Answers to Review Questions
B. Route summarization is most effective when used with contiguous
address space, because contiguous address space tends to have the
most higher-order bits in common.
B. The command no auto-summary is a router-configuration com-
mand that disables the automatic summarization of routes.
C, D. IP unnumbered is not supported on X.25 or SMDS networks.
Since the serial interface has no IP number, you will not be able to ping
the interface to see if it is up. However, you can determine the interface
status with SNMP. Also, IP security options are not supported on an
IP unnumbered interface.
D. If you write out 255.255.255.248 in binary, you will find that the
first 29 bits are ones, and the remaining three bits are zeros. Therefore,
we say that it is a /29.
B, C. If we look at each of these IP addresses and the subnet mask in
binary, we see that the host portion of the address for 172.16.1.8 is all
zeros, which refers to the network. The host portion of 172.16.1.9 is
01, which is valid for a host address. The host portion of 172.16.1.10 is
10, which is also valid for a host address. The host portion of
172.16.1.11 is 11, which refers to the broadcast address.
A. If you write out the last octet in binary, you have 00001010. Since
we are using a 29-bit subnet mask, the last three bits are not part of the
network address, which leaves us with a network address of
00001000. If we convert this number back to decimal, we get 8.
Therefore, the network address is 172.16.0.8.
C and D. IP unnumbered can, in some cases, make a discontiguous
network appear as contiguous across a serial link. Also, if you disable
route summarization, then a router will advertise each individual sub-
net. However, answer D only works with routing protocols that can
carry subnet information, otherwise you still end up with a discontig-
uous network, for example EIGRP and RIP V2.
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