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(Quick#2 question) - Sub-netting on a network

Discussion in 'General Cisco Certifications' started by sendalot, Feb 7, 2013.

  1. sendalot

    sendalot Nibble Poster

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    So, on subnetting a network, when shall two hosts be in different subnet?

    If three routers are connected in a single office, do they all need to be in different subnet?

    Does each port from the router that creates a broadcast domain, need to be in different subnet?

    Then in the case of WAN(i.e VPN), where 1 router in LA, 1 router in Chicago and 1 router in New York, do the routers need to be in the same subnet?

    I'm trying to discern when it's ok for hosts to be in the same subnet. (Of course hosts connected to a switch all need to belong to the same one).

    Thanks.
     
    WIP: A+
  2. SimonD

    SimonD Terabyte Poster Moderator

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    Actually I disagree on your last comment there. There is no reason why all hosts on a switch need to belong to the same subnet, infact you may have reasons why they aren't (for example you may well have a 48 port switch that has a number of vlans on there for whatever reason).

    Don't assume anything when it comes to IT.

    Please have a think about what a router is doing, if you're connected in a single office would you really go down the route of 3 routers if you want to be on the same subnet? The idea of a router is to route between different networks.

    It's very unlikely that in your WAN scenario again that all 3 routers would be on the same subnet, again think about what a router is doing (it's ROUTING), that means that each router needs to have a unique ip address that act's as a gateway between network segments. You would usually expect to see an internal and external address per router, you would then expect that each LAN segment on that router would have a different IP addressing table to allow routing between the rest of the WAN (how would you route out between routers if your infrastructure all share the same IP addressing range?).

    Sorry to say mate but you need to take a step back and get a better understanding of what a router and switch are there for, why you would use one over the other and when you would need to use one over the other.
     
    Certifications: CNA | CNE | CCNA | MCP | MCP+I | MCSE NT4 | MCSA 2003 | Security+ | MCSA:S 2003 | MCSE:S 2003 | MCTS:SCCM 2007 | MCTS:Win 7 | MCITP:EDA7 | MCITP:SA | MCITP:EA | MCTS:Hyper-V | VCP 4 | ITIL v3 Foundation | VCP 5 DCV | VCP 5 Cloud | VCP6 NV | VCP6 DCV | VCAP 5.5 DCA
    WIP: VCP6-CMA, VCAP-DCD and Linux + (and possibly VCIX-NV).
  3. BraderzTheDog

    BraderzTheDog Kilobyte Poster

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    Hi,

    You will rarely see a switch that is purely in a single VLAN, as Simon clarified above quite well you will often have many VLANS on a switch and these will then be either routed locally if the Switch is layer 3 or be routed by the native router. This provides access control and permissions to network resources can be controlled depending upon which subnet the packet originates from.

    If you have a VPN between two sites IE New York and LA you would give the external interfaces of both routers a Public IP address, the ISP will do the rest. The packets should be routable across the WAN from here on in. If you are then wanting to access the local subnets at each end then YES the local networks need to be different. It would also depend upon what type of VPN you are creating? Site to Site or Remote access? If its a site to site you would define if its policy based or route based VPN, if policy based you would then add the local and remote private subnets to the encryption domain. Set the Phase 1 proposal on both sides and then select the Phase 2 proposal. The VPN will work and you can access both LAN's (providing policy is in place) with no problem.

    You may be getting too deep thinking about Site to Site VPN's at ICND1 level, maybe like Simon said just concentrate on small business element of the network until you pass the exam.
     
    Certifications: CCNA R&S, CCNA-SEC, CCSA, JNCIA FWV, MCITP, MCTS, MTA, A+
  4. sendalot

    sendalot Nibble Poster

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    So, in terms of WAN, routers in two different geographical location may or may not be in the same subnet?
    Thanks.
     
    WIP: A+
  5. BraderzTheDog

    BraderzTheDog Kilobyte Poster

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    I don't understand what you mean, can you explain a bit further?

    From what I can tell you have two routers, one in say Paris and the other in New York. They will both have a Public IP address and on the same interface be connected to the internet at both sites. If the IP address in Paris is 142.52.47.12 and the IP address in New York is 80.47.12.10 the ISP will route the packet to the other router and back.

    The Public IP addresses do not need to be in the same subnet the ISP will routes these for you probably using BGP. The only routing of subnets you need to be concerned with would be the private subnets in your local network.

    Hope this helps :)
     
    Certifications: CCNA R&S, CCNA-SEC, CCSA, JNCIA FWV, MCITP, MCTS, MTA, A+
  6. sendalot

    sendalot Nibble Poster

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    Yes! I meant the private side of the subnet in WAN.

    So does the one in Paris have to be in the same subnet as the one in New York?
     
    WIP: A+
  7. Coupe2T

    Coupe2T Megabyte Poster

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    No, as said before, Routers are to route between DIFFERENT networks, when you subnet anetwork, you are breaking it up into seperate networks. So one become 2 for example. It would just be routed across to the other network via ISP.
     
    Certifications: ECDL, Does that Count!?!
    BraderzTheDog likes this.
  8. sendalot

    sendalot Nibble Poster

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    Thank you very much!
     
    WIP: A+

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