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Refer to the exhibit.
In the IS-IS network shown, router R1 has been configured to summarize subnetworks 20.20.1.0/24 and 20.20.2.0/24 as 20.20.0.0/16. Which routers' routing tables will be reduced, compared to their routing tables before the summarization?
Suggested Answer: B
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Router R1 is the one that performs the summarization of the two subnets (20.20.1.0/24 and 20.20.2.0/24) into the summarized route 20.20.0.0/16. However, R1 itself will not see any change in its routing table because it is directly connected to both subnets and already knows about them.
Router R2, which is in Area 49.0002, will benefit from this summarization because it previously had separate routes for both 20.20.1.0/24 and 20.20.2.0/24. After the summarization, R2 will only need to maintain a single route to 20.20.0.0/16, reducing the size of its routing table.
Router R4 does not directly benefit from the summarization because it is only connected to the Level 1 network and has no need for the summarized routes from R1. Thus, the summarization does not affect R4's routing table.
34 comments · newest first
BL
Blair
11 months ago
Are we sure R2's table will actually be smaller?
SA
Santos
11 months ago
I think R1 and R2 both benefit from this.
WY
Wynell
11 months ago
Wait, how does this affect R4?
AR
Arthur
11 months ago
Definitely reduces R2's routing table!
IR
Irving
12 months ago
R1 is summarizing 20.20.1.0/24 and 20.20.2.0/24 as 20.20.0.0/16.
VA
Valentine
12 months ago
I feel like both R2 and R4 might benefit from the summarization, but I need to double-check how summarization works in IS-IS.
QU
Quentin
1 year ago
I practiced a similar question where summarization impacted multiple routers, but I can't recall if R1 is included in this case.
NI
Nieves
1 year ago
I think R2 will definitely have a reduced routing table since it will see the summarized route instead of the individual subnets.
DA
Dana
1 year ago
I remember that summarization reduces the number of routes in the routing table, but I'm not sure which routers are affected here.
AL
Alonzo
1 year ago
I'm a bit confused here. The question mentions that R1 is summarizing the subnets, but it's not clear to me how that affects the other routers. I'll need to think this through carefully and review my understanding of route summarization.
CO
Cortney
1 year ago
Alright, I've got this. The summarization on R1 will reduce the number of routes in the routing tables of the routers that are downstream from R1, which would be R2 and R4. The answer is D.
CL
Clare
1 year ago
Hmm, this seems like a tricky one. I'm not sure I fully understand the concept of route summarization and how it impacts the routing tables of different routers in the network. I'll need to review that before attempting to answer.
KR
Kristel
1 year ago
Okay, let's think this through. The question is asking which routers' routing tables will be reduced after the summarization on R1. I need to visualize the network and understand how the summarization affects the other routers.
DO
Dorthy
2 years ago
I'm going with C. Routing tables, reduced. Sounds like a job for the Routing Fairy!
GE
Gerri
2 years ago
Yeah, it's a good way to keep things more organized and efficient in the network.
TR
Truman
2 years ago
I think C is the correct answer too. Summarization can definitely help reduce routing tables.
VA
Van
2 years ago
C, obviously. R1 is the one doing the summarization, so of course R1 and R2 will have their routing tables reduced. Wait, did I just say 'obviously'? That was a rookie mistake.
CA
Carla
2 years ago
Agreed, C is the correct answer. R1 is the one summarizing, so R1 and R2 will have their routing tables reduced.
VE
Veronica
2 years ago
Definitely C. R1 is the one doing the summarization, so R1 and R2 will see a reduction in their routing tables.
PA
Paulene
2 years ago
Yeah, that makes sense. R1 is the one performing the summarization, so R1 and R2 will benefit from reduced routing tables.
FL
Fletcher
2 years ago
I think it's C too. R1 is the one doing the summarization, so R1 and R2 will have reduced routing tables.
LA
Launa
2 years ago
But wouldn't only router R1 have a reduced routing table since it's the one doing the summarization?
GR
Gracia
2 years ago
I agree with Arthur, because the subnetworks are being summarized by R1.
RU
Rupert
2 years ago
This is a tricky one! I'd go with C, but I can see how someone might think R2 or R4 could be affected too. Good question!
JO
Jolanda
2 years ago
Hmm, I'm not sure. I think it might be B since R2 is directly connected to the summarized subnets.
RE
Reed
2 years ago
B) Router R2
AD
Adria
2 years ago
A) Router R1
AG
Agustin
2 years ago
B) Router R2
BE
Bea
2 years ago
A) Router R1
AR
Arthur
2 years ago
I think routers R1 and R2 will have reduced routing tables.
VI
Vincent
2 years ago
The answer is clearly C. Routers R1 and R2 will have their routing tables reduced since the summarization is happening on R1, which is connected to both R2 and R4.
AD
Adelle
2 years ago
You're right, the correct answer is C) Routers R1 and R2.
FL
Floyd
2 years ago
No, I believe it is C) Routers R1 and R2.
MA
Mariko
2 years ago
I think the answer is A) Router R1.