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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Multicast route setup for multiple interface

Currently I have the below eth5 to receive multicast data for 239.1.1.31. It works. $ ifconfig eth5 Link encap:Ethernet HWaddr E4:11:5B:94:E1:F3 inet addr:10.185.2.2 ...
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How do I throttle network activity in Linux?

How do I throttle network activity, system-wide? Say, I'm running rsync on a large archive with a cron, or a torrent server, or both. It's important that these activities will be running, but they ...
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661 views

Running a custom script when StrongSwan connection is established

I have StrongSwan VPN server set up on a Debian host, and would like to run a custom script when a client connects to it. The only thing I have come up with is periodically checking the contents of ...
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1answer
542 views

TCP packet being retransmitted 7 times when sysctl tcp_retries1 is set to 3 - why?

Ubuntu 12.04 I am trying to better understand how many times TCP will attempt to retransmit a packet when it does not receive confirmation the destination received it. After reading the tcp man page ...
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1k views

What's the difference between eth0:1 and 2nd eth0?

In Ubuntu server, I configured eth0:1 like this in /etc/network/interfaces file # The primary network interface auto eth0 iface eth0 inet static address 192.168.1.111 netmask ...
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Do I need a firewall if the service doesn't listen on all interfaces? [duplicate]

Short version: I have a CentOS 6.5 with two NICs, one connected to the internet and one connected to the internal network. The services that shouldn't be accessible to the internet don't listen on ...
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3answers
80 views

benefits of iptables on VPS? [duplicate]

Say I have a well updated Linux VPS serving HTTP content on port 80 using apache. What would I gain by enabling IPtables? I can see no obscurity gains since the machine has a port open. Also, since ...
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230 views

Http Persistent Connection (keep-alive) and port numbers

Is a persistent http connection (keep-alive), always bound to a specific port, or can it use a range of ports?
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68 views

APF and iptables on router - disallow SSH on specific subnet host

I have a CentOS terminal working as a router with APF installed. Also 1 terminal with 3 NICs (3 IPs) is using that router as a Gateway to access the internet. What I want is APF to block SSH access, ...
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1answer
279 views

Mininet additional veth pair between host and server

For those who don’t know - Mininet is a tool that allows for the automated creation of multiple OVS switches, chroot linux ‘containers’ as hosts and links them all together to prototype OVS powered ...
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246 views

Linux IPSec between Amazon EC2 instances on same subnet

I have a requirement to secure all communications between our Linux instances on Amazon EC2 - we need to treat the EC2 network as compromised and therefore want to protect the data that's being ...
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304 views

iptables - hashlimits, why it calculate all to seconds

I've tried to set 'synflood' limits with hashlimits, those are my snippet of rules: iptables -A SYNFLOOD_CHECK -p tcp --syn -m hashlimit --hashlimit-above 10/s --hashlimit-burst 6 \ ...
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1answer
8k views

Unable to add a static route: SIOADDRT: Network is unreachable

I've been bashing my head against a wall for a few days trying to figure this out: My ifconfig is: eth0 Link encap:Ethernet HWaddr 00:50:56:BB:XX:XX inet addr:192.168.36.132 ...
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1answer
102 views

IPTables: Firewall with just one Eth device? [closed]

Admittedly I am a novice in the area of firewalls. But I have read on the IPtables and Firewall theory and command options. There is a general diagram by Rusty Russell, the creator of IPtables: ...
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2answers
814 views

ARP responds with single MAC address on Linux server with multiple interfaces on the same network

Linux server has 2 active network interfaces: IF:eth1 IP:192.168.1.1/24 MAC:11:11:11:11:11:11 (1GbE) IF:eth2 IP:192.168.1.2/24 MAC:22:22:22:22:22:22 (10GbE) The idea is that the ...
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1answer
123 views

Forward a host network traffic to another host with the exception of the ssh service

I am trying to redirect all the network traffic received in a old host to a different new host. For that i created two new rules on iptables of the old host: echo 1 > /proc/sys/net/ipv4/ip_forward ...
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Proxmox internal network configuration

We have several servers (with one nic) staying in one rack in hetzner. Proxmox is installed on each one, and they are combined in proxmox cluster. The goal is to create network, between virtual ...
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1answer
307 views

How to ping ipv6 interface

I'm trying to get familiar with ipv6 I don't understand why I can't ping this interface at the inet6 addr eth1 Link encap:Ethernet HWaddr 08:00:27:77:9e:77 inet addr:192.168.33.10 ...
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1answer
393 views

Automatically acquire IPV6 address in CentOS 6

The network has fixed IPv4 address, and automatic acquired IPv6 address. Does anyone have an idea how to setup? Thanks a lot! I didn't use NetworkManager. The following is my setting, but it does not ...
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1answer
100 views

How can I configure iptables to forward and forget?

I'm trying to create a front controller where users can connect to a specific port and have their connection redirected to a different IP/port. The reason I'd like to be able to do this is for ...
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2answers
523 views

Routing Internet traffic through computer on another subnet

Ubuntu box server has 2 network interfaces: eth0 50.57.71.100 eth1 10.182.161.100 Ubuntu box client has 1 network interface: eth0 10.177.30.100 server and client can already talk to each other ...
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Improbably high bitrate in the output of “iw wlan0 link”

I am trying to determine the bitrate of a wireless connection that uses the nl80211 driver on a Linux 2.6.39 machine. I am actually using a Netlink socket internally, but the effect is the same as ...
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1answer
186 views

Tunnel interface inside Virtualbox IP forwarding

I am working on a solution to expose a development stack that resides inside a Virtualbox guest up to the Internet through OpenVPN tunnels. OpenVPN client fires up inside the guest VM and connects ...
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2answers
55 views

Network Buffer Usage

I am facing some issues with my Application, and am curious to know the network buffer usage at any given moment. I am using a CentOS 6 linux Machine. I know the Default values are present in ...
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65 views

SCP version of - ssh -A -t -l root 192.16.4.9 ssh -A -t node-17

I'm on a vpn. I ssh to a machine through another machine like so ssh -A -t -l bob 192.16.4.9 ssh -A -t node-17 I now need to scp a file from node-17:/tmp/something. How can I do the above in one ...
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35 views

Routing traffic based on source (Linux)

I have two interfaces on my server; eth0, wich has one public IP address; and eth1, on which 3 IPS are attached. What I'd like to achieve is route traffic coming to the public address configured on ...
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1answer
44 views

Sharing a file system, or how to horizontally scale access to files

My API mostly serves up stuff from the database, but a big part of the product is generating images by combining SVG files with large pattern fills (~50MB tiff files). The API can scale ...
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1answer
56 views

Unable to nmap open port. IPTables has it listed as open

I have an IPtables firewall set up on a single system. I'm trying to nmap it with the following command: sudo nmap -Pn -A (IP addr) I expect everything incoming to be filtered except for ports 22 ...
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1answer
47 views

Command “ip rule show” not showing anything

I try to list all routing rules, and as far as I know this should be accomplished with the "ip rule show" command. In my case there is nothing returned (really nothing at all). Why? Could it have to ...
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2answers
60 views

Forwarding all connections to different address

I have a script that tries to connect to rabbitmq using default url and port (localhost:5672). Is it possible to make linux redirect all connections to this url and port to different server? I am ...
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63 views

Forward connecting IP address to KVM guests

I'm running kvm with iptables configured to use DNAT and masquerading. However the guest machines are logging the host bridge ip not the connecting client IP address. Is there a way to configure ...
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1answer
72 views

Is the ethx mac address of a VM the same as the mac address of the corresponding tap interface?

I have a single node openstack install on an ubuntu machine. For some reason that I cannot figure out, the linuxbridge is dropping packets from this VM. My iptables seem to be fine (atleast as far as ...
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2answers
3k views

Is it possible for L2TP VPN to do auto route configuration for client during connected?

We've setup a L2TP VPN server with this tutorial, everything works like a charm. The only issue is We don't want client to route all traffic using this VPN, only a particular subnet, e.g. ...
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1answer
322 views

Is ISP's Equipment Misconfigured? Getting Martian Packets on Internet Interface

We have a /28 block from our ISP. Let's say 1.1.1.240/28 with a gateway of 1.1.1.241. We are getting martian packets from another customer over at 1.1.1.214. They are sending broadcasts to 1.1.1.255. ...
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1answer
88 views

rsync works one way but not the other

I have a problem with using rsync. When I try to copy a remote file I get the following error: [home ~]$ rsync test.txt qnx: sh: rsync: cannot execute - No such file or directory rsync: connection ...
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1answer
57 views

How to choose source IP from multiple virtual IP's based on specific destination

I am having two private IP attached to an interface. inet 10.255.0.127/24 brd 10.255.0.255 scope global eth1 inet 10.255.0.153/24 brd 10.255.0.255 scope global secondary eth1 When traffic leaves ...
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2answers
143 views

How do I set Securityonion/snort to not capture certain packets?

After looking through my pcaps from Security onion I'd like to filter out a host (let's call it 192.168.4.4) and filter out some traffic (ports 80 & 443), current project is to look at other ...
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2answers
242 views

Iptables MASQUERADE: What is the advantage/disadvantage between these two commands? [closed]

What is the advantage/disadvantage between below 2 commands: iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/16 -j MASQUERADE AND iptables -t nat -A POSTROUTING -j MASQUERADE Some Background ...
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2answers
4k views

AWS VPC + IPtables + NAT: Port Forwarding is not working

Yesterday, I posted a question here but I think was not clear enough in my words. BTW, This question is not a duplicate. I have AWS VPC Setup as below. GOAL/PROBLEM: SSH to Server A from internet. ...
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2answers
169 views

Android/Linux Ping sends another packet before packet timeout

I have to send 10 packet & timeout for each packet should be 3 secs. As Android pings works on Linux ping commands, I am using below ping command in my application: ping -c 10 -W 3 -s 32 ...
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2answers
437 views

IPtables: Forward port to another host is not working

I am trying out something so this is my test setup: Setup: I have AWS VPC with a public and private subnet. I have a host in public subnet with a public IP address (say Host A) I have a host in ...
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2answers
760 views

Results of MTR on STDOUT?

I am trying out mtr (My traceroute) for educational purposes. However it is quite disturbing that I can't manage it to print results to stdout directly. Per default it opens a GTK-Window where it ...
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2answers
170 views

Red hat reporting more NICs than are physically present

We just deployed several servers (hp dl360p g8), and after the initial boot we're noticing that none of the network devices are showing up as cabled. Ethtool shows no link anywhere. Even more weird is ...
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2answers
100 views

Occasional Delay on Website Resources: Packet Loss Due to Bandwidth Cap?

My website loads more slowly than I think it should, due to a few of the assets taking an absurdly long time to download from the server. I've been trying to track down the cause of this. I'm about ...
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128 views

Tomcat fails to return syn requests to F5

I have an F5 LTM sitting in front of two tomcat servers which host 4 applications. When I initially create the pools and add the members to the LTM I can hit all applications. This is the weird part, ...
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1answer
63 views

connect two vpn server

I have 2 VPS in 2 locations. The first vps is located in Iran and has the ip : A.A.A.A. The second vps is located in the USA and has the ip : B.B.B.B. I run pptp/l2tp on server 1 and my VPN users ...
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1answer
804 views

Virtual network interfaces starting on boot even though they are set to onboot=no , what could be the reason?

I've re-installed my main database server with CentOS 6.5 . I've configured the relevant NIC's including 3 virtual interfaces, called em2:0, em2:1 and em4:0. For some unknown reason the NetworkManager ...
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118 views

Port corruption using iptables NAT on Enterprise Linux 6

I am trying to setup a captive web portal redirect on CentOS using the following configuration: This configuration works for the first few packets, but then suddenly the destination port is corrupted ...
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2answers
583 views

Point to Point Connection Between Two Hosts

I am trying to set up a point to point connection between two Linux host machines. I've connected both of them with crossover cable, but they can't ping each other. Here are the configurations for ...
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1answer
510 views

Linux Cannot change tx-checksumming

On a Linux 3.2 kernel: Linux 3.2.0-4-686-pae #1 SMP Debian 3.2.46-1+deb7u1 i686 GNU/Linux on VmWare, i get checksum errors on ipv6 tcp packets. So I can ping6, but not connect by ipv6 to ssh, smtp, ...