In a Cisco network, Enhanced Interior Gateway Routing Protocol (EIGRP) can support multiple routed protocols. Which four routed protocols are supported by EIGRP?

Introduction / Context:
Enhanced Interior Gateway Routing Protocol is a Cisco advanced distance vector or hybrid routing protocol that was originally proprietary. One of its strengths is support for multiple routed protocols. Historically, enterprise networks used various layer three protocols in parallel, such as Internet Protocol, Novell Internetwork Packet Exchange, and AppleTalk. EIGRP was designed to route these different protocols efficiently. Modern networks mainly use Internet Protocol version 4 and Internet Protocol version 6, but exam questions still often reference the historical multi protocol capabilities of EIGRP.

Given Data / Assumptions:

• The focus is on routed protocols, not routing protocols.
• EIGRP is assumed to support several distinct layer three protocols.
• We must identify exactly four such protocols.
• Modern context includes both IPv4 and IPv6, while historical context includes IPX and AppleTalk.

Concept / Approach:
Routed protocols are protocols that carry user data and are forwarded by routers, such as IPv4, IPv6, IPX, and AppleTalk. Routing protocols such as EIGRP, OSPF, and RIP exchange routing information about these routed protocols. Historically, EIGRP was implemented separately for each network layer protocol as distinct processes, for example EIGRP for IP and EIGRP for IPX. Over time, as networks standardised on the Internet Protocol family, support for IPX and AppleTalk became less important, but questions still test knowledge of these capabilities to ensure a broad understanding of legacy environments.

Step-by-Step Solution:
1. Identify modern and legacy routed protocols commonly associated with Cisco multi protocol routing. 2. IPv4 is obviously supported and is the primary protocol for many years. 3. IPv6 is also supported by EIGRP in its newer implementations to allow next generation Internet addressing. 4. Historically, EIGRP supported IPX, which was widely used in Novell NetWare environments. 5. EIGRP also supported AppleTalk, which was used in older Apple Macintosh networks. 6. Therefore, the four routed protocols supported by EIGRP are IPv4, IPv6, IPX, and AppleTalk.

Verification / Alternative check:
Documentation for classical EIGRP describes separate protocol dependent modules for IP, IPX, and AppleTalk. Later enhancements introduced support for IPv6, which required modifications such as interface based configuration rather than global network commands. These references confirm that EIGRP is flexible across multiple routed protocols, which is important for migration strategies where legacy protocols coexist with Internet Protocol for a period of time.

Why Other Options Are Wrong:
IPv4, IPv6, CLNS, and BGP: CLNS relates to connectionless network service used with IS IS, and BGP is a routing protocol rather than a routed protocol. They are not the classic four supported protocols for EIGRP.
IPv4, IPX, SNA, and DECnet: While IPX is valid, Systems Network Architecture and Digital Network Architecture are not the standard EIGRP protocol set described in Cisco exam material.
IPv6, SNA, AppleTalk, and X.25: SNA and X.25 are not the typical routed protocols supported by EIGRP as described in certification references.
Only IPv4 because EIGRP is classful: EIGRP is a classless protocol that supports variable length subnet masks and has implemented support for both IPv4 and IPv6. So this statement is clearly incorrect.

Common Pitfalls:
Learners sometimes confuse routed protocols with routing protocols, listing protocols like OSPF or BGP instead of IPX or AppleTalk. Another common error is to assume that EIGRP only works with IPv4 because that is the most common deployment in modern networks. To avoid these mistakes, remember that EIGRP historically handled multiple network layer protocols through protocol dependent modules, which is why exam questions still highlight IPX and AppleTalk along with IPv4 and IPv6.

Final Answer:
IPv4, IPv6, IPX, and AppleTalk