Point-to-Point Protocol extensions for bridging (RFC1220)
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
1. Status of this Memo
Network Working Group F. Baker, Editor
Request for Comments: 1220 ACC
Point-to-Point Protocol Extensions for Bridging
1. Status of this Memo
This document defines an extension of the Internet Point-to-Point
Protocol (PPP) described in RFC 1171, targeting the use of Point-to-
Point lines for Remote Bridging. It is a product of the Point-to-
Point Protocol Extensions Working Group of the Internet Engineering
Task Force (IETF).
This RFC specifies an IAB standards track protocol for the Internet
community, and requests discussion and suggestions for improvements.
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.
2. Historical Perspective
Two basic algorithms are ambient in the industry for Bridging of
Local Area Networks. The more common algorithm is called
"Transparent Bridging" and has been standardized for Extended LAN
configurations by IEEE 802.1. IEEE 802.5 has proposed an alternative
approach, called "Source Routing", and is in the process of
standardizing that approach for IEEE 802.5 extended networks.
Although there is a subcommittee of IEEE 802.1 addressing remote
bridging, neither standard directly defines Remote Bridging per se,
as that would technically be beyond the IEEE 802 committee's charter.
Both allow for it, however, modeling the line as an unspecified
interface between half-bridges.
This document assumes that the devices at either end of a serial link
- have agreed to utilize the RFC 1171 line discipline in some form.
- may have agreed, by some other means, to exchange other
protocols on the line interspersed with each other and with any
- may be willing to use the link as a vehicle for Remote Bridging.
- may have multiple point-to-point links that are configured in
parallel to simulate a single line of higher speed or
reliability, but message sequence issues are solved by the
3. General Considerations
3.1. Link Quality Monitoring
It is strongly recommended that Point-to-Point Bridge Protocol
implementations utilize Magic Number Loopback Detection and Link-
Quality-Monitoring. This is because the 802.1 Spanning Tree
protocol, which is integral to both Transparent Bridging and Source
Routing (as standardized), is unidirectional during normal operation,
with HELLO PDUs emanating from the Root System in the general
direction of the leaves, without any reverse traffic except in
response to network events.
3.2. Message Sequence
The multiple link case requires consideration of message
sequentiality. The transmitting station must determine either that
the protocol being bridged requires transmissions to ...