draft-ietf-bier-path-mtu-discovery-09.txt   draft-ietf-bier-path-mtu-discovery-10.txt 
BIER Working Group G. Mirsky BIER Working Group G. Mirsky
Internet-Draft ZTE Corp. Internet-Draft ZTE Corp.
Intended status: Standards Track T. Przygienda Intended status: Standards Track T. Przygienda
Expires: May 23, 2021 Juniper Networks Expires: 1 October 2021 Juniper Networks
A. Dolganow A. Dolganow
Individual contributor Individual contributor
November 19, 2020 30 March 2021
Path Maximum Transmission Unit Discovery (PMTUD) for Bit Index Explicit Path Maximum Transmission Unit Discovery (PMTUD) for Bit Index Explicit
Replication (BIER) Layer Replication (BIER) Layer
draft-ietf-bier-path-mtu-discovery-09 draft-ietf-bier-path-mtu-discovery-10
Abstract Abstract
This document describes Path Maximum Transmission Unit Discovery This document describes Path Maximum Transmission Unit Discovery
(PMTUD) in Bit Indexed Explicit Replication (BIER) layer. (PMTUD) in Bit Indexed Explicit Replication (BIER) layer.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on May 23, 2021. This Internet-Draft will expire on 1 October 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. PMTUD Mechanism for BIER . . . . . . . . . . . . . . . . . . 4 3. PMTUD Mechanism for BIER . . . . . . . . . . . . . . . . . . 4
3.1. Data TLV for BIER Ping . . . . . . . . . . . . . . . . . 6 3.1. Data TLV for BIER Ping . . . . . . . . . . . . . . . . . 6
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determined as minimal MTU value of BFIR's links to BIER domain. As determined as minimal MTU value of BFIR's links to BIER domain. As
has been assumed in Section 2, MTUs of all links but the link (B, D) has been assumed in Section 2, MTUs of all links but the link (B, D)
are the same. Thus BFERs E, F, and G would receive BIER Echo Request are the same. Thus BFERs E, F, and G would receive BIER Echo Request
and will send their respective replies to BFIR A. BFR B may pass the and will send their respective replies to BFIR A. BFR B may pass the
packet which is too large to forward over egress link (B, D) to the packet which is too large to forward over egress link (B, D) to the
appropriate network layer for error processing where it would be appropriate network layer for error processing where it would be
recognized as a BIER Echo Request packet. BFR B MUST send BIER Echo recognized as a BIER Echo Request packet. BFR B MUST send BIER Echo
Reply to BFIR A and MUST include Downstream Mapping TLV, defined in Reply to BFIR A and MUST include Downstream Mapping TLV, defined in
[I-D.ietf-bier-ping] setting its fields in the following fashion: [I-D.ietf-bier-ping] setting its fields in the following fashion:
o MTU SHOULD be set to the minimal MTU value among all egress BIER * MTU SHOULD be set to the minimal MTU value among all egress BIER
links, logical links between this and downstream BFRs, that could links, logical links between this and downstream BFRs, that could
be used to reach B's downstream BFERs; be used to reach B's downstream BFERs;
o Address Type MUST be set to 0 [Ed.note: we need to define 0 as * Address Type MUST be set to 0 [Ed.note: we need to define 0 as
valid value for the Address Type field with the specific semantics valid value for the Address Type field with the specific semantics
to "Ignore" it.] to "Ignore" it.]
o I flag MUST be cleared; * I flag MUST be cleared;
o Downstream Interface Address field (4 octets) MUST be zeroed and * Downstream Interface Address field (4 octets) MUST be zeroed and
MUST include in the Egress Bitstring sub-TLV the list of all BFERs MUST include in the Egress Bitstring sub-TLV the list of all BFERs
that cannot be reached because the attempted MTU turned out to be that cannot be reached because the attempted MTU turned out to be
too small. too small.
The BFIR will receive either of the two types of packets: The BFIR will receive either of the two types of packets:
o a positive Echo Reply from one of BFERs to which the probe has * a positive Echo Reply from one of BFERs to which the probe has
been sent. In this case, the bit corresponding to the BFER MUST been sent. In this case, the bit corresponding to the BFER MUST
be cleared from the BMS; be cleared from the BMS;
o a negative Echo Reply with bit string listing unreached BFERs and * a negative Echo Reply with bit string listing unreached BFERs and
recommended MTU value MTU'. The BFIR MUST add the bit string to recommended MTU value MTU'. The BFIR MUST add the bit string to
its BMS and set the size of the next probe as min(MTU, MTU') its BMS and set the size of the next probe as min(MTU, MTU')
If upon expiration of the Echo Request timer BFIR didn't receive any If upon expiration of the Echo Request timer BFIR didn't receive any
Echo Replies, then the size of the probe SHOULD be decreased. There Echo Replies, then the size of the probe SHOULD be decreased. There
are scenarios when an implementation of the PMTUD would not decrease are scenarios when an implementation of the PMTUD would not decrease
the size of the probe. For example, suppose upon expiration of the the size of the probe. For example, suppose upon expiration of the
Echo Request timer BFIR didn't receive any Echo Reply. In that case, Echo Request timer BFIR didn't receive any Echo Reply. In that case,
BFIR MAY continue to retransmit the probe using the initial size and BFIR MAY continue to retransmit the probe using the initial size and
MAY apply probe delay retransmission procedures. The algorithm used MAY apply probe delay retransmission procedures. The algorithm used
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defined retransmission procedures until either the bit string is defined retransmission procedures until either the bit string is
clear, i.e., contains no set bits, or until the BFIR retransmission clear, i.e., contains no set bits, or until the BFIR retransmission
procedure terminates and PMTU discovery is declared unsuccessful. In procedure terminates and PMTU discovery is declared unsuccessful. In
the case of convergence of the procedure, the size of the last probe the case of convergence of the procedure, the size of the last probe
indicates the PMTU size that can be used for all BFERs in the initial indicates the PMTU size that can be used for all BFERs in the initial
BMS without incurring fragmentation. BMS without incurring fragmentation.
Thus we conclude that in order to comply with the requirement in Thus we conclude that in order to comply with the requirement in
[I-D.ietf-bier-oam-requirements]: [I-D.ietf-bier-oam-requirements]:
o a BFR SHOULD support PMTUD; * a BFR SHOULD support PMTUD;
o a BFR MAY use defined per BIER sub-domain MTU value as initial MTU * a BFR MAY use defined per BIER sub-domain MTU value as initial MTU
value for discovery or use it as MTU for this BIER sub-domain to value for discovery or use it as MTU for this BIER sub-domain to
reach BFERs; reach BFERs;
o a BFIR MUST have a locally defined PMTUD probe retransmission * a BFIR MUST have a locally defined PMTUD probe retransmission
procedure. procedure.
3.1. Data TLV for BIER Ping 3.1. Data TLV for BIER Ping
There needs to be a control for probe size in order to support the There needs to be a control for probe size in order to support the
BIER PMTUD. Data TLV format is presented in Figure 2. BIER PMTUD. Data TLV format is presented in Figure 2.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBA1) | Length | | Type (TBA1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data | | Data |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Data TLV format Figure 2: Data TLV format
o Type: indicates Data TLV, to be allocated by IANA Section 4. * Type: indicates Data TLV, to be allocated by IANA Section 4.
o Length: the length of the Data field in octets. * Length: the length of the Data field in octets.
o Data: n octets (n = Length) of arbitrary data. The receiver * Data: n octets (n = Length) of arbitrary data. The receiver
SHOULD ignore it. SHOULD ignore it.
4. IANA Considerations 4. IANA Considerations
IANA is requested to assign a new Type value for Data TLV Type from IANA is requested to assign a new Type value for Data TLV Type from
its registry of TLV and sub-TLV Types of BIER Ping as follows: its registry of TLV and sub-TLV Types of BIER Ping as follows:
+-------+-------------+---------------+ +=======+=============+===============+
| Value | Description | Reference | | Value | Description | Reference |
+-------+-------------+---------------+ +=======+=============+===============+
| TBA1 | Data | This document | | TBA1 | Data | This document |
+-------+-------------+---------------+ +-------+-------------+---------------+
Table 1: Data TLV Type Table 1: Data TLV Type
5. Security Considerations 5. Security Considerations
Routers that support PMTUD based on this document are subject to the Routers that support PMTUD based on this document are subject to the
same security considerations as defined in [I-D.ietf-bier-ping] same security considerations as defined in [I-D.ietf-bier-ping]
6. Acknowledgment 6. Acknowledgment
Authors greatly appreciate thorough review and the most detailed Authors greatly appreciate thorough review and the most detailed
comments by Eric Gray. comments by Eric Gray.
7. References 7. References
7.1. Normative References 7.1. Normative References
[I-D.ietf-bier-ping] [I-D.ietf-bier-ping]
Nainar, N., Pignataro, C., Akiya, N., Zheng, L., Chen, M., Kumar, N., Pignataro, C., Akiya, N., Zheng, L., Chen, M.,
and G. Mirsky, "BIER Ping and Trace", draft-ietf-bier- and G. Mirsky, "BIER Ping and Trace", Work in Progress,
ping-07 (work in progress), May 2020. Internet-Draft, draft-ietf-bier-ping-07, 11 May 2020,
<https://tools.ietf.org/html/draft-ietf-bier-ping-07>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990, DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>. <https://www.rfc-editor.org/info/rfc1191>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 8, line 13 skipping to change at page 8, line 17
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201, "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017, DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>. <https://www.rfc-editor.org/info/rfc8201>.
7.2. Informative References 7.2. Informative References
[I-D.ietf-bier-oam-requirements] [I-D.ietf-bier-oam-requirements]
Mirsky, G., Nainar, N., Chen, M., and S. Pallagatti, Mirsky, G., Kumar, N., Chen, M., and S. Pallagatti,
"Operations, Administration and Maintenance (OAM) "Operations, Administration and Maintenance (OAM)
Requirements for Bit Index Explicit Replication (BIER) Requirements for Bit Index Explicit Replication (BIER)
Layer", draft-ietf-bier-oam-requirements-11 (work in Layer", Work in Progress, Internet-Draft, draft-ietf-bier-
progress), November 2020. oam-requirements-11, 15 November 2020,
<https://tools.ietf.org/html/draft-ietf-bier-oam-
requirements-11>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., [RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279, Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017, DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>. <https://www.rfc-editor.org/info/rfc8279>.
Authors' Addresses Authors' Addresses
Greg Mirsky Greg Mirsky
ZTE Corp. ZTE Corp.
Email: gregimirsky@gmail.com Email: gregimirsky@gmail.com, gregory.mirsky@ztetx.com
Tony Przygienda Tony Przygienda
Juniper Networks Juniper Networks
Email: prz@juniper.net Email: prz@juniper.net
Andrew Dolganow Andrew Dolganow
Individual contributor Individual contributor
Email: adolgano@gmail.com Email: adolgano@gmail.com
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