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IP addressing

Posted on 2004-10-27
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Last Modified: 2010-04-10
I am drawing a network diagram it has in the final stage a bastion host, then a router that is a gateway for five lans, I have the adress ranges for the lans. Q do I have to give a seperate IP address at the router end for each lan or just one, as you see I am a novice.
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Question by:kevinoakes
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    Expert Comment

    by:TannerMan
    Your saying you have a router with 5 networks connecting to it that are the same, as in
    192.168.1.x 255.255.255.0
    192.168.2.x 255.255.255.0
    192.168.3.x 255.255.255.0
    192.168.4.x 255.255.255.0
    192.168.5.x 255.255.255.0

    Now you want to add a dissimilar network
    10.10.22.x

    Is this the jest of it??
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    Author Comment

    by:kevinoakes
    No my router now has an IP adress of 192.168.3.37/24 that is one subnet the lans are 192.168.3./24 and they are on different subnets. I dont need a different network as this is the last router, all i need to know is does the router need one IP address192.168.3.37 or five 192.168.3.37-192.168.3.41 to communicate with each lan, sorry if I am not very clear but this is my first time.
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    by:TannerMan
    You need a unique router between each subnet. Not just one router. Otherwise, your not really routing. Still not clear though, when you say the LAST ROUTER.

    Sorry for all the frustration, but 192.168.3.37/24 is the same network as 192.168.3.x/24. Now if it were like this,,,,then you'd have routable networks

    192.168.3.x /24 (or 255.255.255.0) - Router's WAN interface

    192.168.4.x 255.255.255.0
    192.168.5.x 255.255.255.0
    192.168.6.x 255.255.255.0
    192.168.7.x 255.255.255.0

    Then, to route traffic from networks 192.168.4 - .7 you'd need either a router between each one, OR a router that you can have 5+ interfaces to connect all these networks TO. Which, in your question would mean YES on separate interfaces for each LAN.




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    Author Comment

    by:kevinoakes
    What if I use a switch instead of a router, would this make it any eadsier and would I still need seperate IPs for each lan. Sorry I dont know how to make it any clearer
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    Expert Comment

    by:TannerMan
    If your going to set all networks/lans on 192.168.3.x with a 24 bit mask then yes, your dead on with NO router and add a switch. Or even just a hub if money is tight. Switching is better, by all means.

    As long as you leave it a 192.168.3.x/24 you don't really even have LAN's. Your just all in the same neighborhood, so to speak. By this I mean if you had 10 users on each of these "Lan's" then you could set one 96 port switch in a room and hook every single computer to the same switch. The question is, are these "LAN's" all local to each other? If not, then you will have to go to router's and some type of backbone network to connect them like either frame realy, or site to site VPN's across the internet.

    Hope that helps.
    Maybe tell me PHYSICALLY how your comuters are dispersed.
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    Author Comment

    by:kevinoakes
    Right here goes my first router that is accesed from the web has external address 204.32.16.33/24 the internal address is 204.32.38.34/28 this goes to a bastion host with 204.32.38.19/28 the bastion uses 204.32.38.17/28 to connect to my webserver 204.32.38.17/28 the bastion has 4 NICs you will see why in a moment, to prevent acces to the info servere from outside the bastion connects to server using 192.168.3.33/24 the server is 192.168.3.34/24The bastion also connects next  with 192.168.3.35/24 to the  router 192.168.3.36/24which connects to the LANs which are on seperate subnets ranges are
    1)192.168.3.65 to 192.168.3.94  2)192.168.3.97 to192.168.3.126  and so on which gives 30 hosts for each lan not counting network and broadcast I hope this makes more sense.  also do I need one ore more IP adresses for a switch to connect to the lans
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    by:TannerMan
    OHHHHH, I got you now. Let's make sure I am clear

    bastion host has 4 NICs
    NIC#1 204.32.38.19/28 and connects to the internal interface of your Internet router
    NIC #2 204.32.28.17/28 and connects to your web server
    NIC #3 192.168.3.33/24 and connects to your info server which is 192.168.3.34/24
    NIC #4 192.168.3.35/24 and you want a switch placed between this NIC and the following subnets:

    1)192.68.3.65 - 94
    2)192.168.3.97-126
    and so on.

    If I have it straight you would not need a 5th NIC to put the switch to. Your switch would have all networks plugged into it and the Bastion's NIC #4 above would plug into it as well.

    Hope that helps
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    Author Comment

    by:kevinoakes
    I know I sound stupid so nic #4 communicates with the switch shouldnt the switch have a nic#5 that communicates with the bastion And #6 that communicates with the lans or am I being thick
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    Expert Comment

    by:kidoman
    Hello,

    You know one thing. When I read this question, I knew exactly how i would have framed the question if i had come to EE few months ago. As a undergraduate student I had exactly the same set of doubts and although I knew my theory, the Tanenbums and the Krozs didnt actually give me practical HOWTOs which I could follow and implement.

    FIRST OF: What is a router???

    Maybe I am wrong, but a router is a piece of device which is used to connect two different subnets. A repeater connects the same subnets. I will elaborate a bit so that my answer is clear to u. The use of routers, repeaters, etc. etc all lie in the very fundamental way ethernet operates. A subnet is a network where all the participating hosts are assumed to have the same host id. So a subnet 192.168.33.128/25 refers to the network: 192.168.33.128 where the hosts are numbers 192.168.33.129 - 192.168.33.255. The first addr being unusable because it is the NETWORK ID and the last IP also being unusable because it is the broadcast address. So if a machine 192.168.33.141 wants to send a packet to 192.168.33.154 and both being connected physically using a:
    - SWITCH
    - hub,
    - crossover cable,
    - FDDI ring, etc.
    then the procedure would be as simple as Host A (source) finding out the MAC address associated with the Host B (dest) IP address and the physical layer (meaning the NIC hw) doing the actual delivery.

    BUT BUT BUT, what happens if Host A wants to communicate with 192.168.34.22***. Since it is obviously not in the same subnet, we would send the packet to the default gateway configured for the subnet. All subnets have a gateway (a router for ex.) to be able to communicate with outside world (i.e. subnet.) So the "gateway obviously will lie in the same subnet as the source subnet"**** which is 192.168.33.128 (lets say the router IP addr for this subnet is 192.168.33.191.) The packets will reach this router as it would have reached host b (above....). The the router takes over and takes the packets to the required destination (ofcourse this requires the router is appropiately configured and believe me that is another 5000 points question ;) )

    Read the above paragraph couple of times and allow the matter to sink in. Now coming to your specific problem:

    - NIC 4 has the IP addr 192.168.3.35 and the /24 part dictates that the subnet mask is 255.255.255.0 which
                 ====> that the network ID is 192.168.3.0. So any host (node) having a similar network id
    and """subnet mask"""" (imp) will be able to communicate with NIC 4 and the router would get the packets.

    So what you should do is to connect NIC 4 to a fairly high end switch (since a lot of traffic is going to flow through it) and then connect further swithes to the main switch. Each of these secondary switched will have nodes attached to them with different ranges of IP addresses. Why this setup will work is obvious....? Because 192.168.3.35, 192.168.3.97 to 192.168.3.126, 192.168.3.65 to 192.168.3.94 all lie in the same "192.168.3.0/24" subnet, they would all be able to reach the 192.168.3.35 (NIC 4) router addr. So all the machines would be configured with a 255.255.255.0 netmask and would have the default gateway set to 192.168.3.35. No need for any ROUTER between 192.168.3.35 and the subnets. Just a heirarchial network of switches will do FINE.

    Config for all subnets:

    Default gateway: 192.168.3.35
    Netmask: 255.255.255.0

    Hope this clarified your doubts.

    Cheers,

    Karan
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    Accepted Solution

    by:
    Yes, if your router is to act as an outbound gateway for clients on those subnets, it needs an address on each subnet that can be given out to them to use.

    Depending on your topology, these addresses might be on different physical interfaces of the router, on different subinterfaces of a single "trunked" physical interface, or entered as secondary addresses on an interface that connects to a segment with multiple address spaces.  (The last choice isn't recommended, but sometimes its the easiest way to cope with legacy configurations.)

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    Expert Comment

    by:kidoman
    Hi man,

    Please clarify your situation.

    Karan
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    Author Comment

    by:kevinoakes
    I have sorted it out
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