Questions tagged [linux-networking]
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.
3,320
questions
82
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12
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Transfer 15TB of tiny files
I'm archiving data from one server to another. Initially I started a rsync job. It took 2 weeks for it to build the file list just for 5 TB of data and another week to transfer 1 TB of data.
Then I ...
75
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6
answers
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What is the correct way to open a range of ports in iptables
I have come across articles advising for the following:
iptables -A INPUT -p tcp 1000:2000 -j ACCEPT
And others stating that the above will not work and iptables only supports multiple port ...
65
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6
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Hostnames - What are they all about?
I've recently been "forced" to perform some sysadmin work, while this isn't something that I absolutely love doing I've been reading, experimenting and learning a lot.
There is one fundamental aspect ...
54
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2
answers
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How can I increase the value of somaxconn?
I can check its value by cat /proc/sys/net/core/somaxconn,
is it OK if I change it simply by echo 1024 > /proc/sys/net/core/somaxconn?
54
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6
answers
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e1000e Reset adapter unexpectedly / Detected Hardware Unit Hang
I have a Dell 1U Server with Intel(R) Xeon(R) CPU L5420 @ 2.50GHz, 8 cores running Ubuntu Server Kernel Version 3.13.0-32-generic on x86_64. It has dual 1000baseT networking cards. I have it set up to ...
50
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8
answers
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Delete a iptables chain with its all rules
I have a chain appended with many rules like:
> :i_XXXXX_i - [0:0]
> -A INPUT -s 282.202.203.83/32 -j i_XXXXX_i
> -A INPUT -s 222.202.62.253/32 -j i_XXXXX_i
> -A INPUT -s 222.202.60.62/...
50
votes
2
answers
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iptables and multiple ports
This doesn't work for me:
# iptables -A INPUT -p tcp --dports 110,143,993,995 -j ACCEPT
iptables v1.4.7: unknown option `--dports'
Try `iptables -h' or 'iptables --help' for more information.
...
50
votes
12
answers
214k
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Docker pull: TLS handshake timeout
I get this consistenly (Ubuntu 16.04 LTS):
$ docker pull nginx
Using default tag: latest
Error response from daemon: Get https://registry-1.docker.io/v2/: net/http: TLS handshake timeout
However ...
43
votes
6
answers
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How can you tell what a server actually does? [closed]
I've been handed 3 Linux boxes, 1 front facing with apache on it and another 2 which, as far as I can tell, don't do an awful lot. All running on Redhat.
The question is simple: How can I tell what ...
41
votes
2
answers
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How to reduce number of sockets in TIME_WAIT?
Ubuntu Server 10.04.1 x86
I've got a machine with a FCGI HTTP service behind nginx, that serves a lot of small HTTP requests to a lot of different clients. (About 230 requests per second in the peak ...
40
votes
4
answers
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How to block internet access to certain programs on Linux
Recently, I have encountered a problem of limiting Internet Access to specific programs. Could anybody recommend a good way of doing that, without using any particular software?
33
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4
answers
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Difference between /etc/hosts and /etc/resolv.conf
What is the difference between /etc/hosts and /etc/resolv.conf? Also, is there a good documentation that explain all these configuration files.
Thank you.
Bala
32
votes
8
answers
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how to find out mac addresses of all machines on network
Is there some easy way to find out mac address of all machines on my network rather than doing an SSH into each and ifconfig | grep HWaddr if there are 300 machines on network I really need some easy ...
31
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6
answers
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Can I have dots in a hostname?
I'm using names like "a.alpha" for the hostname of my linux box, but it seems that these names are not completely usable. The response of a hostname shell command is correct (a.alpha).
But the name ...
29
votes
1
answer
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What CAN cause 'RTNETLINK answers : No such process' when adding a route
I have come up against this error a number of times, but haven't yet found an explanation of what the error means, or what can cause the problem.
I'm not posting my configs or the specific route I'm ...
28
votes
9
answers
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How do I use Linux to find unused IP addresses on my network?
I've got access to two computers (A and B) on a network. Both have got a static IP address with a subnet mask of 255.255.255.128 (I checked that a DHCP server was not being used). I want to configure ...
28
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3
answers
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Layer 4 vs Layer 7 Load Balancing
I am trying to decide between using a layer 4 load balancing solution for my datacenter or a layer 7 solution. Unfortunately (for my sanity, that is), my use case is simple enough that both solutions ...
27
votes
11
answers
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Can't start CentOS 7 "network" service
I Can't start CentOS 7 "network" service after disabling and removing "NetworkManager" service.
When I check the network service status, it comes up with the following error:
#systemctl status ...
26
votes
8
answers
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How to persist ethtool settings through reboot
I would like to turn off tcp segmentation offload on a CentOS5 server. Using ethtool the command is ethtool -K eth0 tso off However, this setting only persists for this session. How can I make it ...
26
votes
4
answers
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Linux e1000e (Intel networking driver) problems galore, where do I start?
I'm currently having a major problem with e1000e (not working at all) in Ubuntu Maverick (1.0.2-k4), after resume I'm getting a lot of stuff in dmesg:
[ 9085.820197] e1000e 0000:02:00.0: PCI INT A ...
26
votes
4
answers
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Intermittently high ping times to router via Wi-Fi
On my local network there are (among others) 5 machines (running
Debian Jessie or Arch) wirelessly connected to a Netgear WNDR4000
router. Below is a graph of the ping times to the router
from each of ...
25
votes
4
answers
68k
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multiple MAC addresses on one physical network interface (linux)
Simple question:
How can I setup multiple MAC addresses on one physical network interface (linux)?
Why?
My ISP is checking ip<->mac on GW and I d like to route traffic through my "linuxbox" and ...
24
votes
4
answers
203k
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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 Bcast:...
23
votes
4
answers
13k
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How to simulate DNS server response timeout?
I need to test an application's behavior when it can't resolve a hostname due to a timeout. Setting nameserver 127.0.0.1 in /etc/resolv.conf didn't work: the relevant functions return immediately with ...
22
votes
1
answer
138k
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What does "net_ratelimit: 44 callbacks suppressed" mean on a linux?
I'm trying to tune Snort performance on a Debian based router. I was seeing stuff like:
snort packet recv contents failure: No buffer space available
So I upped the buffers to 8M and when that didn'...
21
votes
2
answers
42k
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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. 10.0.0.0/...
21
votes
4
answers
32k
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How to see on Linux what network interface and source IP address is used for a route to a specific destination host?
If I have multiple network interfaces (here: 2) on a Linux machine (here: Debian Lenny).
How do I see, over what network interface (NIC) a route to a specific destination host is going and what source ...
21
votes
3
answers
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Adding a whole IPv6 /64 block to an network interface on debian
I tried adding a whole IPv6 (/64) block to an interface using
ip route add local 2001:41d0:2:ad64::/64 dev lo
like described here on my Debian server, but I seem to be missing something.
If I ping ...
20
votes
3
answers
2k
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Managing cluster of linux computers behind firewalls
My company's product is essentially a Linux box (Ubuntu) sitting in somebody else's network running our software. Up to now we had less than 25 boxes in the wild and used TeamViewer to manage them.
...
20
votes
2
answers
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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 ...
20
votes
4
answers
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How to "restart" particular network interface on RHEL?
In RHEL, instead of using service network restart command, how can i restart a particular network interface, lets say "eth1", with only one command.
"Only one command" because that is the only ...
20
votes
4
answers
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Resolv Conf Multiple DNS Servers with specific domains
I need the ability to have specific dns servers for multiple networks, and i would like to know how to properly update my /etc/resolv.conf:
lets say I have a major vpn, that I route all my trafiic ...
20
votes
4
answers
46k
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How to generate netflow data in linux
We have a number of Linux servers for which I would like to capture netflow data to be processed by a netflow analyzer. I've been spoiled by the ease in which Mikrotik routers allow netflow data ...
19
votes
4
answers
30k
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How can I switch from a custom linux network namespace back to the default one?
With ip netns exec you can execute a command in a custom network namespace - but is there also a way to execute a command in the default namespace?
For example, after executing these two commands:
...
19
votes
1
answer
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Difference between net.core.rmem_max and net.ipv4.tcp_rmem
What's the difference between net.core.rmem_max and the third value of net.ipv4.tcp_rmem? Which has the higher priority for tcp connections?
For below two examples, what's the max buffer for tcp ...
18
votes
3
answers
102k
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How to set a static IP (client side) in OpenVPN?
I am setting up a VPN network with a lot of little devices (running OpenWRT). In my use case, the devices are all identified by a number and I would like their ip adresses to match their ID (e.g: the ...
18
votes
4
answers
115k
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"Stale NFS file handle" after reboot
On the server node, it is possible to access an exported folder. However, after reboots (both server and client), the folder is no longer accessible from the clients.
On server
# ls /data
Folder1
...
18
votes
4
answers
8k
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How to completely, dynamically disable IPv4 stack from Linux?
How can I disable IPv4 stack from Linux ? I want to do that dynamically, i.e. sometimes I want it enabled and sometimes I want only IPv6 stack. Is there any portable way to do that ? If you know how ...
18
votes
5
answers
11k
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What network loads require NIC polling vs interrupts?
Does anyone have some data or basic calculations that can answer when frame coalescing (NAPI) is required and when a single interrupt per frame is sufficient?
My hardware: IBM BladeServer HS22, ...
17
votes
2
answers
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How can I measure the cumulative network usage of a process, from execution beginning to end
I want to measure how much bandwidth git pull uses, preferably by prefixing git command with desired program, i.e. nettally git pull
Alternatively, is there some sneaky way to accumulate nethogs / ...
17
votes
1
answer
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Should /etc/hosts contain an entry like '127.0.0.1 localhost myhost.example.org myhost'?
When looking at a variety of Linux and FreeBSD systems, I've noticed that on some systems /etc/hosts contains an entry for the public hostname of the host, but not on other systemst.
What is the best ...
17
votes
1
answer
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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 ...
16
votes
5
answers
17k
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OpenVPN for certain IPs, eth0 for everything else
Summary: I'd like to connect to my VPN and have access to certain servers, but for all other traffic I'd like to use my regular networking.
I've setup an OpenVPN server on my VPS, my server.conf file ...
16
votes
2
answers
3k
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Serving 10,000 simultaneous users over Wifi
I'm looking to offer a wifi service at a public event. The traffic will be very minimal, 10KBps should be adequate. Users don't necessarily need to connect to anything other than the private intranet. ...
16
votes
1
answer
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VLAN tags not shown in packet capture (Linux) via tcpdump
I am adding a tagged VLAN onto eth0:
#ip link add link eth0 name eth0.20 type vlan id 20
This results in:
#ip link
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast ...
16
votes
1
answer
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How GRO (generic receive offload) works on more advanced NICs?
I am interested in particular answers:
Does the NIC with GRO edits/creates TCP ACK or any other packets (or is this feature transparent to receiver/sender TCP stacks)?
There should be a timeout/event ...
16
votes
1
answer
69k
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How to troubleshoot latency between 2 linux hosts
The latency between 2 linux hosts is about .23ms. They are connected by one switch. Ping & Wireshark confirm the latency number.
But, i dont have any visibility into what is causing this latency. ...
16
votes
5
answers
13k
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predictable network interface names in systemd
Recent version of Ubuntu and Debian (stretch) bring a new network interface naming scheme.
Now, when updating from a system that's using old style names like "eth0", I'd like to know prior to booting ...
15
votes
5
answers
27k
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Busybox, netstat, no -p
I have an ultra old (don't ask why) BusyBox (BusyBox v1.01 (2008.12.19-21:31+0000) Built-in shell (ash)) on my DreamBox. I would like to find out which process opened which connection using netstat. ...
15
votes
1
answer
38k
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Ufw and Iptables. Which is better and why? [closed]
I am a newbie to this domain, so i kept researching on ufw and iptables. But I cant distinguish them clearly because in every article /blog both of these names are present and I am really confused ...