Reference

The routing glossary

Every term the site uses, in plain English, each linked to the chapter that explains it properly. Type in the box to filter; it searches the definitions too, so "loop" finds split horizon and route leaks. Below the list: the numbers, ports and dates worth knowing by heart.

179the TCP port every BGP session runs on
16"infinity" in RIP: a route 16 hops away is unreachable, which caps a RIP network at 15 hops
89OSPF's IP protocol number: it rides directly on IP, with no TCP or UDP underneath

Common mix-up: the routing table and the forwarding table are not the same thing. The routing table (RIB) holds every route the router has heard of; the forwarding table (FIB) holds only the winners, in a form the hardware can search in nanoseconds.

Glossary

Terms, A to Z

Numbers worth knowing

Ports, protocol numbers and limits

WhatValueWhere it is defined
BGP transportTCP 179RFC 4271
OSPFIP protocol 89RFC 2328 (OSPFv2), RFC 5340 (OSPFv3)
RIPUDP 520 · infinity = 16RFC 2453
BFD (single hop)UDP 3784RFC 5881
4-byte AS numbers232 = 4,294,967,296RFC 6793
MPLS label field20 bitsRFC 3032
RIPngUDP 521RFC 2080
BabelUDP 6696RFC 8966
BFD detection time, 3 × 50 ms150 msRFC 5880, section 6.8.4
AS_TRANSAS 23456RFC 6793
BLACKHOLE community65535:666RFC 7999
VXLANUDP 4789 · 24-bit VNIRFC 7348
Source-specific multicast range232.0.0.0/8 · FF3x::/32RFC 4607
Timeline

Dates on the timeline

YearEvent
1980ARPANET collapses on October 27 when three copies of one routing update form a cycle, RFC 789
1982EGP, the first exterior gateway protocol, RFC 827
1989BGP's first specification, RFC 1105 (Lougheed and Rekhter)
1990IS-IS extended to route IP, RFC 1195
1993Classful addressing replaced by CIDR, RFC 1519
1998OSPF version 2 in its current form, RFC 2328
2006BGP-4 as it is specified today, RFC 4271
2001MPLS architecture, RFC 3031
2013RPKI route origin validation, RFC 6811
2018Segment routing architecture, RFC 8402
Sources

Where the definitions come from

  1. Y. Rekhter, T. Li and S. Hares, RFC 4271: A Border Gateway Protocol 4 (BGP-4), 2006.
  2. J. Moy, RFC 2328: OSPF Version 2, 1998.
  3. D. Katz and D. Ward, RFC 5880: Bidirectional Forwarding Detection, 2010.
  4. P. Mohapatra et al., RFC 6811: BGP Prefix Origin Validation, 2013.
  5. K. Sriram et al., RFC 7908: Problem Definition and Classification of BGP Route Leaks, 2016.
  6. C. Filsfils et al., RFC 8402: Segment Routing Architecture, 2018.
  7. E. Rosen, RFC 789: Vulnerabilities of Network Control Protocols: An Example, 1981.
  8. E. Rosen, RFC 827: Exterior Gateway Protocol (EGP), 1982.
  9. R. Callon, RFC 1195: Use of OSI IS-IS for Routing in TCP/IP and Dual Environments, 1990.
  10. V. Fuller et al., RFC 1519: Classless Inter-Domain Routing (CIDR), 1993.
  11. G. Malkin and R. Minnear, RFC 2080: RIPng for IPv6, 1997.
  12. E. Rosen, A. Viswanathan and R. Callon, RFC 3031: Multiprotocol Label Switching Architecture, 2001.
  13. H. Holbrook and B. Cain, RFC 4607: Source-Specific Multicast for IP, 2006.
  14. Q. Vohra and E. Chen, RFC 6793: BGP Support for Four-Octet Autonomous System (AS) Number Space, 2012.
  15. M. Mahalingam et al., RFC 7348: Virtual eXtensible Local Area Network (VXLAN), 2014.
  16. T. King et al., RFC 7999: BLACKHOLE Community, 2016.
  17. J. Chroboczek and D. Schinazi, RFC 8966: The Babel Routing Protocol, 2021.