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10986 Views 14 Replies Latest reply: May 30, 2011 11:35 AM by Diwakar Sharma -CCNA/CCNP/JNCIA-ER RSS

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Setting Default Route

Jan 27, 2011 8:23 AM

poison3000 77 posts since
Jul 30, 2010

Hi everybody ..

 

I'm confused with two commands are used to set a default route ... the two commands are :

 

  • R1 ( config )# ip route 0.0.0.0 0.0.0.0 se 0/0/1
  • R1 ( config )# ip route default-network 10.0.0.0

 

What the expected behaviour of both commands and when to use them ?

 

Thanks in advance !

  • Chad Spears CCNP CCDA CCNAS 751 posts since
    Jul 27, 2009
    Currently Being Moderated
    1. Jan 27, 2011 9:13 AM (in response to poison3000)
    Re: Setting Default Route

    Poison-

     

    The two commands are:

     

    ip route 0.0.0.0 0.0.0.0 (exit interface/next hop ip address)

    ip default-network (network number)

     

    The major difference between these two are, when you configure a static default route it is only applied to the router on which you configure it on.

    On the other hand, ip default-network will send the default route out it's routing protocol.

     

    To make a default static route (ip route 0.0.0.0 0.0.0.0) propagate throughout the environment, you will need to redistribute the static route into your IGP (Interior Gateway Routing Protocol).

     

    HTH,

    CS

  • Currently Being Moderated
    Re: Setting Default Route

    Great explanation Chad!  We really need a "like" button here. 

  • Chad Spears CCNP CCDA CCNAS 751 posts since
    Jul 27, 2009
    Currently Being Moderated
    3. Jan 27, 2011 3:29 PM (in response to tnewshott)
    Re: Setting Default Route

    Thans Travis

  • Chad Spears CCNP CCDA CCNAS 751 posts since
    Jul 27, 2009
    Currently Being Moderated
    5. Jan 28, 2011 4:17 AM (in response to poison3000)
    Re: Setting Default Route

    Sure thing.  The statement "Gateway of last resort is 192.168.2.1 to network 0.0.0.0"

    would be found on a neighboring router that recieves the canidate default route.

     

    All the statement is saying is of any traffic for which i do not have a route for... send it to 192.168.2.1.

     

    I will work on labbing this up for you to help  better explain.

     

    HTH,

    CS

  • WadeGerencser 7 posts since
    Jun 25, 2010
    Currently Being Moderated
    6. Jan 28, 2011 4:31 AM (in response to poison3000)
    Re: Setting Default Route

    Chad,

     

    I posted my reply just before you and I came on finally too see that you indeed have a great response. I have a question though..sorry to interrupt Poison, but if when you refer the major difference between the two configurations is simply a matter of how the default route / static route is learned dynamically or manually they still, at the end of the day, perform the same function...I mean it like this..figuratively...and please bear with me...its concept here on a simple misunderstanding that has been killing me lately!!

     

    Could you could still configure 4 routers, one with IP route 0.0.0.0 0.0.0.0 s0/0/1 and then the second router by the default-network x.x.x.x  command and then repeat for two more routers..despite the different default route configurations, they still will provide the same function after all correct routes are configured manually and redistributed dynamically so as long as they are not using a less popular routing protocol like IGRP. From what I read on the Cisco site, it said IGRP does not "understand" the 0.0.0.0 syntax in the ip route 0.0.0.0 0.0.0.0 s0/0/1 command so you have to use the default-network x.x.x.x command instaed...anyways...thanks for reading!    

  • Chad Spears CCNP CCDA CCNAS 751 posts since
    Jul 27, 2009
    Currently Being Moderated
    7. Jan 28, 2011 5:42 AM (in response to WadeGerencser)
    Re: Setting Default Route

    Wade-

     

    You got it... they preform the exact same function...they just go about it in different ways.

     

    Honestly, I have never tried the example you mentioned above... however looks like a good question for a lab. 

     

    I will start working on this. I am betting since each route will use its own default route... or default network statement.. and ignore the others.....why?  Well because when you pass off the route to other routers.  They will recieve that route with an AD of the IGP you are using.

     

    Man.....now that I read that......I am sure you are going to be just as confused as I am..... 

     

    Lets lab it up.  I will create a topology and post it here.

     

    HTH,
    CS

  • Devasi Alex 1 posts since
    Jan 28, 2011
    Currently Being Moderated
    Re: Setting Default Route

    good

  • Chad Spears CCNP CCDA CCNAS 751 posts since
    Jul 27, 2009
    Currently Being Moderated
    9. Jan 28, 2011 8:12 AM (in response to WadeGerencser)
    Re: Setting Default Route

    Wade-

     

    So I have created a basic lab setup for this..

     

     

    Lab-Demo.jpg

     

    This is the topology.   I will supply the outputs in a new post to this thread.  **Note**  I did not use the "Ip default-network" command in this demo...  You will see why in a second.

     

    HTH,

    CS

  • Chad Spears CCNP CCDA CCNAS 751 posts since
    Jul 27, 2009
    Currently Being Moderated
    Re: Setting Default Route

    ****************R4*************************

    interface Loopback0
    ip address 4.4.4.4 255.255.255.0
    !
    interface Ethernet0/0
    ip address 172.16.10.4 255.255.255.0
    half-duplex
    !
    interface Serial0/0
    no ip address
    shutdown
    !
    interface Serial0/1
    no ip address
    shutdown
    !
    router eigrp 100
    redistribute static
    network 0.0.0.0
    no auto-summary
    !
    ip http server
    ip classless
    ip route 0.0.0.0 0.0.0.0 4.4.4.1

    ****************R2**************************

    interface Loopback0
    ip address 2.2.2.2 255.255.255.0
    !
    interface FastEthernet0/0
    ip address 172.16.10.2 255.255.255.0
    duplex auto
    speed auto
    !
    interface Serial0/0
    no ip address
    shutdown
    !
    router eigrp 100
    redistribute static
    network 0.0.0.0
    no auto-summary
    !
    ip http server
    ip classless
    ip route 0.0.0.0 0.0.0.0 2.2.2.1

    **************show ip route R1****************

    Gateway of last resort is 172.16.10.4 to network 0.0.0.0

         1.0.0.0/24 is subnetted, 1 subnets
    C       1.1.1.0 is directly connected, Loopback0
         2.0.0.0/24 is subnetted, 1 subnets
    D       2.2.2.0 [90/156160] via 172.16.10.2, 00:17:33, FastEthernet0/0
         3.0.0.0/24 is subnetted, 1 subnets
    D       3.3.3.0 [90/156160] via 172.16.10.3, 00:17:09, FastEthernet0/0
         4.0.0.0/24 is subnetted, 1 subnets
    D       4.4.4.0 [90/156160] via 172.16.10.4, 00:16:50, FastEthernet0/0
         172.16.0.0/24 is subnetted, 1 subnets
    C       172.16.10.0 is directly connected, FastEthernet0/0
    D*EX 0.0.0.0/0 [170/156160] via 172.16.10.4, 00:09:34, FastEthernet0/0
                   [170/156160] via 172.16.10.2, 00:09:34, FastEthernet0/0

    **************show ip route R3******************


    Gateway of last resort is 172.16.10.4 to network 0.0.0.0

         1.0.0.0/24 is subnetted, 1 subnets
    D       1.1.1.0 [90/156160] via 172.16.10.1, 00:19:43, FastEthernet0/0
         2.0.0.0/24 is subnetted, 1 subnets
    D       2.2.2.0 [90/156160] via 172.16.10.2, 00:19:43, FastEthernet0/0
         3.0.0.0/24 is subnetted, 1 subnets
    C       3.3.3.0 is directly connected, Loopback0
         4.0.0.0/24 is subnetted, 1 subnets
    D       4.4.4.0 [90/156160] via 172.16.10.4, 00:19:25, FastEthernet0/0
         172.16.0.0/24 is subnetted, 1 subnets
    C       172.16.10.0 is directly connected, FastEthernet0/0
    D*EX 0.0.0.0/0 [170/156160] via 172.16.10.4, 00:12:10, FastEthernet0/0
                   [170/156160] via 172.16.10.2, 00:12:10, FastEthernet0/0

     

     

    So I am sure from the output above.... you could see where this may create an issue. What do you think?

     

    HTH,
    CS

  • WadeGerencser 7 posts since
    Jun 25, 2010
    Currently Being Moderated
    Re: Setting Default Route

    Chad,

     

    This is hardcore. I have to be honest with you and I admit, I am lost. I do not see where the conflict will arrise. I am not sure what the D*EX means at the end of the ouputs of the sh ip route coammds for R1 and R3 respectivley. I dont know where to begin to look man. I feel bad cause I am about to take my ccna and this to me seems hard to interpret as to why it would cause conflits. Great example man.thats simply awesome~!

  • Chad Spears CCNP CCDA CCNAS 751 posts since
    Jul 27, 2009
    Currently Being Moderated
    12. Jan 28, 2011 10:06 AM (in response to WadeGerencser)
    Re: Setting Default Route

    Wade-

     

    This is more CCNP level material.. but I know you will be there one day, from you post.. I can tell you have fallen in love with Cisco much like everybody on CLN.

     

    The D*EX simply means it is a EIGRP External route with a AD of 170... the * means it is a canidate default route.  Or simply...any traffic that doesnt have a match in the routing table...will be sent to this route.

     

    let me know if you need any help with any of your other CCNA Studies.

     

    HTH,

    CS

  • WadeGerencser 7 posts since
    Jun 25, 2010
    Currently Being Moderated
    Re: Setting Default Route

    Chad,

     

    I knew from the beginning your configurations on all the interfaces was spot on. I got passed that and I realized two things were apparent. Really though..my perception..I feel like R4 and R2 are going to be able to communicate fine. Then the I see that you don't have the configs for R1 and R3...then I again realized all the AS's were good on the diagram, R2 and R4..you have it all exact. Awesome. So.. I trust the other routers. Since you used the ip route 0.0.0.0 0.0.0.0 for R4 and R2 and assigned that virtual address to its loopback,  any traffic it does not have a route for, will be forwarded through the Loopback interface. It will not think like a default-network x.x.x.x command... Having nothing to view from the configs of R3 and R1, I feel like I am still "assuming" the default network x.x.x.x command on R1 and R3 does not have a lower AD than what EIGRP will propagate than what it knows about concerning R2 and R4. I say that weird broken sentence because I have to throw it out. I feel like I make sense of something here for sure..so here is my answer. The EIGRP D*EX output tells me it just chose the 172.16.0.4 cause its value is 0.0.0.0! Match everything? Gateway of last resort was 0.0.0.0 through 172.16.0.4 correct. I hope..then I would say..I get 75% I feel like this situation made me understand that a Gateway of Last Resort is more than just a static route or default route. Its the solution when both static and defaults are used and a decision must be made..and that's the gateway of last resort.

     

     

    Edit: Oops I did not mean forwarded through the loopback yikes so sorry!!!!!!! I get the lo concept. Ok...later : 0

     

    Holy smokes man..I know I have a lot more reading to do..and lab work. Its coming..and again..thanks for the kudos and detailed responses. Cisco is amazing. Most fun I have had in a long time!  

     

    Wade

  • Diwakar Sharma -CCNA/CCNP/JNCIA-ER 79 posts since
    Nov 5, 2009
    Currently Being Moderated
    14. May 30, 2011 11:35 AM (in response to poison3000)
    Re: Setting Default Route

    excellent explaination by chad spears

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