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10516 Views 25 Replies Latest reply: Jul 2, 2011 3:10 PM by Mark Anthony Green, M.Sc, CCNP, CCNA RSS 1 2 Previous Next

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default route propagation in eigrp

Jun 22, 2011 3:29 AM

verg 3 posts since
Feb 10, 2010

What is the difference between

 

ip default network   [ network ]    command

 

and

 

ip route 0.0.0.0 0.0.0.0 [next hop address]

router eigrp  10

redistribute static

 

 

and

 

ip route 0.0.0.0 0.0.0.0 null0

router eigrp 10

redistribute static

 

Do they all set up the default route and propagate it to the other routers downstream?

 

Verghese George

  • rboldy 305 posts since
    Jun 3, 2011
    Currently Being Moderated
    1. Jun 22, 2011 6:48 AM (in response to verg)
    Re: default route propagation in eigrp

    This ip default network command is referencing a "network" as the default so it's slightly different. However the main reason for using this is that you can advertise a static route as your default route without having to advertise ALL static routes -- which is what "redistribute static" does.

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  • Joshua Johnson - CCNP R&S 6,067 posts since
    Sep 22, 2009
    Currently Being Moderated
    2. Jun 22, 2011 1:20 PM (in response to rboldy)
    Re: default route propagation in eigrp

    a.      Default Routing to the Internet Router

    1.       What is the difference between a default route, and a static default route.

    a.        Answer: You can configure a static default route using the ip route 0.0.0.0..... which sets the gateway of last resort locally.  By configuring a default route, using the ip default-network... command you are actually configuring an existing route to also be a default route.  When you configure the default route, the local router does not use this as a gateway of last resort, and is meant to be advertised by a routing protocol for all other routers to use as the gateway of last resort pointing to the prefix of the default-route.

    2.       What is the definition of “gateway of last resort?”

    a.        Answer: The “gateway of last resort” refers to the next-hop router of a routers current default route.

    3.       What are the two main methods of created a default route?

    a.        Answer: You can configure a static default route and then advertise it through EIGRP, or you can use the ip default-network command and then advertise that. 

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  • kalyan 7 posts since
    Jan 27, 2010

    Can you explain about ip default gateway command?and how is it different from the above two commands.

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  • Joshua Johnson - CCNP R&S 6,067 posts since
    Sep 22, 2009
    Currently Being Moderated
    4. Jun 22, 2011 2:20 PM (in response to kalyan)
    Re: default route propagation in eigrp

    ip default-gateway is configured on a router just like when you configure the gateway on a PC.  The router essentially becomes a host device.  For it to function properly, you would also need to configure the ip address and subnet mask on the interface connected to another router, or the rest of the network.  You can also configure an interface to obtain an ip address through DHCP.  ip address dhcp

     

    The only time I ever use this is when I'm using a router to generate ip traffic that would normally come from a PC.

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  • Sey 1,393 posts since
    May 4, 2010
    Currently Being Moderated
    5. Jun 22, 2011 2:44 PM (in response to kalyan)
    Re: default route propagation in eigrp
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  • Brian 2,971 posts since
    Aug 17, 2009

    In addition, the "ip default-gateway" command should be used when ip routing is disable.  As mentioned when you have a router acting as a "host" only.

     

    Regarding the configurations above using the redistribute static command, don't forget to add a metric.  By default only connected routes can be redistributed without a default metric.  All others require either a default metric be set or include the metric in the redistribute command.

     

    HTH

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  • Currently Being Moderated
    8. Jun 30, 2011 6:30 PM (in response to Brian)
    Re: default route propagation in eigrp

    Hi Brian.

     

    OSPF does not require a seed metric for successful redistribution.

     

    Erick

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  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    9. Jun 30, 2011 7:08 PM (in response to Erick)
    Re: default route propagation in eigrp

    Yes I know.  But we are talking about EIGRP correct? 

     

    Brian

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  • Currently Being Moderated
    10. Jun 30, 2011 7:54 PM (in response to Brian)
    Re: default route propagation in eigrp

     

    Regarding the configurations above using the redistribute static command, don't forget to add a metric.  By default only connected routes can be redistributed without a default metric.  All others require either a default metric be set or include the metric in the redistribute command.

     

     

    That's not what you said in your statement. All others excluding OSPF?

     

    Erick

     

    Message was edited by: ErickB

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  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    11. Jul 1, 2011 12:12 AM (in response to Erick)
    Re: default route propagation in eigrp

    Where in that statement did I mention or imply OSPF?    You incorrectly inferred OSPF.  We were talking about routes in EIGRP.  By defalut only connected routes can be redistributed without a defalut metric.  All others require either a default metric be set or include the metric in the redistribute command.  This is referring to all other EIGRP routes as that is what we were talking about and NOT all other routing protocols.

     

    You are correct though, in that OSPF does not require a seed metric for redistribution.  However, that is not what we were discussing.

     

    Brian

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  • Currently Being Moderated
    12. Jul 1, 2011 4:07 AM (in response to Brian)
    Re: default route propagation in eigrp

    Thank you for clarifying your statement because it was rather vague.  When you say all other's, as you can see your statement was misleading to other readers.

     

    Agan, thanks for the clarification.

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  • Joshua Johnson - CCNP R&S 6,067 posts since
    Sep 22, 2009
    Currently Being Moderated
    13. Jul 1, 2011 7:08 AM (in response to Erick)
    Re: default route propagation in eigrp

    Did anyone say you can redistribute from one EIGRP AS to another without setting the metric?

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  • rboldy 305 posts since
    Jun 3, 2011

    You just did ! But remember that these routes will be advertised into the other process as D EX routes with an AD of 170 - therefore it's always good to check for the presence of the same route from another routing-protocol ( perhaps one with a lower AD such as OSPF).

     

    Following on from the confusion here regarding whether we're talking EIGRP or OSPF I thought this might make a good segway to talk about default-route in OSPF

     

    One thing that confused me for a long time was how OSPF default-routes get advertised depending on the area type.

     

    I found this link very helpful:

     

    http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a74.shtml

     

    I've seen it stated in some Cisco and other vendor documentation that a tottally stubby area doesn't have any type3 LSA's which is wrong as by default the no-summay command ( which makes it tottally stubby) advertises a default-route as a type3 LSA. It's also interesting to see how an Totally NSSA does this for both no-summary and default-information originate.

     

    One other thing that surprised me was that if the default-information originate command is used on any router this router automatically becomes an ASBR - it doesn't need to have a link to another routing protocol or process because this command generates a Type-5 LSA (Type-7 in an NSSA) and E2 default-route which automatically make the router an ASBR. These routers will more than likely be both an ABR and ASBR and show ip ospf will tell you this. This doesn't really make any difference in the real-world but it's good to know.

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