C201 PRACTICE QUESTIONS AND VERIFIED
ANSWERS
What is the most important difference between BGP-4 and earlier versions of BGP? - ANS
BGP-4 is classless. Earlier versions are classful.
What two problems was CIDR developed to alleviate? - ANS CIDR was developed to
alleviate the explosion of Internet routing tables and to slow the depletion of Class B
network addresses.
What is the difference between classful and classless IP routers? - ANS Classful IP routers
perform routing table lookups on the major class network address first and then match the
subnet. Classless IP routers ignore the class of the destination address and try to make a
longest match on the address prefix.
What is the difference between classful and classless IP routing protocols? - ANS Classful IP
routing protocols advertise only a network or subnet address, without any information
about the prefix length. As a result, routers receiving the advertisement must make certain
assumptions about the address prefix. Classless IP routing protocols include information
that allows the receiving router to parse the address prefix. As a result, VLSM and
summarization are possible with classless protocols.
Given the addresses 172.17.208.0/23, 172.17.210.0/23, 172.17.212.0/23, and
172.17.214.0/23, summarize the addresses with a single aggregate, using the longest
possible address mask. - ANS 172.17.208.0/21
What is an address prefix? - ANS An IP address prefix is the part of an IP address that a
router considers when making routing decisions. In a classful environment, the prefix is a
major class network address or one of its subnets. In a classless environment, the prefix can
be any number of leading bits in the 32-bit address.
ANSWERS
What is the most important difference between BGP-4 and earlier versions of BGP? - ANS
BGP-4 is classless. Earlier versions are classful.
What two problems was CIDR developed to alleviate? - ANS CIDR was developed to
alleviate the explosion of Internet routing tables and to slow the depletion of Class B
network addresses.
What is the difference between classful and classless IP routers? - ANS Classful IP routers
perform routing table lookups on the major class network address first and then match the
subnet. Classless IP routers ignore the class of the destination address and try to make a
longest match on the address prefix.
What is the difference between classful and classless IP routing protocols? - ANS Classful IP
routing protocols advertise only a network or subnet address, without any information
about the prefix length. As a result, routers receiving the advertisement must make certain
assumptions about the address prefix. Classless IP routing protocols include information
that allows the receiving router to parse the address prefix. As a result, VLSM and
summarization are possible with classless protocols.
Given the addresses 172.17.208.0/23, 172.17.210.0/23, 172.17.212.0/23, and
172.17.214.0/23, summarize the addresses with a single aggregate, using the longest
possible address mask. - ANS 172.17.208.0/21
What is an address prefix? - ANS An IP address prefix is the part of an IP address that a
router considers when making routing decisions. In a classful environment, the prefix is a
major class network address or one of its subnets. In a classless environment, the prefix can
be any number of leading bits in the 32-bit address.
