Accommodating a Maximum Transit Unit/Maximum Receive Unit (MTU/MRU) Greater Than 1492 in the Point-to-Point Protocol over Ethernet (PPPoE)
RFC 4638
| Document | Type | RFC - Informational (September 2006; No errata) | |
|---|---|---|---|
| Authors | Mike Duckett , Jerome Moisand , Tom Anschutz , Diamantis Kourkouzelis , Peter Arberg | ||
| Last updated | 2015-10-14 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized (tools) htmlized bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 4638 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Mark Townsley | ||
| Send notices to | james.d.carlson@sun.com | ||
Network Working Group P. Arberg
Request for Comments: 4638 D. Kourkouzelis
Category: Informational Redback Networks
M. Duckett
T. Anschutz
BellSouth
J. Moisand
Juniper Networks
September 2006
Accommodating a Maximum Transit Unit/Maximum Receive Unit (MTU/MRU)
Greater Than 1492 in the
Point-to-Point Protocol over Ethernet (PPPoE)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
IESG Note
As of this writing, no current IEEE standard supports the use of
"jumbo frames" (MTU greater than 1500). Although this document
contains recommended mechanisms to detect problems in the path,
interoperability and reliability of non-standard extensions cannot be
assured. Both implementors and users of the protocol described here
should exercise caution in its use.
Abstract
The Point-to-Point Protocol over Ethernet (PPPoE), as described in
RFC 2516, mandates a maximum negotiated Maximum Receive Unit (MRU) of
1492. This document outlines a solution that relaxes this
restriction and allows a maximum negotiated MRU greater than 1492 to
minimize fragmentation in next-generation broadband networks.
Arberg, et al. Informational [Page 1]
RFC 4638 PPPoE MRU/MTU Increase September 2006
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................4
3. Proposed Solution ...............................................4
4. PPPoE Discovery Stage ...........................................5
5. LCP Considerations ..............................................5
5.1. MRU Negotiations ...........................................5
5.2. MRU Test and Troubleshooting ...............................6
6. Security Considerations .........................................7
7. IANA Considerations .............................................7
8. Acknowledgements ................................................7
9. Normative References ............................................7
10. Informative References .........................................8
1. Introduction
As broadband network designs are changing from PC-initiated PPPoE [1]
sessions in a combined Ethernet/Asynchronous Transfer Mode (ATM)
setup, as shown in Figure 1, to more intelligent PPPoE-capable
Residential Gateway (RG) and Gigabit Ethernet/ATM broadband network
designs, as shown in Figures 2 and 3, the need to increase the
maximum transmit and receive unit in the PPPoE protocol is becoming
more important in order to reduce fragmentation in the network.
<------------------ PPPoE session ------------------>
+-----+ +-----+
+--+ +---+ | | | |
|PC|--------------|CPE|-----------|DSLAM|-----------| BRAS|
+--+ <Ethernet> +---+ <ATM> | | <ATM> | |
+-----+ +-----+
Figure 1. Initial broadband network designs with PPPoE
In the network design shown in Figure 1, fragmentation is typically
not a problem, since the subscriber session is PPPoE end to end from
the PC to the BRAS. Therefore, a PPP-negotiated MRU of 1492 octets
is fully acceptable, as it makes the largest PPPoE frame adhere to
the standard Ethernet MTU of 1500 octets.
Arberg, et al. Informational [Page 2]
RFC 4638 PPPoE MRU/MTU Increase September 2006
<----- IPoE -----> <--------- PPPoE session --------->
+-----+ +-----+
+--+ +---+ | | | |
|PC|--------------| RG|-----------|DSLAM|------------| BRAS|
+--+ <Ethernet> +---+ <ATM> | | <GigE> | |
+-----+ +-----+
Figure 2. Next-generation broadband network designs with PPPoE
In the network design shown in Figure 2, fragmentation becomes a
major problem, since the subscriber session is a combination of IPoE
and PPPoE. The IPoE typically uses a Maximum Transit Unit (MTU) of
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