Important RFCs:
RFC 760: DoD Standard Internet Protocol (IP) [Obsoleted by RFC 791, but still worth reading]
RFC 768: User Datagram Protocol (UDP)
RFC 791: Internet Protocol (IP)
RFC 792: Internet Control Message Protocol (ICMP)
RFC 793: Transmission Control Protocol (TCP)
RFC 826: Ethernet Address Resolution Protocol (ARP)
RFC 854: Telnet Protocol Specification
RFC 950: Internet Standard Subnetting Procedure
RFC 959: File Transfer Protocol (FTP)
RFC 1001: Protocol Standard for a NetBIOS Service on TCP/UDP Transport: Concepts and Facilities
RFC 1002: Protocol Standard for a NetBIOS Service on a TCP/UDP Transport: Detailed Specifications
RFC 1034: Domain Names-Concepts and Facilities
RFC 1035: Domain Names-Implementation and Specification
RFC 1058. Routing Information Protocol (RIP)
RFC 1122: Requirements for Internet Hosts-Communication Layers
RFC 1517: Applicability Statement for the Implementation of Classless Inter-Domain Routing (CIDR)
RFC 1518: An Architecture for IP Address Allocation with CIDR
RFC 1520: Exchanging Routing Information Across Provider Boundaries in the CIDR Environment
RFC 1661: The Point-to-Point Protocol (PPP)
RFC 1700: Assigned Numbers [Obsoleted by IANA Number Resources but still worth a peruse]
RFC 1752: The Recommendation for the IP Next Generation Protocol
RFC 1812: Requirements for IP Version 4 Routers
RFC 1878: Variable Length Subnet Table For IPv4
RFC 1918: Address Allocation for Private Internets
RFC 1939: Post Office Protocol (POP), Version 3
RFC 2072: Router Renumbering Guide
RFC 2281: Cisco Hot Standby Router Protocol (HSRP)
RFC 2328: Open Shortest Path First (OSPF), Version 2
RFC 2390: Inverse Address Resolution Protocol (Inverse ARP)
RFC 2453: Routing Information Protocol (RIP), Version 2
RFC 2460: Internet Protocol, Version 6 (IPv6) Specification
RFC 2474: Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
RFC 2475: An Architecture for Differentiated Service
RFC 2516: A Method for Transmitting PPP over Ethernet (PPPoE)
RFC 2608: Service Location Protocol (SLP), Version 2
RFC 2616: Hypertext Transfer Protocol (HTTP), Version 1.1
RFC 2650: Using Routing Policy Specification Language (RPSL) in Practice
RFC 2819: Remote Network Monitoring (RMON) Management Information Base (MIB)
RFC 3022: Traditional IP Network Address Translator (Traditional NAT)
RFC 3376: Internet Group Management Protocol (IGMP), Version 3
RFC 3416: Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)
RFC 3501: Internet Message Access Protocol (IMAP), Version 4rev1
RFC 3768: Virtual Router Redundancy Protocol
RFC 4271: A Border Gateway Protocol 4 (BGP4)
RFC 4301: Security Architecture for the Internet Protocol
RFC 4502: Remote Network Monitoring Management Information Base Version 2 using SMIv2 (RMONv2)
RFC 4632: Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan
RFC 4862: IPv6 Stateless Address Autoconfiguration
RFC 5321: Simple Mail Transfer Protocol (SMTP)
RFC 7868: Enhanced Interior Gateway Routing Protocol (EIGRP)
RFC 5340: OSPF for ipv6(OSPF V3)
RFC 2858: Multiprotocol Extensions for BGP-4