For the idea of private, I mean it like 10.*.*.* idea of ipv4. It seems ipv6 don't conserve ip addresses like these any more.
So, what if I want to create a private subnet which I don't want the others to know my subnet number or access my subnet with ip address. I can create my own range of ip subnet number, but it seems in that way, it would conflicts with global ip address.
I know the idea of link local address, but I think that's useless when I want several links to constitute a network.
If you are just setting up a private local network for development/testing and don't have any actual IPv6 connectivity of your own (or your ISP is stupid and only gave you a /64) then unique local addresses will work fine for you.
However, unique local addresses cannot be used for connectivity to the global Internet. If you need this, you should get global addresses and a proper firewall (as NAT is not needed and strongly discouraged in IPv6).
To get a /48 ULA prefix, visit this generator and throw in a MAC address. (Using a MAC address to generate the prefix is specified by RFC 4193, which defines unique local addresses.)
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.
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.
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
What are the effects of incorrectly setting the netmask? I have a C++ application that sets the network mask of a device. If the netmask is set incorrectly, tftp doesn't seem to work properly. Why would this happen? What other problems occur when the netmask is not properly set for a device/PC?
While this question is probably more about IP networks than programming it is a challenging subject for many developers.
The netmask delimits the host address (your PC or server) and the network address (the part of the logical network infrastructure in which your system lives). The two parts are used to deliver the data packet to the correct device. The network address is obtained by ANDing the netmask with the IP Address. Consider the following scenario:
IP Address: 10.0.1.1
Netmask: 255.255.0.0
The host address portion of the IP address for our PC is 1.1, so the PC knows that any host addresses starting 10.0. are local to it. Any addresses that then start 10.1, etc, are not 'local' and will need to be forwarded to a router. If you have another device intended to be on the same network that is:
IP Address: 10.0.2.1
Netmask: 255.255.255.0
Here the netmask is wrong for our example setup, this device is now going to see the network address as 10.0.2 and the host address as 1, if it tries to communicate with 10.0.1.1 it will see a network address of 10.0.1! Not local and so will refer it to the default router for forwarding. If the netmask was correctly set (i.e. the same as the first example, assuming that's the correct setting for your network) then the second device would see the first as local, i.e. on the 10.0 network and wouldn't attempt to forward the packet to a router.
Many protocols will happily cope with this but tftp is intended to operate within a single network and so will fail as there's a perception that the target is on a different network.
This may not describe your exact situation but I hope that the example demonstrates the important principle that configuration matters, you can't have an inaccurately configured environment and expect it to work.
The netmask determines which IP adresses are local (non-routed); IP adresses outside that range go through the router. If the netmask is wrong, the program tries to directly access sites where it has to go through the router, or vice versa.
The netmask defines, which part of the IP-address is used as address for the network and which part is used for the workstations.
First Example:
IP1: 192.168.20.4
IP2: 192.168.192.4
NM: 255.255.0.0
Both IPs are in the same net. They can communicate with each other without needing a router. That's because the IP-addresses will result in the same bitmask when you or it with the netmask.
Second Example:
IP1: 192.168.20.4
IP2: 192.168.192.4
NM: 255.255.128.0
Now both IPs are in different networks because when you or the IP-addresses with the Netmask, the resulting bitmask will be different and they wont be able to communicate with each other without a router that routes between the two networks.
You can test this by yourself with ipcalc.
Possible implications of mismatched netmask are explained here. In short:
The host is likely to construct routing table incorrectly.
The host will miss some broadcast packets and not send broadcasts properly.
Mis-function of TFTP is almost for sure caused by the first reason. It affects any other IP protocol in the same way.
Other answers mention only the first problem (which is OK, as the second one is rather marginal). Note that it is not the netmask of the interface itself which determines how the IP packets would be routed - it is the routing subsystem of the host; but the netmask is normally used for constructing the routing table.