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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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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14 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
8 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 ...
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22 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
25 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
18 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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25 views

How to setup VM network such that they all have different public IP addresses

For example, in Azure or Digital Ocean or EC2, we have an option of creating unlimited number of virtual machines. How does each of these VMs come to have different public IP addresses. More ...
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How to use two NICs [1onboard and 1 lan card] of my server [Ubuntu]? [on hold]

Good day, my scenario is I want to configure both of my NIC so that 2 different networks [192.168.4.2/200 and 192.168.1.2/200] can access my Web server. I jut want to know if it is possible? and How? ...
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18 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
23 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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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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+100

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
17 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
38 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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13 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
47 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 ...
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1answer
31 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
33 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
57 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
15 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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9 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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26 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
26 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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20 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) [...
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28 views

Inherited debian cluster nightmare

Hi and thanks in advance. So my research group at my university inherited an 8 node cluster. Me being the only member who is Linux savvy was given the task of managing it. So to start I'll describe ...
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78 views

Pacemaker: How to configure default gateway for virtual IP?

I have three nodes and three virtual IP addresses in the same subnet. It doesn't matter which address is assigned to which node. The IPs are public addresses. The nodes are load balancers that ...
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41 views

hostapd Wired 802.1x with Bridge

I've got a PCEngines APU running Debian Jessie. I'm trying to configure hostapd to perform wired 802.1x authentication against a remote domain controller running NPS on 2008 R2. I would like 2 of it'...
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1answer
20 views

Cacti generate old graph

I have a cacti system (Version 0.8.8b). The cacti system has been running for a year. I would like to generate retroactive daily graphs, because cacti can't show the old daily graphs. How to ...
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2answers
41 views

Load Balancing & High Availability Network Limitations

I'm in the process of coming up with a highly available Apache / MySql group of virtual servers using HAProxy Reverse Proxy & Keepalive. I'm aware that I'm going to be using a floating public ip, ...
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22 views

vnstat and dstat report different totals

I'm trying to monitor bandwidth going through one of my interfaces, and I've discovered that dstat and vnstat both seem to report different rates... vnstat: [root@... ~]# vnstat -i eth8 -l ...
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1answer
41 views

How to create a HTTPS Proxy?

I have to setup access to a remote API service in which requests are IP-Whitelisted. The problem I have is that my web-nodes are in the cloud and their IP addresses often change. Therefore I want to ...
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35 views

static network setup still using DHCP

I'm configuring an Ubuntu 14.04LTS server on our internal network. Everything works and runs as expected. Its assigned a static IP, here's /etc/network/interfaces # The loopback network interface ...
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0answers
49 views

How does AWS configure the 169.254.169.254 address on an instance?

AWS uses 169.254.169.254 as a link local address, which you can use to pull meta data about the instance, ie: curl http://169.254.169.254/latest/meta-data/ How/where is this IP configured on the ...
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1answer
35 views

IP Range - Subnet network configuration on CentOS 6.4

I have problems to configure an subnet /25 on an vps with CentOs 6.4 have tried different version. The original eth0 settings are: DEVICE=eth0 #HWADDR=de:8f:24:e9:7b:04 TYPE=Ethernet UUID=64e110dd-...
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Why would rsync be limiting syncs to ~252Kilobytes?

Here's a head scratcher for you... or at least it is for me. I am transferring a Wordpress site away from WP Engine to an Amazon instance. I am trying to upload the original Wordpress files from my ...
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35 views

How do I reduce private network latency below 0.5ms?

We are migrating from one host to another. Our cluster consists of 10 dedicated linux servers which must communicate on a private network. At the old host we observed latencies below 0.2ms between our ...
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23 views

KVM/libvirt: NAT forwarding virtual bridge to host bridge

I currently have a VM setup where only a few 'special' VMs are allowed to have outward facing IP addresses and the rest aren't. All of them are configured with two interfaces attached to a virtual ...
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1answer
22 views

Using a VPC from the office vs. VPN from home: Not all hosts are reachable

Here is my situation: Our whole office is VPNed to an Amazon VPC through openvpn. We have 3 VPC subnets: 10.1.25.x (Prod) 10.0.3.x (Staging) 10.0.1.x (build env) While in this office, all is ...
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2answers
59 views

Installing Mellanox ConnectX-2 10gbe PCIe Card on Centos 6

I just installed a Mellanox ConnectX-2 10gbe PCIe x8 Card into my server running CentOS 6.7. On boot, dmesg shows the mlx4_core driver being loaded automatically however I see no eth1 device ...
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10 views

Can the VRRP ID of 2 different systems clash (keepalived and cisco/force10)

Since Keepalived and Cisco/Force10 both use VRRP, and use an ID Range of 0-255: 1) Would using the same number in the same vlan cause a issues. 2) Would using a different number in the same vlan ...
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2answers
60 views

How can I determine which network adapter is SFP+ in CentOS?

I have a server which has an SFP+ module. We are going to utilize this to get 10gb speeds. I have adapters em1, em2, em3, em4. How can I determine which adapter is the SFP+ adapter in Centos 6.5?
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1answer
53 views

Dropped packets in all Linux and Unix

I have a problem. I have motherboard by Supermicro – X11SBA-LN4F. There are 4 ethernet ports. In first port i have internet. In second port i have my local network. When, i write "ifconfig" or "...
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1answer
22 views

netstat shows inequal amount of mutual connection between two hosts

I'm trying to investigate why the amounts of connections between two physical hosts 10.240.48.9 и 10.241.169.7 (CentOS 6) don't match each other (diagnosed from the each one respectively): On 10.241....
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How to size BIND9 DNS server requirements [duplicate]

Ive been asked to size a number of DNS servers to be able to handle a certain number of requests per second. Is there any handy guide to how to calculate hardware requirements for this?
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43 views

IPTABLES - Prerouting Issue - Port 443

I have a NAT server setup with 4 servers behind it. I have a PREROUTING entry to allow https/443 INTO my environment, specifically to to a web server running IIS on port 443. This works fine. ...
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1answer
50 views

HAProxy/Keepalived and DNS

We have some HAProxy/keepalived clusters on CentOS7 and found that the virtual IPs managed with keepalived have registered in DNS. Does anyone know of a way to block dns registration for address ...
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1answer
36 views

Restarting network interfaces that have changed with ansible

I've got an ansible role that - name: add virtual interface configs for vlan template: src=ifcfg-eth.vlan.j2 dest=/etc/sysconfig/network-scripts/ifcfg-{{ item.device }} with_items: "{{ ...
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Firewall-Rules on Proxmox-Node cause VPS to be offline

I'm using proxmox to virtualize some small machines based on KVM. To do so I created the following network-config on the KVM-VPS: # This file describes the network interfaces available on your ...