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static route , default route confusion please help meee

Discussion in 'General Cisco Certifications' started by kobem, Dec 6, 2006.

  1. kobem

    kobem Megabyte Poster

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    this question was on my mind and asking here




    first picture


    [​IMG]

    in this picture we configure the gateway router as default route but i think it has more than one way out(i think it has three way) , more than one interface to other networks(one way to down , one way to right
    and one way to up)

    isn't this wrong?


    second picture

    [​IMG]

    can't we use dynamic routing protocols here ? the router in the middle is configured as static
    and the others are configured as default.

    And why do we use static route for hub here?
    And where is the remote network for hub router in the static route configuration here?





    for default route definition)
    (we use default route to send packets with a remote destination network
    not in the routing table to the next-hop router)
    what does this mean "with a remote destination network not in the routing table to the next-hop router" ?

    (does this mean : i am a router and across me there is a router (directly connected to me) remote destination network according to me or that router?







    how do i understand whether my router knows remote network?


    last one i have a router and should i use static route or dynamic routing protocols how do i understand this?
     
    Certifications: CCNA
  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    I'll leave it to Cisco experts to explain what is happening in the diagrams!
    The routing table has a set of lines with specific destinations each linked to the interface to use for that destination.

    The default route is usualy another line showing where packets that don't match the specific lines should be sent. This is frequently to another router, which may have more specific information about the final destination. That router is often called the 'next-hop' router.

    It will depend on the configuration, and the routing protocol you are using.

    This will depend on the exact application and layout.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  3. NetEyeBall

    NetEyeBall Kilobyte Poster

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    Lets start with the default route.

    A default route is a static route that you define to mean that all traffic goes out to the next hop router (That you define in your static route statement).

    IP ROUTE [Destination] [Subnet Mask] [Next Hop Router]

    for example:

    2511(config)#ip route 0.0.0.0 0.0.0.0 192.168.1.2

    Here is the output of Show ip route:

    Router#sh ip route

    Gateway of last resort is 192.168.1.2 to network 0.0.0.0

    192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
    C 192.168.1.0/24 is directly connected, Serial0
    C 192.168.1.2/32 is directly connected, Serial0
    S* 0.0.0.0/0 [1/0] via 192.168.1.2

    All my traffic from the 2511 (destined for another network) will go out S0 to 192.168.1.2 and will either be routed on or die depending on the routing table in 192.168.1.2's router.

    Why would you use static routes versus dynamic routes? More then likely you wouldn't unless you had a stub network. A stub network is a network with one way out. The diagram you have of the hub and spoke network is a good example. All the spokes only have one way out. So you could use a default route there if you wanted to. On the hub router you would have to make static routes for each stub network.

    But you probably won't do this in real life. Static routes require more work to put into place, and maintain. They are suitable for very small networks. I have used them in the past for a manufacturing company simply because I didn't know EIGRP or OSPF at the time, and the company wasn't going to be changing any time soon. So they worked fine.

    I would however use EIGRP or OSPF on the hub and spoke as it would make my life much easier if I had to change the networks around or do any adds/changes.

    I am sure I didn't answer all your questions but I hope I answered some.
     
    Certifications: CCNA, A+, N+, MCSE 4.0, CCA
    WIP: CCDA, CCNP, Cisco Firewall
  4. kobem

    kobem Megabyte Poster

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    thanks but

    in the first picture , where is the next-hop router for the gateway
    router?

    and gateway router has two interfaces other than going to the internet so is this a stub network (not one way in ?)

    can't we use other things like routing protocols ?
     
    Certifications: CCNA
  5. NetEyeBall

    NetEyeBall Kilobyte Poster

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    The 1st diagram for the router in the top left connected to the ISP is not a stub network. You would need to use either static routes or a dynamic routing protocol to correctly route between all 5 networks.

    The next hop router for the 1st diagram is any of the connected routers. So it would have 3 next hop routers.

    Does that make sense?

    A single default route would not work with that diagram.

    However, You would need a default route set up so that traffic destined for an unknown network (ie one not in the routing table) would be forwarded on to the ISP router.
     
    Certifications: CCNA, A+, N+, MCSE 4.0, CCA
    WIP: CCDA, CCNP, Cisco Firewall

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