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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Linux networking essentials

Can someone suggest a book which contains all the essentials required for linux networking. I need something that common to all linux distributions rather than specific distribution. Thank you Bala
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How virbr0-nic is created?

How can I create a virtual network interface like virbr0-nic? I am trying to find a way to create a NIC like virbr0-nic but everything which I can find on the Internet is how to create an interface ...
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Why there are always 10% of loss when testing with mtr command?

For example, if I run this command against example.com, with mtr command, I always get 10% of loss, no matter how many time I run, why exactly is 10%? mtr --report 192.0.43.10 HOST: localhost Loss% ...
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How can I Nat certain boxes in my datacenter so that they are coming from a single IP

I want to NAT a certain group of servers in my datacenter so that they all access clients from a single IP. This will make it much easier for documentation that we provide clients. However there ...
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1answer
62 views

Difference between ip link eth down and ip link dev eth down

What's the difference between ip link set eth0 down and ip link set dev eth0 down ? The difference between the commands does not appear to be documented anywhere.
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DNS points to the right IP, but I can't connect using DNS

UPDATE: This is now strictly a local problem, connecting remotely works (a dumb mistake I made.) I think it's now it's a loopback issue, which is a different issue, and likely answered in another ...
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118 views

IPtables NAT puzzler: Why is traffic from the firewall host being NATed even though it's not coming from one of the prescribed source addresses?

I run a small network where a linux web/mail server also provides NAT for a collection of windows boxes. One of these windows machines is apparently misbehaving (ZeroAccess botnet even though I can't ...
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1answer
907 views

iptables: why only OUTPUT rules are needed for samba clients?

I tried the following iptables rules for samba client and they worked. Please note that policy for INPUT, OUTPUT and FORWARD were all set to DROP iptables -A OUTPUT -m state --state NEW,ESTABLISHED ...
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3k views

how to setup subdomains for AWS EC2 Ubuntu Instance?

I am trying to setup subdomains for my AWS EC2 ubuntu instance, but without enough knowledge I couldn't proceed anymore. I have a parked domain name example.com on a domain name service provider. My ...
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Server sending out packets bigger then MTU

I have a server that I am transferring data off of. We were having some problems that were traced back to the fact that the server is sending out jumbo size frames despite the fact that ifconfig is ...
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1answer
2k views

Port appears open locally but closed from another machine

I am currently trying to set up a Hadoop distributed compute cluster on my network. Currently. my cluster nodes are encountering a problem communicating with my master server. Right now I am working ...
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2k views

Eth0 Interface Not Coming Up on Fedora 14

I'm trying to upgrade some old Fedora 13 servers to Fedora 14 following Fedora's docs. The yum commands ran very quickly and seemingly without error. However, when I rebooted after finishing the ...
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Ubuntu Ignoring packets from network A on eth0 when eth4 configured on network A

I have an Ubuntu 12.04 (final beta, up-to-date) server with two configured network interfaces: root@mac:/home/sysadm# ifconfig eth0 Link encap:Ethernet HWaddr 00:1e:4f:28:fd:7b inet ...
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1answer
763 views

How to change netmask with iproute2?

With ifconfig we can change the netmask with the folowing: ifconfig eth0 netmask <new netmask> How can we do this with the command ip? I know ifconfig is deprecated and this mostly why I ...
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2answers
411 views

Using linux server as router for network

I would like to setup my Debian Lenny server as a router for my home network using iptables, but so far have been unsuccessful. Below is a diagram of the desired network architecture INTERNET - ...
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104 views

Two LAN cables when using Remote Access Card?

I recently bought a HP MicroServer N54L and a HP Remote Access Card. Connecting to the server over a KVM viewer for BIOS setup etc. works fine, but when it comes to installing Ubuntu 14.04. the ...
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1answer
122 views

iptables: does a scanner knows if you DROP packets?

I know how REJECT and DROP chain works. But, as I read here REJECT vs DROP when using iptables, user Dagelf said that the server still replies with TCP SYN/ACK. Does the scanner knows that a packet ...
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475 views

Assign different Hostname to different NIC

I have four network card on my server, I have assigned each with an specific IP now I want to set an different hostname for all the interface? What is the difference between setting the hostname in ...
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2answers
979 views

Linux: how can i configure dot1ad(double tag) on a interface?

I am on SUSE, and able to configure dot1q(single tag) for an interface. How can I configure double tagging on an interface? Thanks.
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247 views

A thin client running Linux in a wireless network environment

I am the sole IT person for a small private school. The school has about 60 PCs. All PCs are on a wireless network; there's no Ethernet network in the building. I would like to migrate the school ...
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1answer
153 views

iptables to drop for a while IPs with recently failed connections

I want to decrease the likelihood of a successful ssh attack on a linux system. The only port that is open is 22 (I use port forwarding for everything else), and of course I made sure that ssh accepts ...
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1answer
2k views

Linux server equivalent of Cisco Discovery Protocol (CDP)?

I am wondering if there are any Linux tools out there which might aid in identification of hosts directly connected to each other (much like Cisco Discovery Protocol on switches)? I have found ...
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168 views

Pro Linux Administration Guide / Book [closed]

We run a cluster of 45 linux machines with a lot of different stuff running (nginx, Varnish, Apache, MySQL, memcache etc) and load getting balanced on different machines. We do around 3000 requests ...
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How do I enable TUN/TAP forwarding?

I have a program which writes packets (destination address 10.3.0.2) to the TUN/TAP interface. Network: host1|tun0----eth1(10.3.0.1)|-------------------host2|eth1(10.3.0.2)| Wireshark captures ...
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How do you deal with malicious IP's?

I'm trying to figure out how to protect my server against what it seems to be a botnet (I'm just guessing) Everyday, more and more IP's fill my application logs with invalid request (eg: GET requests ...
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995 views

Linux IPv6 loopback routes getting automatically added

We have a router running Debian Lenny that has been happily routing IPv6 for several months. Our upstream has advised that our address range is changing, and both are currently operational, so I ...
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136 views

Sending Data extremely slow or RDS

I have the following two profiles for a basic SELECT STATEMENT: select count(*) from mturk_completion; Here are the two profiles: # My Local machine, using a local db Status ...
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1answer
557 views

Cannot ping to localhost into CentOS

I'm connecting to my server (Centos 7) with ssh and I try to ping to localhost: ping 127.0.0.1 but doesn't work: ping 127.0.0.1 PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data. ^C --- 127.0.0.1 ping ...
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101 views

Is Linux limiting my application's UDP transfers, and how can I see it?

I am currently developping two applications to work over a custom video streaming "protocol". Basically: The server captures video frames from a webcam, slices them into parts, and sends these parts ...
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1answer
1k views

Using Firewall-cmd to create address specific restrictions in centos 7

How do I create a firewall rule using firewall-cmd tool (new firewalld) such that I will limit specific network to access only one service and allow all on all service in one zone. For example: I ...
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1answer
496 views

Keepalived load balancing MySQL. Backup server time-out

Dear beloved people at ServerFault. I'm trying (and failing) to setup a load balanced MySQL server array. Please enlighten me, show me the error in my ways. Current setup: two MySQL servers with ...
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how to configure two ip blocks for use on a network

My ISP has given me a /30 and a /27 ip block I can use. for the sake of not giving out my ips I'll use 192.168.1.192/30 and 192.169.1.224/27. I'm not using a router in my setup, I only have a switch. ...
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Server Won't Autonegotiate to 1Gb Interface

I'm having an issue where some of my servers are not autonegotiating to the 1GB/s speed from their 1Gb NIC interfaces. These servers are Dell R610s running RHEL 5 wired to a Cisco switch. I have ...
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IPv6 configuration SIOCSIFADDR file exist

I am configuring IPv6 address in a Debian machine, and this is what I have in my interface file. auto eth0 iface eth0 inet6 static pre-up modprobe ipv6 address 2001:23:207:141:0:0:0:0 ...
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262 views

Linux NetBIOS name relay

I have a bridge, over WiFi, that is using parprouted to fudge ARP so that routing works. Is there anything like dhcrelay (which relays DHCP requests) but for NetBIOS (Windows File and Print Sharing) ...
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1answer
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strongSwan ipsec setup, couple of questions

i am trying to setup a IPsec bridge between my home network and my office network. I want to use StrongSwan to encrypt the traffic as IPsec i am trying to follow this guide A brief description of ...
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1answer
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Iptables - Forwarding + Masquerading

I am new to iptables and trying to set my linux server as a gateway for my other computers.So naturally I am playing with iptables and needed some help My server has 2 NIC cards, eth0(WAN) and ...
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4answers
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Hostname problems in CentOS 5.5

I just set up a CentOS 5.5 machine on my local network and attempted to modify the hostname by editing /etc/sysconfig/network file. When I'm logged in locally the change to the hostname is reflected ...
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How to configure a Linux network namespace that allows UDP broadcast

I'm trying to use the ip netns family of commands in Linux to create a network namespace in which I can run a program that uses UDP broadcast. I do not need access to the Internet, or any interface on ...
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138 views

IPv6 Stateless Autoconfiguration route advertisements

In our network, we have a Cisco router acting as the core router, connecting all our sites to the main site. We also have a Linux firewall connecting us to the Internet. Site 1 --\ ...
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1answer
182 views

How to route traffic through different interfaces based on the port number?

iptables -A PREROUTING -i usb0 -t mangle -p tcp --dport 8080 -j MARK --set-mark 1 iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain ...
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1answer
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Linux bridging for KVM

I have a Debian Wheezy machine on which I tried to setup KVM with bridged networking. Unfortunately, the bridge does not appear to forward traffic correctly. My setup is the following: The physical ...
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1answer
5k views

Diagnosing packet loss / high latency in Ubuntu

We have a Linux box (Ubuntu 12.04) running Nginx (1.5.2), which acts as a reverse proxy/load balancer to some Tornado and Apache hosts. The upstream servers are physically and logically close (same ...
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1answer
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OpenVSwitch between namespaces

I'm trying to configure a bridge between two TAP interfaces each created inside their own network namespace, on Linux. I'm using OpenVSwitch as software bridge. These are the steps that I believe ...
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1answer
149 views

Linux router: bandwidth of client

I am trying to build a linux router (captive portal) with a local RADIUS server for authentication. I want to log the bandwidth being used by each client on my network. I want to associate bandwidth ...
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1answer
120 views

How can I create an environment to test OpenVPN with in a test lab?

I have a test lab that I would like to use to test a site-to-site VPN setup with using OpenVPN. What is the minimum amount of hardware that I need and how should it be configured so that I can mimic a ...
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iptables: How to forward packets with destination port 80 from eth0 to eth1?

I've http and https traffic coming from several machines to my eth0 on my Linux machine, but I want to forward these traffic to eth1 which has the access to the internet. And do the complimentary ...
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548 views

Limiting a process' network access on Linux?

I've been researching how to sandbox processes, and I came across cgroups, which looked promising. I'm not super interested in using virtualization or strace for this, since I want programs to run as ...
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Linux does not get IPv6 default gateway from Cisco ASA5510 on autoconf

My ASA 5510 has the following configuration for an interface. My Ubuntu box (2.6.35) connected to this network will correctly autoconf an IPv6 address, but it will not set a default route. interface ...
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302 views

Simple Internal DNS Set-up

I have a few domains pointing to my router which then forwards them onto a server within my firewall. The server is running apache2 and everything works well - my website pops up. I have set up a few ...