EIGRP Default Network Route

Hi Shashank,

The 192.168.23.0 /24 network is used as the default network which means R1 will send packets with an unknown destination there. However, R2 still has to know where to forward packets to…it has no clue how to reach 3.3.3.0 /24 so that’s why we need the default route.

Rene

As an EIGRP default routing alternative, why not this?:

R2(config)#int fa1/0

R2(config-if)#ip summary-address eigrp 12 0.0.0.0 0.0.0.0

Wouldn’t that work?

Hi Tim,

Yep that’s a perfect example. The only downside is that you have to do it on the interface level but it will work :slight_smile:

Rene

Hi Rene,

What is the benefit of redistribute connected network ?

I noticed in your answer to John you have used “redistribute connected metric 1 1 1 1 1” command to redistribute the static route that you have configured it beforehand, but I did not understand why you used “connected” keyword instead of “static” keyword ? and when we redistribute connected network ?

thanks.

Hussein Sameer

Hi Hussein,

I see I made an error there, it should be “redistribute static” (just edited it).

Redistribute connected only redistributes directly connected interfaces into EIGRP.

Rene

I enjoy your site very much! Thank you for all the great information!

Regarding this statement -

"In EIGRP we can use the network 0.0.0.0 command to advertise this. This might sound strange but it works, normally you can only use the network command to advertise networks on interfaces but EIGRP wil [sic] make an exception for this default route."
Rather than an exception, isn't this the equivalent of "network 0.0.0.0 255.255.255.255"? EIGRP will use a classful wildcard if none is provided, so 0.0.0.0 will count as a class A.

Testing on IOS 15.2(4), “network 0.0.0.0” enables EIGRP for all interfaces. If you have any static routes to Null0 (default or not), these count as a directly connected interface (this can be confirmed by “sh ip route”) and thus are also advertised. Likewise, “redistribute connected” should also work for Null0 static routes, though they will count as EIGRP external routes.

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