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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Root server with changed network settings - how to avoid to be shut out?

I just worked on a local Linux server in my office, connecting to it via SSH. I changed some network settings. Specifically, I added a simple network bridge that replaced the previous ethernet ...
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2answers
125 views

can two nic have same subnet but different network? [closed]

Business case: A computer has eth0 and eth1 and eth0 address is 192.168.1.2 (static). The eth0 is used by a configuration software to configure the address of eth1 in the field. eth0 is only for ...
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1answer
51 views

How can I open a port on just one server IP?

I am setting up a dedicated server for gameserver hosting, which will also host a couple of other server applications (such as a web server). The dedicated server has a total of four IP addresses, ...
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59 views

Add VPN Connection with nmcli

Does anyone know how I can add a VPN connection to the my network settings in Linux with a simple command line entry? I've skimmed through the Red Hat nmcli documentation and haven't found anything, ...
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1answer
74 views

Limit input on a given port with tc filter and u32 match

I'm trying to rate-limit all incoming traffic on ports 8128-8191. I've read everything I found, checked everything ten times, it still doesn't work. The commands: tc qdisc del dev eth0 root tc ...
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1answer
140 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 ...
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0answers
63 views

nmcli static routes are ignored

I'm in doubt about how NetworkManager through nmcli manages static routes. I have a CentOS 7.1.1503 server with three network interfaces: [root@brick ~ ]# nmcli con show NOMBRE UUID ...
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1answer
94 views

How to identify and address the root cause of a connection timeout?

Background: I'm trying to connect to an SFTP server to transfer some files. However, I noticed that I can't connect from it from one particular server. I'm able to connect from other machines on the ...
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1answer
449 views

SSH: DH_GEX group out of range

We recently applied a vendor-supplied patch for OpenSSH. This patch disabled a few key exchange protocols in response to the recent Logjam attack. After applying this patch, we have a few vendors ...
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1answer
15 views

Write online/offline state to log file

I'm looking for a way to log the online/offline state of a Linux host to a log file locally. I tried to use ping for this but it didn't log timeouts/dropped packages it only shows successful ...
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1answer
71 views

Tracking pppoe interfaces

I have a set of PPP interfaces on my Linux server. But on bouncing(ifdown; ifup) the interfaces which are not working, the PPP interfaces takes the lowest possible interface number. If I have a PPP ...
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1answer
48 views

Block user network access except back to address of ssh client

On a linux server, how can I set up permissions so that a certain group of users are allowed to log in via ssh, but all network connections by their processes are blocked unless the connection is back ...
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19 views

Network Traffic fluctuating, even with loopback

I am using iperf tool to benchmark my network interfaces on two identical machines (Dell Blade Server M620). Both have given different results. On 1st machine, I ran server and clients as: Server ...
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0answers
248 views

*-network UNCLAIMED : How can I fix this issue

Out of the blue my second ethernet port stopped working. Both of them are part of the motherboard. I can see both of the ports in bios. They were working, but I was using only one of them up to now. ...
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1answer
57 views

Additional static IPv6 address on Ubuntu 14

My ISP gave me a /64 IPv6 subnet, so I'm trying to add a static IPv6 address on top of the one that is already configured in my Ubuntu 14.04.3 LTS. So far, all my attempts failed and I don't know ...
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1answer
41 views

Make Linux server route packets destined for its external ip to localhost

I've a router with a certain static ip a.b.c.d that's connected to a Linux server on one side and to the internet on the other. Accessing a software installed on the Linux server from outside using ...
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1answer
140 views

How to configure dual homed server in order for both network segments to communicate?

We want to add an additionnal network segment (LAN2) and need some machines on LAN1 to access ressources on LAN2. Some machines on LAN2 also need to access ressources on LAN1 and the WAN segment. ...
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3answers
64 views

Configuring Open VPN subnet on windows machine

I'm trying to make my Open VPN client to be a part of my azure network. In order to so I need to provision IP addresses that's within a specific range, so I added this to the server.ovpn file on the ...
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2answers
79 views

Best practice for using multiple links between switches when link aggregation is not supported?

I have a half-dozen servers and workstations in an office. The systems are connected to a Cisco SG200 gigabit switch in the room. The room has two gigabit wall-port ethernet outlets. I have the switch ...
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1answer
59 views

Can't Access VMware VM Remotely

I have a VM several layers away that I want to access remotely, but I can't get to it for some reason. I've tried several things to figure it out, and I wonder if I am missing something. I would ...
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1answer
83 views

Ubuntu 14.04 TCP established hash table entries

A bit of background I am running two servers under high traffic one with ubuntu 12.04 (linux 3.2.0-69-generic) and one with ubuntu 14.04 (linux 3.13.0-52-generic). I am now trying to secure both. ...
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0answers
17 views

How are kernel networking settings handled in OpenVZ containers?

I’m a little confused on how containers handle networking. For our normal systems, we’re enforcing things like Disable Source Routed Packet Acceptance, Disable Send Packet Redirects, etc. We usually ...
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28 views

Why, on a linux router, clients can still connect even after the network adapter is down or the iptables routing is disabled?

I have a Linux machine which I use as a wireless VPN router. It has a very classic router setup, whose highlights are: openvpn to connect to the VPN, which is connected to eth0, and makes the tun0 ...
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1answer
20 views

Is is possible to locate specific devices on my network based on type of device?

I have a bunch of Linux-based personal entertainment devices (with displays) that are connected to the network. I often have the need to SSH into them to set certain information. It takes me a while ...
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143 views

Samba connection fails from OS X

The server is running Ubuntu 12.04 and Samba 3.6.3. Windows users can mount their shares without problems, using the path \\my_server.com\username and account \username. However, when I try to ...
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17 views

Output traffic on different interfaces based on origin subnet

This a diagram of my current network, http://s1.postimg.org/5689b415b/actual_diagram.png Objective Route 172.16.0.x/18 subnet web traffic to ADSL connection What do you think of this approach, will ...
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0answers
81 views

How to allow VPN traffic only over shared internet connection on Linux?

I have a CentOS server where I set up Internet connection sharing. eth0 is connected to ISP, eth1 is connected to local network, so local traffic route is eth1 => eth0 => Internet. For ...
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90 views

Forward UDP Multicast to Unicast on Different NIC

My network topology: Machine A <-> 10.0.0.* Machine B <-> 192.168.0.* Machine C Machine A and C are not allowed to connect with each other for policy reasons. I want to use Machine B to ...
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1answer
32 views

routing for adding ips to 2 interfaces from same subnet

I am trying to add 2 different ips from same subnetmask to two different interfaces. So far it is working fine with the config below. Now I want to add an ip alias as well My eth0.cfg is: auto eth0 ...
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1answer
172 views

tcp_tw_reuse and tcp_tw_recycle not working in specific environment

We are running HAProxy to direct mysql traffic from PHP to a set of mysql servers. However, due to an issue with the way the mysql-client sends TCP packets, we get a ton of connections in TIME_WAIT ...
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0answers
128 views

UDP packets seen on interface level but not delivered to application on RedHat

I have a problem with receiving UDP traffic on a RHEL6 server. When capturing the traffic with tcpdump, the packets are visible (checksums are correct, the destination IP and MAC match the machine's ...
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1answer
25 views

Detect traffic loss between OS and NGINX

I have a analytics-tracking linux server (Ubuntu on EC2) running NGINX & Redis (this project - https://github.com/FTBpro/count-von-count) When I go over the NGINX logs, I see that the traffic is ...
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1answer
41 views

Proxy a URL to a dynamically set port

Say I have URL=www.mysite.com/20000/ I want to get a proxy that can then direct traffic to www.mysite.com:20000. The catch is I don't know what the URL's/ports will be ahead of time. So I can't ...
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0answers
36 views

OpenVPN: routing to two VPNs

Using Ubuntu 14.04 (up to date). I'd like to use two VPNs (openvpn) a the same time. LAN is: 10.1.1.0/24 The 1st VPN, homemade, is only routing the 192.168.1.0/24 network via the tunnel. Routes ...
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1answer
218 views

How does nginx websocket proxy work?

I'm wondered about how nginx handles tons active websocket connections? There is a lot of limitations, like a number of open files, maximum of 65k TCP connections between IP <-> (IP, port) and so ...
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86 views

TCP Out-of-order packets over GRE causing disconnect

I'm experiencing an issue with a small percentage of TCP connections over a GRE tunnel between two servers. The topology is basically Internet <-> GRE Tunnel <-> Backend The GRE tunnel and the ...
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13 views

How do I work out the netmask for a multicast address [duplicate]

I have a simple test setup: local network 2 Linux PCs: one sender, one receiver on the sending pc and one receiver on another pc. If I send out on 224.0.0.1, the receivers get the payload. If I send ...
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0answers
39 views

Local Network not working on one server while the other one works fine

So I have two servers (davros - working, kraken - not working) on the same subnet (10.10.28.0/24). They both have the same configurations and yet only one of them works. (Also, I should note that ...
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1answer
24 views

Xen routing from VM-bridge-eth1 to cable to eth2-bridge-VM

I have a Debian server running Xen 4.4. The server has multiple ethernet interfaces. I would like to set up: vm1 (IP 10.1.1.2/24) <--> xenbr1 (IP 10.1.1.1/24) <--> eth1 vm2 (IP 10.1.2.2/24) ...
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1answer
46 views

How to filter local traffic with iptables?

Can iptables be used to filter local traffic? I am confused by how this should be set up. For example, here is a diagram of how I picture the set up would be: I just don't see how iptables would ...
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2answers
135 views

Multiple public IP addresses on CentOS server

Is it possible to have multiple public IP addresses (500) on one server running CentOS and switch them without restarting networking service. I would like to use one public IP per specific service ...
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1answer
82 views

Getting a VLAN IP address

is there anyway to get a static IP address from a VLAN port on a CISCO switch ?. what I'm looking for is a software weather it's a Linux or windows software when I plug Ethernet cable from my laptop ...
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1answer
79 views

Is there any way to configure a vlan interface on linux to only receive the untagged frames?

Scenario: eth0 trunk interface with vlans 10 11 12 13 14 15 native vlan on switch configured to 10 eth0.11 vlan interface, sees any traffic that came in on eth0 tagged with vlan 11 ... ...
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1answer
189 views

Ubuntu Server 15.04 as Router and DHCP Server with multiple subnets

at my company i got assigned to build a new network, where 1 ubuntu server manages DHCP for 3 subnets, allows communication of these subnets between each other and shares the connection to the public ...
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0answers
70 views

Network disconnecting frequently in centos 7

I am in a problem. i am having a scenario with a centos 7 server hosting a website. everything was fine. but i had a power failure which affected the UPS with an overload, causing it to reset. So my ...
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1answer
99 views

SFTP connections to docker container break when using packet forwarding instead of port binding

Setup I am trying to make a setup that allows me to directly connect to docker containers from my LAN without binding individual ports to the docker hosts IP addresses. I have turned on IP ...
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1answer
46 views

95/5 Network Billing - cap speeds once close to using up 5%

Is anyone aware of a good way to limit overages due to 95/5 burstable billing by capping a server's bandwidth once it gets close to having large peaks more than 5% of the time during the month? I'm ...
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41 views

Two NICs, Different Subnets

I have two NICs on a given machine (CentOS 7). One (say enoX) has an IP in the range 10.0.0.0/8 and the other one (say enoY) has an IP in the range 172.0.0.0/8. Now, I can access SSH and HTTP on enoX ...
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0answers
97 views

kvm network bridge on centos 6

I have a Centos 6 KVM host. I installed the KVM following this manual: https://wiki.centos.org/HowTos/KVM Its network has been configured as a bridge: [root@server ~]# ifconfig br0 Link ...
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357 views

RTNETLINK: Device or resource busy - DELL 2950

I cant start second NIC on Dell Poweredge 2950, OMSA installed, the NIC cards is BCM5708C ,version of Operating System Centos 6.7. The first card worling correctly [root@alfa ~]# ifup eth1 RTNETLINK ...