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.
1,254
questions with no upvoted or accepted answers
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Disable NIC Receive Side Scaling hashing
On a benchmark lab system running Fedora Core 27 I've got Intel X710 10GE cards and 12-core Xeon processors, configured with 12 NIC queues and RX Flow Hashing based on both IP addresses and port ...
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Linux VXLAN Hardware offloading
When looking at several guides to setup VxLAN networks on Linux there seems to be 2 options:
Open vSwitch (OVS)
Native Linux VxLAN device.
When using OVS there is an option to use vxlan encap/decap ...
4
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Run a systemd timer only when network traffic is low
I would like to run a systemd timer daily, with lax time accuracy. However, I would want the timer to run only if the network is continuous idle/low load (for at least 2 minutes).
Is there any way to ...
4
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1
answer
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QEMU versatilepb default network adapter
I'm using qemu to emulate a raspberry pi. I'm starting qemu like this:
qemu-system-arm -kernel ./qemu-rpi-kernel/kernel-qemu-4.1.13-jessie \
-cpu arm1176 -m 256 -M versatilepb \
-append "...
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Limiting incoming traffic with tc police
I have a requirement to limit the total incoming traffic to 5mbit. I know this can be achieved by using the following tc command:
tc filter add dev eth0 parent ffff: protocol ip u32 match u32 0 0 ...
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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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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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How to tell whether a linux tcp socket had recent activity?
Most of the time, when changing or upgrading a network service, I would do this during maintenance hours but some services are rarely used so it is tempting to just check whether it is currently in ...
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Send all Outline traffic over proxy to another server
i have setup an outline server on my first server lets call it outline server; and i have successfully connected to that server via outline client application.
but i need to redirect all that traffic ...
3
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Wifi 6E access point in Linux
Context: I'm looking to set up a 6 GHz (Wifi 6E) Access Point in Linux. I have two Intel AX210s (WiFi cards) on two computers.
nmcli only supports 2.4GHz + 5GHz
hostapd seems to support WiFi 6 but ...
3
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3
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Unwanted DHCP setting on server
I'm configuring a new Debian 11 server running on a private network. It is determinedly taking a DHCP address in addition to the static IP I am manually configuring. I don't understand where it gets ...
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Kernel TCP tuning for buffer overrun and packet collapse
We have a Nginx+Ruby application where the data between Nginx and the application are interfaced through a socket.
As part of performance improvement, when we analyzed the netstat statistics on the ...
3
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1
answer
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Linux TCP payload filter
I use nftables, but it hasn't got anything like iptables' string nor u32 match, so it couldn't reliably gather payload offset.
If not via nftables' raw payloads, how could I analyze TCP payload ...
3
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678
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SSH with a dynamically-allocated remote forwarded port -- how to find the port number
I need to establish an arbitrary remote-forwarded port to a specific local port when connecting to a server. I don't have admin rights on the server, which is a significant compute resource used by a ...
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WireGuard Failover for MySQL Galera Cluster
I'm setting up four servers across four locations in an attempt to create a geo-redundant MySQL Galera cluster. Two of the servers are behind NAT, and I'm currently attempting to use WireGuard to ...
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firewalld: two NICs, two zones. Zone is ignored
I have a server running CentOS/RHEL 7.7 with two network interfaces. These interfaces are configured and work properly. The first interface, ens33, is part of the firewalld "public" zone. All the ...
3
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1
answer
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Connect from Windows host to QEMU inside Docker
I am trying to establish a connection between Windows 10 running Docker container (Linux), which runs QEMU to host a QNX OS. This picture should make it more clear:
Structure
I would like to ...
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bonding network interface speed changed to 0
I have Suse12 system with Intel 82599ES nic(with 2*10-Gigabit SFI/SFP+ port),two ports are bonded by lacp.Recently,the system network is unreachable,lasted 3 minutes.
Looking through the message log, ...
3
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1
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What does rx_csum_offload_errors mean?
I see too many rx_csum_offload_errors on ethtool output and it constantly increases. What is the reason of these errors and how can I fix it?
# ethtool -S enp12s0f0 | grep error
rx_errors: 0
...
3
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1
answer
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Linux kernel 4.9 not responding to neighbour solicitation
I have this small network where Linux kernel 4.9 acts as a v6 router. There are two other servers connected to this router and both have ipv6 address configured on interfaces connecting to this router....
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Configure multiple static IPv6 addresses with dynamic prefix
is it possible to add multiple IP addresses to an interface where the host part is static and the prefix is dynamically determined from router advertisements?
All ressouces I found told me to set a ...
3
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How to create a Linux virtual machine in AWS with multiple network interface cards each having a public IP
AWS. Centos 7.5 m5.large EC2 instance. VPC with 2 subnets. The instance has two network interfaces, one per a subnet. A Network Security Group is configured to allow all TCP inbound and outbound ...
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585
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New AWS Linux EC2 loses all networking about 7 minutes after bootup
I created a new AWS EC2 instance (error occurs with AWS Linux & AWS Linux 2). And I can SSH in fine to start installing thing but every time after 5-10 minutes I can no longer type in the terminal ...
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How can I test network connectivity to a Keberos KDC (UDP/88)
How can I test network connectivity to a Keberos KDC (UDP/88)? Does Kerberos have a standard way to communicate that gives any output?
HTTP for example,
nc -v google.com 80
GET
will dump the ...
3
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498
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Any limit on initcwnd?
We are trying to decrease the initial latency on TCP connections to our servers. In some test we found that when we download a file below 15587 bytes the total downloading time (apache benchmark total)...
3
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1
answer
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packets transmitted, 0 received (no internet connection) on centos 6.6 vps
I have centos 6.6 vps server.
When I use command: yum update get error:
Error: Cannot find a valid baseurl for repo: base
when I check for ping and use command: ping -c4 google.com get error:
ping: ...
3
votes
1
answer
530
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iptables block IP for x hours not working?
On my Linux server, I want to ban IPs that access certain ports for 24 hours using IPtables. For this, I use the following IPtables rules:
# Check if IP is on banlist, if yes then drop
-A INPUT -m ...
3
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0
answers
4k
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Mosquitto MQTT - Not able to connect from external client
Ok, this has been throwing me for a loop for the past few days.
Information
I have Mosquitto MQTT 1.4.10 with WebSockets enabled setup and running on Ubuntu Server 14.4. Any client on my LAN can ...
3
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1
answer
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How to set DSCP values for outgoing traffic from my linux server to check whether QOS is working correctly or not?
I have to validate whether my router's QOS policies are working correctly.I have come up with an approach to tag the packets with DSCP values using IPTABLES.
Can anyone confirm whether my approach is ...
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2
answers
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Is there a way to know network interface names before booting rhel 7?
We are trying to auto deploy kvm vms of rhel 7. We need to set udev rules and we're finding the interface names can be different and this breaks the udev rules.
Wondering if there is a file we can ...
3
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answers
624
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OpenSwan IPSec log explanation
I am trying to understand the IPSec logs. Would be really great if someone can help me to understand the main things I look for and how to troubleshoot any ipsec issue. Would be really great of ...
3
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bridge interface causes boot to hang for many minutes
I have a bridge br0 which is being used as docker's bridge interface and bridges to our vpn with an ipv6 interface. When I set up this bridge manually, everything works fine and I can connect to the ...
3
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1
answer
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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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answers
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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.
...
3
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0
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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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907
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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 ...
3
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What is the ip xfrm tmpl and how is it different than an SA?
The Linux ip xfrm policy command creates an IPsec policy, associating particular traffic with an SA. It uses something called a "template" (tmpl), which, as far as I can tell, is just a means of ...
3
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1
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668
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Linux route unexpected mtu
i'm observing rather strange (at least for me) behaviour for few routes in my network. i use gre interfaces on top of ipsec tunnels. these gre interfaces have mtu 1400 on my entire network. normally i ...
3
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0
answers
591
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Maximum transfer rate iSCSI bonding vs multipath
I want to get the maximum tranfer rate with iSCSI from my virtual machine (Linux) to my Linux Storage Host.
I don't know iSCSi well so I'm not sure which way is the best for performance.
A: Just ...
3
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0
answers
3k
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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 ...
3
votes
1
answer
956
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Linux Server Virtual Ethernet interface stops responding to arp requests
I'm hoping someone has had this issue before as it is driving me nuts. I have 2500 linux embedded Linux servers. We use these servers partly to act as gateways to other devices sat on a private ...
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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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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 ...
3
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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 ...
3
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1
answer
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ssh connection freeze after password phase
I'm trying to connect to a server (Oracle Linux 6.3) and after I insert the password the session just freeze.
I checked the audit log and I've authenticated successfully, after I restarted the ...
3
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0
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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(...
3
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1
answer
399
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Buffer-stuffing denial-of-service attack
I started seeing this odd sort of effect that resembles denial-of-service attack against a Linux server. The effect is that the network becomes at least partially unusable very much the same as what ...
3
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2
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575
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Traffic not routing as expected
In the following output, why does vpn1 route/ping to 10.100.0.1 instead of to 10.100.0.112?
10.100.0.1 is network gateway with no nat. 10.100.0.112 is dual home host with nat enabled.
root@vpn1:~# ...
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1
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How to mimic "DMZ Host" or "Default Host" NAT funcionality with iptables?
My previous DSL modem had a function called "DMZ Host" (which in other platforms seems to be named Default Host). When you select a computer in your network to be the DMZ Host, it forwards every non-...
3
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2
answers
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How to assign multiple IPv6 Alias addresses to one network interface
I have an IPv6 Range which i am trying to assign on a centos6 server. I have updated my below files for IPv6 configuration:
[root@test ~]# cat /etc/sysconfig/network
NETWORKING=yes
NETWORKING_IPV6=...