Questions tagged [ipv4]

Use the ipv4 tag ONLY if the nature of your question specifically involves IPv4 addresses or networking -- often in contrast to IPv6. Most networking currently involves IPv4 addresses, so you should NOT include this tag with every networking question.

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`dig -4` returns IPv6 address

Why would dig -4 return an IPv6 address? % dig -v DiG 9.16.5 % % dig -4 @8.8.8.8 TXT o-o.myaddr.l.google.com | grep TXT ; <<>> DiG 9.16.5 <<>> -4 @8.8.8.8 TXT o-o.myaddr.l....
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How to avoid IP collisions of RNDIS devices?

Scenario is like this: I have a couple of devices using autoip and mdns over rndis (ethernet over USB) to connect to a host: You connect them with usb, the PC detects an rndis device, both ends choose ...
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ETH0 no address ip with ifconfig

I've created a new LXC on debian jessie, but it doesn't have an ipv4 address. When I connect to my LXC and do ifconfig: eth0 Link encap:Ethernet HWaddr blabla inet6 addr: blabla/64 ...
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IPv4 iptables blocks things, but output policy is ACCEPT, what is the problem with my INPUT DROP chain?

This is my IPv4 iptables list at this moment: Chain INPUT (policy DROP) target prot opt source destination ACCEPT all -- anywhere anywhere ctstate ...
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Why does my Linux system have both private address and APIPA (link-local) assigned address on IPv4 interface

On Linux Kernel 4.19.94+, I could see IPv4 private and link-local address assigned to the interface eth0 as shown below. My understanding is that Automatic Private IP Addressing (APIPA) IP address (...
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376 views

How to add an IPv6 address?

The official Debian networking documentation tells to use: ifup 6to4 But ifup is not found (ifupdown and ifupdown2 are commands not found too, even after having been installed). Does it have ...
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1answer
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Network issues after setup a read only file system

I'm new to Linux (Raspbian Buster / Raspberry Pi 4 model B) and I have some network issues after setup a read only file system. I followed this guide to realize the ro fs. My raspberry is connected ...
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1answer
304 views

Why does lsof indicate my IPv4 socket is IPv6?

I am looking at the output of lsof -i and I am getting confused! For example, the following connection between my java process and the database shows as IPv6: [me ~] % lsof -P -n -i :2315 -a -p xxxx ...
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1answer
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ssh - packet_write_wait when connecting ipv4 connecting via ipv6 works - What are the next steps to debug?

What could cause ssh connections over ipv4 to drop after around a minute idle. When connecting to the same server using ipv6 the connection stays alive. If running top, or otherwise interacting with ...
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Different IP:hostName mappings for same host in `/etc/hosts`. Why does this work?

My scenario Relevant entries in my /etc/hosts (I have them written in the same order you see them here) 172.22.5.107 www.wordpress-rend-adri.com 192.168.1.116 www.wordpress-rend-adri.com I use ...
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Ansible fact is undefined: `ansible_all_ipv4_addresses` is undefined

The task includes an option with an undefined variable. The error was: ansible_all_ipv4_addresses is undefined. Why would I be getting this error, if I am connecting over ipv4? I'm trying to dump ...
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Ip address is of 32 bit, which means 4 bytes. Yet all answers to question on 13 root dns servers say otherwise [closed]

All of the articles I read that explains why there are 13 root dns servers saying each ip address takes 32 bytes and hence (13 x 32) = 416 bytes leaving up to 96 bytes for other protocol information. ...
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1answer
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hostapd clients don't get ipv4 addresses

I'm trying to setup a raspberrypi 4 as a wifi access point. Following the official documentation I managed to bridge my eth0 interface and setup hostapd. The bridges IP is provided by an exisiting ...
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1answer
175 views

nftables rules not blocking traffic

I am testing NFtables and am attempting to set up a basic routing firewall on a linux machine with 2 interfaces, ens37 and ens38. Here is the ifconfig output for these 2 interfaces. ens37: flags=4163&...
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What happened to the “-4” option for command line FTP?

It used to be that you could force command line FTP to use IPv4 like so: ftp -4 ftp.example.com However, at some point in the relatively recent past the "-4" (and for that matter, the "-6") option ...
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Cannot open/access ports on Ubuntu

I created an Apache web server on Ubuntu 18.04.2 LTS, using the guide described here. Afterwards the web server worked completely fine. Later on I installed Libvirt onto the web server, after which ...
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How can I get the ipv4 address from `ip link` like I used to see with ifconfig?

When I run ip to get the ip address, I'm getting $ ip link 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/loopback 00:00:00:00:...
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1answer
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How to connect to a IPv6 service using IPv4 connection on CentOS 7?

I'm trying to work out how to connect an inbound IPv4 connection to a port listening on a IPv6 port on a CentOS box. To demonstrate on a vanilla CentOS 7 server: Confirm bindV6only is disabled $...
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1answer
1k views

ntp using ipv6 address instead of ipv4

I have a laptop running a version of Linux ( 3.12 ). I have ntpd installed and configured to sync with time.google.com. The problem I am having is if I am plugged into a network that only provides ...
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How do I use grep to output only the names of files that contain any ipv4 address

I am using Red Hat Enterprise 6 and I'm trying to search through the /etc/ directory for files that contain any IPv4 address.
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Do the default settings of NetworkManager detect if there is a conflicting IPv4 address on the network?

Added support for detecting duplicate IPv4 addresses, with a timeout configurable through the ipv4.dad-timeout connection property. -- NEWS dad-timeout / int32 / -1 Timeout in ...
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does :::80 in netstat output means only ipv6 or ipv6+ipv4?

If I am listening on :::80, is it listening on all ipv6 or all ipv6+ipv4? This is my netstat -tln: tcp 0 0 :::8080 :::*
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1answer
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Get Wireless LAN IPv4 Address Of Device

I want to know the easiest way and I would perfer a single line command that works on most or all Linux distros. I want to get the devices IPv4 address. The reason why I want to know this is because ...
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3answers
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How can check ipv4 address in shell. Like is it *.*.1.* or *.*.0.*?

So here I tried to get from the ifconfig file, but same with errors with simple ifconfig command !#/bin/sh if [/home/pi/ifconfig | grep -Eo ‘inet (addr:)?([0-9]*\.){3}[0-9]*’ | grep -Eo ‘([0-9]*\.){3}...
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1answer
121 views

Setting 'DF'-bit in IP-header inside pcap file

There is some .pcap-file with fragmented IP traffic. I replay this file with tcpreplay, but also I need to replay it with DF (don't fragment) bit set in some packets. I supposed that tcprewrite will ...
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1answer
782 views

IPv4 and IPv6 sockets with same port

Is it possible to have a single process that would have two sockets, one using the AF_INET and one using the AF_INET6 families, while both being bound to the same port number, e.g. 20000? If the IPv6 ...
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2answers
255 views

iptables blocks SSH connection

I've recently upgraded my Raspberry Pi from Raspbian 8 (Jessie) to 9 (Stretch). The Pi in accessible on my LAN both via IPv4 and IPv6. I have applied some iptables rules (IPv4 only) to block hosts ...
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1answer
98 views

IPv6 superuser ports

Does IPv6 have the 0-1024 superuser requirements for ports? I saw in the changelog for Linux 4.11 that they added a sysctl option to change it, but it only lists it under IPv4. Also does Open/FreeBSD ...
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iptables ipv4 configuration for OpenVPN Connectvity

I'm following this tutorial in order to setup my openvpn server: https://linode.com/docs/networking/vpn/set-up-a-hardened-openvpn-server/ When i reached the part to replace the ipv4 configuration, ...
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Bash: Extract one of the four sections of an IPv4 address

We can use the syntax ${var##pattern} and ${var%%pattern} to extract the last and first section of an IPv4 address: IP=109.96.77.15 echo IP: $IP echo 'Extract the first section using ${var%%pattern}: ...
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1answer
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IPv6 socket creation failed: Address family not supported by protocol

OS: GNU/Linux Debian 9.2 64-bit I disabled IPv6 on one of my servers. And now I'm getting this in mail: exim paniclog ... IPv6 socket creation failed: Address family not supported by protocol How ...
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1answer
450 views

SSH Tunnel broker over IPV4 for machines behind CNAT

I am not sure if I should be asking this in Unix & Linux or Network Engineering Here is the physical scenario [Host 1]----[Carrier-grade NAT]---->AWS<----[Carrier-grade NAT]----[Host 2] ...
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2answers
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Using Linux as router with nftables - masquerade not forwarding reply back

I have a Linux machine which I'm using as a router. It has 5 network interfaces: three separate LANs which it routes between, and two WANs. At the moment I just have one WAN as the default route, and ...
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1answer
11k views

How do i check if DHCP is enabled?

I have a VM running Debian 9 and the latest version of VirtualBox. I have VirtualBox configured to use the bridged adapter and it was working fine yesterday. But when I came and got on it this morning....
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1answer
664 views

Get DHCP running with Kernel 4.14-rc5

I tried to solve my problem that my touchpad is not running on my Lenovo 720-15IKB by installing the latest rc kernel 4.14.rc5 as described here, which really worked! The touchpad is working then! ...
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1answer
1k views

Not getting dynamic IP address by dhclient on a virtual Fedora

I run a course that includes practical classes on system administration. For that years ago I created a Fedora 20 virtual image -- it need not be a modern and secure one as it is only for executing ...
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2answers
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Apache server not listening on IPv4 but listening on IPv6

We are facing one weird problem on one of our RHEL apache server. Actually, it is not listening on port 80 from remote hosts. When we locally browse http://localhost it is opening default page. When ...
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1answer
231 views

What is ICMP reply for all-zero host-bit IPv4 address?

We all know that the first address of any sub-net is network identifier and it can't be assigned to any hosts. For example in network 10.1.1.4/30, the address 10.1.1.4 is network identifier. If ...
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vsftpd works with ipv6 but not with ipv4

I am running an ftp server via vstfpd. /etc/vsftpd.conf: listen=YES #listen_ipv6=YES anonymous_enable=NO local_enable=YES write_enable=YES use_localtime=YES xferlog_enable=YES #...
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1answer
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Change the listening address to IPv4 from IPv6

I use netstat -plnt check the vsftpd deamon, it is listening the IPv6(tcp6) address, so I use the FileZilla can not connect the VM. [root@localhost src]# netstat -plnt Active Internet connections (...
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1answer
8k views

wget uses ipv6 address and takes too long to complete

On a server wget-1.16 takes 8 minutes to complete: $ wget http://http.debian.net/debian/dists/stable/Release -O - --2017-06-12 23:44:40-- http://http.debian.net/debian/dists/stable/Release [...
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3answers
672 views

Find local processes starting TCP connections

With tcpdump I see many SYN packets ... and source IP is Localhost. I wish to find which processes are trying to connect. Note the connections don't reach ESTABLISHED state, they seems to be random ...
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1answer
896 views

Routing packets between IPv4 and IPv6 networks on different Interfaces

I have a Linux-Board with two Ethernet-Interfaces (eth0, eth1). On eth0 I have a IPv4 network, on eth1 there's a IPv6 network. Now I want to route packets from specific devices on the IPv4-network to ...
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Why is BIND not automatically trying all nameservers, especially when an IPv6 nameserver is unreachable?

I am running a recursive local name server using BIND on Ubuntu. I have an IPv4 network at the moment. It appears as though BIND defaults to listen for queries and recursively resolve names on both ...
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1k views

Mapping IPv6 to IPv4 addresses

I'm trying to figure out what commands I can use to help me map IPv6 to IPv4 addresses on a local network. I would like to be able to do the operation both ways (IPv4 -> IPv6 and IPv6 -> IPv4) where ...
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834 views

iptables limit the number of connections in the system for both ipv4 ipv6

A connection is a 5 tuple (ip src/dst, port src/dst, protocol). What about different connections between ipv4 and ipv6? If I define the iptables rule: iptables -A INPUT -p tcp -m connlimit --...
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1answer
12k views

Add IPv6 address to existing IPv4 interface not working

Probably a simple answer but I can't seem to find it. I am running a multihomed Debian Stable(latest) and on interface eth1 I need both IPv4 and IPv6 address. My /etc/network/interfaces looks like ...
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3answers
3k views

How does Linux choose between default gateways?

I have a computer with two NICS, one eth one wlan. wlan is on 10.0.0.0/24 eth is on 192.168.0.0/16 Kernel routing table is: $ route -n Kernel IP routing table Destination Gateway ...
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1answer
681 views

Can not resolve names but can ping addresses when connected to IPV4 router, all works fine with IPV6 router

At my place I have a router that gives me an IPV4 address. My Gentoo PC works fine but my Gentoo laptop stopped resolving names. I visited my parents and tried connecting to their router, which gives ...
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3k views

IPv6 over TCP or TCP6

My understanding is that tcp6 is used for connections over IPv6 & tcp is used for connections over IPv4. and ::ffff:127.0.0.1 is representing IPv6 address which is mapped to IPv4 address. ...