< draft-zzhang-bier-tether-00.txt   draft-zzhang-bier-tether-01.txt >
BIER Z. Zhang BIER Z. Zhang
Internet-Draft Juniper Networks Internet-Draft Juniper Networks
Intended status: Standards Track N. Warnke Intended status: Standards Track N. Warnke
Expires: April 24, 2019 Deutsche Telekom Expires: August 3, 2019 Deutsche Telekom
I. Wijnands I. Wijnands
Cisco Systems Cisco Systems
October 21, 2018 January 30, 2019
Tethering A BIER Router To A BIER-incapable Router Tethering A BIER Router To A BIER-incapable Router
draft-zzhang-bier-tether-00 draft-zzhang-bier-tether-01
Abstract Abstract
This document specifies optional procedures to optimize the handling This document specifies optional procedures to optimize the handling
of Bit Index Explicit Replication (BIER) [RFC8279] incapable routers, of Bit Index Explicit Replication (BIER) incapable routers, by
by tethering a BIER router to a BIER incapable router. tethering a BIER router to a BIER incapable router.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119. document are to be interpreted as described in RFC2119.
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
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 24, 2019. This Internet-Draft will expire on August 3, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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------ BFR2 ------- BFER2 ------ BFR2 ------- BFER2
/ /
BFER1 --- BFR1 ---- X ------- BFR3 ------- BFER3 BFER1 --- BFR1 ---- X ------- BFR3 ------- BFER3
......... .........
\ \
------ BFRn ------- BFERn ------ BFRn ------- BFERn
For BFR1 to forward BIER traffic towards BFR2...BFRn, it needs to For BFR1 to forward BIER traffic towards BFR2...BFRn, it needs to
tunnel individual copies through X. This degrades to "ingress" tunnel individual copies through X. This degrades to "ingress"
replication on those BFRs. If X's connections to BFRs are long replication to those BFRs. If X's connections to BFRs are long
distance or bandwidth limited, and n is large, it becomes very distance or bandwidth limited, and n is large, it becomes very
inefficient. inefficient.
A solution to the inefficient tunneling from BFRs is to tether a BFRx A solution to the inefficient tunneling from BFRs is to tether a BFRx
to X: to X:
------ BFR2 ------- BFER2 ------ BFR2 ------- BFER2
/ /
BFER1 --- BFR1 ---- X ------- BFR3 ------- BFER3 BFER1 --- BFR1 ---- X ------- BFR3 ------- BFER3
/ \ ......... / \ .........
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BIER packets to BFRx, who will then tunnel to BFR2, ..., BFRn. There BIER packets to BFRx, who will then tunnel to BFR2, ..., BFRn. There
could be fat and local pipes between the tethered BFRx and X, so could be fat and local pipes between the tethered BFRx and X, so
ingress replication from BFRx is acceptable. ingress replication from BFRx is acceptable.
For BFR1 to tunnel BIER packets to BFRx, the BFR1-BFRx tunnel need to For BFR1 to tunnel BIER packets to BFRx, the BFR1-BFRx tunnel need to
be announced in IGP as a forwarding adjacency so that BFRx will be announced in IGP as a forwarding adjacency so that BFRx will
appear on the SPF tree. This need to happen in a BIER specific appear on the SPF tree. This need to happen in a BIER specific
topology so that unicast traffic would not be tunneled to BFRx. topology so that unicast traffic would not be tunneled to BFRx.
Obviously this is operationally cumbersome. Obviously this is operationally cumbersome.
Section 6.9 of BIER architecture specification describes a method Section 6.9 of BIER architecture specification [RFC8279] describes a
that tunnels BIER packets through incapable routers without the need method that tunnels BIER packets through incapable routers without
to announce tunnels. However that does not work here, because BFRx the need to announce tunnels. However that does not work here,
will not appear on the SPF tree of BFR1. because BFRx will not appear on the SPF tree of BFR1.
There is a simple solution to the problem though. Even though X does There is a simple solution to the problem though. Even though X does
not support BIER forwarding, it could advertises BIER information as not support BIER forwarding, it could advertises BIER information as
if it supported BIER so BFRs will send BIER packets to it. The BIER if it supported BIER so BFRs will send BIER packets to it. The BIER
packets have a BIER label in front of the BIER header and X will use packets have a BIER label in front of the BIER header and X will use
the BIER label to label switch to BFRx, who will in turn do BIER the BIER label to label switch to BFRx, who will in turn do BIER
forwarding to other BFRs but via tunneling as described in section forwarding to other BFRs but via tunneling as described in section
6.9 of BIER architecture spec. 6.9 of BIER architecture spec.
Even though X advertises as if it supported BIER, BFRx needs to know Even though X advertises as if it supported BIER, BFRx needs to know
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and other BFRs will use BFRx (instead of X's children on the SPF and other BFRs will use BFRx (instead of X's children on the SPF
tree) to replace X during its post-SPF processing as described in tree) to replace X during its post-SPF processing as described in
section 6.9 of BIER architecture spec. That way, X does not need any section 6.9 of BIER architecture spec. That way, X does not need any
special knowledge, provisioning or procedure. special knowledge, provisioning or procedure.
The two options both have pros and cons - the first option only needs The two options both have pros and cons - the first option only needs
X and BFRx to support the new procedure while the second option does X and BFRx to support the new procedure while the second option does
not require anything to be done to the BIER incapable X. not require anything to be done to the BIER incapable X.
BFRx could also be connected to other routers in the network so that BFRx could also be connected to other routers in the network so that
It could send BIER packets through other routers as well, not it could send BIER packets through other routers as well, not
necessarily tunneling through X. To prevent routing loops, smallest necessarily tunneling through X. To prevent routing loops, smallest
metric, which is 1, must be announced for links between X and BFRx in metric, which is 1, must be announced for links between X and BFRx in
both directions. both directions.
While the example shows a local connection between BFRx and X, it While the example shows a local connection between BFRx and X, it
does not have to be like that. As long as packets can arrive at BFRx does not have to be like that. As long as packets can arrive at BFRx
without requiring X to do BIER forwarding, it should work. For without requiring X to do BIER forwarding, it should work. For
example, X could label switch incoming BIER packets through a tunnel example, X could label switch incoming BIER packets through a tunnel
to BFRx, or other BFRs could tunnel BIER packets to BFRx based on X's to BFRx, or other BFRs could tunnel BIER packets to BFRx based on X's
advertisement that BFRx is its helper. This does require a BIER advertisement that BFRx is its helper. This does require a BIER
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BFRx MUST not send BIER packets natively to X even if X advertises BFRx MUST not send BIER packets natively to X even if X advertises
BIER information. BFRx knows that X does not really support BIER BIER information. BFRx knows that X does not really support BIER
either from provisioning or from the BIER Helper Node sub-sub-TLV either from provisioning or from the BIER Helper Node sub-sub-TLV
advertised by X. advertised by X.
Either of the following two methods may be used for ISIS [RFC8401] Either of the following two methods may be used for ISIS [RFC8401]
and OSPF [I-D.ietf-bier-ospf-bier-extensions]. and OSPF [I-D.ietf-bier-ospf-bier-extensions].
A future revision will specify the extensions when BGP is used as the A future revision will specify the extensions when BGP is used as the
BIER signaling protocol [I-D.ietf-bier-ospf-bier-extensions]. BIER signaling protocol [I-D.ietf-bier-idr-extensions].
3.1. Advertising from Helped Node 3.1. Advertising from Helped Node
For non-MPLS encapsulation, X MUST advertise a BIER Helper Node sub- For non-MPLS encapsulation, X MUST advertise a BIER Helper Node sub-
sub-TLV that specifies the BIER prefix of the helper BFRx. Other sub-TLV that specifies the BIER prefix of the helper BFRx. Other
BFRs MUST use the Section 6.9 procedure modified as following: X is BFRs MUST use the Section 6.9 procedure modified as following: X is
treated as BIER incapable (because of the BIER Helper Node sub-sub- treated as BIER incapable (because of the BIER Helper Node sub-sub-
TLV), and is replaced with the BFRx (instead of X's children on the TLV), and is replaced with the BFRx (instead of X's children on the
SPF tree) during the post-SPF processing. SPF tree) during the post-SPF processing.
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6. Acknowledgements 6. Acknowledgements
The author wants to thank Eric Rosen and Antonie Przygienda for their The author wants to thank Eric Rosen and Antonie Przygienda for their
review, comments and suggestions. review, comments and suggestions.
7. Normative References 7. Normative References
[I-D.ietf-bier-idr-extensions] [I-D.ietf-bier-idr-extensions]
Xu, X., Chen, M., Patel, K., Wijnands, I., and T. Xu, X., Chen, M., Patel, K., Wijnands, I., and T.
Przygienda, "BGP Extensions for BIER", draft-ietf-bier- Przygienda, "BGP Extensions for BIER", draft-ietf-bier-
idr-extensions-05 (work in progress), March 2018. idr-extensions-06 (work in progress), January 2019.
[I-D.ietf-bier-ospf-bier-extensions] [I-D.ietf-bier-ospf-bier-extensions]
Psenak, P., Kumar, N., Wijnands, I., Dolganow, A., Psenak, P., Kumar, N., Wijnands, I., Dolganow, A.,
Przygienda, T., Zhang, Z., and S. Aldrin, "OSPFv2 Przygienda, T., Zhang, Z., and S. Aldrin, "OSPFv2
Extensions for BIER", draft-ietf-bier-ospf-bier- Extensions for BIER", draft-ietf-bier-ospf-bier-
extensions-18 (work in progress), June 2018. extensions-18 (work in progress), June 2018.
[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,
 End of changes. 11 change blocks. 
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