EIGRP Default Network Route

I don’t see any attachments.

Andrew, can you see the attachment now?

Nope. Do you? Maybe just paste the config into a code window.

19 posts were merged into an existing topic: EIGRP Default Network Route

The second configuration did not work for me as well. I can the interface of the ISP router and get replies but not the loopback of 3.3.3.3

So it seems to be partly working.
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the routes seem fine I am using this version of IOS: c3640-jk9s-mz.124-16.bin

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here is another pic

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if want to see something else I will upload.

I also took wireshark on the interface between ISP and R2.

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Now to me that seems to say its getting there correctly from the default route but from my understanding no response found means that it is unable to find its way back. So I tried to change the ip route on ISP to fastethernet 0/0 instead of and IP but that did not work.

I am betting if I changed and added a default route on ISP it would work but not sure that would be a good thing to default route back into the network lol…

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Hi @wilder7bc,

The ip default-network command is one of the weirder commands out there. I think I originally tried it on 12.4 when I wrote the lesson. On IOS 15.x, I can’t make it work…

The funny thing is, when I load my config, R1 doesn’t see 192.168.23.0/24 as a default network:

R1#show ip route 

D     192.168.23.0/24 [90/3072] via 192.168.12.2, 00:03:30, GigabitEthernet0/1

Once I remove and re-add the network command on R2, it does get propagated to R1:

R2(config-router)#router eigrp 12
R2(config-router)#no network 192.168.23.0
R2(config-router)#network 192.168.23.0 

Here’s R1 again:

R1#show ip route 

Gateway of last resort is not set

D*    192.168.23.0/24 [90/3072] via 192.168.12.2, 00:00:02, GigabitEthernet0/1

It now shows the asterisk but still no gateway of last resort.

In your case, the output of R1 looks good to me. The host unreachable message in your Wireshark output from 192.168.23.3 to 192.168.12.1 means that R3 is telling R1 that it doesn’t know how to reach 3.3.3.3. This tells us that:

  1. The packet from R1 makes it to R3.
  2. 3.3.3.3 doesn’t exist on R3.

Looking at your output, you don’t have 3.3.3.3 on an interface on the ISP router? :slight_smile:

Rene

if R2s fa0/1 interface is configured as a NAT interface would the ISP router still need the static route pointing to the internal 192 network between R1/R2?

thanks

Dave

Hello David

Typically an ISP router should not need a default route (or any kind of knowledge of internal networks) to reach internal networks of an enterprise network. This was done in the lesson just as a quick and dirty way with which connectivity can be established between all devices in the topology and pings can be used to test connectivity. Typically you would have NAT running on the edge router and that would be sufficient to allow the pings to work in the absence of the static route on the ISP router. Alternatively, you would have BGP running on the edge router that would inform Internet routers of the internal routable IP addresses that need to be advertised, thus not needing a static route in the ISP router.

I hope this has been helpful!

Laz

Hello Rene ,
I am a little bit confused on the static defualt route
R2(config)#ip route 0.0.0.0 0.0.0.0 FastEthernet 0/1 .To use an interface as a next hope isn’t just for point to point connection like serial interface ,how come it can be used on FastEthernet interface? I tried to replace the interface fa0/1 with ip address 192.168.23.3 (ISP address ) and advertise the network 0.0.0.0 to R1. But on the R1 routing table it only shows

D 192.168.23.0/24 [90/30720] via 192.168.12.2, 00:26:57, FastEthernet0/0
why the 0.0.0.0 default route is not on the R1 Routing table ?
After I switch the ISP address back to interface fa0/1 on R2 ,everything go back to normal .

Hello Minghui

When you use an Ethernet port as an exit interface, what will happen depends on several factors including the IOS version and the platform that you are using. In some platforms/IOS combinations, what Rene has implemented will work as configured. However, there are some other situations in which it doesn’t. The following link shows a couple of examples where you have an IP address as a next hop IP or an interface as an exit interface. In this example, the use of an exit interface fails.


If you configure a static route using an Ethernet exit interface, the forwarding router will assume the destination device is directly connected to that interface and it will try to find the MAC address of the destination by sending an ARP request out of the interface to the destination address. If it is successful, routing will occur successfully.

If you attempt to advertise the 0.0.0.0 network with a default routing using a next hop address, EIGRP will not directly advertise the 0.0.0.0 network. Rene mentions this in his notes:


As Rene mentions, if you don’t use this method, you can use redistribution to redistribute static routes into EIGRP. More on redistribution can be found here:

I hope this has been helpful!

Laz

Hi Rene,

In EIGRP, if there are 2 routers and there are 2 links in between them. I want to make one link as primary and another as secondary. How we can do it? Please help.

Hello Swapnil

If you have two links between two routers, and you are running EIRGP between them, and if they are equal cost routes (the same speed links for example), then by default EIGRP will load balance between the two links. This is known as equal cost load balancing (ECLB).

Now by adjusting several parameters, you are able to make one link be preferred over the other. This can be done by changing the bandwidth value assigned to one of the two interfaces, so that the metric of EIGRP for that particular path is increased. This will cause routing to take place via the path with a lower cost unless that path fails. This results in routing everything via the one path (underutilizing the other link) until a failure occurs. You can find out more about how to achieve this in the following lesson:


Now if you want to adjust the parameters such that more traffic is sent via the first link and less traffic is sent via the second link, then you can configure what is called Unequal cost load balancing. EIGRP, unlike OSPF supports this feature, and you can find out more about it at this lesson:

I hope this has been helpful!

Laz