Andrew S. Tanenbaum Edition 5th Exercise 5 Question 32 (Page No. 492)

Question

The set of IP addresses from 29.18.0.0 to 19.18.128.255 has been aggregated to
29.18.0.0/17. However, there is a gap of 1024 unassigned addresses from 29.18.60.0
to 29.18.63.255 that are now suddenly assigned to a host using a different outgoing
line. Is it now necessary to split up the aggregate address into its constituent blocks,
add the new block to the table, and then see if any reaggregation is possible? If not,
what can be done instead?

Comments

@ajaysoni1924

shouldn't it be 29.18.0.0-29.18.128.255?

there's is 19 instead of 29

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that should be 29 only but in the book it is given 19 instead of 29

Answer 1

To solve the problem, we can just add a new entry for the gap to the routing table:

 

	Base address	Mask
29.18.0.0/16	00011101 00010010 00000000 00000000	11111111 11111111 00000000 00000000
29.18.60.0/22	00011101 00010010 00111100 00000000	11111111 11111111 11111100 00000000

 

The CIDR entries in its routing table in the route has two entries for addresses from 29.18.0.0 to 29.18.128.255:

 

Address/mask	Next hop
29.18.0.0/16	y.y.y.y
29.18.60.0/22	x.x.x.x

Source: https://cis.temple.edu/~latecki/Courses/CIS617-04/FinalQuestions/Yu.doc