IPv6 connectivity. [root@da01 ~]# yum ...
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1answer
26 views

TCP retransmission delays - lost acks

Maybe somebody will be able to help me out with this. I'm trying to find out if there is anything that can be optimized server-side to reduce delays in case of packet loss. Environment: Windows 2012 ...
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4answers
49 views

How to get list of all the hostname / DNS of the Linux box

I have a Linux box and I know I can get the list of IP addresses assigned to that box using following command /sbin/ifconfig -a but how to I get the list of hostnames / DNS for that Linux box using ...
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40 views

Pervent connman disable wired interface

I'm running application over Centos 7 using Connman to manage connectivity. I have one issue working in the following scenario: Wired connection is enabled and online, have inet connection in this ...
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1answer
63 views

cannot use localhost but 127.0.0.1 works

My usecase is that I manage remote computers using reverse SSH tunneling. This works great as our customer enable the tunnel and I can then log on using it. However, on one machine the tunneling ...
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5 views

Configure network card without knowing its name [migrated]

I have a domestic headless server that boots from (and has the root filesystem in) a removable USB stick. I install it from my laptop (following this nice checklist) and edit the configuration files ...
2
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1answer
55 views

Close all _existing_ TCP connections on some ports using IPTables?

Say I have a quick network partition test that I'd like to run, like disconnecting two halves of a ReDiS cluster from each other, and I want to use IPTables to temporarily disconnect one group of ...
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2answers
38 views

How can i set my new ip adress? [Debian / Ubuntu] [closed]

I have my own VPS at OVH and it comes with a default ip address in France. So for geolocation needs, i bought one for in the UK. Now i have Ubuntu server 16.40 running, and i want to set my newly ...
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2answers
88 views

Linux block outgoing traffic to a specific ip without iptables

I basically need to run the following iptables -A OUTPUT -d 169.254.169.254 -j DROP except I cannot use iptables because the program is running in a docker container and I cannot use the --privileged ...
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1answer
27 views

KVM - Adding public IP over bridge

I am working on setting up a KVM environment and normally I just take it for granted that the networking has been set up. I am running into difficulty getting the public IPs accessible from the VMs. ...
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12 views

Sar command “sar -n EDEV -f /var/log/sa/sa16 -s 11:00:00 -e 15:00:00”

sar -n EDEV -f /var/log/sa/sa16 -s 11:00:00 -e 15:00:00 I am using above command on Red Hat Enterprise Linux Server release 5.9, and below is the output to that:(Dev error form 11 am to 3 pm). I have ...
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28 views

Iptables u32 matching nat

I'm currently setting up IPtables to redirect certain UDP payloads to my application. Here is an example of what I have working so far: iptables -t nat -I PREROUTING -p udp -d {IPDST} --dport 27055 -...
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1answer
36 views

Debugging dropped UDP messages on Linux

Here's my setup: I have 1 host that has a 1 Gbit Ethernet connection and 2 hosts with 100 mbit connections (connected to the 1Gbit host through different switches). In a test, I send 1000 1kb ...
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22 views

Same mac addresses discovered in VM for bridges on host machine

I have two bridges on host machine, named br0 and br1 (having different mac addresses). A VM is connected by bridged networking through br0. Now VM is able to ping br0, which is normal. But it is also ...
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6 views

Username lookup for TCP Wrapper

I would like to ask people in this community regarding to TCP Wrapper. My OS environment is below. [root@server1 ~]# cat /etc/redhat-release Red Hat Enterprise Linux Server release 7.2 (Maipo) [...