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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fallback route to drop packets if output interface that is NATed to goes down?

Background: I establish a connection to a 3rd party VPN and NAT packets marked as part of a particular cgroup (in order to selectively run processes through the VPN or not) to the 3rd party's VPN tun ...
3
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1answer
86 views

notify when a TCP port start listening

I need to be notified exactly when an application start LISTENING on any/specified TCP port. is there anything like configuring an application to log this event using a library in any programming ...
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2answers
176 views

How to disable/delete network manager

I'm on CentOS 6.4 64 bit in rescue mode and network manager keeps overwriting my resolv.conf and the command chkconfig is "unknown" so how do I disable/delete network manager?
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1answer
1k views

How to place a virtual machine in DMZ?

I have an Ubuntu 12.04 server running few virtual machines with KVM. I would like to expose some of these virtual machines on the internet, to make it possible for customers to test the products we'...
3
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1answer
11k views

Checkpoint VPN on Linux

I need to setup a Checkpoint VPN client with a customer who gave me these settings: Authentication Type: P12 certificate Password: * Peer Site: IP_ADDRESS They tell me the VPN server is: IPSO 6....
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1answer
5k views

Configure Avahi nss-mdns not to use local suffix with hostnames because of issue in mounting Samba share

How to configure Avahi & nss-mdns to resolve names in my small home network in the same manner as Windows does with NetBIOS or more recently LLMNR. For Linux, there are two options: Winbind aka ...
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1answer
121 views

Launch application to linux console on startup

I have a small router without a keyboard and mouse, and I'd like to have it display network statistics using "jnettop" whenever the machine is booted up. How can I get the machine to display this ...
3
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1answer
807 views

Linux: ip alias versus iproute

When setting up a web server with multiliple IP-based virtual hosts, I've always used the eth0:x alias notation in /etc/network/interfaces. The wiki on my hosting provider states however that this ...
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3answers
193 views

A different network interface becomes the default route if the active default goes down

I have two network interfaces eth0 and eth1 and I just wanna know how get the "eth1" as default route automatically if the "eth0" goes down?
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2answers
668 views

Iptables Forwarding problem

I had initally asked question about sertting up my linux box for natting for my home network and was given suggestions in the thread here. Did not want to clutter the old question so starting a new ...
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2answers
941 views

your approach to complex iptables rulesets

i'm interested how do you write your complex packet-filtering rulesets on linux router acting as firewall. one with default-drop policy. i usually go with such approach [ just an artificial example ]:...
3
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1answer
61 views

Find network percentage of NIC [closed]

So I have created a Linux resource monitoring tool that pulls various resource information. One of the fields I am trying to pull is the percent of network throughput on my NIC. So if I have a 1 Gb(...
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1answer
89 views

Route Between Two Virtual Interfaces on one NIC Linux

I have an Ubuntu machine that is my firewall The Machine has 2 NIC Cards. eth0 and eth1. eth1 is connected to a modem that gives it an IP of 10.10.1.X eth1 is required to provide DHCP on 192.168.2.X ...
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1answer
794 views

DNAT port range with different internal port range with Iptables

The standard way of DNATing a single port to a different port on an internal network is something like that: ip(6)tables -t nat -A PREROUTING -i wan0 -p tcp --dport 80 --to-destination 10.0.0.1:8080 ...
3
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1answer
168 views

how to realize a traffic volume limit with linux

I am helping to organize a little conference. There is no internet connection, so we are limited to a mobile LTE connection with a limited volume. We have a Ubuntu-based server that acts as a router, ...
3
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1answer
36 views

Please clarify for me how tcpwrappers works

We've recently gone through a security audit and among several valid and other, quite pointless findings is one that states that tcpwrappers is not disabled. I've never used tcpwrappers so I don't ...
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3answers
5k views

How can I achieve OpenVPN client routing without NAT on Linode

I've set up an OpenVPN network, and it is working properly in the sense that I can access the inner/LAN machines from the remote client. However, my problem is that all traffic from the remote ...
3
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1answer
953 views

Split tunneling through two VPNs simeltaneously

I want to run two OpenVPN client instances on an Ubuntu Server 14.04. I have both .conf files that can work independently (both are set to different interfaces - tun0 and tun1). I want to run both at ...
3
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1answer
9k 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 DC,...
3
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1answer
2k views

Unable to set proxy to “subscription-manager repos --list” -command

I have RHEL6 system that is registered to rhn via subscription-manager. I'am trying to install package java-1.6.0-sun-devel which is in rhel-6-server-optional-rpms repository, According to this Redhat ...
3
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2answers
5k views

Keep source IP after NAT [closed]

Until today I used a cheapy router so I can share my internet connection and keep a webserver online too, while using NAT. Users IP ($_SERVER['REMOTE_ADDR']) was fine, I was seeing class A IPs of ...
3
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1answer
1k views

Configure IPv6 routing

I've got IPv6 addresses from SIXXS. My host is connected with SIXXS network over a AICCU tunnel ("sixxs" interface). My host address is 2001:::2, the host on the end has address 2001:::1. On my host ...
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1answer
4k views

What is the difference between MULTICAST and ALLMULTI ifconfig ifconfig flags

What is the precise difference between the ifconfig flags MULTICAST and ALLMULTI? Also How do I change the default flags under Ubuntu?
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1answer
138 views

Create a multi-homed linux load balancer with two internet connections and one LAN connection

OK,... this has possibly been answered, unfortunately, I have not found anything that looks like it might be the resolution. Ive looked at these pages and they have some useful information, but not ...
3
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2answers
163 views

Why can I not exceed 32k or 65k TIME-WAIT connections?

I've been trying to tune up our Ubuntu 14.04 LTS web server instances, hosting both web applications and reverse-proxying nginx, to handle as many req/s as possible with the given hardware. It's a c4....
3
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2answers
315 views

same subnet,different VLAN in Virtual machine

I have 2 VLAN,VLAN 100 and 101 but only one subnet i am trying to make this work with virtual machine so that VM will have two IP address in same subnet but will actually be in two VLAN. steps ...
3
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2answers
257 views

how to prevent any service to bind to a given interface?

I need to set up a server (preferably RedHat/CentOS/Fedora but the Debian family would work out as well) with no services available on a given interface. I cannot use iptables (which would be the ...
3
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1answer
460 views

What's the expected behaviour of multiple hostname entries with different IP addresses in /etc/hosts?

I know this has been discussed in several places, but there doesn't seem to be a definitive answer yet - at least not for RHEL 6. I'm just hoping someone might be able to point to how it's working so ...
3
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1answer
590 views

Why rinetd is working locally but not working remotly?

/etc/rinetd.conf 0.0.0.0 443 10.30.224.7 636 allow * >lsop -i|grep rinetd rinetd 27099 root 4u IPv4 2553556 TCP *:https (LISTEN) Also iptables -L -n returns nothings. Still, ...
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2answers
4k views

Delete specific conntrack entries?

in a multi-ISP configuration, I'm routing and NATing specific traffic, e.g. VoIP, through specific interface - to a distinct provider. When one of the interfaces (or routes) becomes unavailable, all ...
3
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2answers
12k views

I'm having problems getting CentOS to recognize an Intel Ethernet card. Any suggestions please?

I have a dual-port Intel Pro/1000 (82571EB) PCIe card. I've installed in into a Dell PowerEdge 1950 running CentOS 6.2 x64. The card is detected and the kernel module is loaded, but a start-up ...
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2answers
6k views

Why is my second PCIe network card not recognized by Linux?

The machine is an IBM ThinkCentre (model 8115LUA) with two PCI slots - x1 and x16 if I recall (the designations) correctly. There are two identical network cards in these PCIe slots. Initially, the ...
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3answers
1k views

How to Hide OS Fingerprint of Virtual Machine?

Is it possible to make a linux virtual machine appear as the host machine to a network tool like nmap or Blue's Port Scanner without recompiling the kernel?
3
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1answer
309 views

How to properly permanent enable ip forwarding in Linux with systemd?

I try to enable ip forwarding (between enp0s3 and tun0 interfaces) and write net.ipv4.ip_forward = 1 in /etc/sysctl.conf. After restart I have $ cat /proc/sys/net/ipv4/ip_forward 1 But forwarding ...
3
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1answer
49 views

How to setup embedded Linux private vlan

I am trying to setup a vlan between 2 embedded Linux SOCs on wireless IPTV STB (set top box) using vconfig. The physical connection between the SOCs is a Marvell 88E60xx switch. The issue is that the ...
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0answers
79 views

What would cause named to send out hundreds of bogus responses?

My DNS server running RHEL 6.6 is actively sending unsolicited DNS responses to a couple of IP's. By unsolicited I mean that there is no incoming request from the external IP, the DNS server seems to ...
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0answers
48 views

What's the recommended way to restrict Internet access per process using SELinux?

Before I have tried to do this using a phony user and iptables to execute commands that needs to be restricted. However now the commands need to read configuration set by each user's environment vars ...
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0answers
23 views

Linux: What is the right way to configure the HOSTNAME directive in /etc/sysconfig/network? [duplicate]

There's a (quiet) argument between me and my boss in regard to the right way to configure HOSTNAME directive in /etc/sysconfig/network file: As far as I know, in the HOSTNAME directive you should ...
3
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0answers
216 views

Hyper-V lost synthetic NIC after Debian 8 dist-upgrade?

I'm running a Debian 8 vm on Hyper-V (Win Srv 2012R2) and when I did a dist-upgrade of stable, I lost all network connectivity. Using the console, I was able to see the network interfaces as UP but ...
3
votes
1answer
163 views

When is route lookup performed when a packet flows through iptables?

Iptables is often illustrated using diagram I fail to understand when route lookup (routing tables) is performed: inside the "Routing Decision" grey boxes? If so, does it mean a packet is routed ...
3
votes
1answer
184 views

Linux Server Virtual Ethernet interface stops responding to arp requests

I'm hoping someone has had this issue before as it is driving me nuts. I have 2500 linux embedded Linux servers. We use these servers partly to act as gateways to other devices sat on a private ...
3
votes
1answer
964 views

Limiting bandwidth with hashlimit (e.g. kb/s — not connections!) doesn't work, though the man page says it should

According to the iptables-extensions man page hashlimit can do bandwidth limiting: "flows exceeding 512kbyte/s" => --hashlimit-mode srcip,dstip,srcport,dstport --hashlimit-above 512kb/s ...
3
votes
1answer
800 views

qemu with tun virtual networking issues

I'm trying to setup a virtual networking environment using open-wrt qemu and vde2 The script to boot two qemu instances and conenct them together is the following IMAGE=/home/northpole/openwrt/trunk/...
3
votes
1answer
232 views

Buffer-stuffing denial-of-service attack

I started seeing this odd sort of effect that resembles denial-of-service attack against a Linux server. The effect is that the network becomes at least partially unusable very much the same as what ...
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2answers
312 views

Traffic not routing as expected

In the following output, why does vpn1 route/ping to 10.100.0.1 instead of to 10.100.0.112? 10.100.0.1 is network gateway with no nat. 10.100.0.112 is dual home host with nat enabled. root@vpn1:~# ...
2
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3answers
433 views

Which private IP addresses can I use? [closed]

I have a dedicated server where I'm running several web-facing virtual machines on public IP addresses; I pay my hosting provider for each IP. I would also like to run virtual machines with private ...
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4answers
4k views

How to change persistent-net-generator.rules to be PCI bus dependent and not MAC based?

I am using CentOS 6.2 with VMware. I often have to clone my systems. Every time I clone it is adds a new rule to 70-persistent-net.rules file like so. SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ...
2
votes
2answers
5k views

Server becomes unreachable and comes back up on its own (most likely a network issue)

I'm having a strange problem with a server I have sitting at my workplace (it's behind a NAT, if that's important). The issue is that at some times, it becomes unreachable and then comes back up again,...
2
votes
5answers
55k views

No network connectivity for my CentOS 6 installed in VMWare Fusion in MacOSX Lion

I installed CentOS 6.2 (CentOS-6.2-x86_64-minimal.iso) with VMWare Fusion(Version 4.1.2). (Not with EasyInstall). I am using MacOSX Lion, connect to internet via WIFI. The centos installed does not ...
2
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6answers
2k views

How can I restrict SSH access when the source IP is dynamic

I want to protect SSH access to our live web server from all IP's except our office static IP. There are some employees who connects to this live server from their dynamic IP's. So, it is not always ...