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

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140
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4answers
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What's the difference between ip address 0.0.0.0 and 127.0.0.1?

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 what's 0.0.0.0? It ...
62
votes
6answers
15k 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, ...
56
votes
15answers
10k 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-...
48
votes
7answers
3k views

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 ...
35
votes
5answers
5k views

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 ...
31
votes
5answers
3k views

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....
22
votes
4answers
32k views

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 ...
22
votes
3answers
23k views

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?!...
22
votes
11answers
38k views

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 ...
21
votes
4answers
1k 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 ...
20
votes
4answers
27k views

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 ...
20
votes
1answer
13k views

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 ...
17
votes
17answers
63k 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.
16
votes
2answers
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....
16
votes
2answers
2k views

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 ...
15
votes
7answers
38k 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 ...
15
votes
6answers
143k views

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
14
votes
4answers
28k views

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 ...
14
votes
5answers
3k 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 ...
13
votes
3answers
6k views

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"?
13
votes
6answers
13k 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 ...
11
votes
4answers
13k 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 ...
11
votes
5answers
621 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 ...
10
votes
3answers
1k 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 ...
10
votes
2answers
5k 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?
9
votes
2answers
4k 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 ...
9
votes
1answer
27k views

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 ...
8
votes
5answers
13k views

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 ...
8
votes
7answers
1k views

Best choice of private addresses for a “device area network”

I'm building an appliance consisting of several subdevices connected by ethernet inside the appliance. The appliance will connect to the customer network. The customer network can be using private ...
8
votes
2answers
344 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 ...
8
votes
3answers
13k views

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 ...
8
votes
4answers
8k 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 ...
8
votes
2answers
900 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.
7
votes
4answers
2k views

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 ...
7
votes
5answers
10k views

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 ...
7
votes
7answers
49k 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 ...
7
votes
4answers
29k 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....
7
votes
6answers
8k views

How can I find out who is hosting a certain domain? [duplicate]

I've got a friend who has been completely abandoned by his previous website guy. Yes, the guy was cut rate, and yes, you get what you pay for. Anyway, he has asked me to help him untangle all that ...
6
votes
3answers
641 views

ntpd gets “connect: invalid argument” on 0.0.0.2

It appears the reply for pool.ntp.org changed recently. This is making my CentosOS 6 ntp servers unhappy. $ host pool.ntp.org pool.ntp.org has address 0.0.0.2 pool.ntp.org has address 83.209.8.142 ...
6
votes
3answers
7k views

What is this “Thing” on my network?

I was using AMD's magic packet utility to build a list of computers to do wake-on-lan and it found these entries: 224.0.0.22 igmp.mcast.net 01-00-5e-00-00-16 224.0.0.252 *NameNotFound* 01-00-5e-00-...
6
votes
7answers
4k views

Static IP Address assignment vs DHCP address assignment

I manage a small-ish network that consists of less than 70 nodes. The previous system administrators opted to have a dhcp server and manually set dhcp addess. I have opted to rather use dhcp ...
6
votes
6answers
4k 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 ...
6
votes
2answers
3k views

DMZ subnet: to NAT or not to NAT?

I'm looking at setting up a DMZ behind a Cisco ASA that will contain a large number of HTTP front-end load balancers and SSL offload services - over 100 IPs, concentrated on a smaller number of hosts. ...
6
votes
2answers
805 views

Amazon EC2 multiple private IP addresses per instance

I have a scenario where an application requires multiple private IP addresses but does not require the resources of multiple instances. In this case, I would like to run multiple jboss instances on ...
5
votes
10answers
16k views

Use first or last free IP for the default gateway?

Please assume a simple LAN on 192.168.100.0/24. Would you configure the default router on 192.168.100.1 or 192.168.100.254 and why? Thanks
5
votes
11answers
17k views

What is a good default IP address?

My company makes Ethernet devices. These devices have very little I/O. No keyboard, no video output. When the customer gets the device he must configure it for his network. I'd like to choose an ...
5
votes
6answers
2k views

I have a Cisco Catalyst 2940 and want to connect to it via the network. How to find its IP address?

Since my computer has not serial port, the serial cable is of no help. Does the Catalyst 2940 acquire an address via DHCP? At least my DHCP server doesn't show any address which has been requested ...
5
votes
3answers
20k 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 ...
5
votes
5answers
401 views

What is the least expensive way to obtain 1,000s of public IP addresses?

What is the least expensive way to obtain 1,000s of public IP addresses? I'm needing to serve secure (https) pages for 1,000s of SSL certificates, and need a separate IP address for each SSL cert. ...
5
votes
9answers
3k views

Management of Static IP Addresses in the data center

The university where I work uses DHCP for the vast majority of our IP addressing needs. Workstations and the like. However for servers we obviously use static IP addresses. The current method to ...