More EIGRP summary route questions

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ITPro,

Apologies for the length of this one, but it is driving me a little crazy. Practice question I came across reads as follows:

Which command was used to create the following configuration?

Router# show ip protocol
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
Redistributing: eigrp 1
Automatic network summarization is in effect
Routing for Networks:
192.168.1.80/28 
192.168.1.128/28
Routing Information Sources:
Gateway Distance Last Update
192.168.1.85 90 0:04:01
Distance: internal 90 external 170

A. Router(config-router)# network 192.168.1.0 0.0.0.15

B. Router(config-router)# network 192.168.1.0 255.255.255.0

C. Router(config-router)# network 192.168.1.80
Router(config-router)# network 192.168.1.128

D. Router(config-router)# network 192.168.1.0

They are saying the answer is "D".. I am really confused though... If I were to be faced with having to advertise the two networks that are displayed in the questions output (192.168.1.80/28 and 192.168.1.128/28), I would simply issue these commands within the EIGRP AS number prompt:

network 192.168.1.80 0.0.0.15
network 192.168.1.128 0.0.0.15

So I was really suprised to find that none of the answers really fit, and more so that the answer was "D"... So I decided to try this on two different routers running IOS 15+. A 2911 and an 1841 with the same result. Tested with and without "auto-summary". Take a look at my output below.. Notice how the "show ip protocols" networks is just "192.168.0.1"? Did I find a bad question or is there something I am missing?

R3(config-router)#do show run | section eigrp
router eigrp 1
network 192.168.1.0




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-IPv4 Protocol for AS(1)
    Metric weight K1=1, K2=0, K3=1, K4=0, K5=0
    NSF-aware route hold timer is 240
    Router-ID: 192.168.4.1
    Topology : 0 (base)
      Active Timer: 3 min
      Distance: internal 90 external 170
      Maximum path: 4
      Maximum hopcount 100
      Maximum metric variance 1

  Automatic Summarization: enabled
  Maximum path: 4
  Routing for Networks:
    192.168.1.0
  Routing Information Sources:
    Gateway         Distance      Last Update
  Distance: internal 90 external 170




R3(config-router)#do show run int gi0/0.1
Building configuration...

Current configuration : 103 bytes
!
interface GigabitEthernet0/0.1
 encapsulation dot1Q 88
 ip address 192.168.1.81 255.255.255.240
end

R3(config-router)#do show run int gi0/0.2
Building configuration...

Current configuration : 104 bytes
!
interface GigabitEthernet0/0.2
 encapsulation dot1Q 89
 ip address 192.168.1.129 255.255.255.240
end

@Adam-Tyler,

I'm going to say this is not a good question.

If you leave the wildcard mask off of the eigrp configuration. It will work like a distance-vector protocol and use the default subnet mask for the network advertisements. This configuration would require the wildcard masks that you specified and not the generic one that is listed.

Be careful about where you're getting practice questions from. Some offer practice questions but do not verify or check answers.

Thanks.. That was really driving me crazy.. Glad I didn't just take it as fact and move on... Good advice about being careful with practice tests, but this question came directly out of the ITPro.TV practice exam. The link right from the CCNA Routing and Switching course. |;-)

Regards,
Adam Tyler

@Adam-Tyler,

If it's from Transcender, please read the explaination on why they say D is correct. If there is some valid explanation it would be nice to know but I couldn't get it do what it said when trying to configure it. So I would disagree with transcender at this point.

Here is the explanation from the question..
~~

Explanation:
The network 192.168.1.0 command instructs the router to activate EIGRP on every interface that belongs to the class C network 192.168.1.0. The exhibit indicates that the router is running EIGRP on two subnets of 192.168.1.0 (192.168.1.80/28 and 192.168.1.128/28). Since both of these are subnets of the same class C network number, only the class C address needs to be referenced with a network statement.

All interfaces that will participate in EIGRP must be specified with a network command that specifying the network of which the interface is a member. Failure to do so will result in neighbor relationships not forming. In the example below, Router A and Router B are directly connected, but not forming a neighbor relationship. The network they share is the 192.168.5.0/24 network. The output of the show run command for both routers reveals that Router B does not have EIGRP running on the 192.168.5.0 network.

RouterA#show run Router B#show run
<output omitted> <output omitted>
router eigrp 36 router eigrp 36
network 192.168.5.0 network 10.0.0.0

The network 192.168.1.0 0.0.0.15 command is incorrect because only the class C network number (192.168.1.0) needs to be referenced to enable EIGRP on all subnets. It is actually valid to include an inverse mask with EIGRP network statements, but it is unnecessary in this case, and the network/mask provided does not match either of the routed networks.

The network 192.168.1.0 255.255.255.0 command is incorrect because the mask is unnecessary in this case, and if masks are included, they must be expressed inversely (0.0.0.255).

It is unnecessary to configure two network commands in this example, as both networks are subnets of the same class C network (192.168.1.0), and a single network command can enable EIGRP on both. Additionally, if specific subnets are referenced in network commands, it is necessary to include an inverse mask after them, or EIGRP will automatically summarize the command to the classful boundary.

@Adam-Tyler,

Ah, ok, they're saying that if you do this manual route summarization it should cover both networks. I looked over the info again from the first post. The key was where it tells you Automatic Summarization: enabled so the display will show the routing for the summarized network. I should have paid better attention to the question.
So it will only display the default summarized route for the class C. Now, I get it. Thanks for posting back on this one!

Hi Ronnie.. So I attempted to turn on and off the "Automatic Summarization" feature and it didn't seem to change this output from "show ip protocols".. Would I need to re-enter the advertised network commands for each to be displayed?

Regards,
Adam Tyler

@Adam-Tyler,

I think you would need to restart the routing process itself, e.g. clear ip eigrp 1 neighbors this should allow the process to clear everything out and allow for the advertisement of your changes to propogate.

Ronnie,

I'll lab this again and try it over the next day or so. Thanks.

Regards,
Adam Tyler