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Versions: (draft-mrw-trill-over-ip)  00 01 02 03         Standards Track
          04 05 06 07 08 09 10 11 12 13 14 15 16                        
INTERNET-DRAFT                                           Margaret Cullen
Intended Status: Proposed Standard                     Painless Security
Updates: 7177, 7178                                      Donald Eastlake
                                                            Mingui Zhang
                                                           Dacheng Zhang
Expires: April 30, 2017                                 October 31, 2016

      TRILL (Transparent Interconnection of Lots of Links) over IP

   The TRILL (Transparent Interconnection of Lots of Links) protocol
   supports both point-to-point and multi-access links and is designed
   so that a variety of link protocols can be used between TRILL switch
   ports. This document standardizes methods for encapsulating TRILL in
   IP (v4 or v6) so as to use IP as a TRILL link protocol in a unified
   TRILL campus. It updates RFC 7177 and updates RFC 7178.

Status of This Document

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Distribution of this document is unlimited. Comments should be sent
   to the authors or the TRILL Working Group mailing list

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
   Shadow Directories can be accessed at

Margaret Cullen, et al                                          [Page 1]

INTERNET-DRAFT                                             TRILL over IP

Table of Contents

      1. Introduction............................................4
      2. Terminology.............................................5

      3. Use Cases for TRILL over IP.............................6
      3.1 Remote Office Scenario.................................6
      3.2 IP Backbone Scenario...................................6
      3.3 Important Properties of the Scenarios..................6
      3.3.1 Security Requirements................................7
      3.3.2 Multicast Handling...................................7
      3.3.3 Neighbor Discovery...................................8

      4. TRILL Packet Formats....................................9
      4.1 General Packet Formats.................................9
      4.2 General TRILL Over IP Packet Formats..................10
      4.2.1 Without Security....................................10
      4.2.2 With Security.......................................10
      4.3 QoS Considerations....................................11
      4.4 Broadcast Links and Multicast Packets.................12
      4.5 TRILL Over IP IS-IS SubNetwork Point of Attachment....13

      5. TRILL over IP Encapsulation Formats....................14
      5.1 Encapsulation Considerations..........................14
      5.2 Encapsulation Agreement...............................15
      5.3 Broadcast Link Encapsulation Considerations...........16
      5.4 Native Encapsulation..................................17
      5.5 VXLAN Encapsulation...................................17
      5.6 Other Encapsulations..................................18

      6. Handling Multicast.....................................19

      7. Use of IPsec and IKEv2.................................20
      7.1 Keying................................................20
      7.1.1 Pairwise Keying.....................................20
      7.1.2 Group Keying........................................21
      7.2 Mandatory-to-Implement Algorithms.....................21

      8. Transport Considerations...............................22
      8.1 Congestion Considerations.............................22
      8.2 Recursive Ingress.....................................23
      8.3 Fat Flows.............................................24
      8.4 MTU Considerations....................................25
      8.5 Middlebox Considerations..............................25

      9. TRILL over IP Port Configuration.......................27
      9.1 Per IP Port Configuration.............................27
      9.2 Additional per IP Address Configuration...............27
      9.2.1 Native Multicast Configuration......................28
      9.2.2 Serial Unicast Configuration........................28

Margaret Cullen, et al                                          [Page 2]

INTERNET-DRAFT                                             TRILL over IP

Table of Contents (continued)

      9.2.3 Encapsulation Specific Configuration................28 UDP Source Port...................................28 VXLAN Configuration...............................29 Other Encapsulation Configuration.................29
      9.2.4 Security Configuration..............................29

      10. Security Considerations...............................30
      10.1 IPsec................................................30
      10.2 IS-IS Security.......................................31

      11. IANA Considerations...................................32
      11.1 Port Assignments.....................................32
      11.2 Multicast Address Assignments........................32
      11.3 Encapsulation Method Support Indication..............32

      Normative References......................................34
      Informative References....................................36

      Authors' Addresses........................................39

Margaret Cullen, et al                                          [Page 3]

INTERNET-DRAFT                                             TRILL over IP

1. Introduction

   TRILL switches (RBridges) are devices that implement the IETF TRILL
   protocol [RFC6325] [RFC7177] [RFC7780].  TRILL provides transparent
   forwarding of frames within an arbitrary network topology, using
   least cost paths for unicast traffic. It supports VLANs and Fine
   Grained Labels [RFC7172] as well as multipathing of unicast and
   multi-destination traffic. It uses IS-IS [IS-IS] [RFC7176] link state
   routing and encapsulation with a hop count.

   RBridge ports can communicate with each other over various protocols,
   such as Ethernet [RFC6325], pseudowires [RFC7173], or PPP [RFC6361].

   This document defines a method for RBridge ports to communicate over
   IP (v4 or v6). TRILL over IP allows RBridges to form a single TRILL
   campus, or multiple TRILL networks to be connected as a single TRILL
   campus via a TRILL over IP backbone.

   TRILL over IP connects RBridge ports using IPv4 or IPv6 as a
   transport in such a way that the ports with IP connectivity appear to
   TRILL to be connected by a single multi-access link. If more than two
   RBridge ports are connected via a single TRILL over IP link, any pair
   of them can communicate.

   To support the scenarios where RBridges are connected via IP paths
   (including those over the public Internet) that are not under the
   same administrative control as the TRILL campus and/or not physically
   secure, this document specifies the use of IPsec [RFC4301]
   Encapsulating Security Protocol (ESP) [RFC4303] for security.

   To dynamically select a mutually supported TRILL over IP
   encapsulation, normally one with good fast path hardware support, a
   method is provided for agreement between adjacent TRILL switch ports
   as to what encapsulation to use. Alternatively, where a common
   encapsulation is supported by the TRILL switch ports on a link, they
   can simply be configured to use that encapsulation.

   This document updates [RFC7177] and [RFC7178] as described in Section
   5 by making adjacency between TRILL over IP ports dependent on having
   a method of encapsulation in common and by redefining an interval of
   RBridge Channel protocol numbers to indicate encapsulation method
   support for TRILL over IP links.

Margaret Cullen, et al                                          [Page 4]

INTERNET-DRAFT                                             TRILL over IP

2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The following terms and acronyms have the meaning indicated:

   DRB - Designated RBridge. The RBridge (TRILL switch) elected to be in
         charge of certain aspects of a TRILL link that is not
         configured as a point-to-point link [RFC6325] [RFC7177].

   ENCAP Hdr - Encapsulation headers in use between the IP Header and
         the TRILL Header. See Section 5.

   ESP - IPsec Encapsulating Security Protocol [RFC4303].

   FGL - Fine Grained Label [RFC7172].

   Hdr - Used herein as an abbreviation for "Header".

   HKDF - Hash based Key Derivation Function [RFC5869].

   MTU - Maximum Transmission Unit.

   RBridge - Routing Bridge. An alternative term for a TRILL switch.

   SNPA - Sub-Network Point of Attachment.

   Sz - The campus wide MTU [RFC6325] [RFC7780].

   TRILL - Transparent Interconnection of Lots of Links or Tunneled
         Routing in the Link Layer. The protocol specified in [RFC6325],
         [RFC7177], [RFC7780], and related RFCs.

   TRILL switch - A device implementing the TRILL protocol.

   VNI - Virtual Network Identifier. In VXLAN [RFC7348], the VXLAN
         Network Identifier.

Margaret Cullen, et al                                          [Page 5]

INTERNET-DRAFT                                             TRILL over IP

3. Use Cases for TRILL over IP

   This section introduces two application scenarios (a remote office
   scenario and an IP backbone scenario) which cover typical situations
   where network administrators may choose to use TRILL over an IP
   network to connect TRILL switches.

3.1 Remote Office Scenario

   In the Remote Office Scenario, a remote TRILL network is connected to
   a TRILL campus across a multihop IP network, such as the public
   Internet. The TRILL network in the remote office becomes a part of
   TRILL campus, and nodes in the remote office can be attached to the
   same VLANs or Fine Grained Labels [RFC7172] as local campus nodes. In
   many cases, a remote office may be attached to the TRILL campus by a
   single pair of RBridges, one on the campus end, and the other in the
   remote office. In this use case, the TRILL over IP link will often
   cross logical and physical IP networks that do not support TRILL, and
   are not under the same administrative control as the TRILL campus.

3.2 IP Backbone Scenario

   In the IP Backbone Scenario, TRILL over IP is used to connect a
   number of TRILL networks to form a single TRILL campus. For example,
   a TRILL over IP backbone could be used to connect multiple TRILL
   networks on different floors of a large building, or to connect TRILL
   networks in separate buildings of a multi-building site. In this use
   case, there may often be several TRILL switches on a single TRILL
   over IP link, and the IP link(s) used by TRILL over IP are typically
   under the same administrative control as the rest of the TRILL

3.3 Important Properties of the Scenarios

   There are a number of differences between the above two application
   scenarios, some of which drive features of this specification. These
   differences are especially pertinent to the security requirements of
   the solution, how multicast data frames are handled, and how the
   TRILL switch ports discover each other.

Margaret Cullen, et al                                          [Page 6]

INTERNET-DRAFT                                             TRILL over IP

3.3.1 Security Requirements

   In the IP Backbone Scenario, TRILL over IP is used between a number
   of RBridge ports, on a network link that is in the same
   administrative control as the remainder of the TRILL campus. While it
   is desirable in this scenario to prevent the association of
   unauthorized RBridges, this can be accomplished using existing IS-IS
   security mechanisms. There may be no need to protect the data
   traffic, beyond any protections that are already in place on the
   local network.

   In the Remote Office Scenario, TRILL over IP may run over a network
   that is not under the same administrative control as the TRILL
   network. Nodes on the network may think that they are sending traffic
   locally, while that traffic is actually being sent, in an IP tunnel,
   over the public Internet. It is necessary in this scenario to protect
   the integrity and confidentiality of user traffic, as well as
   ensuring that no unauthorized RBridges can gain access to the RBridge
   campus.  The issues of protecting integrity and confidentiality of
   user traffic are addressed by using IPsec for both TRILL IS-IS and
   TRILL Data packets between RBridges in this scenario.

3.3.2 Multicast Handling

   In the IP Backbone scenario, native IP multicast may be supported on
   the TRILL over IP link. If so, it can be used to send TRILL IS-IS and
   multicast data packets, as discussed later in this document.
   Alternatively, multi-destination packets can be transmitted serially
   by IP unicast to the intended recipients.

   In the Remote Office Scenario there will often be only one pair of
   RBridges connecting a given site and, even when multiple RBridges are
   used to connect a Remote Office to the TRILL campus, the intervening
   network may not provide reliable (or any) multicast connectivity.
   Issues such as complex key management also make it difficult to
   provide strong data integrity and confidentiality protections for
   multicast traffic. For all of these reasons, the connections between
   local and remote RBridges will commonly be treated like point-to-
   point links, and all TRILL IS-IS control messages and multicast data
   packets that are transmitted between the Remote Office and the TRILL
   campus will be serially transmitted by IP unicast, as discussed later
   in this document.

Margaret Cullen, et al                                          [Page 7]

INTERNET-DRAFT                                             TRILL over IP

3.3.3 Neighbor Discovery

   In the IP Backbone Scenario, TRILL switches that use TRILL over IP
   can use the normal TRILL IS-IS Hello mechanisms to discover the
   existence of other TRILL switches on the link [RFC7177], and to
   establish authenticated communication with them.

   In the Remote Office Scenario, an IPsec session will need to be
   established before TRILL IS-IS traffic can be exchanged, as discussed
   below. In this case, one end will need to be configured to establish
   a IPSEC session with the other. This will typically be accomplished
   by configuring the TRILL switch or a border device at a Remote Office
   to initiate an IPsec session and subsequent TRILL exchanges with a
   TRILL over IP-enabled RBridge attached to the TRILL campus.

Margaret Cullen, et al                                          [Page 8]

INTERNET-DRAFT                                             TRILL over IP

4. TRILL Packet Formats

   To support TRILL two types of TRILL packets are transmitted between
   TRILL switches: TRILL Data packets and TRILL IS-IS packets.

   Section 4.1 describes general TRILL packet formats for data and IS-IS
   independent of link technology. Section 4.2 specifies general TRILL
   over IP packet formats including IPsec ESP encapsulation. Section 4.3
   provides QoS Considerations.  Section 4.4 discusses broadcast links
   and multicast packets. And Section 4.5 provides TRILL IS-IS Hello
   SubNetwork Point of Attachment (SNPA) considerations for TRILL over

4.1 General Packet Formats

   The on-the-wire form of a TRILL Data packet in transit between two
   neighboring TRILL switch ports is as shown below:

      |  Link Header   |  TRILL   |  Native Frame  |   Link    |
      | for TRILL Data |  Header  |     Payload    |  Trailer  |

   The encapsulated Native Frame Payload is similar to an Ethernet frame
   with a VLAN tag or Fine Grained Label [RFC7172] but with no trailing
   Frame Check Sequence (FCS).

   TRILL IS-IS packets are formatted on-the-wire as follows:

      |   Link Header   |  TRILL IS-IS  |   Link    |
      | for TRILL IS-IS |    Payload    |  Trailer  |

   The Link Header and Link Trailer in these formats depend on the
   specific link technology. The Link Header contains one or more fields
   that distinguish TRILL Data from TRILL IS-IS. For example, over
   Ethernet, the Link Header for TRILL Data ends with the TRILL
   Ethertype while the Link Header for TRILL IS-IS ends with the L2-IS-
   IS Ethertype; on the other hand, over PPP, there are no Ethertypes in
   the Link Header but PPP protocol code points are included that
   distinguish TRILL Data from TRILL IS-IS.

Margaret Cullen, et al                                          [Page 9]

INTERNET-DRAFT                                             TRILL over IP

4.2 General TRILL Over IP Packet Formats

   In TRILL over IP, we use an IP (v4 or v6) header followed by an
   encapsulation header as the link header. (On the wire, the IP header
   will normally be preceded by the lower layer header of a protocol
   that is carrying IP; however, this does not concern us at the level
   of this document.)

   There are multiple IP based encapsulations usable for TRILL over IP
   that differ in exactly what appears after the IP header and before
   the TRILL Header or the TRILL IS-IS Payload. These encapsulations are
   further detailed in Section 5. In the general specification below,
   those encapsulation fields will be represented as "ENCAP Hdr".

4.2.1 Without Security

   When TRILL over IP link security is not being used, a TRILL over IP
   packet on the wire looks like one of the following:

      TRILL Data Packet
        |   IP    | ENCAP Hdr | TRILL   |   Native frame   |
        | Header  | for Data  | Header  |     Payload      |
        <--- link header ---->

      TRILL IS-IS Packet
        |   IP    | ENCAP Hdr |   TRILL IS-IS   |
        | Header  | for IS-IS |     Payload     |
        <--- link header ---->

   As discussed above and further specified in Section 5, the ENCAP Hdr
   indicates whether the packet is TRILL Data or IS-IS.

4.2.2 With Security

   TRILL over IP link security uses IPsec Encapsulating Security
   Protocol (ESP) in tunnel mode [RFC4303]. Since TRILL over IP always
   starts with an IP Header (on the wire this appears after any lower
   layer header that might be required), the modifications for IPsec are
   independent of the TRILL over IP ENCAP Hdr that occurs after that IP
   Header. The resulting packet formats are as follows for IPv4 and

Margaret Cullen, et al                                         [Page 10]

INTERNET-DRAFT                                             TRILL over IP

    With IPv4:
   | new IP Hdr  | ESP | TRILL IP Hdr | ENCAP Hdr | ESP   |ESP|
   |(any options)| Hdr | (any options)| + payload |Trailer|ICV|
                       |<---------- encryption ---------->|
                 |<-------------- integrity ------------->|

    With IPv6:
   | new  |new ext| ESP | orig |orig ext| ENCAP Hdr | ESP   |ESP|
   |IP Hdr| Hdrs  | Hdr |IP Hdr| Hdrs   | + payload |Trailer|ICV|
                        |<----------- encryption ---------->|
                  |<--------------- integrity ------------->|

   As shown above, IP Header options are considered part of the IPv4
   Header but are extensions ("ext") of the IPv6 Header. For further
   information on the IPsec ESP Hdr, Trailer, and ICV, see [RFC4303] and
   Section 7 below. "ENCAP Hdr + payload" is the encapsulation header
   (Section 5) and TRILL data or the encapsulation header and IS-IS
   payload, that is, the material after the IP Header in the diagram in
   Section 4.2.1.

   This architecture permits the ESP tunnel end point to be separated
   from the TRILL over IP RBridge port (see, for example, Section 1.1.3
   of [RFC7296]).

4.3 QoS Considerations

   In IP, QoS handling is indicated by the Differentiated Services Code
   Point (DSCP [RFC2474] [RFC3168]) in the IP Header.  The former Type
   of Service (TOS) octet in the IPv4 Header and the Traffic Class octet
   in the IPv6 Header has been divided as shown in the following diagram
   adapted from [RFC3168]. (TRILL support of ECN is beyond the scope of
   this document. See [TRILLECN].)

            0     1     2     3     4     5     6     7
         |          DSCP FIELD               | ECN FIELD |

           DSCP: Differentiated Services Codepoint
           ECN:  Explicit Congestion Notification

   Within a TRILL switch, priority is indicated by configuration for
   TRILL IS-IS packets and for TRILL Data packets by a three bit (0
   through 7) priority field and a Drop Eligibility Indicator bit (see

Margaret Cullen, et al                                         [Page 11]

INTERNET-DRAFT                                             TRILL over IP

   Sections 8.2 and 7 of [RFC7780]). (Typically TRILL IS-IS is
   configured to use the highest two priorities depending on the IS-IS
   PDU.) The priority affects queuing behavior at TRILL switch ports and
   may be encoded into the link header, particularly if there could be
   priority sensitive devices within the link. For example, if the link
   is a bridged LAN, it is commonly encoded into an Outer.VLAN tag's
   priority and DEI fields.

   TRILL over IP implementations MUST support setting the DSCP value in
   the outer IP Header of TRILL packets they send by mapping the TRILL
   priority and DEI to the DSCP. They MAY support, for a TRILL Data
   packet where the native frame payload is an IP packet, mapping the
   DSCP in this inner IP packet to the outer IP Header with the default
   for that mapping being to copy the DSCP without change.

   The default TRILL priority and DEI to DSCP mapping, which may be
   configured per TRILL over IP port, is an follows. Note that the DEI
   value does not affect the default mapping and, to provide a
   potentially lower priority service than the default priority 0,
   priority 1 is considered lower priority than 0. So the priority
   sequence from lower to higher priority is 1, 0, 2, 3, 4, 5, 6, 7.

      TRILL Priority  DEI  DSCP Field (Binary/decimal)
      --------------  ---  -----------------------------
                  0   0/1  001000 / 8
                  1   0/1  000000 / 0
                  2   0/1  010000 / 16
                  3   0/1  011000 / 24
                  4   0/1  100000 / 32
                  5   0/1  101000 / 40
                  6   0/1  110000 / 48
                  7   0/1  111000 / 56

4.4 Broadcast Links and Multicast Packets

   TRILL supports broadcast links. These are links to which more than
   two TRILL switch ports can be attached and where a packet can be
   broadcast or multicast from a port to all or a subset of the other
   ports on the link as well as unicast to a specific other port on the

   As specified in [RFC6325], TRILL Data packets being forwarded between
   TRILL switches can be unicast on a link to a specific TRILL switch
   port or multicast on a link to all TRILL switch ports. TRILL IS-IS
   packets are always multicast to all other TRILL switches on the link
   except for IS-IS MTU PDUs, which may be unicast [RFC7177]. This
   distinction is not significant if the link is inherently point-to-
   point, such as a PPP link; however, on a broadcast link there will be

Margaret Cullen, et al                                         [Page 12]

INTERNET-DRAFT                                             TRILL over IP

   a packet outer link address that will be unicast or multicast as
   appropriate. For example, over Ethernet links, the Ethernet multicast
   addresses All-RBridges and All-IS-IS-RBridges are used for
   multicasting TRILL Data and TRILL IS-IS respectively. For details on
   TRILL over IP handling of multicast, see Section 6.

4.5 TRILL Over IP IS-IS SubNetwork Point of Attachment

   IS-IS routers, such as TRILL switches, establish adjacency through
   the exchange of Hello PDUs on a link [IS-IS] [RFC7177]. The Hellos
   transmitted out a port indicate what neighbor ports that port can see
   on the link by listing what IS-IS refers to as the neighbor port's
   SubNetwork Point of Attachment (SNPA). (For an Ethernet link, which
   may be a bridged network, the SNPA is the port MAC address.)

   In TRILL Hello PDUs on a TRILL over IP link, the IP addresses of the
   IP ports connected to that link are their actual SNPA (SubNetwork
   Point of Attachment [IS-IS]) addresses and, for IPv6, the 16-byte
   IPv6 address is used as the SNPA; however, for easy in re-using code
   designed for the common case of 48-bit SNPAs, in TRILL over IPv4 a
   48-bit synthetic SNPA that looks like a unicast MAC address is
   constructed for use in the SNPA field of TRILL Neighbor TLVs
   [RFC7176] [RFC7177] in such Hellos. This synthetic SNPA is derived
   from the port IPv4 address is as follows:

                           1 1 1 1 1 1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      |  0xFE         |  0x00         |
      |  IPv4 upper half              |
      |  IPv4 lower half              |

   This synthetic SNPA (MAC) address has the local (0x02) bit on in the
   first byte and so cannot conflict with any globally unique 48-bit
   Ethernet MAC. However, when TRILL operates on an IP link, TRILL sees
   only IP addresses on that link, not MAC stations, even if the TRILL
   over IP Link is being carried over Ethernet. Therefore conflict on
   the link between a real MAC address and a TRILL over IP synthetic
   SNPA (MAC) address would be impossible in any case.

Margaret Cullen, et al                                         [Page 13]

INTERNET-DRAFT                                             TRILL over IP

5. TRILL over IP Encapsulation Formats

   There are a variety of TRILL over IP encapsulation formats possible.
   By default TRILL over IP adopts a hybrid encapsulation approach.

   There is one format, called "native encapsulation" that MUST be
   implemented. Although native encapsulation does not typically have
   good fast path support, as a lowest common denominator it can be used
   by low bandwidth control traffic to determine a preferred
   encapsulation with better performance. In particular, by default, all
   TRILL IS-IS Hellos are sent using native encapsulation and those
   Hellos are used to determine the encapsulation used for all TRILL
   Data packets and all other TRILL IS-IS PDUs (with the exception of
   IS-IS MTU-probe and MTU-ack PDUs used to establish adjacency).

   Alternatively, the network operator can pre-configure a TRILL over IP
   port to use a particular encapsulation chosen for their particular
   network's needs and port capabilities. That encapsulation is then
   used for all TRILL Data and IS-IS packets on ports so configured.
   This is expected to frequently be the case for a managed campus of
   TRILL switches.

   Section 5.1 discusses general consideration for the TRILL over IP
   encapsulation format.  Section 5.2 discusses encapsulation agreement.
   Section 5.3 discusses broadcast link encapsulation considerations.
   The subsequent subsections discuss particular encapsulations.

5.1 Encapsulation Considerations

   An encapsulation must provide a method to distinguish TRILL Data
   packets and TRILL IS-IS packets, or it is not useful for TRILL. In
   addition, the following criteria can be helpful is choosing between
   different encapsulations:

   a) Fast path support - For most applications, it is highly desirable
      to be able to encapsulate/decapsulate TRILL over IP at line speed
      so a format where existing or anticipated fast path hardware can
      do that is best. This is commonly the dominant consideration.

   b) Ease of multi-pathing - The IP path between TRILL over IP ports
      may include equal cost multipath routes internal to the IP link so
      a method of encapsulation that provides variable fields available
      for existing or anticipated fast path hardware multi-pathing is

   c) Robust fragmentation and re-assembly - The MTU of the IP link may
      require fragmentation in which case an encapsulation with robust
      fragmentation and re-assembly is important. There are known

Margaret Cullen, et al                                         [Page 14]

INTERNET-DRAFT                                             TRILL over IP

      problems with IPv4 fragmentation and re-assembly [RFC6864] which
      generally do not apply to IPv6. Some encapsulations can fix these
      problems but the encapsulations specified in this document do not.
      Therefore, if fragmentation is anticipated with the encapsulations
      specified in this document, the use of IPv6 is RECOMMENDED.

   d) Checksum strength - Depending on the particular circumstances of
      the TRILL over IP link, a checksum provided by the encapsulation
      may be a significant factor. Use of IPsec can also provide a
      strong integrity check.

5.2 Encapsulation Agreement

   TRILL Hellos sent out a TRILL over IP port indicate the
   encapsulations that port is willing to support through a mechanism
   initially specified in [RFC7178] and [RFC7176] that is hereby
   extended.  Specifically, RBridge Channel Protocol numbers 0xFD0
   through 0xFF7 are redefined to be link technology dependent flags
   that, for TRILL over IP, indicate support for different
   encapsulations, allowing support for up to 40 encapsulations to be
   specified.  Support for an encapsulation is indicated in the Hello
   PDU in the same way that support for an RBridge Channel was
   indicated. (See also section 11.3.)  "Support" indicates willingness
   to use that encapsulation for TRILL Data and TRILL IS-IS packets
   (although TRILL IS-IS Hellos are still sent in native encapsulation
   by default unless the port is configured to always use some other

   If, in a TRILL Hello on a TRILL over IP link, support is not
   indicated for any encapsulation, then the port from which it was sent
   is assumed to support only native encapsulation (see Section 5.4).

   An adjacency is formed between two TRILL over IP ports if the
   intersection of the sets of encapsulation methods they support is not
   null. If that intersection is null, then no adjacency is formed. In
   particular, for a TRILL over IP link, the adjacency state machine
   MUST NOT advance to the Report state unless the ports share an
   encapsulation [RFC7177]. If no encapsulation is shared, the adjacency
   state machine remains in the state from which it would otherwise have
   transitioned to the Report state.

   If any TRILL over IP packet, other than an IS-IS Hello or MTU PDU in
   native encapsulation, is received in an encapsulation for which
   support is not being indicated by the receiver, that packet MUST be
   discarded (see Section 5.3).

   If there are two or more encapsulations in common between two
   adjacent ports for unicast or the set of adjacent ports for

Margaret Cullen, et al                                         [Page 15]

INTERNET-DRAFT                                             TRILL over IP

   multicast, a transmitter is free to choose whichever of the
   encapsulations it wishes to use. Thus transmissions between adjacent
   ports P1 and P2 could use different encapsulations depending on which
   port is transmitting and which is receiving.

   It is expected to be the normal case in a well configured network
   that all the TRILL over IP ports connected to an IP link (i.e., an IP
   network) that are intended to communicate with each other will
   support the same encapsulation(s).

5.3 Broadcast Link Encapsulation Considerations

   To properly handle TRILL protocol packets on a TRILL over IP link in
   the general case, either native IP multicast mode is used on that
   link or multicast must be simulated using serial IP unicast, as
   discussed in Section 6. (Of course, if the IP link happens to
   actually be point-to-point no special provision is needed for
   handling IP multicast addressed packets.)

   It is possible for the Hellos from a TRILL over IP port P1 to
   establish adjacency with multiple other TRILL over IP ports (P2, P3,
   ...) on a broadcast link. In a well configured network one would
   expect all of the IP ports involved to support the same
   encapsulation(s); but, for example, if P1 supports multiple
   encapsulations, it is possible that P2 and P3, do not have an
   encapsulation in common that is supported by P1. [IS-IS] can handle
   such non-transitive adjacencies that are reported as specified in
   [RFC7177]. This is generally done, albeit with reduced efficiency, by
   forwarding through the designated RBridge (router) on the link. Thus
   it is RECOMENDED that all TRILL over IP ports on an IP link be
   configured to support one encapsulation in common that has good fast
   path support.

   If serial IP unicast is being used by P1, it can use different
   encapsulations for different transmissions.

   If native IP multicast is available for use by P1, it can send one
   transmission per encapsulation method by which it has a disjoint set
   of adjacencies on the link. If the transmitting port has adjacencies
   with overlapping sets of ports that are adjacent using different
   encapsulations, use of native multicast with different encapsulations
   may result in packet duplication. It would always be possible to use
   native IP multicast for one encapsulation for which the transmitting
   port has adjacencies, perhaps the encapsulation for which it has the
   largest number of adjacencies, and serially unicast to other
   receivers. These considerations are the reason that a TRILL over IP
   port MUST discard any packet received with an encapsulation for which
   it has not established an adjacency with the receiver. Otherwise,

Margaret Cullen, et al                                         [Page 16]

INTERNET-DRAFT                                             TRILL over IP

   packets would be further duplicated.

5.4 Native Encapsulation

   The mandatory to implement "native encapsulation" format of a TRILL
   over IP packet, when used without security, is TRILL over UDP as
   shown below. This provides simple and direct access by TRILL to the
   native datagram service of IP.

               | IP       | UDP    |  TRILL                |
               | Header   | Header |  Payload              |

   Where the UDP Header is as follows:

       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      |      Destination Port         |
      |           UDP Length          |        UDP Checksum           |
      |  TRILL Payload ...

      Source Port - see Section 8.3

      Destination Port - indicates TRILL Data or IS-IS, see Section

      UDP Length - as specified in [RFC0768]

      UDP Checksum - as specified in [RFC0768]

   The TRILL Payload starts with the TRILL Header (not including the
   TRILL Ethertype) for TRILL Data packets and starts with the 0x83
   Intradomain Routeing Protocol Discriminator byte (thus not including
   the L2-IS-IS Ethertype) for TRILL IS-IS packets.

5.5 VXLAN Encapsulation

   VXLAN [RFC7348] IP encapsulation of TRILL looks, on the wire, like
   TRILL over Ethernet over VXLAN over UDP over IP.

Margaret Cullen, et al                                         [Page 17]

INTERNET-DRAFT                                             TRILL over IP

            | IP     | UDP    | VXLAN  | Ethernet | TRILL     |
            | Header | Header | Header | Header   | Payload   |

   The outer UDP uses a destination port number indicating VXLAN and the
   outer UDP source port MAY be used for entropy as with native
   encapsulation (see Section 8.3). The VXLAN header after the outer UDP
   header adds a 24 bit Virtual Network Identifier (VNI). The Ethernet
   header after the VXLAN header and before the TRILL header consists of
   source MAC address, destination MAC address, and Ethertype. The
   Ethertype distinguishes TRILL Data from TRILL IS-IS. The destination
   and source MAC addresses in this Ethernet header are not used.

   A TRILL over IP port using VXLAN encapsulation by default uses a VNI
   of 1 for TRILL IS-IS traffic and a VNI of 2 for TRILL data traffic
   but can be configured as described in Section to use some
   other fixed VNIs or to map from VLAN/FGL to VNI.

5.6 Other Encapsulations

   It is anticipated that additional TRILL over IP encapsulations will
   be specified in future documents and allocated a link technology
   specific flag bit as per Section 11.3. A primary consideration for
   whether it is worth the effort to specify use of an encapsulation by
   TRILL over IP is whether it has good existing or anticipated fast
   path support.

Margaret Cullen, et al                                         [Page 18]

INTERNET-DRAFT                                             TRILL over IP

6. Handling Multicast

   By default, both TRILL IS-IS packets and multi-destination TRILL Data
   packets are sent to an All-RBridges IPv4 or IPv6 IP multicast Address
   as appropriate (see Section 11.2); however, a TRILL over IP port may
   be configured (see Section 9) to use a different multicast address or
   to use serial IP unicast with a list of one or more unicast IP
   addresses of other TRILL over IP ports to which multi-destination
   packets are sent. In the serial unicast case the outer IP header of
   each copy of the packet sent shows an IP unicast destination address
   even through the TRILL header has the M bit set to one to indicate
   multi-destination. Serial unicast configuration is necessary if the
   TRILL over IP port is connected to an IP network that does not
   support IP multicast. In any case, unicast TRILL packets (those with
   the M bit in the TRILL Header set to zero) are sent by unicast IP.

   Even if a TRILL over IP port is configured to send multi-destination
   packets with serial unicast, it MUST be prepared to receive IP
   multicast TRILL packets.  All TRILL over IP ports default to
   periodically transmitting appropriate IGMP (IPv4 [RFC3376]) or MLD
   (IPv6 [RFC2710]) packets, so that the TRILL multicast IP traffic can
   be sent to them, but may be configured not to do so.

   Although TRILL fully supports broadcast links with more than 2
   RBridges connected to the link there may be good reasons for
   configuring TRILL over IP ports to use serial unicast even where
   native IP multicast is available. Use of serial unicast provides the
   network manager with more precise control over adjacencies and how
   TRILL over IP links will be formed in an IP network. In some
   networks, unicast is more reliable than multicast. If multiple point-
   to-point TRILL over IP connections between two parts of a TRILL
   campus are configured, TRILL will in any case spread traffic across
   them, treating them as parallel links, and appropriately fail over
   traffic if a link fails or incorporate a new link that comes up.

Margaret Cullen, et al                                         [Page 19]

INTERNET-DRAFT                                             TRILL over IP

7. Use of IPsec and IKEv2

   All TRILL switches (RBridges) that support TRILL over IP MUST
   implement IPsec [RFC4301] and support the use of IPsec Encapsulating
   Security Protocol (ESP [RFC4303]) in tunnel mode to secure both TRILL
   IS-IS and TRILL Data packets. When IPsec is used to secure a TRILL
   over IP link and no IS-IS security is enabled, the IPsec session MUST
   be fully established before any TRILL IS-IS or data packets are
   exchanged. When there is IS-IS security [RFC5310] provided,
   implementers SHOULD use IS-IS security to protect TRILL IS-IS
   packets. However, in this case, the IPsec session still MUST be fully
   established before any TRILL Data packets transmission, since IS-IS
   security does not provide any protection to data packets, and SHOULD
   be fully established before any TRILL IS-IS packet transmission other
   than IS-IS Hello or MTU PDUs.

   All RBridges that support TRILL over IP MUST implement the Internet
   Key Exchange Protocol version 2 (IKEv2) for automated key management.

7.1 Keying

   The following subsections discuss pairwise and group keying for TRILL
   over IP IPsec.

7.1.1 Pairwise Keying

   When IS-IS security is in use, IKEv2 SHOULD use a pre-shared key that
   incorporates the IS-IS shared key in order to bind the TRILL data
   session to the IS-IS session.  The pre-shared key that will be used
   for IKEv2 exchanges for TRILL over IP is determined as follows:

      HKDF-Expand-SHA256 ( IS-IS-key,
         "TRILL IP" | P1-System-ID | P1-Port | P2-System-ID | P2-Port )

   In the above "|" indicates concatenation, HKDF is as in [RFC5869],
   SHA256 is as in [RFC6234], and "TRILL IP" is the eight byte US ASCII
   [RFC0020] string indicated. "IS-IS-key" is an IS-IS key usable for
   IS-IS security of link local IS-IS PDUs such as Hello, CSNP, and
   PSNP. This SHOULD be a link scope IS-IS key. P1-System-ID and
   P2-System ID are the six byte System IDs of the two TRILL RBridges,
   and P1-Port and P2-Port are the TRILL Port IDs [RFC6325] of the ports
   in use on each end. System IDs are guaranteed to be unique within the
   TRILL campus.  Both of the RBridges involved treat the larger
   magnitude System ID, comparing System IDs as unsigned integers, as P1
   and the smaller as P2 so both will derive the same key.

Margaret Cullen, et al                                         [Page 20]

INTERNET-DRAFT                                             TRILL over IP

   With [RFC5310] there could be multiple keys identified with 16-bit
   key IDs. The key ID when an IS-IS key is in use is transmitted in an
   IKEv2 ID_KEY_ID identity field [RFC7296] with Identification Data
   length of 2 bytes (Payload Length 6 bytes). The Key ID of the IS-IS-
   key is used to identify the IKEv2 shared secret derived as above that
   is actually used. ID_KEY_ID identity field(s) of other lengths MAY
   occur but their use is beyond the scope of this document.

   The IS-IS-shared key from which the IKEv2 shared secret is derived
   might expire and be updated as described in [RFC5310].  The IKEv2
   pre-shared keys derived from an IS-IS shared key MUST expire within a
   lifetime no longer than the IS-IS-shared key from which they were
   derived.  When the IKEv2 shared secret key expires, or earlier, the
   IKEv2 Security Association must be rekeyed using a new shared secret
   derived from a new IS-IS shared key.

   IKEv2 with certificate based security MAY be used but details of
   certificate contents and use policy for this application of IKEv2 are
   beyond the scope of this document.

7.1.2 Group Keying

   In the case of a TRILL over IP port configured as point-to-point (see
   Section of [RFC6325]), there is no group keying and the
   pairwise keying determined as in Section 7.1.1 is used for multi-
   destination TRILL traffic, which is unicast.

   In the case of a TRILL over IP port configured as broadcast but where
   the port is configured to use serial unicast (see Section 8), there
   is no group keying and the pairwise keying determined as in Section
   7.1.1 is used for multi-destination TRILL traffic, which is unicast.

   The case of a TRILL over IP port configured as broadcast and using
   native multicast is beyond the scope of this document. For security
   as provided in this document, multicast is handled via serial

7.2 Mandatory-to-Implement Algorithms

   All RBridges that support TRILL over IP MUST implement IPsec ESP
   [RFC4303] in tunnel mode. The implementation requirements for ESP
   cryptographic algorithms are as specified for IPsec. That
   specification is currently [RFC7321].

Margaret Cullen, et al                                         [Page 21]

INTERNET-DRAFT                                             TRILL over IP

8. Transport Considerations

   This section discusses a variety of important transport

8.1 Congestion Considerations

   Section 3.1.3 of [RFC5405] discussed the congestion implications of
   UDP tunnels. As discussed in [RFC5405], because other flows can share
   the path with one or more UDP tunnels, congestion control [RFC2914]
   needs to be considered.

   The default initial determination of the TRILL over IP encapsulation
   to be used through the exchange of TRILL IS-IS Hellos is a low
   bandwidth process. Hellos are not permitted to be sent any more often
   than once per second, and so are very unlikely to cause congestion.

   One motivation for including UDP in a TRILL encapsulation is to
   improve the use of multipath (such as ECMP) in cases where traffic is
   to traverse routers which are able to hash on UDP Port and IP
   address. In many cases this may reduce the occurrence of congestion
   and improve usage of available network capacity. However, it is also
   necessary to ensure that the network, including applications that use
   the network, responds appropriately in more difficult cases, such as
   when link or equipment failures have reduced the available capacity.

   The impact of congestion must be considered both in terms of the
   effect on the rest of the network of a UDP tunnel that is consuming
   excessive capacity, and in terms of the effect on the flows using the
   UDP tunnels. The potential impact of congestion from a UDP tunnel
   depends upon what sort of traffic is carried over the tunnel, as well
   as the path of the tunnel.

   TRILL is used to carry a wide range of traffic. In many cases TRILL
   is used to carry IP traffic. IP traffic is generally assumed to be
   congestion controlled, and thus a tunnel carrying general IP traffic
   (as might be expected to be carried across the Internet) generally
   does not need additional congestion control mechanisms. As specified
   in [RFC5405]:

      "IP-based traffic is generally assumed to be congestion-
      controlled, i.e., it is assumed that the transport protocols
      generating IP-based traffic at the sender already employ
      mechanisms that are sufficient to address congestion on the path.
      Consequently, a tunnel carrying IP-based traffic should already
      interact appropriately with other traffic sharing the path, and
      specific congestion control mechanisms for the tunnel are not

Margaret Cullen, et al                                         [Page 22]

INTERNET-DRAFT                                             TRILL over IP

   For this reason, where TRILL is sent using UDP and used to carry IP
   traffic that is known to be congestion controlled, the UDP paths MAY
   be used across any combination of a single or cooperating service
   providers or across the general Internet.

   However, TRILL is also used to carry traffic that is not necessarily
   congestion controlled. For example, TRILL may be used to carry
   traffic where specific bandwidth guarantees are provided.

   In such cases congestion may be avoided by careful provisioning of
   the network and/or by rate limiting of user data traffic. Where TRILL
   is carried, directly or indirectly, over UDP over IP, the identity of
   each individual TRILL flow is in general lost.

   For this reason, where the TRILL traffic is not congestion
   controlled, TRILL over UDP/IP MUST only be used within a single
   service provider that utilizes careful provisioning (e.g., rate
   limiting at the entries of the network while over-provisioning
   network capacity) to ensure against congestion, or within a limited
   number of service providers who closely cooperate in order to jointly
   provide this same careful provisioning. As such, TRILL over UDP/IP
   MUST NOT be used as a general TRILL encapsulation over the general
   Internet, or over non-cooperating service providers, to carry traffic
   that is not congestion-controlled.

   Measures SHOULD be taken to prevent non-congestion-controlled TRILL
   over UDP/IP traffic from "escaping" to the general Internet, for
   example the following:

   a. Physical or logical isolation of the TRILL over IP links from the
      general Internet.

   b. Deployment of packet filters that block the UDP ports assigned for

   c. Imposition of restrictions on TRILL over UDP/IP traffic by
      software tools used to set up TRILL over UDP paths between
      specific end systems (as might be used within a single data

   d. Use of a "Managed Circuit Breaker" for the TRILL traffic as
      described in [circuit-breaker].

8.2 Recursive Ingress

   TRILL is specified to transport data to and from end stations over
   Ethernet and IP is frequently transported over Ethernet. Thus, an end
   station native data Ethernet frame "EF" might get TRILL ingressed to

Margaret Cullen, et al                                         [Page 23]

INTERNET-DRAFT                                             TRILL over IP

   TRILL(EF) that was subsequently sent to a next hop RBridge out a
   TRILL over IP over Ethernet port resulting in a packet on the wire of
   the form Ethernet(IP(TRILL(EF))).  There is a risk of such a packet
   being re-ingressed by the same TRILL campus, due to physical or
   logical misconfiguration, looping round, being further re-ingressed,
   and so on. (Or this might occur through a cycle of TRILL campuses.)
   The packet would get discarded if it got too large but if
   fragmentation is enabled, it would just keep getting split into
   fragments that would continue to loop and grow and re-fragment until
   the path was saturated with junk and packets were being discarded due
   to queue overflow. The TRILL Header TTL would provide no protection
   because each TRILL ingress adds a new TRILL header with a new TTL.

   To protect against this scenario, a TRILL over IP port MUST, by
   default, test whether a TRILL packet it is about to transmit appears
   to be a TRILL ingress of a TRILL over IP over Ethernet packet. That
   is, is it of the form TRILL(Ethernet(IP(TRILL(...)))? If so, the
   default action of the TRILL over IP output port is to discard the
   packet rather than transmit it. However, there are cases where some
   level of nested ingress is desired so it MUST be possible to
   configure the port to allow such packets.

8.3 Fat Flows

   For the purpose of load balancing, it is worthwhile to consider how
   to transport TRILL packets over any Equal Cost Multiple Paths (ECMPs)
   existing internal to the IP path between TRILL over IP ports.

   The ECMP election for the IP traffic could be based, for example with
   IPv4, on the quintuple of the outer IP header { Source IP,
   Destination IP, Source Port, Destination Port, and IP protocol }.
   Such tuples, however, could be exactly the same for all TRILL Data
   packets between two RBridge ports, even if there is a huge amount of
   data being sent between a variety of ingress and egress RBridges. On
   solution to this is to use the UDP Source Port as an entropy field.
   (This idea is also introduced in [gre-in-udp].) For example, for
   TRILL Data, this entropy field could be based on some hash of the
   Inner.MacDA, Inner.MacSA, and Inner.VLAN or Inner.FGL. Unfortunately,
   this can conflict with middleboxes inside the TRILL over IP link (see
   8.5).  Therefore, in order to better support ECMP, a RBridge SHOULD
   set the Source Port to a range of values as an entropy field for ECMP
   decisions; this range SHOULD be the ephemeral port range
   (49152-65535) except that, if there are middleboxes in the path (see
   Section 8.5), it MUST be possible to configure the range of different
   Source Port values to a sufficiently smaller range to avoid
   disrupting connectivity.

Margaret Cullen, et al                                         [Page 24]

INTERNET-DRAFT                                             TRILL over IP

8.4 MTU Considerations

   In TRILL each RBridge advertises in its LSP number zero the largest
   LSP frame it can accept (but not less than 1,470 bytes) on any of its
   interfaces (at least those interfaces with adjacencies to other TRILL
   switches in the campus) through the originatingLSPBufferSize TLV
   [RFC6325] [RFC7177]. The campus minimum MTU (Maximum Transmission
   Unit), denoted Sz, is then established by taking the minimum of this
   advertised MTU for all RBridges in the campus. Links that do not meet
   the Sz MTU are not included in the routing topology. This protects
   the operation of IS-IS from links that would be unable to accommodate
   the largest LSPs.

   A method of determining originatingLSPBufferSize for an RBridge with
   one or more TRILL over IP ports is described in [RFC7780]. However,
   if an IP link either can accommodate jumbo frames or is a link on
   which IP fragmentation is enabled and acceptable, then it is unlikely
   that the IP link will be a constraint on the originatingLSPBufferSize
   of an RBridge using the link. On the other hand, if the IP link can
   only handle smaller frames and fragmentation is to be avoided when
   possible, a TRILL over IP port might constrain the RBridge's

   Because TRILL sets the minimum values of Sz at 1,470 bytes, there may
   be links that meet the minimum MTU for the IP protocol (1,280 bytes
   for IPv6, 576 bytes for IPv4) on which it would be necessary to
   enable fragmentation for safe TRILL use.

   The use of TRILL IS-IS MTU PDUs, as specified in Section 5 of
   [RFC6325] and in [RFC7177], can provide added assurance of the actual
   MTU of a link.

8.5 Middlebox Considerations

   This section gives some middlebox considerations for the IP
   encapsulations covered by this document, namely native and VXLAN

   The requirements for the usage of the zero UDP Checksum in a UDP
   tunnel protocol are detailed in [RFC6936]. These requirements apply
   to the TRILL over IP encapsulations specified herein (native and
   VXLAN), which are applications of UDP tunnel.

   Besides the Checksum, the Source Port number of the UDP header is
   also pertinent to the middlebox behavior. Network Address/Port
   Translator (NAPT) is the most commonly deployed Network Address
   Translation (NAT) device [RFC4787]. For a UDP tunnel protocol, the
   NAPT device establishes a NAT session to translate the {private IP

Margaret Cullen, et al                                         [Page 25]

INTERNET-DRAFT                                             TRILL over IP

   address, private source port number} tuple to a {public IP address,
   public source port number} tuple, and vice versa, for the duration of
   the UDP session. This provides the UDP tunnel protocol application
   with the "NAT-pass-through" function. NAPT allows multiple internal
   hosts to share a single public IP address. The port number, i.e., the
   UDP Source Port number, is used as the demultiplexer of the multiple
   internal hosts.

   However, the above NAPT behavior conflicts with the behavior that the
   UDP Source Port number is used as an entropy (See Section 8.3).
   Hence, the network operator MUST ensure the TRILL switch ports
   sending through local or remote NAPT middleboxes limit the entropy
   usage of the UDP Source Port number, possibly to a single value.

Margaret Cullen, et al                                         [Page 26]

INTERNET-DRAFT                                             TRILL over IP

9. TRILL over IP Port Configuration

   This section specifies the configuration information needed at a
   TRILL over IP port beyond that needed for a general RBridge port.

9.1 Per IP Port Configuration

   Each RBridge port used for a TRILL over IP link should have at least
   one IP (v4 or v6) address. If no IP address is associated with the
   port, perhaps as a transient condition during re-configuration, the
   port is disabled. Implementations MAY allow a single port to operate
   as multiple IPv4 and/or IPv6 logical ports. Each IP address
   constitutes a different logical port and the RBridge with those ports
   MUST associate a different Port ID (see Section 4.4.2 of [RFC6325])
   with each logical port.

   By default a TRILL over IP port discards output packets that fail the
   possible recursive ingress test (see Section 10.1) unless configured
   to disable that test.

9.2 Additional per IP Address Configuration

   The configuration information specified below is per TRILL over IP
   port IP address.

   The mapping from TRILL packet priority to TRILL over IP
   Differentiated Services Code Point (DSCP [RFC2474]) can be
   configured. If supported, mapping from an inner DSCP code point, when
   the TRILL payload is IP, to the outer TRILL over IP DSCP can be
   configured. (See Section 4.3.)

   Each TRILL over IP port has a list of acceptable encapsulations it
   will use as the basis of adjacency. By default this list consists of
   one entry for native encapsulation (see Section 7). Additional
   encapsulations MAY be configured and native encapsulation MAY be
   removed from this list by configuration. Additional configuration can
   be required or possible for specific encapsulations as described in
   Section 9.2.3.

   Each IP address at a TRILL over IP port uses native IP multicast by
   default but may be configured whether to use serial IP unicast
   (Section 9.2.2) or native IP multicast (Section 9.2.1). Each IP
   address at a TRILL over IP is configured whether or not to use IPsec
   (Section 9.2.4).

   Regardless of whether they will send IP multicast, TRILL over IP

Margaret Cullen, et al                                         [Page 27]

INTERNET-DRAFT                                             TRILL over IP

   ports emit appropriate IGMP (IPv4 [RFC3376]) or MLD (IPv6 [RFC2710])
   packets unless configured not to do so. These are sent for the IP
   multicast group the port would use if it sent IP multicast.

9.2.1 Native Multicast Configuration

   If a TRILL over IP port address is using native IP multicast for
   multi-destination TRILL packets (IS-IS and data), by default
   transmissions from that IP address use the IP multicast address (IPv4
   or IPv6) specified in Section 11.2. The TRILL over IP port may be
   configured to use a different IP multicast address for multicasting

9.2.2 Serial Unicast Configuration

   If a TRILL over IP port address has been configured to use serial
   unicast for multi-destination packets (IS-IS and data), it should
   have associated with it a non-empty list of unicast IP destination
   addresses with the same IP version as the version of the port's IP
   address (IPv4 or IPv6). Multi-destination TRILL packets are serially
   unicast to the addresses in this list. Such a TRILL over IP port will
   only be able to form adjacencies [RFC7177] with the RBridges at the
   addresses in this list as those are the only RBridges to which it
   will send TRILL Hellos. IP packets received from a source IP address
   not on the list are discarded.

   If this list of destination IP addresses is empty, the port is

9.2.3 Encapsulation Specific Configuration

   Specific TRILL over IP encapsulation methods may provide for further
   configuration as specified below. UDP Source Port

   As discussed above, the native starts with a UDP header where the
   source UDP port can be used for entropy (Section 8.3). The range of
   UDP source port values used defaults to the ephemeral port range
   (49152-65535) but can be configured to any other range including to a
   single value.

Margaret Cullen, et al                                         [Page 28]

INTERNET-DRAFT                                             TRILL over IP VXLAN Configuration

   A TRILL over IP port using VXLAN encapsulation can be configured with
   non-default VXLAN Network Identifiers (VNIs) that are used in that
   field of the VXLAN header for all TRILL IS-IS and TRILL Data packets
   sent using the encapsulation and required in those received using the
   encapsulation. The default VNI is 1 for TRILL IS-IS and 2 for TRILL
   Data. A TRILL packet received with the an unknown VNI is discarded.

   A TRILL over IP port using VXLAN encapsulation can also be configured
   to map the Inner.VLAN of a TRILL Data packet being transported to the
   value it places in the VNI field and/or to copy the Inner.FGL of a
   TRILL Data packet to the VNI field. Other Encapsulation Configuration

   Additional encapsulation methods, beyond the native UDP encapsulation
   and VXLAN encapsulation specified in this document, are expected to
   be specified in future documents and may require further

9.2.4 Security Configuration

   A TRILL over IP port can be configured, for the case where IS-IS
   security [RFC5310] is in use, as to whether or not IPsec must be
   fully established and used for any TRILL IS-IS transmissions other
   than IS-IS Hello or MTU PDUs (see Section 7). There may also be
   configuration whose details are outside the scope of this document
   concerning certificate based IPsec or use of shared keys other than
   IS-IS based shared key or how to select what IS-IS based shared key
   to use.

Margaret Cullen, et al                                         [Page 29]

INTERNET-DRAFT                                             TRILL over IP

10. Security Considerations

   TRILL over IP is subject to all of the security considerations for
   the base TRILL protocol [RFC6325]. In addition, there are specific
   security requirements for different TRILL deployment scenarios, as
   discussed in the "Use Cases for TRILL over IP", Section 3 above.

   For communication between end stations in a TRILL campus, security
   may be possible at three levels: end-to-end security between those
   end stations, edge-to-edge security between ingress and egress
   RBridges [LinkSec], and link security to protect a TRILL hop. Any
   combination of these can be used, including all three.

   TRILL over IP link security protects the contents of TRILL Data and
      IS-IS packets, including the identities of the end stations for
      data and the identities of the edge RBridges, from observers of
      the link and transit devices within the link such as bridges or IP
      routers, but does not encrypt the link local IP addresses used in
      a packet and does not protect against observation by the sending
      and receiving RBridges on the link.

   Edge-to-edge TRILL security would protect the contents of TRILL data
      packets including the identities of the end stations for data from
      transit RBridges but does not encrypt the identities of the edge
      RBridges involved and does not protect against observation by
      those edge RBridges. It is anticipated that edge-to-edge TRILL
      security will be covered in future documents.

   End-to-end security does not protect the identities of the end
      stations or edge RBridge involved but does protect the content of
      TRILL data packets from observation by all RBridges or other
      intervening devices between the end stations involved.  End-to-end
      security should always be considered as an added layer of security
      to protect any particularly sensitive information from unintended
      disclosure. Such end station to end station security is generally
      beyond the scope of TRILL

   If VXLAN encapsulation is used, the unused Ethernet source and
   destination MAC addresses mentioned in Section 5.5, provide a 96 bit
   per packet side channel.

10.1 IPsec

   This document specifies that all RBridges that support TRILL over IP
   links MUST implement IPsec for the security of such links, and makes
   it clear that it is both wise and good to use IPsec in all cases
   where a TRILL over IP link will traverse a network that is not under
   the same administrative control as the rest of the TRILL campus or is

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   not secure. IPsec is important, in these cases, to protect the
   privacy and integrity of data traffic. However, in cases where IPsec
   is impractical due to lack of fast path support, use of TRILL edge-
   to-edge security or use by the end stations of end-to-end security
   can provide significant security.

   Further Security Considerations for IPsec ESP and for the
   cryptographic algorithms used with IPsec can be found in the RFCs
   referenced by this document.

10.2 IS-IS Security

   TRILL over IP is compatible with the use of IS-IS Security [RFC5310],
   which can be used to authenticate TRILL switches before allowing them
   to join a TRILL campus. This is sufficient to protect against rogue
   devices impersonating TRILL switches, but is not sufficient to
   protect data packets that may be sent in TRILL over IP outside of the
   local network or across the public Internet. To protect the privacy
   and integrity of that traffic, use IPsec.

   In cases were IPsec is used, the use of IS-IS security may not be
   necessary, but there is nothing about this specification that would
   prevent using both IPsec and IS-IS security together.

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11. IANA Considerations

   IANA considerations are given below.

11.1 Port Assignments

   IANA is requested to assign destination UDP Ports for the TRILL IS-IS
   and TRILL Data:

       UDP Port        Protocol           Reference
      ----------      ---------------    -----------------
       (TBD1)          TRILL IS-IS        [this document]
       (TBD2)          TRILL Data         [this document]

11.2 Multicast Address Assignments

   IANA is requested to assign one IPv4 and one IPv6 multicast address,
   as shown below, which correspond to both the All-RBridges and All-IS-
   IS-RBridges multicast MAC addresses that have been assigned for
   TRILL. Because the low level hardware MAC address dispatch
   considerations for TRILL over Ethernet do not apply to TRILL over IP,
   one IP multicast address for each version of IP is sufficient.

   (Values recommended to IANA in square brackets)

      Name             IPv4                  IPv6
   ------------     ------------------   --------------------------
   All-RBridges     TBD3[]   TBD4[FF0X:0:0:0:0:0:0:BAC1]

   The hex digit "X" in the IPv6 variable scope address indicates the
   scope and defaults to 8. The IPv6 All-RBridges IP address may be used
   with other values of X.

11.3 Encapsulation Method Support Indication

   The existing "RBridge Channel Protocols" registry is re-named and a
   new sub-registry under that registry added as follows:

   The TRILL Parameters registry for "RBridge Channel Protocols" is
   renamed the "RBridge Channel Protocols and Link Technology Specific
   Flags" registry. [this document] is added as a second reference for
   this registry. The first part of the table is changed to the

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         Range      Registration        Note
      -----------   ----------------   ----------------------------
      0x002-0x0FF   Standards Action
      0x100-0xFCF   RFC Required       allocation of a single value
      0x100-0xFCF   IESG Approval      allocation of multiple values
      0xFD0 0xFF7   see Note           link technology dependent,
                                          see subregistry

   In the existing table of RBridge Channel Protocols, the following
   line is changed to two lines as shown:

        0x004-0xFF7   Unassigned
        0x004-0xFCF   Unassigned
        0xFD0-0xFF7   (link technology dependent, see subregistry)

   A new indented subregistry under the re-named "RBridge Channel
   Protocols and Link Technology Specific Flags" registry is added as

      Name: TRILL over IP Link Flags
      Registration Procedure: Expert Review
      Reference: [this document]

          Flag      Meaning                        Reference
      -----------  ------------------------------  ---------
            0xFD0  Native encapsulation supported  [this document]
            0xFD1  VXLAN encapsulation supported   [this document]
      0xFD2-0xFF7  Unassigned

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Normative References

   [IS-IS] - "Intermediate system to Intermediate system routeing
         information exchange protocol for use in conjunction with the
         Protocol for providing the Connectionless-mode Network Service
         (ISO 8473)", ISO/IEC 10589:2002, 2002".

   [RFC0020] - Cerf, V., "ASCII format for network interchange", STD 80,
         RFC 20, DOI 10.17487/RFC0020, October 1969, <http://www.rfc-

   [RFC0768] - Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
         10.17487/RFC0768, August 1980, <http://www.rfc-

   [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119,
         March 1997, <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2474] - Nichols, K., Blake, S., Baker, F., and D. Black,
         "Definition of the Differentiated Services Field (DS Field) in
         the IPv4 and IPv6 Headers", RFC 2474, DOI 10.17487/RFC2474,
         December 1998, <http://www.rfc-editor.org/info/rfc2474>.

   [RFC2710] - Deering, S., Fenner, W., and B. Haberman, "Multicast
         Listener Discovery (MLD) for IPv6", RFC 2710, DOI
         10.17487/RFC2710, October 1999, <http://www.rfc-

   [RFC2914] - Floyd, S., "Congestion Control Principles", BCP 41, RFC
         2914, DOI 10.17487/RFC2914, September 2000, <http://www.rfc-

   [RFC3168] - Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
         of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI
         10.17487/RFC3168, September 2001, <http://www.rfc-

   [RFC3376] - Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
         Thyagarajan, "Internet Group Management Protocol, Version 3",
         RFC 3376, DOI 10.17487/RFC3376, October 2002, <http://www.rfc-

   [RFC4301] - Kent, S. and K. Seo, "Security Architecture for the
         Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December
         2005, <http://www.rfc-editor.org/info/rfc4301>.

   [RFC4303] - Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
         4303, DOI 10.17487/RFC4303, December 2005, <http://www.rfc-

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INTERNET-DRAFT                                             TRILL over IP

   [RFC5405] - Li, T. and R. Atkinson, "IS-IS Cryptographic
         Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008,

   [RFC5310] - Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
         and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC
         5310, DOI 10.17487/RFC5310, February 2009, <http://www.rfc-

   [RFC5869] - Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-
         Expand Key Derivation Function (HKDF)", RFC 5869, DOI
         10.17487/RFC5869, May 2010, <http://www.rfc-

   [RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
         Ghanwani, "Routing Bridges (RBridges): Base Protocol
         Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,

   [RFC7176] - Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
         D., and A. Banerjee, "Transparent Interconnection of Lots of
         Links (TRILL) Use of IS-IS", RFC 7176, DOI 10.17487/RFC7176,
         May 2014, <http://www.rfc-editor.org/info/rfc7176>.

   [RFC7177] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H.,
         and V. Manral, "Transparent Interconnection of Lots of Links
         (TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177, May 2014,

   [RFC7178] - Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D.
         Ward, "Transparent Interconnection of Lots of Links (TRILL):
         RBridge Channel Support", RFC 7178, DOI 10.17487/RFC7178, May
         2014, <http://www.rfc-editor.org/info/rfc7178>.

   [RFC7321] - McGrew, D. and P. Hoffman, "Cryptographic Algorithm
         Implementation Requirements and Usage Guidance for
         Encapsulating Security Payload (ESP) and Authentication Header
         (AH)", RFC 7321, DOI 10.17487/RFC7321, August 2014,

   [RFC7348] - Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
         L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
         eXtensible Local Area Network (VXLAN): A Framework for
         Overlaying Virtualized Layer 2 Networks over Layer 3 Networks",
         RFC 7348, DOI 10.17487/RFC7348, August 2014, <http://www.rfc-

   [RFC7780] - Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
         Ghanwani, A., and S. Gupta, "Transparent Interconnection of
         Lots of Links (TRILL): Clarifications, Corrections, and

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INTERNET-DRAFT                                             TRILL over IP

         Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016,

Informative References

   [RFC4787] - Audet, F., Ed., and C. Jennings, "Network Address
         Translation (NAT) Behavioral Requirements for Unicast UDP", BCP
         127, RFC 4787, DOI 10.17487/RFC4787, January 2007,

   [RFC6234] - Eastlake 3rd, D. and T. Hansen, "US Secure Hash
         Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI
         10.17487/RFC6234, May 2011, <http://www.rfc-

   [RFC6361] - Carlson, J. and D. Eastlake 3rd, "PPP Transparent
         Interconnection of Lots of Links (TRILL) Protocol Control
         Protocol", RFC 6361, DOI 10.17487/RFC6361, August 2011,

   [RFC6864] - Touch, J., "Updated Specification of the IPv4 ID Field",
         RFC 6864, DOI 10.17487/RFC6864, February 2013, <http://www.rfc-

   [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, <http://www.rfc-

   [RFC7172] - Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R.,
         and D. Dutt, "Transparent Interconnection of Lots of Links
         (TRILL): Fine-Grained Labeling", RFC 7172, DOI
         10.17487/RFC7172, May 2014, <http://www.rfc-

   [RFC7173] - Yong, L., Eastlake 3rd, D., Aldrin, S., and J. Hudson,
         "Transparent Interconnection of Lots of Links (TRILL) Transport
         Using Pseudowires", RFC 7173, DOI 10.17487/RFC7173, May 2014,

   [RFC7296] - Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
         Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)",
         STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014,

   [circuit-breaker] - Fairhurst, G., "Network Transport Circuit
         Breakers", draft-ietf-tsvwg-circuit-breaker, work in progress.

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INTERNET-DRAFT                                             TRILL over IP

   [gre-in-udp] - Crabbe, E., Yong, L., and X. Xu, "Generic UDP
         Encapsulation for IP Tunneling", draft-yong-tsvwg-gre-in-udp-
         encap, work in progress.

   [LinkSec] - Eastlake, D., D. Zhang, "TRILL: Link Security", draft-
         eastlake-trill-link-security, work in progress.

   [TRILLECN] - Eastlake, D., B. Briscoe, "TRILL: ECN (Explicit
         Congestion Notification) Support", draft-eastlake-trill-ecn-
         support, work in progress.

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   The following people have provided useful feedback on the contents of
   this document: Sam Hartman, Adrian Farrel, and Mohammed Umair.

   Some material in Section 10.2 is derived from draft-ietf-mpls-in-udp
   by Xiaohu Xu, Nischal Sheth, Lucy Yong, Carlos Pignataro, and
   Yongbing Fan.

   The document was prepared in raw nroff. All macros used were defined
   within the source file.

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Authors' Addresses

      Margaret Cullen
      Painless Security
      14 Summer Street, Suite 202
      Malden, MA 02148

      Phone: +1-781-605-3459
      Email: margaret@painless-security.com
      URI:   http://www.painless-security.com

      Donald Eastlake
      Huawei Technologies
      155 Beaver Street
      Milford, MA  01757

      Phone: +1 508 333-2270
      Email: d3e3e3@gmail.com

      Mingui Zhang
      Huawei Technologies
      No.156 Beiqing Rd. Haidian District,
      Beijing 100095 P.R. China

      EMail: zhangmingui@huawei.com

      Dacheng Zhang
      Huawei Technologies

      Email: dacheng.zhang@huawei.com

Copyright, Disclaimer, and Additional IPR Provisions

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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INTERNET-DRAFT                                             TRILL over IP

   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Margaret Cullen, et al                                         [Page 40]