Questions tagged [netmask]

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Why are two IP addresses within the same subnet unable to ping each other?

I was setting up ip addresses between two devices and I noticed something odd. I feel like I am missing an important fundamental here: Context: Device A: 10.30.0.1/12 Device B: 10.2.0.2/12 if I set up ...
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networking default gateway, default route

in ipv4 cidr notation you can have an ip address like 10.10.20.0/24 it's expanded to network : 10.10.20.0 first ip : 10.10.20.1 last ip : 10.10.20.254 broadcast: 10.10.20.255 netmask : 255.255.255....
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Confused about routing and netmasks

I'm having some issues with OpenVPN and multiple VPNs. Not earth shattering, but after bringing up a combination of VPNs I didn't intend to I've ended up in a situation I don't understand. Looking at ...
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2 answers
328 views

changing netmask of loopback interface

I can change netmask of loopback inteface (usually lo interface has 127.0.0.1/8): pi@raspberrypi:~ $ ifconfig lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 ...
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My static ips are inaccessible only from CenturyLink users across all ports

The Problem: How do you diagnose an ISP specific connectivity problem? I host a few sites on local machine. I pay for a business class account with Centurylink and have a lot of 5 static ips. The ...
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Error: any valid prefix is expected rather than "172.31.1.102/255.255.255.8" [closed]

The command ifup from ifupdown fails when using some mask for static configuration on Ubuntu 20.04 LTS. Example of working configuration $ cat /etc/network/interfaces auto lo iface lo inet loopback ...
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How does a router route an ip packet if two subnets are attached with different netmasks but same prefix

Imagine we have 3 subnets attached to one router: Host A: 192.168.1.1 Netmask: 255.255.255.0 Host B: 192.168.2.2 Netmask: 255.255.255.0 Host C: 192.168.2.3 Netmask: 255.255.0.0 If Host A sends an IP ...
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Bad mask for IP 192.168.0.0 Cisco Packet Tracer [closed]

I have to do next task: connect three LAN networks with Cisco packet tracer. I have to use net addresses 192.168.0.0/24; 192.168.10.0/24; 192.168.20.0/24. When I am trying to set router address 192....
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-1 votes
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Network setting for similar looking subnets

I have a CentOS 7 PC (with 2 NIC cards) and 2 servers. I'd like to access these servers from the 2 NICs in a different way. Something like one server can be reached only from NIC1, and the other ...
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7 answers
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What does the netmask in an IP address actually tell you?

There are several questions out there asking what the CIDR netmask is, and how it's calculated. But after reading all the top answers, I'm still left wondering, how does the netmask let us distinguish ...
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How to change Google compute instance primary network device eth0 netmask /32

When I create an instance in the default VPC, and check ifconfig, it says netmask is /32, as shown below: eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1460 inet 10.138.0.2 ...
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Is it a bad idea to use /128 subnet when a machine is alone in a /64 subnet?

Example: I got a virtual machine with its own /64 subnet and the default gateway is reachable via a link-local address. In this subnet there is only one machine, the virtual machine itself. The ...
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I can ping Web, but not browse it -- why are my DNS settings failing?

Update 6 @ 2:56p on Nov 21 I am working on a creating a small network of virtual machines and containers. So far, I am stuck configuring the host though. There is no virtual machine involved in this ...
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Adding single IP as /32 working well, but not by adding /27 mask

i've got additional /27 IP's subnet for my Debian server. I was trying multiple configurations, but without success on adding whole subnet. Running ip addr add 231.231.231.0/32 dev eth0 Working ...
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Connection through VPN

I'm a Java Developer and for a few weeks I'll be in charge of the network as well. A client of ours wants a VPN connection to his network which I already mounted (Using a TP-link router to stablish ...
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Does it make sense, in terms of performance, to have more than one subnet on the same switch?

We're on a /20 subnet (255.255.240.0), which means 4k addresses. A consultant told us that moving to a subnet with less addresses might increase performance. This network is heavy in file transfers ...
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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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RHEL with two interfaces - Can't ping/ssh into second interface

I have a RHEL Server 'foo' with two interfaces: eth0: inet addr:172.16.15.75 Bcast:172.16.15.95 Mask:255.255.255.224 eth1: inet addr:172.16.15.242 Bcast:172.16.15.247 Mask:255.255.255.248 root@...
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Difference between connecting from inside and outside a subnet [closed]

Let's say provider granted me IP addresses 10.20.30.1 - 10.20.30.254, so the subnet address is 10.20.30.0 and mask 255.255.255.0. I set my router to 10.20.30.1 and computers to 10.20.30.2 and higher. ...
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18 votes
3 answers
4k views

Is it possible to SSH access a server with a misconfigured subnet?

We have a server where one of our engineers misconfigured the subnet and now we are locked out of this server and the only access that I know of would work is a serial console from IDC (it means ...
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1 answer
381 views

How can I tell what's happening to my packets?

I'm trying to bring up a little box on my network. I just reflashed the firmware and it's supposed to come up as 192.168.1.1 by default. My router is a DSL modem at 192.168.0.1; it usually uses a ...
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2 votes
1 answer
661 views

Why do I lose network connectivity for a virtual machine outside /24?

I have a bunch of virtual machines (Ubuntu Server 14.04) hosted on a single real server (Ubuntu Server 14.04 with KVM). The number of virtual machines grow, and I'll soon have more than 254 of them. ...
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1 answer
505 views

Can 2 IP's in the same network communicate with 2 different netmask

I need to expand a network really quick and don't have time or access to change the netmask of all devices. Can the following communicate? IP 1 - 192.168.10.10 mask 255.255.255.0 IP 2 - 192.168.10....
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1 vote
1 answer
1k views

Bridged network setup with gateway not in netmask

i'm currently stuck at setting up the bridged networking on a dedicated server to allow the KVM-guests to use ips from an extra subnet. As far as i know, the address, broadcast and gateway must always ...
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4 votes
4 answers
2k views

What is the proper netmask for an alias IP address?

I did a lot of searching, but there seems to be conflicting info on what the proper netmask for an aliased IP address should be. Some of the conflicting info seems to be FreeBSD-specific. I'm looking ...
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3 votes
3 answers
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What's the formal definition of the magic number of a network? [closed]

I know what the magic number of a network is. I know how to compute it - 2 ^ ((32 - n) % 8). I know what it's used for and how to use it. I don't how how to define it formally. In a recent interview ...
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7 votes
3 answers
19k views

Change netmask (but not ip) of network interface

The ifconfig command can change both the ip address and netmask of a network interface: ifconfig eth0 10.10.10.10 netmask 255.255.255.0 Is it possible to change the netmask of the network interface ...
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24 votes
8 answers
29k views

Why can't all zeros in the host portion of IP address be used for a host?

I know that if I have a network 83.23.159.0/24 then I have 254 usable host IP addresses because: 83.23.159.0 (in binary: host portion all zeros) is the subnet address 83.23.159.1-254 are host ...
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1 vote
1 answer
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Solaris spoof mac impossible

I need to spoof the MAC address in Solaris 10, running in a ESXi VM. The MAC I need is outside the range permitted by vSphere. So I add an "ether" entry to /etc/hostname.e1000g0 so the file says ...
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-1 votes
2 answers
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Why can't my networks reach each other?

We have two Buffalo WZR-HP-G300NH2 routers, with the default firmware, DD-WRT v24SP2-MULTI (10/31/11) std - build 17798. Each has a separate cable internet connection with a public static IP address. ...
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6 votes
3 answers
6k views

Changing netmask from /24 to /16 on a Windows 2003 domain

I have a Windows 2003 domain using 192.168.0.0/24 with all static addresses (no dhcp). I want to move to 192.168.0.0/16 because we need more addresses. I understand that we need to change netmask ...
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1 vote
1 answer
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255.255.255.255 broadcast address meaning

Lets suppose we have a computer with three NICs: NIC_1: 172.16.1.1/24 NIC_2: 192.168.1.1/24 NIC_3: 103.55.34.32/24 We send a packet with the destination IP address being 255.255.255.255. 1) if ...
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23 votes
1 answer
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Why OpenVPN use network 0.0.0.0 netmask 128.0.0.0 as a default route?

If you use redirect-gateway def1 option in OpenVPN config file,the server will add a default gateway on your route table, what I want to know is why OpenVPN did not use network 0.0.0.0 netmask 0.0.0.0 ...
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0 votes
2 answers
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Unreachable host inside network

I'm trying to use some unusual network configurations. Host1 (internet gateway): IP: 192.168.0.1 Mask: 255.255.0.0 Host2: IP: 192.168.1.10 Mask: 255.255.0.0 Default gateway: 192.168.0.1 I can't ...
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2 votes
2 answers
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Hazards of increasing network size by changing the netmask

We are running a small network with address range 192.168.0.0/24. So we only have 254 IPs available. We want to increase this range slightly, to allow more hosts in the network. So if I change the ...
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4 votes
2 answers
544 views

Subnet Mask problem

I'm studying for a test and found myself in a "dead end" with a question about netmasks. The question is: Based on the next figure, once both sub-nets are configured, it's observed that hosts in a ...
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4 votes
2 answers
2k views

Same netmask or /32 for secondary IP on Linux

There appear to be (at least) two ways to add a secondary IP address to an interface on Linux. By secondary, I mean that it'll accept traffic to the IP address, and responses to connections made to ...
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0 votes
3 answers
166 views

What netmask should be used on an aliased address in same subnet as the primary IP?

I have an interface with an IP in a class B subnet. I want to add another IP in the came class B as an alias on the same interface. What netmask should I use? Some people say to use 255.255.255.255, ...
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-1 votes
6 answers
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Is there a tool for subnetting for free?

I'd like a program that I can write in an IP address and give it the Subnet mask and have it divide the networks in C level networks. Thanks. Something that I can download please, not a website.
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3 votes
1 answer
38k views

Bad mask /XX for address X.X.X.X in Router Cisco (Packet Tracer), VLSM

Im trying to do a practice in packet tracer. Im configuring a 1841 Router (but the problem happens in all routers). When I try to set an IP address with a mask different of the by defect mask for ...
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3 votes
5 answers
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How can I get linux to honor new netmask without hard restart of networking subsystem?

I'm not sure "honor" is the right word for this, but it's the best I could come up with. I have a scenario where I have two servers on the same network. They have primary and secondary IPs, all on ...
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