What is RFC?
Request for Comments
An RFC (Request for Comments) is a numbered document in the series that defines internet protocols and standards, mostly produced and published through the IETF.
The series began in 1969, when RFC 1 was written during the ARPANET project, and the name reflects those informal early days. Today an RFC is published only after a long process: most start as Internet-Drafts, are discussed and revised in an IETF working group, and are approved before the RFC Editor assigns a number. Once published, an RFC is never edited. If a protocol changes, a new RFC is issued that "updates" or "obsoletes" the old one, which is why BGP-4 is RFC 4271 rather than a revision of an earlier number, and why TCP's current core specification, RFC 9293, obsoletes RFC 793. Each RFC has a status: Proposed Standard and Internet Standard are on the standards track, Best Current Practice (BCP) documents record operational advice, and Informational and Experimental RFCs are not standards at all. Many specifications use the words MUST, SHOULD and MAY with the precise meanings defined in RFC 2119.
Network engineers meet RFCs constantly. Vendor documentation cites them to say which features are supported, and the behaviour of a protocol is ultimately settled by the RFC rather than by any one implementation. Reading the relevant RFC is the surest way to resolve an argument about how BGP or OSPF should behave, though it's worth checking for later RFCs that update it. A common mistake is to assume every RFC is a standard. Some are informational, some are historic, and a few published on 1 April each year are jokes. Documentation address ranges such as 192.0.2.0/24 and 2001:db8::/32 are themselves reserved by RFCs, so examples never clash with real networks. RFCs are free to read at rfc-editor.org.
Lessons that use RFC
- BGP FundamentalsIntermediate · 75 min
How the Border Gateway Protocol glues the internet together: autonomous systems, sessions, path attributes, best-path selection, iBGP scaling and a hands-on eBGP lab with real FRR configuration.
- RPKI and Route Origin ValidationIntermediate · 70 min
Cryptographically signed routing origins: the RPKI trust chain, creating safe ROAs, Valid/Invalid/NotFound, validators and RTR, a real FRR + StayRTR lab, and what ROV can't stop (forged origins, leaks), plus where ASPA comes in.
- IPv4 over an IPv6-only core (RFC 8950)Intermediate · 40 min
Carry IPv4 routes over IPv6 BGP sessions with IPv6 next hops, so core routers need no IPv4 addresses at all. Built on VyOS: the missing router ID, what breaks without the extended next hop capability, native IPv4 on the wire, and why traceroute shows 192.0.0.8.
- BGP communities, prepending and RTBHIntermediate · 45 min
Tag routes with large communities, steer inbound traffic with AS-path prepending (and see why providers' local preference limits it), and stop a DDoS at your provider's edge with remotely triggered blackholing. Built on VyOS with two transit providers, including the two RTBH mistakes the lab made first.
- IRR, RPSL and AS-SETsIntermediate · 60 min
How networks publish what they announce and how their neighbours turn it into filters: Internet Routing Registries, whois queries, RPSL objects and attributes, AS-SET expansion, bgpq4, and the pitfalls of unsigned routing data.
- Switching basics: layer 2, VLANs and IP addressingBeginner · 40 min
How a switch learns MAC addresses and floods broadcasts, how IP subnets and default gateways decide where packets go, how VLANs split a switch into separate networks, and how trunks and a router connect them. Built on a real switch, three PCs and a VyOS router.
- OSPF FundamentalsBeginner · 70 min
The link-state IGP that runs inside most networks: neighbour adjacencies, LSA flooding, SPF, costs, DR/BDR, areas and LSA types, a hands-on FRR lab, and how OSPF underpins BGP.
- Linux Network ConnectivityBeginner · 80 min
Find out why a Linux machine can't reach something, layer by layer: interfaces and addresses, routes and ip route get, ARP and the neighbour table, ping and traceroute, DNS, and listening sockets — with real output from a three-host lab.