Directed ARP (RFC1433)
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2019-Feb-10
Internet Society Requests For Comment (RFCs)
J. Garrett: AUTHOR [+2]
Directed ARP is a dynamic address resolution procedure that enables hosts and routers to resolve advertised potential next-hop IP addresses on foreign IP networks to their associated link level addresses. This memo defines an Experimental Protocol for the Internet community.
Network Working Group J. Garrett Request for Comments: 1433 AT&T Bell Laboratories J. Hagan University of Pennsylvania J. Wong AT&T Bell Laboratories March 1993
Status of this Memo
This memo defines an Experimental Protocol for the Internet community. Discussion and suggestions for improvement are requested. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.
A router with an interface to two IP networks via the same link level interface could observe that the two IP networks share the same link level network, and could advertise that information to hosts (via ICMP Redirects) and routers (via dynamic routing protocols). However, a host or router on only one of the IP networks could not use that information to communicate directly with hosts and routers on the other IP network unless it could resolve IP addresses on the "foreign" IP network to their corresponding link level addresses. Directed ARP is a dynamic address resolution procedure that enables hosts and routers to resolve advertised potential next-hop IP addresses on foreign IP networks to their associated link level addresses.
The authors are indebted to Joel Halpern of Network Systems Corporation and David O’Leary who provided valuable comments and insight to the authors, as well as ongoing moral support as the presentation of this material evolved through many drafts. Members of the IPLPDN working group also provided valuable comments during presentations and through the IPLPDN mailing list. Chuck Hedrick of Rutgers University, Paul Tsuchiya of Bell Communications Research, and Doris Tillman of AT&T Bell Laboratories provided early insight as well as comments on early drafts.
Garrett, Hagan & Wong [Page 1]
RFC 1433 Directed ARP March 1993
A "link level network" is the upper layer of what is sometimes referred to (e.g., OSI parlance) as the "subnetwork", i.e., the layers below IP. The term "link level" is used to avoid potential confusion with the term "IP sub-network", and to identify addresses (i.e., "link level address") associated with the network used to transport IP datagrams.
From the perspective of a host or router, an IP network is "foreign" if the host or router does not have an address on the IP network.
Multiple IP networks may be administered on the same link level network (e.g., on a large public data network). A router with a single interface on two IP networks could use existing routing update procedures to advertise that the two IP networks shared the same link level network. Cost/performance benefits could be achieved if hosts and routers that were not on the same IP network could use that advertised information, and exchange packets directly, rather than through the dual addressed router. But a host or router can not send packets directly to an IP address without first resolv...