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Questions tagged [netmask]

41 questions
26
votes
8 answers

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 addresses 83.23.159.255 (in binary: host portion…
Grezzo
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23
votes
1 answer

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 as a default gateway instead of netmask…
Forcyy
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18
votes
3 answers

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 asking an IDC engineer to help us with this). What has…
Alexey Kamenskiy
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7
votes
3 answers

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 eth0 without knowing (and changing) it's ip…
Randomblue
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6
votes
3 answers

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 from all computer from 255.255.255.0 to…
David
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4
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4 answers

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 for the "most technically proper" answer, if…
Jeff
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4
votes
2 answers

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 sub-net can't access hosts in the other sub-net.…
Bernardo Oliveira
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4
votes
2 answers

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 that IP will use it as a source, but any traffic…
derobert
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4
votes
2 answers

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 sites are accessible from anywhere in the world…
Altimus Prime
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3
votes
5 answers

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 the same subnet. For the sake of discussion, they…
jj33
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3
votes
7 answers

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 two IP addresses? For example, if I give you…
CodyBugstein
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3
votes
0 answers

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 /etc/sysconfig/network-scripts/ifcfg-eth0, I see…
Jeff Widman
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3
votes
3 answers

What's the formal definition of the magic number of a network?

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 I was left speechless after being asked to deliver…
Aadit M Shah
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3
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1 answer

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 this Class of address (using VLSM), the router said…
a0rtega
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2
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2 answers

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 connection. Though there are two bridges in…
gbambo
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