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

    default route propagation in eigrp

    verg

      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

        • 1. Re: default route propagation in eigrp
          rboldy

          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.

          • 2. Re: default route propagation in eigrp
            Joshua Johnson - CCNP R&S

            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. 

            • 3. Re: default route propagation in eigrp
              kalyan

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

              • 4. Re: default route propagation in eigrp
                Joshua Johnson - CCNP R&S

                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.

                • 5. Re: default route propagation in eigrp
                  Sey
                  • 6. Re: default route propagation in eigrp
                    verg

                    Thanks  to rboldy, Joshua and Sey . Keith's video was very useful.

                    • 7. Re: default route propagation in eigrp
                      Brian

                      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

                       

                      • 8. Re: default route propagation in eigrp
                        Erick

                        Hi Brian.

                         

                        OSPF does not require a seed metric for successful redistribution.

                         

                        Erick

                        • 9. Re: default route propagation in eigrp
                          Brian

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

                           

                          Brian

                           

                          • 10. Re: default route propagation in eigrp
                            Erick

                             

                            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

                            • 11. Re: default route propagation in eigrp
                              Brian

                              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

                               

                              • 12. Re: default route propagation in eigrp
                                Erick

                                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.

                                • 13. Re: default route propagation in eigrp
                                  Joshua Johnson - CCNP R&S

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

                                  • 14. Re: default route propagation in eigrp
                                    rboldy

                                    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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