< draft-ietf-tcpm-tcp-edo-11.txt   draft-ietf-tcpm-tcp-edo-12.txt >
TCPM WG J. Touch TCPM WG J. Touch
Internet Draft Independent consultant Internet Draft Independent Consultant
Updates: 793 Wes Eddy Updates: 793 Wes Eddy
Intended status: Standards Track MTI Systems Intended status: Standards Track MTI Systems
Expires: April 2022 October 12, 2021 Expires: October 2022 April 15, 2022
TCP Extended Data Offset Option TCP Extended Data Offset Option
draft-ietf-tcpm-tcp-edo-11.txt draft-ietf-tcpm-tcp-edo-12.txt
Abstract
TCP segments include a Data Offset field to indicate space for TCP
options but the size of the field can limit the space available for
complex options such as SACK and Multipath TCP and can limit the
combination of such options supported in a single connection. This
document updates RFC 793 with an optional TCP extension to that
space to support the use of multiple large options. It also explains
why the initial SYN of a connection cannot be extending a single
segment.
Status of this Memo Status of this Memo
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Abstract
TCP segments include a Data Offset field to indicate space for TCP
options but the size of the field can limit the space available for
complex options such as SACK and Multipath TCP and can limit the
combination of such options supported in a single connection. This
document updates RFC 793 with an optional TCP extension to that
space to support the use of multiple large options. It also explains
why the initial SYN of a connection cannot be extending a single
segment.
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction...................................................3
2. Conventions used in this document..............................3 2. Conventions used in this document..............................3
3. Motivation.....................................................3 3. Motivation.....................................................3
4. Requirements for Extending TCP's Data Offset...................4 4. Requirements for Extending TCP's Data Offset...................4
5. The TCP EDO Option.............................................4 5. The TCP EDO Option.............................................4
5.1. EDO Supported.............................................5 5.1. EDO Supported.............................................5
5.2. EDO Extension.............................................5 5.2. EDO Extension.............................................5
skipping to change at page 12, line 17 skipping to change at page 12, line 17
7. Interactions with Middleboxes 7. Interactions with Middleboxes
Middleboxes are on-path devices that typically examine or modify Middleboxes are on-path devices that typically examine or modify
packets in ways that Internet routers do not [RFC3234]. This packets in ways that Internet routers do not [RFC3234]. This
includes parsing transport headers and/or rewriting transport includes parsing transport headers and/or rewriting transport
segments in ways that may affect EDO. segments in ways that may affect EDO.
There are several cases to consider: There are several cases to consider:
- Typical NAT/NAPT devices, which modify only IP address and/or TCP - Typical NAT/NAPT devices, which modify only IP address and/or TCP
port number fields (with associated TCP checksum updates) port number fields (with associated TCP checksum updates)
- Middleboxes that try to reconstitute TCP data streams, such as - Middleboxes that try to reconstitute TCP data streams, such as for
for deep-packet inspection for virus scanning deep-packet inspection for virus scanning
- Middleboxes that modify known TCP header fields - Middleboxes that modify known TCP header fields
- Middleboxes that rewrite TCP segments - Middleboxes that rewrite TCP segments
7.1. Middlebox Coexistence with EDO 7.1. Middlebox Coexistence with EDO
Middleboxes can coexist with EDO when they either support EDO or Middleboxes can coexist with EDO when they either support EDO or
when they ignore its impact on segment structure. when they ignore its impact on segment structure.
NATs and NAPTs, which rewrite IP address and/or transport port NATs and NAPTs, which rewrite IP address and/or transport port
fields, are the most common form of middlebox and are not affected fields, are the most common form of middlebox and are not affected
by the EDO option. by the EDO option.
 End of changes. 12 change blocks. 
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