IP address

Discussion in 'Computing and Networks' started by Lightfire, Apr 23, 2012.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    what does means in IP????? does the first three signify somethin.

  2. panic mode

    Senior Member

    Oct 10, 2011
    the ip address is just that - an address.
    in general they represent number.
    since thee is not enough of unique IP addresses for everything that has ethernet interface, there is combination of IP address and Mask that allow creation of isolated LANs and still provide means to connect them to each other (through router).

    subnet mask is often but it does not have to be.
    convert that to binary form for more insight:

    note that all 1's are on the left, and all zeroes are on the right.

    parts where you see 1 in subnet mask (viewed in binary form) tells you which bits in IP address must be same for all devices that are on a same network.

    suppose we choose to change the mask to

    the more zeroes are in the subnet mask, the more devices can be on same LAN.
    by resetting two of the bits, we basically increased number of possible nodes on this LAN four times (2^2=4).
    all nodes on same lan need same subnet mask.

    note, bits in IP address are NOT arranged same way (1 and 0 can be mixed up) but if you have ONE ip address in form
    then those bits that correspond to "1" in subnet mask must be same in all IP addresses.

    so we place mask and IP next to each other:
    11111111.11111111.11111100.00000000 (mask)
    11000000.11001100.00000111.01010101 (IP)

    note that where mask has 1s, IP address is

    this part (1s and 0s, not the last ten bits marked 'x') must be same for all IP addresses on this LAN (unless we change mask to something else).

    the other part (previously covered by 'x') represents bit-field that must be UNIQUE on this LAN. you cannot have two devices with this part same.

    so valid IP addresses in this case (corresponding to this subnet mask) are
    etc until

    note that we varied last 10 bits (because there was 10 zeroes in that place in subnet mask).

    also first and last address in range are actually reserved so range is really

    feel free to convert those binary numbers back into decimal.
    hope the introduction was clear enough.

    there is more to it but this is the most basic.
    some ranges are reserved for LANs like

    so back to your question, if the mask is then first three octets represent LAN, last octet represents single node (computer, printer, whatever...) on that LAN.

    you can use same ethernet switch and all devices with same subnet mask such as
    supposedly that few nodes are using addresses

    This is one LAN.

    but suppose we have few more nodes like
    also using same subnet mask.

    they are actually another LAN (even though they are physically connected to same ethernet switch, they cannot talk to nodes from other LAN, they can only talk among themselves). to let them talk to each other we could add router that handles connections between 192.168.1.x and 192.168.2.x nodes.

    but suppose we change subnet mask to in all of devices, then both of those "two" LANs would become one bigger LAN (because we cleared one more octet in subnet mask, they now all see each other) and no router is needed.
    Last edited: Apr 23, 2012
    mrmount likes this.
  3. c0de3

    Active Member

    May 1, 2009
    Panic gave you a lot of detail that is great as it relates to IP addresses. Your question is pretty vague though, so I'm not sure what you're looking for. The actual address you give would be set as on most devices I'm familiar with.

    If you see this address it is normally a route entry. The route to is the route the system will use if it doesn't have a "more specific" route.

    You also ask about the "first three". Again, Panic gave you a lot of detail on the first three octets (in your example that is: 000.000.000.)

    If you are asking about the first three bits, stop asking and throw away the book that is talking about it.... :)
  4. electronis whiz

    Well-Known Member

    Jul 29, 2010
    lightfire that is an example of an ip adress but is not actily a valid adress. valid adresses can be from 1-255 with the exception of 127 for loopback, 255 for broadcasts. you are close with the first 3 part. the first part of an ip adress is the network portion. depending on wether class A, B, C these can vary but is determined by the subnet mask. class A uses only the first octet for network meaning that 252 ( 255- 127, 255, 0 because there not valid) networks are posible in class a with a lot of hosts. hte subnet mask would be these adresses are used by some ISPs publicly. then class b has about = number of networks and hosts. and its netmask is class C has many networks and 252 host per. C is comon for internal networks and has a subnet mask of all of these classes can be used publicly or privitely. the subnet mask blocks off the network portion and leaves the nodes IP adress. you can get into subnetting and supernetting witch modify the defult subnet masks in the last octet. subneting is where you can shrink the netmask adding 1 extra digit to the host portion. supernetting adds networks but shrinks the hosts portion.
  5. coldpenguin

    Active Member

    Apr 18, 2010
    That is wrong. The address is a valid address, on a valid network. However, may not be a /usable/ device address on a class B or C network (which is where most people get confused and end up saying 0 is not a valid number). Class C networks BTW. have 254 valid addresses for devices, and 256 addressable IP addresses (1-254, and 0-255). The reason why some people think that only 252 addreses are available is that router addresses are often .1 or .254, so if you are playing with an unknown network, don't use these addresses.

    Actually it is a little old-hat, but is a valid address, it is a non-network specific broadcast address. (as the network address is actually a broadcast address as well).

    If you see a machine on a network addressing, it is addressing a broadcast address (if you see this happen, it will almost certainly be a UDP packet, as TCP in this type of communication would be invalid). In theory, any machine which would answer would also answer

    If however you have done something like: route -n, then the value of is shown as the default gateway address (being the network address of the default network).

    Most high-level devices do not display to humans, but they convert them do normal decimal, i.e., or 010.003 would be 10.3

    IF you are dealing with lower-level devices, then double check whether you are in hex, octal decimal or binary, as it can make significant differences to the results.

    Also note, although is conventionally used as a loopback address to the OS or adaptor, that does not preclude the ability to use, or any other number on the 127 network as a real routable address