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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41 views

Right way of measuring overlay network performance

I am currently examining the performance (especially UDP throughput) of different Docker overlay networks. I do this by creating point-to-point connections between two hosts that are connected with a ...
3
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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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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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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 ...
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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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47 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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140 views

VRF on Linux using network namespaces

My ultimate goal is to implement Virtual Routing and Forwarding (VRF) in Linux. The method that seems to be most widely accepted is to set up different network name spaces (one for each separate ...
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30 views

network access issue and triage

We have two hosts in same vlan with same route rules. One of them is able to connect to an outside IP while on another I get failed: Connection timed out when testing the connectivity through netcat. ...
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96 views

Debug slow lan (ssh, nfs) file transfer

I've got two linux boxes attached to a gigabit switch. They both have gigabit NICs, cables are cat7. Testing the network with iperf shows a fast connection but transferring files with rsync, scp, or ...
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42 views

Debian-Server: Incoming SSH/PING/TELNET/… works - outgoing does not

I've mentioned a strange behavior of my linux-system: After rebooting the system I can connect to it via SSH and the server responses to PING. But the server itself can not ping any other servers. # ...
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104 views

Dynamically enable IPSec for IP connections between many servers

For a given list of internet server (example): S001 - 45.67.89.12 S002 - 67.78.90.34 S... S999 - 98.76.65.54 I want to talk from each server to any other server to any TCP service using the public ...
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89 views

HTTP DELETE timeout between Nginx and Application

We're facing a really weird error using HTTP DELETE, the symptom is occasionally the user gets a 504 (timeout) error in the browser. The requests flow through the steps described below: Browser -> ...
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19 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 ...
2
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110 views

How to write firewalld rule with rich language

How can I write a rule for firewalld using rich language which restricts packets from a particular port and particular protocol. For IP tables I wrote a rule like: firewall-cmd --permanent --...
2
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501 views

OpenVPN sndbuf and rcvbuf

I would like to know what is the difference between the sndbuf and rcvbuf buffer used by OpenVPN and net.core.w/rmem_default or net.ipv4.tcp_r/wmem. What does OpenVPN do when some value a provided ...
2
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326 views

How to use iptables or IFB to mark incoming traffic by device?

I'm trying to use iptables to mark incoming packets based on the device where those packets arrived (rather than their originating IP address or port etc), but haven't found a way of getting this to ...
2
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106 views

Linux - Outgoing connections from process timeout after the process restarts

banging my head against the wall with this one... I have an Ubuntu Linux server, on top of which our own process which holds 40K persistent connections to external services. When the process starts,...
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246 views

Routing with multiple NICs on debian

I have a machine with two NICs on different network segments, I've set up routing for the different segments. It works if I run all the routing commands manually, but I can't get it to work when ...
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161 views

What are the advantages NAPI before the IRQ Coalesce?

As known there are two approach to avoid some overheads of hardware interrupts in highload networks, when there are too many hardware interrupts, that switching to them takes too much time. It is very ...
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65 views

IPsec - strange behavior

I have set up site-to-site ipsec connection between linux(debian) and mikrotik router. The tunnel is up linux configuration: config setup interfaces=%defaultroute keep_alive=60 ...
2
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474 views

php-fpm process in D state ,cause nfs wait rpc_wait_bit_killable

my wordpress site which is in clustered environment using NFS,nginx,php-fpm,mysql the infrastructure is hosted on amazon ec2.Under high load/traffic the php5-fpm process goes in D state(...
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75 views

PIV authentication on redhat

I'm looking for a solution, or set of technologies, (etc) - for setting up a mixed (win 7, rhel 6.5) network with centralized login using smart cards (PIV). I know that this is possible using a ...
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623 views

access tap interface in network namespace across machines

I want to be able to access services running on a TAP interface within a namespace from outside the machine where it is running. I have setup that looks like this - VM1/Machine1 +eth0 : Public ...
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188 views

How can I set ntop not to shorten host names?

With most screens in ntop, there is a list of hosts. Unfortunately, in almost every one, the host name is shorted, for some reason. When the host names follow the company standard, this results in the ...
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582 views

VMware - Broadcom 1000Gbps NIC does not link at 100Mbps to a Cisco switch port

Today we've stumbled on a very awkward situation with our VMWare Server. The server is with ESX 3.5 that has a 1Gbps NIC. We bought a brand new managed Cisco Linksys switch with 10/100Mbps interface ...
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1k views

StrongSwan - Windows 7 0 IPSec IKEv2 connection problems

I am trying to configure a roadwarrior scenario between a linux box with StrongSwan and a Windows Box with Agile VPN. I successfully configured my StrongSwan and my Windows box to connect. The Windows ...
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22 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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51 views

How to connect to a service on a local network machine whch which only listens to localhost?

I have a service which only listens to localhost on port 7400. There is a service running on a windows and an ubuntu machine on a private network. How can another computer on the same network ...
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41 views

Proxmox: Add IPs from different subnets to LXC-container

I am using proxmox 4.1. If I add IP-addresses to my CentOS-7-LXC I can only do that if this IP is from the same subnet. If I'm using another subnet with another gateway the container is not pingable ...
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25 views

How to ensure via shorewall that the network is closed at boot time?

I use Shorewall (on Ubuntu 16.04) and would like to ensure that between the start of the boot process and the moment iptables rules are applied the network is in a closed state. There provision for ...
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22 views

what makes RPS different from IRQ balance

i was reading about RPS[Recieve Packet Steering] and how it makes Packets distributed on different cpus. I believe IRQbalance also does the same thing by distributing interrupts on different cpu. ...
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27 views

keep ossec iptables rules after restarting OSSEC

I have 6 OSSEC installations (5 agents + 1 server, all Debian 8) all configured to block repeated offenders using iptables from 10 minutes to 1 month. I have the need to restart one or more of the ...
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27 views

iperf actual send rate always lower than the expected target bandwidth until some equilibrium reached. Why?

I did an UDP iperf 2.0.5-Ubuntu test between two VMs on the same hypervisor. As can be seen in the iperf output below I started my first test with "-b 686M" flag. However, iperf reported that it was ...
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29 views

CentOS 7 ifup scripts actually doesn't change interface name

It has occurred to me that in CentOS7. While one can still specify interface names in sysconfig, the ifup scripts actually does not change interface fact "via ip link set dev ${DEVICE} name". For ...
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57 views

Using LINK_REQUIRED parameter with wicked

I'm running SLES 12 and trying to configure network interfaces; this is my first experience with wicked. I'm using "ifup" to up the ethernet devices. I ran into an issue of not being able to ifup the ...
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55 views

IP Multicast between Windows and Linux

Our team is developing linux/windows applications for our network that are talking to each other via multicast. We had it working when we only had linux boxes on the network, but we recently added a ...
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28 views

rx_queue value in /proc/net/udp grows to twice the SO_RCVBUF value

When using an SO_RCVBUF of 10485760 (which is also the current limit as stipulated by sysctl's net.core.rmem_max setting, and sending UDP packets faster than the receiving side is able to handle, the ...
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82 views

How to prevent persistent naming of network interfaces, like eth1

I have a freshly installed Debian Jessie. I had two NICs, which were eth0 and eth1, now I took out one, however I still have eth1 left in the system: % dmesg ... tg3 0000:03:00.0 eth0: Tigon3 [partno(...
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56 views

Change NAT IP for Proxmox (Keep host IP)

I have a Proxmox server with many IPv4 addresses available to it. As it stands, an instance (Either LXC or KVM) that connects out to the Internet will be connecting from the host's IP address. For ...
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47 views

iptables/nat/prerouting ignores UDP packets?

The same effect on many servers with various kernel versions. There are multiple Iptables DNAT rules: iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 12345 -j DNAT --to-destination 10.20.30....
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57 views

How to configure Spark client running in a Docker container for two-way communication with a remote Spark cluster?

spark-submit seems to require two-way communication with a remote Spark cluster in order to run jobs. This is easy to configure between machines (10.x.x.x to 10.x.x.x and back) but becomes confusing ...
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105 views

Why is CentOS 7 ignoring NETMASK?

I have a networking issue that I eventually tracked down to an incorrect network prefix setting. ip addr is reporting that the current prefix is /8 when it should be /24. However, when I look in /...
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54 views

Can Spark be configured to listen on multiple network interfaces/ip addresses?

The nodes in my Spark cluster have two network interfaces each, one public and one private. Using the SPARK_MASTER_IP environment variable, I can configure Spark to listen on port 7077 on one or the ...
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136 views

How to diagnose netstat: no namelist

I had to replace an NIC on my HP Proliant Microserver, running FreeNAS 9.3 In my crashplan jail, I now get "netstat: no namelist" as a response when I execute the netstat command. How to I diagnose ...
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247 views

Strange iperf3 behaviour with UDP streams

I am using iperf3 verson 3.0.11 to measure the throughput of a UDP stream between two virtual machines. The virtual machines are deployed via OpenStack. Of the physical hosts, one is located in ...
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124 views

tcpdump on bridge interface (virbr) does not receive any packets destined for one of its addresses

Here's the configuration for the interface: # ifconfig virbr0 virbr0: flags=4355 mtu 1500 inet 192.168.11.1 netmask 255.255.255.255 broadcast 255.255.255.255 ether 52:54:00:99:e3:...
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106 views

Error while trying to bring up network in SLES12.1

I am trying to bring up the eth0 adapter in SLES12 sp1 using ifup eth0 but every time I am getting an error saying: wicked: Reading config file /etc/wicked/client.xml wicked: Reading config file /...
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24 views

restart client after download .img file from PXE

I want to install pfsense using pxe. In Windows 7, I have installed the Tftpd32 software and set it up (conf file is below). The client machine downloads the image file (pfsense.img) successfully ...
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63 views

SSH (interactive) hangs during full upload bandwidth use

I work daily on SSH from a Linux desktop to an AWS EC2 Amazon Linux server and the connection has performed very reliably for two years, but in the last few days I have seen the SSH command line hang ...
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35 views

how to combine ips to increase server bandwidth?

I have several ips. Each of them is limited to 2MB/s by the network provider. How can I assign multiple ips to one server to increase my server's outgoing bandwidth? My server runs CentOS 7. Thanks!