Solved

EIGRP autosummarization

Posted on 2011-03-20
14
616 Views
Last Modified: 2012-05-11
I am trying to understand this practice question on cisco Adv test:

 10.10.10.0/24----E0 RTR1 S0----172.16.10.0/24---S0 RTR2 S1---192.168.20.0/24---S1 RTR3---E0

RTR1 config:
router eigrp 4
  network 10.0.0.0
  network 172.16.0.0
  no auto-summary

Auto-summarization is disabled on RTR1 but is enabled on RTR2 and RTR3. Which
two routes will be seen on the routing table of RTR3:
A. 10.0.0.0/8
B. 10.10.0.0/16
C. 10.10.10.0/24
D. 172.16.0.0/16
E. 172.16.0.0/24
F. 172.16.10.0/24
0
Comment
Question by:totaram
  • 6
  • 5
  • 3
14 Comments
 
LVL 50

Expert Comment

by:Don Johnston
ID: 35177666
A & D

When auto-summary is enabled, routes will be summarized to the classfull boundaries.
0
 

Author Comment

by:totaram
ID: 35177697
Thats what I thought, answer is C,D.
0
 
LVL 50

Expert Comment

by:Don Johnston
ID: 35177712
Says who? :-)
0
Flexible connectivity for any environment

The KE6900 series can extend and deploy computers with high definition displays across multiple stations in a variety of applications that suit any environment. Expand computer use to stations across multiple rooms with dynamic access.

 
LVL 6

Expert Comment

by:gcl_hk
ID: 35178004
10.10.10.0/24 is advertise by RTR1, even RTR2 have enabled auto summary, as the 10.10.10.0/24 is learn from neighbor, so auto summarization will not modify it and advertise to others by default
0
 

Author Comment

by:totaram
ID: 35178012
The answer provided with the question bank...

Could it be that since the two interfaces on RTR1 are directly connected, the no auto summarization  advertises them as what they are tp both RTR2 & RTR3.??
0
 
LVL 6

Expert Comment

by:gcl_hk
ID: 35178014
I have tried on lab.... and the result for your reference.

en
conf t
host R3
int g0/1
no sh
ip add 10.10.10.3 255.255.255.0
int fa0/0/1
no sh
ip add 172.16.10.3 255.255.255.0
router eigrp 4
network 10.0.0.0
network 172.16.0.0
no auto-summary

en
conf t
host R4
int fa0/0
no sh
ip add 172.16.10.4 255.255.255.0
int s0/0/0
ip add 192.168.20.4 255.255.255.0
router eigrp 4
network 172.16.0.0
network 192.168.20.0

en
conf t
host R2
int s0/0
clockrate 64000
ip add 192.168.20.2 255.255.255.0
router eigrp 4
network 192.168.20.0

10.10.10.0/24 - G0/1 --- R3 --- F0/0/1 - 172.16.10.0/24 - F0/0 --- R4 --- S0/0/0 - 192.168.20.0/24 - S/0 --- R2

R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

D    172.16.0.0/16 [90/2172416] via 192.168.20.4, 00:22:03, Serial0/0
C    192.168.20.0/24 is directly connected, Serial0/0
     10.0.0.0/24 is subnetted, 1 subnets
D       10.10.10.0 [90/2174976] via 192.168.20.4, 00:21:04, Serial0/0
0
 

Author Comment

by:totaram
ID: 35178037
You gave the output on R2, what is 'sh ip route' on R3??

I think you are right if command 'no passive int' is defined on R1. I guess default is passive interface...
0
 
LVL 6

Accepted Solution

by:
gcl_hk earned 63 total points
ID: 35178055
R3????

R3#sh ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, + - replicated route

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 3 subnets, 3 masks
D        10.0.0.0/8 [90/30720] via 172.16.10.4, 00:04:11, FastEthernet0/0/1
C        10.10.10.0/24 is directly connected, GigabitEthernet0/1
L        10.10.10.3/32 is directly connected, GigabitEthernet0/1
      172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C        172.16.10.0/24 is directly connected, FastEthernet0/0/1
L        172.16.10.3/32 is directly connected, FastEthernet0/0/1
D     192.168.20.0/24
           [90/2172416] via 172.16.10.4, 00:40:14, FastEthernet0/0/1

R4#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.10.0/24 is directly connected, FastEthernet0/0
D       172.16.0.0/16 is a summary, 00:41:17, Null0
C    192.168.20.0/24 is directly connected, Serial0/0/0
     10.0.0.0/24 is subnetted, 1 subnets
D       10.10.10.0 [90/30720] via 172.16.10.3, 00:40:16, FastEthernet0/0

0
 

Author Comment

by:totaram
ID: 35178078
Sorry, didn't realize that you had named them differently.. the last one does have the interface address in routing table.
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 62 total points
ID: 35180268
Now I see what's going on. The auto-summary feature only works on directly connected routes. Since R2 learned the 10.10.10.0 route, it won't summarize when it sends it to R3.

And since R2 is connected to the 172.16.10.0 network, it will summarize that to R3.

0
 

Author Comment

by:totaram
ID: 35181218
"Since R2 learned the 10.10.10.0 route, it won't summarize when it sends it to R3."

How did R2 learn 10.10.10.0/24 route, it is not directly connected to R2, 172.16.0.0/16 is connected to R2 and R1.

0
 
LVL 50

Expert Comment

by:Don Johnston
ID: 35181287
>How did R2 learn 10.10.10.0/24 route,

R1 advertised it via EIGRP.
0
 

Author Comment

by:totaram
ID: 35181430
I see... R1 is no-auto summary and the other subnet (172.16.0.0) is directly connected, so auto-summary :-)
0
 
LVL 50

Expert Comment

by:Don Johnston
ID: 35181782
Correct.
0

Featured Post

Easy, flexible multimedia distribution & control

Coming soon!  Ideal for large-scale A/V applications, ATEN's VM3200 Modular Matrix Switch is an all-in-one solution that simplifies video wall integration. Easily customize display layouts to see what you want, how you want it in 4k.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

In the hope of saving someone else's sanity... About a year ago we bought a Cisco 1921 router with two ADSL/VDSL EHWIC cards to load balance local network traffic over the two broadband lines we have, but we couldn't get the routing to work consi…
This article will inform Clients about common and important expectations from the freelancers (Experts) who are looking at your Gig.
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
Here's a very brief overview of the methods PRTG Network Monitor (https://www.paessler.com/prtg) offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

735 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question