Which routing protocol is classful?

A. Intermediate System-to-Intermediate System (IS-IS) and OSPF
B. Routing Information Protocol Version 1 (RIPv1) and RIPv2
C. IGRP and RIPv1
D. Enhanced Interior Gateway Routing Protocol (EIGRP) and Open Shortest Path First (OSPF)
Correct Answer: C
Section: Routing
Explanation
Explanation/Reference:
Classless Versus Classful Routing Protocols
Routing protocols can be classified based on their support of VLSM and CIDR. Classful routing protocols do not advertise subnet masks in their routing updates;
therefore, the configured subnet mask for the IP network must be the same throughout the entire internetwork. Furthermore, the subnets must, for all practical
purposes, be contiguous within the larger internetwork. For example, if you use a classful routing protocol for network 130.170.0.0, you must use the chosen mask
(such as 255.255.255.0) on all router interfaces using the 130.170.0.0 network. You must configure serial links with only two hosts and LANs with tens or
hundreds of devices with the same mask of 255.255.255.0. The big disadvantage of classful routing protocols is that the network designer cannot take advantage
of address summarization across networks (CIDR) or allocation of smaller or larger subnets within an IP network (VLSM). For example, with a classful routing
protocol that uses a default mask of /25 for the entire network, you cannot assign a /30 subnet to a serial point-to-point circuit.
Classful routing protocols are Classless routing protocols advertise the subnet mask with each route. You can configure subnetworks of a given IP network
number with different subnet masks (VLSM). You can configure large LANs with a smaller subnet mask and configure serial links with a larger subnet mask,
thereby conserving IP address space. Classless routing protocols also allow flexible route summarization and supernetting (CIDR). You create supernets by
aggregating classful IP networks. For example, 200.100.100.0/23 is a supernet of 200.100.100.0/24 and 200.100.101.0/24.

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