EIGRP Default Network Route

Hi Kay,

This has been awhile so I just had to check it again. You are correct, if you use network 0.0.0.0 then it will advertise a default route + activates EIGRP on all interfaces with a subnet on it.

I think that this behavior is different though on the older IOS versions but I’d have to check it. I thought that on older versions it would only advertise the interfaces, not the default route (even if you have one)…would have to check to confirm this though.

Rene

Hi Rene

The ip default-network command works on IOS 12.4 but it doesn’t work on IOS 15 anymore.

I tested and did not work!!

what should i do in new version

and why change version 12

Thanks

 

Hmm I should try that. The command is still accepted right?

The easiest method is probably advertising a default route through redistribution or by using the summary-address command on an interface. I never really liked the ip default-network command.

Rene you should give this section a rewrite - you suggest 2 methods which are both not mentioned by cisco and are partly legacy.

Default-route injection into eigrp should be done via redistribution (prefered) or via summarization on the interface:

We should be aware of all possible methods but always prefer the best practices from cisco.

Hi Philipp,

I’ll take another look, might be a good idea to edit this one.

Rene

Hi Rene,

I am trying to emulate this scenario in GNS 3 but strangely, eigrp adjacency is not forming b/w R1 and R2.

R1#sh run | b router eigrp
router eigrp 1
 network 192.168.12.0
 no auto-summary

R2#sh run | b router eigrp
router eigrp 1
 network 192.168.12.0
 network 192.168.23.0
 no auto-summary

R1#sh ip ei nei
IP-EIGRP neighbors for process 1

R2#sh ip ei nei
IP-EIGRP neighbors for process 1

R1#sh ip prot
Routing Protocol is "eigrp 1"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 1
  Redistributing: eigrp 1
  EIGRP NSF-aware route hold timer is 240s
  Automatic network summarization is not in effect
  Maximum path: 4
  Routing for Networks:
    192.168.12.0
  Routing Information Sources:
    Gateway         Distance      Last Update
  Distance: internal 90 external 170

R2#sh ip proto
Routing Protocol is "eigrp 1"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 1
  Redistributing: eigrp 1
  EIGRP NSF-aware route hold timer is 240s
  Automatic network summarization is not in effect
  Maximum path: 4
  Routing for Networks:
    192.168.12.0
    192.168.23.0
  Routing Information Sources:
    Gateway         Distance      Last Update
  Distance: internal 90 external 170

R1#sh ip ei to
IP-EIGRP Topology Table for AS(1)/ID(192.168.12.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 192.168.12.0/24, 1 successors, FD is 281600
        via Connected, FastEthernet0/0

R2#sh ip ei to
IP-EIGRP Topology Table for AS(1)/ID(192.168.23.2)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 192.168.12.0/24, 1 successors, FD is 281600
        via Connected, FastEthernet0/1
P 192.168.23.0/24, 1 successors, FD is 28160
        via Connected, FastEthernet1/0

Please advise as to why the neighborship is not forming. Have I done anything wrong in configs?

Thanks

Aravind

I can tell by your output that you are using 12.x code :slight_smile: (that doesn’t matter–just an observation).

I don’t see anything obviously wrong here. Obviously, you have done the basics like ensuring your interfaces are “no shut” and that R1 and R2 have connectivity?

Maybe put paste in a show run so we can see everything.

Hi Andrew,

I am using c3725-adventerprisek9-mz.124-15.T10.bin as IOS image file.

I have attached running configs from R1, R2 & ISP for your review.

Thanks

Aravind

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.
Capture

the routes seem fine I am using this version of IOS: c3640-jk9s-mz.124-16.bin

Capture

here is another pic

Capture

if want to see something else I will upload.

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

Capture

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…

Capture

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