Transparent Interconnection of Lots of Links (TRILL) over IP
draft-ietf-trill-over-ip-03
The information below is for an old version of the document.
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| Authors | Margaret Cullen , Donald E. Eastlake 3rd , Mingui Zhang , Dacheng Zhang | ||
| Last updated | 2015-07-06 | ||
| Replaces | draft-mrw-trill-over-ip | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-trill-over-ip-03
INTERNET-DRAFT Margaret Cullen
Intended Status: Proposed Standard Painless Security
Updates: 7177, 7178 Donald Eastlake
Mingui Zhang
Huawei
Dacheng Zhang
Alibaba
Expires: January 5, 2016 July 6, 2015
Transparent Interconnection of Lots of Links (TRILL) over IP
<draft-ietf-trill-over-ip-03.txt>
Abstract
The Transparent Interconnection of Lots of Links (TRILL) protocol is
implemented by devices called TRILL Switches or RBridges (Routing
Bridges). TRILL 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 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 author or the DNSEXT mailing list <dnsext@ietf.org>.
Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
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http://www.ietf.org/shadow.html.
Margaret Cullen, et al [Page 1]
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Table of Contents
1. Introduction............................................4
2. Terminology.............................................4
3. Use Cases for TRILL over IP.............................5
3.1 Remote Office Scenario.................................5
3.2 IP Backbone Scenario...................................5
3.3 Important Properties of the Scenarios..................5
3.3.1 Security Requirements................................6
3.3.2 Multicast Handling...................................6
3.3.3 RBridge Neighbor Discovery...........................7
4. TRILL Packet Formats....................................8
5. Some Link Protocol Specifics............................9
6. TRILL over IP Port Configuration.......................10
6.1 Per IP Port Configuration.............................10
6.2 Additional per IP Address Cofiguration................10
6.2.1 Native Multicast Configuration......................10
6.2.2 Serial Unicast Configuration........................11
6.2.3 Encapsulation Specific Configuration................11
6.2.3.1 VXLAN Configuration...............................11
6.2.3.2 Other Encapsulation Configuration.................12
6.2.4 Security Configuration..............................12
7. TRILL over IP Encapsulation Formats....................13
7.1 Encapsulation Agreement...............................14
7.2 IPsec ESP Format......................................14
7.3 Broadcast Link Encapsulation Considerations...........15
7.4 Native Encapsulaton...................................15
7.5 VXLAN Encapsulation...................................16
7.6 Other Encpaulsations..................................17
8. Handling Multicast.....................................18
9. Use of IPsec...........................................19
9.1 Default Keys..........................................19
9.2 Mandatory-to-Implement Algorithms.....................19
10. Transport Considerations..............................20
10.1 Recursive Ingress....................................20
10.2 Fat Flows............................................20
10.3 Congestion Considerations............................21
10.4 MTU Considerations...................................22
10.5 QoS Considerations...................................23
11. Middlebox Considerations..............................24
12. Security Considerations...............................25
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Table of Contents (continued)
13. IANA Considerations...................................26
13.1 Port Assignments.....................................26
13.2 Multicast Address Assignments........................26
13.3 Encapsulation Method Support Indication..............26
Normative References......................................28
Informative References....................................30
Acknowledgements..........................................31
Authors' Addresses........................................32
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1. Introduction
TRILL switches (RBridges) are devices that implement the IETF TRILL
protocol [RFC6325] [RFC7177] [rfc7180bis].
RBridges provide transparent forwarding of frames within an arbitrary
network topology, using least cost paths for unicast traffic. They
support not only VLANs and Fine Grained Labels [RFC7172] but also
multipathing of unicast and multi-destination traffic. They use IS-IS
link state routing and encapsulation with a hop count.
Ports on different RBridges can communicate with each other over
various link types, such as Ethernet [RFC6325], pseudowires
[RFC7173], or PPP [RFC6361].
This document defines a method for RBridges to communicate over IP
(v4 or v6). TRILL over IP will allow Internet-connected RBridges to
form a single TRILL campus, or multiple TRILL over IP networks within
a campus 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 appear to TRILL to be
connected by a single multi-access link. Therefore, 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
(such as 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 [RFC4303] to secure all or part of
such paths.
To support the use of TRILL over IP encapsulation with good fast path
hardware support, a method is provided for agreement between adjacent
TRILL switches as to what encapsulation to use. This document
updates [RFC7177] and [RFC7178] as described in Section 7 by
redefining an interval of RBridge Channel protocol numbers to
indicate encapsulation method support for TRILL over IP and by making
adjacency between TRILL over IP ports dependent on having a method of
encapsulation in common.
2. Terminology
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 [RFC2119].
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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
campus.
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.
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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.
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3.3.3 RBridge Neighbor Discovery
In the IP Backbone Scenario, RBridges that use TRILL over IP can use
the normal TRILL IS-IS Hello mechanisms to discover the existence of
other RBridges on the link [RFC7177], and to establish authenticated
communication with those RBridges.
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 RBridge 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.
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4. TRILL Packet Formats
To support the TRILL base protocol standard [RFC6325], two types of
packets are transmitted between RBridges: TRILL Data packets and
TRILL IS-IS packets.
The on-the-wire form of a TRILL Data packet in transit between two
neighboring RBridges is as shown below:
+--------------+----------+----------------+-----------+
| TRILL Data | TRILL | Native Frame | Link |
| Link Header | Header | Payload | Trailer |
+--------------+----------+----------------+-----------+
Where 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:
+--------------+---------------+-----------+
| TRILL IS-IS | TRILL IS-IS | Link |
| Link Header | 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 TRILL Data Link Header ends with the TRILL Ethertype
while the TRILL IS-IS Link Header ends with the L2-IS-IS Ethertype;
on the other hand, over PPP, there are no Ethertypes but PPP protocol
code points are included that distinguish TRILL Data from TRILL IS-
IS.
In TRILL over IP, we will use IP (v4 or v6) in the link header. (On
the wire, the IP header will be preceeded by the lower layer protocol
that is carrying IP, such as Ethernet.) However, there are several IP
based encapsulations usable for TRILL over IP as further discussed in
Section 7 that differ in exactly what appears after the IP header and
before the TRILL header.
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5. Some Link Protocol Specifics
TRILL Data packets can be unicast to a specific RBridge or multicast
to all RBridges on a link. TRILL IS-IS packets are always multicast
to all other RBridge on the link (except for MTU PDUs, which may be
unicast [RFC7177]. On Ethernet links, the Ethernet multicast address
All-RBridges is used for TRILL Data and All-IS-IS-RBridges for TRILL
IS-IS.
To properly handle TRILL base protocol packets on a TRILL over IP
link in the general case, either native IP multicast mode must be
used on that link, or multicast must be simulated using serial IP
unicast, as discussed in Section 8. (Of course, if the IP link
happens to actually be point-to-point no special provision is needed
for handling multicast addressed packets.)
In TRILL Hello PDUs used on TRILL IP links, the IP addresses of the
connected IP ports are their real 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
common 48-bit IS-IS SNPAs, for 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] on that
link. This synthetic SNPA derived from an 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, at the IP level, where TRILL operates on an IP
link, TRILL sees only IP stations, not MAC stations, even if the
TRILL over IP Link is being carried over Ethernet, so conflict on the
link in TRILL IS-IS between a real MAC address and the synethic SNPA
(MAC) address as above would be impossible in any case.
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6. 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.
6.1 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 an TRILL over IP port discards output packets that fail
the possible recursive ingress test (see Section 10.1) unless
configured to disable that test.
6.2 Additional per IP Address Cofiguration
The configuration information specified below is per IP address at a
TRILL over IP port.
The mapping from TRILL packet priority to Differentiated Services
Code Point (DSCP [RFC2474]) can be configured (see Section 10.5).
Each TRILL over IP port has a list of acceptable encapsulations it
will use. By default this list consists of one entry for native
encapsulation. (See Section 7.) Additional configuration is possible
for specific encapsulations as described in Section 6.2.3.
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 6.2.2) or native IP multicast (Section 6.2.1). Each IP
address at a TRILL over IP is configured whether or not to use IPsec
(Section 6.2.3).
6.2.1 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 appropriate IP multicast
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address (IPv4 or IPv6) specified in Section 13.2. The TRILL over IP
port may be configured to use a different IP multicast address for
multi-destination packets.
6.2.2 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 ports 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.
If this list of destination IP addresses is empty, there is no way to
transmit a multi-destination TRILL over IP packet such as a TRILL
Hello. Thus it is impossible to achieve adjacency [RFC7177] or if
adjacency had been achieved (perhaps the list was non-empty and has
just been configured to be empty), no way to maintain such adjacency.
Thus, in the empty list case, TRILL Data multi-destination packets
cannot be sent and TRILL Data unicast packets will not start flowing
or, if they are already flowing, will soon cease, effectively
disabling the port.
6.2.3 Encapsulation Specific Configuration
Specific TRILL over IP encapsulation methods may provide for futher
configuration as specified in the subsections below.
6.2.3.1 VXLAN Configuration
A TRILL over IP port using VXLAN encapsulation can be configured with
a non-default VXLAN Network Identifier (VNI) which is used in that
field of the VXLAN header for all TRILL packets sent using the
encapsulation and required in all TRILL packets received using the
encapsulation. In this case, a TRILL packet received with the wrong
VNI is discarded.
A TRILL over IP port using VXLAN encapsulation can also be configured
to place the Inner.VLAN or Inner.FGL of a TRILL Data packet being
transported in the VNI field.
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6.2.3.2 Other Encapsulation Configuration
[Specific configuration for other encapsulation methods will be added
here.]
6.2.4 Security Configuration
tbd ...
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7. TRILL over IP Encapsulation Formats
There are a variety of TRILL over IP formats possible. In all cases,
there must be a method specified, with each format, to distinguish
TRILL Data and TRILL IS-IS packets, or that format is not useful for
TRILL. The following criteria can be helpful is choosing between
different encapsulations:
a) Fast path support - For most applications, it is highly desireable
to be able to encapsulate/decpasulate TRILL over IP at line speed
so a format where existing or anticipated fast path hardware can
do that is best.
b) Ease of multi-pathing - The IP path between TRILL over IP port may
include internal equal cost multipath routes so a method of
encapsulation that provides variable fields available for existing
or anticipated fast path hardware multi-pathing is better.
c) Fragmentaton and robust ID support - tbd
d) Checksum strength - Depending on the particular circumstances of
the TRILL over IP link, a checksum provided by the encapsulation
may be an important factor. Use of IPsec as provided herein can
also provide a strong integrity check.
TRILL over IP adopts a hybrid encapsulation approach by default.
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
with low bandwidth control messages to detetmine 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 encpasulation used for all TRILL
Data packets and all other TRILL IS-IS PDUs with the possible
exception of IS-IS MTU-probe and MTU-ack PDUs as discussed in Section
7.
Alternatively, the network operator can pre-configure a TRILL over IP
port to use a particular encapsulation choosen for their particular
network needs and TRILL over IP port capabiliies for all TRILL data
and IS-IS packets.
Section 7.1 discusses encapsulation agreement. Section 7.2 discusses
TRILL over IP IPsec ESP format, which is independent of
encapsulation. Section 7.3 discusses broadcast link encapsulation
considerations. The subsequent subsections discuss particular
encapsulations.
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7.1 Encapsulation Agreement
TRILL Hellos sent out a TRILL over IP port indicate the
encapsulations that port is willing to use through the mechanism
described in [RFC7178] and [RFC7176]. RBridge Channel Protocol
numbers 0xFC0 through 0xFF7 are hereby redefined to be link
technology dependent flags that, for TRILL over IP, indicate support
for different encapsulations, allowing for up to 24 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 13.3.) "Support" indicates willingness
to use that encapsulation for TRILL data and TRILL IS-IS other than
Hellos. Even if support is not indicated for native encapsulation, by
default support for native encapsulation of TRILL Hellos is assumed.
If no encapsulation support is indicated in a TRILL Hello, then the
port from which it was sent is assumed to support only native
encapsualtion (see Section 7.4).
An adjacency is formed between two TRILL over IP ports ONLY if the
intersection of the sets of encapsulation methods they support is not
null. If that intersection is null, then no adjaceny 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 any TRILL over IP packet, other than a IS-IS Hello or MTU PDU in
native encapsulation, is received in an encapsulation for which
support is not being indicated, it MUST be discarded (see Section
7.3).
It expected to normally be the case in a well configured network that
all the TRILL over IP ports connected to an IP network that are
intended to communicate with each other will support the same
encapsulation. But the network will operate correctly if this is not
true.
7.2 IPsec ESP Format
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 right after any
required Layer 2 header), the modifications when IPsec is in effect
are independent of the TRILL over IP encapsulation fields that occur
after that IP Header and before the TRILL Header. The resulting
packet formats are as follows for IPv4 and IPv6:
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------------------------------------------------------------
IPv4 | new IP hdr | | TRILL IP hdr | TRILL | ESP | ESP|
|(any options)| ESP | (any options) | Encap2 |Trailer| ICV|
------------------------------------------------------------
|<--------- encryption ---------->|
|<------------- integrity ------------->|
-------------------------------------------------------------
IPv6 | new |new ext | | orig |orig ext | TRILL | ESP | ESP|
|IP hdr| hdrs |ESP|IP hdr| hdrs | Encap2 |Trailer| ICV|
------------------------------------------------------------.
|<--------- encryption ----------->|
|<------------ integrity ------------->|
The "TRILL Encap2" above includes whatever additional fields are
required by the encapsulation in use followed by the TRILL Header and
then the native frame payload (see Section 4).
This architecture permits the ESP tunnel termination to be separated
from the TRILL over IP RBridge port and, for example, placed at a
physical or administrative security boundary.
7.3 Broadcast Link Encapsulation Considerations
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,
...) forming a broadcast link. In a well configured network one would
expect such multiple other IP ports to support the same encapsulation
but, if P1 supports multiple encapsulations, it is possible that P2
and P3, for example, do not have an encapsulation in common that is
supported by P1. IS-IS can handle such non-transitive adjacencies
which are reported as specified in [RFC7177]. If serial IP unicast is
being used by P1, it can use different encapsulatons for different
transmission. If native IP multicast is being used by P1, it will
have to send one transmission per encapsulation method by which it
has an adjanceny on the link. (It is for this reason that a TRILL
over IP port MUST discard any packet received with the wrong
encapsulation. Otherwise, packets would be duplicated.)
7.4 Native Encapsulaton
The mandatory to implement "native encapsulaton" format of a TRILL
over IP packet, when used without security, is TRILL over UDP as
shown below.
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+----------+--------+-----------------------+
| 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 10.2
Destination Port - indicates TRILL Data or IS-IS, see Section 13
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.
7.5 VXLAN Encapsulation
VXLAN [RFC7348] IP encapsulation of TRILL looks, on the wire, as
TRILL over Ethernet over VXLAN over UDP over IP.
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 7.2). The VXLAN header after the outer UDP
header adds a 24 bit Virtual Network Identifier. The Ethernet header
after the VXLAN header and before the TRILL header provides an
Ethertype field that distinguishes TRILL data from TRILL IS-IS;
however, the destination and source MAC addresses in this inner
Ethernet header before the TRILL header are not used and represent 12
wasted bytes.
A TRILL over IP port using VXLAN encapsulation by default uses a VNI
of 1 but can be configured as described in Section 6.2.3.1.
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7.6 Other Encpaulsations
[Additional encpasulations will be added here as additional
subsections.]
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8. 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 13.2); however, a TRILL over IP port may
be configured (see Section 6) 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 that case the outer IP
header shows the IP unicast 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 are sent by unicast IP.
When a TRILL over IP port is using IP multicast, it MUST periodically
transmit appropriate IGMP (IPv4 [RFC3376] or MLD (IPv6 [RFC2710])
packets so that the TRILL multicast IP traffic will be sent to it.
Although TRILL fully supports broadcast links with more than 2
RBridges connected to the link, even where native IP multicast is
available, there may be good reasons for configuring TRILL over IP
ports to use serial unicast. In some networks, unicast is more
reliable than multicast. If multiple unicast connections between
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 ceases to operate or
incorporate a new link that comes up.
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9. Use of IPsec
All RBridges that support TRILL over IP MUST implement IPsec
[RFC4301] and support the use of IPsec Encapsulating Security
Protocol (ESP [RFC4303]) 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, implementors may elect use IS-IS
security to protect TRILL IS-IS packets. However, in this case, the
IPsec session still MUST be fully established before any data packets
transmission since IS-IS security does not provide any protection to
data packets.
9.1 Default Keys
The default pre-shared keys for IPsec usage are derived as follows:
HMAC-SHA256 ("TRILL IP"| IS-IS-shared key )
In the above "|" indicates concatenation, HMAC-SHA256 is as described
in [FIPS180] [RFC6234] and "TRILL IP" is the eight byte US ASCII
[RFC0020] string indicated. "IS-IS-shared key" is a link (or wider
scope) IS-IS key usable for IS-IS security of link local IS-IS local
PDUs such as Hello, CSNP, and PSNP. With [RFC5310] there could be
multiple keys identified with 16-bit key IDs. In this case, the Key
ID of IS-IS-shared key is also used to identify the derived key.
Although we are using pre-shared keys at the IPsec level, the IS-IS-
shared keys from which they are derived expire and can be updated as
described in RFC 5310. The derived keys MUST expire within the
lifetime as the IS-IS-shared keys from which they were derived.
9.2 Mandatory-to-Implement Algorithms
All RBridges that support TRILL over IP MUST implement the following
algorithms for IPsec ESP, as recommended in [RFC4308]:
Protocol ESP [RFC4303]
ESP encryption AES with 128-bit keys in CBC mode [RFC3602]
ESP integrity AES-XCBC-MAC-96 [RFC3566]
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10. Transport Considerations
This section discusses a variety of transport considerations.
10.1 Recursive Ingress
TRILL is designed to transport end station traffic to and from end
stations over IEEE 802.3 and IP is frequently transported over IEEE
802.3 or similar protocols. Thus, an end station native data frame EF
might get TRILL ingressed to TRILL(EF) which was then sent oout a
TRILL over IP over 802.3 port resulting in an 802.3 frame of the form
802.3(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, etc. The
packet might 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 Header and TTL.
To protect against this scenario, a TRILL over IP port MUST by,
default, test whether a TRILL packet it is about to transmit is, in
fact a TRILL ingress of a TRILL over IP over 802.3 or the like
packets. That is, is it of the form TRILL(802.3(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.
10.2 Fat Flows
For the purpose of load balancing, it is worthwhile to consider how
to transport the TRILL packets over the Equal Cost Multiple Paths
(ECMPs) existing internal to the IP path between two TRILL over IP
ports.
The ECMP election for the IP traffic could be based, at least for
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.
Therefore, in order to better support ECMP, a RBridge SHOULD set the
Source Port as an entropy field for ECMP decisions. (This idea is
also introduced in [gre-in-udp].) For example, for TRILL Data this
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entropy field could be based on the Inner.MacDA, Inner.MacSA, and
Inner.VLAN or Inner.FGL.
10.3 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 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 necessary".
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
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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 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
TRILL-over-UDP.
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
center).
d. Use of a "Managed Circuit Breaker" for the TRILL traffic as
described in [circuit-breaker].
10.4 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
RBridges in the campus) through the originatingLSPBufferSize TLV
[RFC6325] [RFC7177]. The campus minimum MTU, denoted Sz, is then
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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 some LSPs.
A method of determining originatingLSPBufferSize for an RBridge with
one or more TRILL over IP ports is described in [rfc7180bis].
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 originatingLSPBufferSize. 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, theoretically
68 bytes for IPv4) on which it would be necessary to enable
fragmentation for TRILL use.
The optional use of TRILL IS-IS MTU PDUs, as specified in [RFC6325]
and [RFC7177] can provide added assurance of the actual MTU of a
link.
10.5 QoS Considerations
Within TRILL, priority is indicated by a three bit (0 through 7)
priority field in TRILL data packets and by configuration for TRILL
IS-IS packets. When TRILL packets are sent on a TRILL over IP link,
this priority is mapped to a Differential Services Code Point (DSCP
[RFC2474] Section 4.2.2).
The default mapping, which may be configured per TRILL over IP port,
is an follows. Note that, to provide a potentially lower priority
service than the default 0, priority 1 is considered lower priority
than 0. So the priority squence from lower to higher priority is 1,
0, 2, 3, 4, 5, 6, 7.
TRILL Priority DiffServ Field (Binary/decimal)
-------------- -------------------------------
0 00100000 / 8
1 00000000 / 0
2 01000000 / 16
3 01100000 / 24
4 10000000 / 32
5 10100000 / 40
6 11000000 / 48
7 11100000 / 56
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11. Middlebox Considerations
TBD ...
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12. 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 above.
This document specifies that all RBridges that support TRILL over IP
MUST implement IPsec, 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 not physically secure. IPsec is
necessary, in these cases to protect the privacy and integrity of
data traffic.
TRILL over IP is compatible with the use of IS-IS Security [RFC5310],
which can be used to authenticate RBridges before allowing them to
join a TRILL campus. This is sufficient to protect against rogue
RBridges, but is not sufficient to protect data packets that may be
sent in IP outside of the local network, or even 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. In cases where
both types of security are enabled, by default, a key derived from
the IS-IS key will be used for IPsec.
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13. IANA Considerations
IANA considerations are given below.
13.1 Port Assignments
IANA has allocated the following destination UDP Ports for the TRILL
IS-IS and Data channels:
UDP Port Protocol
---------- ---------------------
(TBD1) TRILL IS-IS Channel
(TBD2) TRILL Data Channel
13.2 Multicast Address Assignments
IANA has allocated one IPv4 and one IPv6 multicast address, as shown
below, which correspond to the All-RBridges and All-IS-IS-RBridges
multicast MAC addresses that the IEEE Registration Authority has
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[233.252.14.0] TBD4[FF0X:0:0:0:0:0:0:205]
Note: when these IPv4 and IPv6 multicast addresses are used and the
resulting IP frame is sent over Ethernet, the usual IP derived MAC
address is used.
[Need to discuss scopes for IPv6 multicast (the "X" in the addresses)
somewhere. Default to "site" scope but MUST be configurable?]
13.3 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 Flags"
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registry. [this document] is added as a second reference for this
registry. The first part of the table is changed to the following:
Range Registration Note
----------- ---------------- ----------------------------
0x002-0x0FF Standards Action
0x100-0xFBF RFC Required allocation of a single value
0x100-0xFBF IESG Approval allocation of multiple values
0xFC0 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:
OLD
0x004-0xFF7 Unassigned
NEW
0x004-0xFBF Unassigned
0xFC0-0xFF7 (link technology dependent, see subregistry)
A new subregistry under the newly named "RBridge Channel Protocols
and Link Technology Flags" registry is added as follows:
Name: TRILL over IP Link Flags
Registration Procedure: IETF Review
Reference: [this document]
Flag Meaning
----------- ------------------------------
0xFC0 Native encapsulation supported
0xFC1 VXLAN encapsulation supported
0xFC2-0xFF7 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-
editor.org/info/rfc20>.
[RFC0768] - Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
10.17487/RFC0768, August 1980, <http://www.rfc-
editor.org/info/rfc768>.
[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-
editor.org/info/rfc2710>.
[RFC2914] - Floyd, S., "Congestion Control Principles", BCP 41, RFC
2914, DOI 10.17487/RFC2914, September 2000, <http://www.rfc-
editor.org/info/rfc2914>.
[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-
editor.org/info/rfc3376>.
[RFC3566] - Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96
Algorithm and Its Use With IPsec", RFC 3566, DOI
10.17487/RFC3566, September 2003, <http://www.rfc-
editor.org/info/rfc3566>.
[RFC3602] - Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602, DOI
10.17487/RFC3602, September 2003, <http://www.rfc-
editor.org/info/rfc3602>.
[RFC4301] - Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December
Margaret Cullen, et al [Page 28]
INTERNET-DRAFT TRILL over IP
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-
editor.org/info/rfc4303>.
[RFC4308] - Hoffman, P., "Cryptographic Suites for IPsec", RFC 4308,
DOI 10.17487/RFC4308, December 2005, <http://www.rfc-
editor.org/info/rfc4308>.
[RFC5405] - Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008,
<http://www.rfc-editor.org/info/rfc5304>.
[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-
editor.org/info/rfc5310>.
[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,
<http://www.rfc-editor.org/info/rfc6325>.
[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,
<http://www.rfc-editor.org/info/rfc7177>.
[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>.
[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-
editor.org/info/rfc7348>.
[rfc7180bis] - Eastlake, D., et al, "TRILL: Clarifications,
Corrections, and Updates", draft-ietf-trill-rfc7180bis, work in
progress.
Margaret Cullen, et al [Page 29]
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[FIPS180] - "Secure Hash Standard (SHS)", United States of American,
National Institute of Science and Technology, Federal
Information Processing Standard (FIPS) 180-4, March 2012.
Informative References
[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-
editor.org/info/rfc6234>.
[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,
<http://www.rfc-editor.org/info/rfc6361>.
[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-
editor.org/info/rfc7172>.
[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,
<http://www.rfc-editor.org/info/rfc7173>.
[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.
[circuit-breaker] - Fairhurst, G., "Network Transport Circuit
Breakers", draft-ietf-tsvwg-circuit-breaker, work in progress.
Margaret Cullen, et al [Page 30]
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Acknowledgements
The following people have provided useful feedback on the contents of
this document: Sam Hartman, Adrian Farrel.
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.
Margaret Cullen, et al [Page 31]
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Authors' Addresses
Margaret Cullen
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Phone: +1 781 405-7464
Email: margaret@painless-security.com
URI: http://www.painless-security.com
Donald Eastlake
Huawei Technologies
155 Beaver Street
Milford, MA 01757
USA
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
Alibaba
Beijing, Chao yang District
P.R. China
Email: dacheng.zdc@alibaba-inc.com
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Margaret Cullen, et al [Page 32]
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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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described in the Simplified BSD License.
Margaret Cullen, et al [Page 33]