Network Working Group X. Xu
Internet-Draft Huawei
Intended status: Standards Track November 22, 2017
Expires: May 26, 2018

Encapsulating Non-MPLS-BIER in UDP


Bit Index Explicit Replication (BIER) is a new multicast forwarding paradigm which doesn't require an explicit tree-building protocol nor intermediate routers to maintain any multicast state. BIER has two types of encapsulation formats: one is MPLS-BIER encapsulation, the other is non-MPLS-BIER encapsulation. This document proposes a mechanism of encapsulating non-MPLS-BIER packets over UDP tunnels.

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Table of Contents

1. Introduction

Bit Index Explicit Replication (BIER) [RFC8279] is a new multicast forwarding paradigm which doesn't require an explicit tree-building protocol nor intermediate routers to maintain any multicast state. As described in Section 6.9 of [RFC8279], a BFR may need to tunnel a BIER pacekt over a certain kind of tunnel, e.g., UDP tunnel.

[I-D.ietf-bier-mpls-encapsulation] defines two types of BIER encapsulation formats: one is MPLS-BIER encapsulation, the other is non-MPLS-BIER encapsulation. MPLS-BIER packets can be transported over UDP tunnels by using the MPLS-in-UDP encapsulation as described in [RFC7510] . This document proposes a mechanism of encapsulating non-MPLS BIER packets over UDP tunnels.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

2. Terminology

This memo makes use of the terms defined in [RFC8279]and [I-D.ietf-bier-mpls-encapsulation].

3. Encapsulation in UDP

      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
     |    Source Port = Entropy      |        Dest Port = TBD1       |
     |           UDP Length          |        UDP Checksum           |
     |                                                               |
     ~                    Non-MPLS BIER Packet                       ~
     |                                                               |
            Figure 1: Non-MPLS-BIER-in-UDP Encapsulation Format

Non-MPLS-BIER-in-UDP encapsulation format is shown as follows:

4. Processing Procedures

This Non-MPLS-BIER-in-UDP encapsulation causes non-MPLS BIER packets to be forwarded across an IP transit core via "UDP tunnels". While performing Non-MPLS-BIER-in-UDP encapsulation, an encapsulator would generate an entropy value and encode it in the Source Port field of the UDP header. The Destination Port field is set to a value (TBD1) allocated by IANA to indicate that the UDP tunnel payload is a Non-MPLS-BIER packet. Transit routers, upon receiving these UDP encapsulated non-MPLS-BIER packets, could balance these packets based on the hash of the five-tuple of UDP packets. Decapsulators receiving these UDP encapsulated Non-MPLS-BIER packets MUST decapsulate these packets by removing the UDP header and then forward them accordingly.

Similar to all other IP-based tunneling technologies, Non-MPLS-BIER-in-UDP encapsualtion introduces overheads and reduces the effective Maximum Transmision Unit (MTU) size. Non-MPLS-BIER-in-UDP encapsulation may also impact Time-to-Live (TTL) or Hop Count (HC) and Differentiated Services (DSCP). Hence, Non-MPLS-BIER-in-UDP MUST follow the corresponding procedures defined in [RFC2003].

Encapsulators MUST NOT fragment Non-MPLS-BIER packet, and when the outer IP header is IPv4, encapsulators MUST set the DF bit in the outer IPv4 header. It is strongly RECOMMENDED that IP transit core be configured to carry an MTU at least large enough to accommodate the added encapsulation headers. Meanwhile, it is strongly RECOMMENDED that Path MTU Discovery [RFC1191] [RFC1981] or Packetization Layer Path MTU Discovery (PLPMTUD) [RFC4821] is used to prevent or minimize fragmentation.

5. Congestion Considerations

As it is explicitly stated in the Application Statements (Section 1.2), this Non-MPLS-BIER-in-UDP encapsulation method MUST only be used within networks that are well-managed, therefore, congestion controll mechanism is not needed.

6. Applicability Statements

This Non-MPLS-BIER-in-UDP encapsulation technology MUST only be used within networks which are well-managed by a service provider and MUST NOT be used within the Internet. In the well-managed network, traffic is well-managed to avoid congestion and fragementation on encapsulated packets (i.e., Non-MPLS-BIER packets) are not needed.

7. Acknowledgements


8. IANA Considerations

One UDP destination port number indicating Non-MPLS-BIER needs to be allocated by IANA:

   Service Name: Non-MPLS-BIER-in-UDP Transport Protocol(s):UDP 
   Assignee: IESG <> 
   Contact: IETF Chair <>. 
   Description: Encapsulate Non-MPLS-BIER packets in UDP tunnels. 
   Reference: This document. 
   Port Number: TBD1 -- To be assigned by IANA.

One UDP destination port number indicating Non-MPLS-BIER with DTLS needs to be allocated by IANA:

   Service Name: Non-MPLS-BIER-in-UDP-with-DTLS 
   Transport Protocol(s): UDP 
   Assignee: IESG <> 
   Contact: IETF Chair <>. 
   Description: Encapsulate Non-MPLS-BIER packets in UDP tunnels with DTLS. 
   Reference: This document. 
   Port Number: TBD2 -- To be assigned by IANA.

9. Security Considerations

The security problems faced with the Non-MPLS-BIER-in-UDP tunnel are exactly the same as those faced with MPLS-in-UDP tunnel [RFC7510]. In other words, the Non-MPLS-BIER-in-UDP tunnel as defined in this document by itself cannot ensure the integrity and privacy of data packets being transported through the Non-MPLS-BIER-in-UDP tunnel and cannot enable the tunnel decapsulator to authenticate the tunnel encapsulator. In the case where any of the above security issues is concerned, the Non-MPLS-BIER-in-UDP tunnel SHOULD be secured with IPsec or DTLS. IPsec was designed as a network security mechanism and therefore it resides at the network layer. As such, if the tunnel is secured with IPsec, the UDP header would not be visible to intermediate routers anymore in either IPsec tunnel or transport mode. As a result, the meaning of adopting the Non-MPLS-BIER-in-UDP tunnel as an alternative to the Non-MPLS-BIER-in-GRE or Non-MPLS-BIER-in-IP tunnel is lost. By comparison, DTLS is better suited for application security and can better preserve network and transport layer protocol information. Specifically, if DTLS is used, the destination port of the UDP header will be filled with a value (TBD2) indicating Non-MPLS-BIER with DTLS and the source port can still be used as an entropy field for load-sharing purposes.

10. References

10.1. Normative References

[I-D.ietf-bier-mpls-encapsulation] Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J., Aldrin, S. and I. Meilik, "Encapsulation for Bit Index Explicit Replication in MPLS and non-MPLS Networks", Internet-Draft draft-ietf-bier-mpls-encapsulation-12, October 2017.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, DOI 10.17487/RFC1191, November 1990.
[RFC1981] McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 1996.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, DOI 10.17487/RFC2003, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007.
[RFC6935] Eubanks, M., Chimento, P. and M. Westerlund, "IPv6 and UDP Checksums for Tunneled Packets", RFC 6935, DOI 10.17487/RFC6935, April 2013.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement for the Use of IPv6 UDP Datagrams with Zero Checksums", RFC 6936, DOI 10.17487/RFC6936, April 2013.
[RFC8279] Wijnands, IJ., Rosen, E., Dolganow, A., Przygienda, T. and S. Aldrin, "Multicast Using Bit Index Explicit Replication (BIER)", RFC 8279, DOI 10.17487/RFC8279, November 2017.

10.2. Informative References

[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R. and D. Black, "Encapsulating MPLS in UDP", RFC 7510, DOI 10.17487/RFC7510, April 2015.

Author's Address

Xiaohu Xu Huawei EMail: