Questions tagged [ip-address]

IP address is a numerical label assigned to each device participating in a computer network that uses IP for communication.

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What's the difference between IP address 0.0.0.0 and 127.0.0.1?

I know that 127.0.0.1 ~ 127.255.255.254 are the loopback IP addresses for most modern operating systems, and these IP addresses can be used to refer to our own computer. But what's 0.0.0.0? It seems ...
Jichao's user avatar
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171 votes
10 answers
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How bad is IPv4 address exhaustion really?

For years the press has been writing about the problem that there are now very few IPv4 addresses available. But on the other hand, I'm using a server hosting company which gladly gives out public ...
oz1cz's user avatar
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124 votes
5 answers
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What is this IP address: 169.254.169.254?

I have always noticed an IP something "169.254.x.x" in my routing table even when I am not connected to any network in my Windows operating system. In Linux, when I list my routing table. $ ...
pradeepchhetri's user avatar
104 votes
6 answers
67k views

Why can't MX records point to an IP address?

I understand you should not point a MX record at an IP address directly, but should instead point it to an A record, which, in turns, points to the IP address of your mail server. But, in principle, ...
dayuloli's user avatar
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73 votes
3 answers
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Block range of IP Addresses

I am getting bombarded with attempted hacks from China all with similar IPs. How would I block the IP range with something like 116.10.191.* etc. I am running Ubuntu Server 13.10. The current line ...
Stephen Cioffi's user avatar
70 votes
15 answers
16k views

Are IP addresses "trivial to forge"?

I was reading through some of the notes on Google's new public DNS service: Performance Benefits Security Benefits I noticed under the security section this paragraph: Until a standard system-wide ...
Jeff Atwood's user avatar
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65 votes
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associate name with ip for ssh?

Let's say I just have an ip address for a server and I don't have a domain with it (it's just a database server, so it doesn't need a domain). I don't want to have to remember the ip address every ...
Matthew's user avatar
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51 votes
7 answers
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How to take full ownership of an IP address?

My business is... troublesome. What I do is legal in every country on earth, but some people don't like it, and make it so tough on my poor ISPs that I am forced to go looking for new providers more ...
darkAsPitch's user avatar
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50 votes
7 answers
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Get IP addresses and computer names in the same network

What is the command that can be used to get the IP address and the names of the computers that are located in the same network? I am running Windows
Graviton's user avatar
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49 votes
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why is loopback IP address from 127.0.0.1 to 127.255.255.254?

I do know that 127.0.0.1 ~ 127.255.255.254 are the loopback IP addresses for most modern operating systems and we could use these IP addresses to refer to our own computer. But isn't 127.0.0.1 enough?!...
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36 votes
6 answers
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Is it valid to have part of an IPv4 address set to zero?

I am working on a change in a Java EE application that would authenticate based on the user's IP address using ServletRequest.getRemoteAddr. We store IP address ranges (FROM_IP and TO_IP) in a ...
Ritesh's user avatar
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36 votes
7 answers
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Is 0.1.2.3 a valid IP address?

Are IP addresses with all zeroes in the first octet valid? For example, can 0.1.2.0/24 be a valid subnet, with network address 0.1.2.0, broadcast address 0.1.2.255 and an usable address range from 0....
Massimo's user avatar
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35 votes
1 answer
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How to disable http basic auth in nginx for a specific ip range?

I'm developing an application with facebook login. So far it's not public and is protected by http basic auth in nginx. Is it possible to disable http auth for facebook's ip range so that we can have ...
VoY's user avatar
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33 votes
7 answers
137k views

How do you have one IP address and many websites?

How can I have it where I have one IP address that sits on the Internet but many web names? For example, when a hosting company has a shared IP but I get unlimited domain names (along with everyone ...
johnny's user avatar
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32 votes
14 answers
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How can I display the IP address of an interface?

If I want to display the IP address that is assigned to eth1, how can I do this in Bash?
user47556's user avatar
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30 votes
18 answers
155k views

Shell Command for Getting IP Address?

Is there a bash command to find the IP address for an Ubuntu box? I need to find the IP address so I can ssh into the machine later.
opierce's user avatar
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29 votes
4 answers
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How does a computer obtain an IP address via DHCP?

How does the computer know which device on the network to query? How does the default gateway factor into this? Pretty much, what is the chain of events that occurs when a computer tries to obtain an ...
Bigbio2002's user avatar
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27 votes
3 answers
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Is there an "official" name to the 0.0.0.0 IP address?

As 127.0.0.1 is known as the loopback address, is there a shorter term to refer to 0.0.0.0 other than "the IP address who means all IP address on local machine"?
Willian Mitsuda's user avatar
26 votes
6 answers
37k views

IPv4 CIDR Ranges for Everything except RFC1918

I'm looking for a list of CIDR blocks for "The Internet", i.e. everything from 0.0.0.0 to 223.255.255.255, excluding RFC1918 address space of 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 (yes, I know ...
Jed Daniels's user avatar
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25 votes
4 answers
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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 ...
grapefruyt's user avatar
24 votes
2 answers
72k views

What is a link-local address?

I could find some information on the Internet but it is hard for me to understand this information because of the use of technical words. Could somebody please help me with that. Did I correctly ...
Roman's user avatar
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23 votes
11 answers
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Windows Server 2008: specifying the default IP address when NIC has multiple addresses

I have a Windows Server which has ~10 IP addresses statically bound. The problem is I don't know how to specify the default IP address. Sometimes when I assign a new address to the NIC, the default ...
22 votes
4 answers
2k views

Customer site is out of IP addresses, they want to go from /24 to /12 netmask... Bad idea?

One of my client sites called to ask me to change the subnet masks of the Linux servers I manage there while they re-IP/change the netmask of their network based on a 10.0.0.x scheme. "Can you change ...
ewwhite's user avatar
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22 votes
3 answers
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Why is ARIN (etc.) allocating such large blocks of IPv6 addresses?

The whole issue of IPv4 depletion and waste seems to be finally getting behind us with the (somewhat) increased deployment of IPv6. The sole purpose of IPv6 was to solve the issue of IPv4 address ...
jduncanator's user avatar
21 votes
5 answers
14k views

Are people really going to use public IPv6 addresses on their private networks? [duplicate]

I have been reading the Debian System Administrator's Handbook, and I came across this passage in the gateway section: ...Note that NAT is only relevant for IPv4 and its limited address space; in ...
Questionmark's user avatar
18 votes
7 answers
144k views

Why does a VLAN have an IP address?

A dumb question for the majority, but I am interested to know "why does a VLAN have an IP address?" Is this address different from the default gateway? Or is this address, same as broadcast address ...
RainDoctor's user avatar
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18 votes
3 answers
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How can I do traffic shaping in Linux by IP?

We have a transparent proxy setup. I tried looking for traffic shaping in Linux, and all I could find online was to limit traffic by interface (eth0/eth1...). I need to limit the bandwidth (never ...
Osama ALASSIRY's user avatar
17 votes
4 answers
33k views

Why are Class C IP addresses preferred in private networks?

Why are Class C IP addresses preferred over A and B in private networks? My possible answer is "In class C, the number of host IP address available in the network is less than class A or B thus ...
mauris's user avatar
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16 votes
5 answers
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Making iptables easier to maintain

My network is completely locked down except for a few sites which are whitelisted. This is all done through iptables, which looks something like this: # Allow traffic to google.com iptables -A ...
Big McLargeHuge's user avatar
16 votes
2 answers
2k views

In the output of `last`, what does suffix ".d" after an IP address mean?

In order to find out who was logged in recently on my server I am using the command: There were logins from very strange IP addresses e.g.: username@pc:/home/user$ last username pts/16 59.224....
Jimmy88's user avatar
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16 votes
7 answers
96k views

Assigning a fixed IP address to a machine in a DHCP network

I want to assign a fixed private IP address to a server so that local computers can always access it. Currently, the DHCP address of the server is something like 192.168.1.66. Should I simply assign ...
OuzoPower's user avatar
  • 357
16 votes
3 answers
10k views

How IP addresses are mapped to Autonomous System Numbers?

How are IP addresses mapped to Autonomous System Numbers (ASNs)? Is there a reference database for it? Then how are these Autonomous Systems geographically located?
Parsa's user avatar
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16 votes
1 answer
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How are cellphone IP addresses assigned?

When my cellphone accesses a website via the tower and its GPRS gateway, NAT ensures that the sites receive a public IP. Would all phones using a single tower have the same IP? If yes, then how can ...
Robin Rodricks's user avatar
15 votes
5 answers
7k views

google.com different IP in different countries. How?

If you ping google.com from different countries you will get replies from local google servers. How does that work? Can a DNS record have multiple A addresses? Could someone point me to the technology ...
HeavyWave's user avatar
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14 votes
3 answers
94k views

nginx not serving requests to external IP address

I have nginx running on port 81. I can telnet using telnet 127.0.0.1 81 and everything is fine. But when I try to telnet to my machine from my Mac (an external IP address), I just get this error: ...
Eamorr's user avatar
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13 votes
3 answers
29k views

Are same IP address with different submask unique? [duplicate]

Possible Duplicate: How does Subnetting Work? In a same block of IPv4 addresses, can there be same IPs with different submasks? For example, can I have this: 180.70.65.140/26 180.70.65.140/25 ...
xenon's user avatar
  • 321
12 votes
6 answers
34k views

How do you choose your IP addressing?

In the life of a system administrator, always will come a moment when an IP subnet needs to be defined. Be it your small home LAN or the endless company WAN where madness lurks in the depths of ...
12 votes
4 answers
22k views

Can I find the web hosting company from an IP address?

If I have an IP address, is there a way to find the web hosting service that this IP address belongs to? I tried using whois and traceroute but no luck so far. The case is that my friend bought a ...
ufk's user avatar
  • 333
11 votes
4 answers
22k views

Get the interface and ip address used to connect to a specific host (ip)

I'm sure this has been asked and answered before, but I wasn't able to find it, so hopefully this will at least link someone to the right place. I want to find out my local interface and ip address ...
umop's user avatar
  • 213
11 votes
5 answers
175k views

Can I use nmap to discover IPs and mac addresses?

When I need to locate the IPs of devices by their mac address on a Windows system, I normally use Advanced IP Scanner (from radmin.com) to scan the network, then I use arp -a to list the mac addresses....
vfclists's user avatar
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11 votes
2 answers
42k views

Why do people use 172.x.x.x instead of 192.x.x.x [closed]

Since I was a kid, I've always installed our home network with the default 192.168.1.x/24, but whenever i log into my university's network, i notice that they use 172.x.x.x, and the same thing goes ...
Hammi Cloud's user avatar
11 votes
3 answers
39k views

SSL certificate for a public IP address?

I just tried buying a Comodo Positive SSL but it was rejected due to not supporting a public IP address, but instead they only support a domain name. Does anyone know any SSL certificate provider ...
hsym's user avatar
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11 votes
5 answers
2k views

Understand IP addresses and location

I risk posing an ill formed question here, but I'll give it a whirl. Does it generally stand to reason that the nearer IP address A is to IP address B numerically, then the nearer IP address A is ...
John Berryman's user avatar
11 votes
3 answers
19k views

nginx as proxy using a specific source ip

I'm using nginx to serve static file and proxy other requests to some Tomcat instance. The problem is that I don't know how to choose which IP address will nginx use to connect to Tomcat. Each Tomcat ...
msbrogli's user avatar
  • 283
10 votes
2 answers
13k views

How do I move static IP address from one ISP to another

We have a linux server pointing to a static IP address from one major ISP. We recently changed that ISP to a new ISP and I am wondering if there is a way we can move the static IP address to work ...
Charles's user avatar
  • 101
10 votes
2 answers
1k views

How even is the distribution of digits in the last part of an IPv4 address?

I have a redirect script operating on a website I created. It sends 1/3 of visitors to site A, 1/3 of visitors to site B and 1/3 to site C. It works by dividing the last part of the users IPv4 ...
Adjam's user avatar
  • 219
10 votes
6 answers
11k views

How reliable are IP address-based firewall restrictions?

On some of my production systems that need to be accessible outside of the LAN I will sometimes add a firewall restriction at the edge to only permit traffic on, say, RDP from a specific origin IP ...
tacos_tacos_tacos's user avatar
10 votes
2 answers
3k views

How often do IP blocks get reassigned to different regions?

Title says it all, really. I'm asking because I've got a subscription to MaxMind, and I'd like to know how important it is to stay on top of updates to their geolocation database.
Daniel Schaffer's user avatar
9 votes
1 answer
2k views

How do I get a distinctive IP Address? [closed]

I see Google has 8.8.8.8 and CloudFlare has 1.1.1.1. How do I get myself a distinctive IP address? What's involved in acquiring something that has a pattern in it?
ChaseLouisPowers's user avatar
9 votes
3 answers
2k views

Should I split my data network into 2 separate VLANs?

I am currently using 10.54.0.0 /19 for all my desktop clients and printers. We have approx 550 clients/printers. Besides bandwidth, which is barely being utilized, are there any other reason to ...
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