Suppose we have switches S1 through S4; the forwarding-table destinations are the switches themselves. The tables for S2 and S3 are as below, where the next_hop value is specified in neighbor form: S2: ⟨S1,S1⟩ ⟨S3,S3⟩ ⟨S4,S3⟩ S3: ⟨S1,S2⟩ ⟨S2,S2⟩ ⟨S4,S4⟩ From the above we can conclude that S2 must be directly connected to both S1 and S3 as its table lists them as next_hops; similarly, S3 must be directly connected to S2 and S4. (a). The given tables are consistent with the network diagrammed in exercise 6.0. Are the tables also consistent with a network in which S1 and S4 are not directly connected? If so, give such a network; if not, explain why S1 and S4 must be connected. (b). Now suppose S3’s table is changed to the following. Find a network layout consistent with these tables in which S1 and S4 are not directly connected. Do not add additional switches. S3: ⟨S1,S4⟩ ⟨S2,S2⟩ ⟨S4,S4⟩ While the table for S4 is not given, you may assume that forwarding does work correctly. However, you should not assume that paths are the shortest possible. Hint: It follows from the S3 table above that the path from S3 to S1 starts S3 ⟶ S4; how will this path continue? The next switch along the path cannot be S1, because of the hypothesis that S1 and S4 are not directly connected.

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Suppose we have switches S1 through S4; the forwarding-table destinations are the switches themselves. The tables for S2 and S3 are as below, where the next_hop value is specified in neighbor form:

S2: ⟨S1,S1⟩ ⟨S3,S3⟩ ⟨S4,S3⟩

S3: ⟨S1,S2⟩ ⟨S2,S2⟩ ⟨S4,S4⟩

From the above we can conclude that S2 must be directly connected to both S1 and S3 as its table lists them as next_hops; similarly, S3 must be directly connected to S2 and S4.

(a). The given tables are consistent with the network diagrammed in exercise 6.0. Are the tables also consistent with a network in which S1 and S4 are not directly connected? If so, give such a network; if not, explain why S1 and S4 must be connected.

(b). Now suppose S3’s table is changed to the following. Find a network layout consistent with these tables in which S1 and S4 are not directly connected. Do not add additional switches.

S3: ⟨S1,S4⟩ ⟨S2,S2⟩ ⟨S4,S4⟩

While the table for S4 is not given, you may assume that forwarding does work correctly. However, you should not assume that paths are the shortest possible. Hint: It follows from the S3 table above that the path from S3 to S1 starts S3 ⟶ S4; how will this path continue? The next switch along the path cannot be S1, because of the hypothesis that S1 and S4 are not directly connected.

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