can one location have more than 1 IP address? I have 2 IP addresses and need to know if they originate from the same source. Thanks
You're missing clear definitions of "location" and "source" in your question but lets go with the assumption that you mean "physical machine" for both (as it's obvious that multiple machines will have different addresses and that a single machine can change its IP address over time).
In that case, the answer is yes. The operating system may bind as many IP addresses to a physical network port (and a single MAC -- the physical addressing used by Ethernet) as it wishes.
Binding multiple IP addresses was the standard way of doing "virtual web hosting" before HTTP/1.1 arrived with the "Host" header. The provider would use DNS to map different host names to different IPs on the same network (usually the same subnet as well) and then assign all of them to the same interface. The webserver would get address information from an incoming connection and based on the local IP address would know which virtual host was being accessed.
This led to a higher-than-typical use of public IP addresses but the practice is now gone with the proliferation of HTTP/1.1.
I'm not sure how Windows presents it, but Linux will present a physical interface with multiple IP addresses as multiple logical interfaces such as "eth0", "eth0:1", "eth0:2", etc. Each logical interface has a unique IP address even though they share the same physical interface.
This is hard to tell. Especially it is hard to tell if these IP addresses are from different times. Today I may have a different IP address than tomorrow.
Even they are from the same time, a load balancer im my internal equipment might send my packets over the fail-over line if the 1st one is overloaded or broken down.
One network adapter normally has only one IP address at once and a typical end user only has one network connection active, but even then the IP address can change. The user could switch from wireless to wired and back or a power outage might reset the ISP's DHCP server (assigning everyone a new IP address).
If you want to identify the user even if his IP address changes, you need to identify the user by his session id, stored in cookies. As two users can have the same IP address (a whole company could be behind a NAT), you should never rely on IP addresses for identification.
Related
I recently got to know about DHCP that it dynamically assigns ip addresses to a computer. But what if two DHCP servers across the world assign a same ip address to two different computers. Doesn't it conflicts with the uniqueness property of ip addresses.
For example two DHCP servers assign ip address x to computer1 and computer2 and i wanted to send a mail to computer1 by looking at DNS server it should be send to ip address x. But there is a conflict as two different computers have same ip address x. could someone please clear my doubt.
Let say I want to contact a server whose domain name is example.Com and ip address stored in DNS server is 127.18.1.1 and DHCP changes the ip address for this server to some random value 127.19.1.1 then how is the address resolved since I'm contacting to example.com which has 127.18.1.1
There are a number of ways that this problem is avoided.
Firstly, by keeping networks small, segregating machines into specific functions, geographic areas, etc you reduce the risk of having a large pool of addresses in use.
Secondly, if you must have multiple DHCP servers on a network, then the address space should be split between them. So if you have 192.168.0.0/24, one server would handle 192.168.0.0/25 and another would handle 192.168.127.0/25
Thirdly, most DHCP servers will ping the IP address that they are going to offer before offering it. If the address gets a response it will be marked as Conflicted and won't be offered again.
I am trying to understand how exactly routing works:
if 2 computers are on the same network
if they are on different networks.
More specifically I am trying to understand this: Routing
I am also trying to understand the difference between
IP Address,
Net Address,
Mac Address.
From what I understand:
1) IP Address: is used when computers communicate on the internet only.
2) Net Address: is a local version of the IP address and each device on the network has a unique net address. It's used when devices on the same network want to communicate with each other.
3) Mac Address: is a globally unique address and no other computer in the world has the same Mac address. In reality this is not true because it can be changed. It's used when ???
When a computer wants to communicate with another on the same network, they use net address, right? If the computers are on different networks what exactly happens?
Question: Can someone please fix my mistakes if any and explain what I am missing?
Thank you very much.
There are many network types, but since the most used ones are Ethernet and IP networks (and you seem to be asking about them), I will answer shortly based on them.
IP addresses are always used. They may not be used for deciding who gets the packets directly, but they are the basis even in local networks, since it is an IP network. There can also be other network types that have their own mechanisms, but they are not that common.
In local Ethernet the machines ask via ARP protocol "who has this IP address?" and get a reply with a MAC address. After that they send and receive packets based on that MAC address. The packets still have the IP address information, otherwise the receiving machine wouldn't know what is the destination. Do note that the receiving machine might be a firewall or other middleware device, not the actual computer that has the address. Also a single machine and network card may have several IP addresses set up for it.
In IP networks the IP address is used for routing. All routing devices have a routing table that will tell where the packets should go. If it's a simple device, it usually has a local network and everything else goes via a default gw, which will know better what to do with the packets.
A home router will just push them to the operator, there another router will know what addresses go to their networks, others are pushed forward via another connection, until a bigger place is reached where there are inter-operator connections and they choose again the correct route. And then it goes to smaller and smaller pipes the other way around.
I'm currently revising for an exam and I'm stuck on a question which is:
"Explain the static and dynamic host configuration approaches."
I'm unsure if the answer is correct but what I've write is this:
static host configuration are hard-coded addresses that will only work on one specific network segment, which is intended for stationary computers
dynamic host configurations work best with portable computers like laptops that move between network segments.
that's my answer, could anyone help me to understand if this is correct or not?
You are correct about the difference. But there s a lot more than what you have stated.
DHC : Used to configure IP addresses automatically to the systems without any intervention of network administrator.
For Eg. When you register for a new internet connection, your ISP(network administrator, in this case) will provide you access to the DHCP server which ll allot you the IP address on the runtime.
To prevent the same IP address being assigned to two different computers
Also the main use is, ISP s will have a range of IP addresses with them. You ll be assigned any of their IPs dynamically by DHCP Server when your lease time expires for a particular IP that have been assigned earlier
SHC : Used to manually configure the IP addresses to systems.
When you knew how many systems are going to be present exactly inside the network
And when you want to uniquely identify a system in the ntwk using its IP address
For Eg. When you configure LAN in your house, between, say, around 4 computers. You will know exactly the number of systems in the group. So you don't have to allot a DHCP Server to allot the IP addresses for these 4 systems. YOu manually configure them
Hope that helps :)
Was just wondering why I seem to get different values for my IP address from different sources. If I go to one of the many different 'what's my ip' sites on the net I get a completely different value from when I use ipconfig (on win7)
And no, it's not the subnet mask I'm looking at, these are the actual ipv4 addresses, why would they be resolving to different addresses? Are these 'what's my IP' sites only able to hit an exchange and not determine the IPs of my actual box itself?
If your PC is on a network and not directly connected to your ISP via a modem, there will be at least one router between your machine and the internet. That router will almost certainly be doing NAT (Network Address Translation) and possibly DHCP (Dynamic Host Configuration Protocol) too.
The router will have been assigned an address by the ISP when it established the connection. This address might be static (unchanging) or, more commonly, dynamic (changes periodically as the ISP sees fit). So your 'public' address - the one the router has been assigned and which is visible to the internet - may change from time to time.
Your PC will be connected to the router, and will either have a fixed IP address assigned to it (typically in the 192.168.x.x range) through your OS networking config, or will be given one by the router each time it connects (when you switch on or reboot) via DHCP. In this case, the address will be in whatever range the DHCP service has been told to use (again, the default is likely to be in the 192.168.x.x range).
So your PC has its' own internal address, and your router has its' public address. When you exchange internet traffic, the machine at the other end of the connection will see your public address, not your internal address - the router takes care of forwarding data to the right internal address automatically.
Depending on what IP-checker service you're using, it might display your public address (from the router, which may change if the ISP assigns dynamic addresses) or your internal address (typically when a script runs inside the browser and asks the machine directly).
The answer won't clarify anything, but I'll tell you anyway.
They're both right.
No, your machine doesn't really have two IP addresses, but the IP it shows as depends on who's looking, and from where.
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What you're seeing is the result of what's called a NAT router. NAT stands for "Network Address Translation". The router manages the IP addresses on a LAN, or Local Area Network, and then translates to the appropriate IP address it was assigned on the external network, usually the internet.
details
... say for CentOS?
From what I understand a virtul IP can let you abstract the address from the physical interface(s) the traffic actually goes through. If your server has two network cards it can have a single virtual IP and have the traffic go through either network physical interface. If hardware failure occurs on one of the two network cards, the traffic can keep going with the second one as a backup. I assume that this is more relevant on servers where such parts can be hotswapped.
A Virtual IP address is a secondary IP set on a host, it's just another IP bound to an adapter (adapters if bonded). This IP is useful for many things but most commonly used for webservers to run multiple SSL certificates for multiple sites.
In CentOS you pretty much copy the /etc/sysconfig/network-scripts/ifcfg-eth0 (whichever for the adapter you want) to /etc/sysconfig/network-scripts/ifcfg-eth0:1, In there change the devicename=eth0 to devicename=eth0:1 and change the IP for the new "virtual IP" you want.
Check out this article on Virtual IP address. As indicated it usually floats between machines, and is sometimes used to fail-over a service from one device to another. Are you thinking of a virtual interface instead perhaps?
/Allan