IPng Working Group A. Conta
INTERNET-DRAFT M. Mueller
(Lucent)
July 1997
Transmission of IPv6 Packets over Frame Relay.
Specification
draft-conta-ipv6-trans-fr-00.txt
Status of this Memo
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Distribution of this memo is unlimited.
Abstract
This memo describes the transmission of IPv6 packets over
Frame Relay, the IPv6 Frame Relay interface token, the IPv6 Frame
Relay link local addresses, the IPv6 Frame Relay link layer
Information formatting for Neighbor Discovery.
1. Introduction
This document specifies the frame format for transmission of
IPv6
packets and the method of forming IPv6 link-local addresses on
Frame
Relay links. It also specifies the content of the
Source/Target
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Link-layer Address option used in Neighbor Discovery [ND] or
Inverse
Neighbor Discovery [IND] messages when those messages are
transmitted
over a Frame Relay link.
The information in this document applies to Frame Relay devices
which
serve as end stations (DTEs) on a public or private Frame Relay
net-
work (for example, provided by a common carrier or PTT.)
In a Frame Relay network, a number of virtual circuits form the
con-
nections between the attached stations. The resulting set of
inter-
connected devices forms a private Frame Relay group which may
be
either fully interconnected with a complete "mesh" of virtual
cir-
cuits, or only partially interconnected. In either case, each
vir-
tual circuit is uniquely identified at each Frame Relay interface
by
a Data Link Connection Identifier (DLCI). In most
circumstances,
DLCIs have strictly local significance at each Frame Relay
interface.
A Frame Relay virtual circuit acts like a virtual-link, with its
own
link parameters, distinct from the parameters of other virtual
cir-
cuits established on the same wire or fiber. Such parameters are
the
input/output maximum frame size, incoming/outgoing
requested/agreed
throughput, incoming/outgoing acceptable throughput,
incom-
ing/outgoing burst size, incoming/outgoing frame rate.
A DLCI can be of 10, 17, or 24 bits in length, spanning a 2,
3,
respectively 4 octet Frame Relay header.
This document is intended to apply to both switched and
permanent
Frame Relay virtual circuits.
The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED,
RECOMMENDED,
SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted
as
defined in RFC 2119.
2. Maximum Transmission Unit
The minimum frame size for a Frame Relay link is 5, 6, or 7
octets,
depending on the size of the DLCI (10, 17, or 24 bits). A Frame
Relay
network must support at least a maximum size of 262 octets.
IPv6
requires a minimum MTU size of 576 octets.
In general, Frame Relay devices are configured to have an MTU of
at
least 1600 octets. Therefore, the default MTU size for a Frame
Relay
is considered to be 1600.
A smaller than default MTU can be configured but of course
not
smaller than the minimum MTU of 576 octets.
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An adequate larger than default MTU can be configured to avoid
frag-
mentation. The maximum MTU size is controlled by the CRC
generation
mechanisms employed at the HDLC level. CRC16 will protect frames
up
to 4096 bytes in length, which reduces the effective maximum MTU
size
to approximately 4080 bytes. A larger desired MTU size (such as
that
used by FDDI or Token Ring), would require the CRC32 mechanism,
which
is not yet widely used and is not mandatory for frame relay
systems
conforming to Frame Relay Forum and ITU-T standards.
Implementations may allow, if upper layers provide adequate
error
protection/detection mechanisms, configuring a Frame Relay link
with
a larger than 4080 octets MTU but with a lesser error
protec-
tion/detection mechanism at link layer.
Although a Frame Relay circuit allows the definition of distinct
max-
imum frame sizes for input and output, for simplification
purposes,
this specification assumes symmetry, i.e. the same MTU for both
input
and output.
Furthermore, implementations limit the setting of the Frame Relay
to
the link level, which is enforced on all of the VCs that use
the
link, i.e. MTU can NOT be set for each VC using a link.
3. Frame format
IPv6 packets are transmitted in standard [ENCAPS] SNAP frame
encapsu-
lation format:
0 1 (Octets)
+-----------------------+-----------------------+
(Octets)0 | Q.922 Address |
+-----------------------+-----------------------+
2 | Control (UI) 0x03 | pad 0x00 |
+-----------------------+-----------------------+
4 | NLPID 0x80 (SNAP) | | SNAP
Header
+-----------------------+ OUI =3D 0x00-00-00 +
Indicating
6 | | IPv6
+-----------------------+-----------------------+
8 | IPv6 PID 0x86DD |
+-----------------------+-----------------------+
10 | IPv6 packet |
| . |
| . |
+-----------------------+-----------------------+
The IPv6 does not have an NLPID defined at this time, therefore
at
this point only the SNAP encapsulation is used.
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4. Stateless Autoconfiguration
The interface token [CONF] for an IPv6 Frame Relay interface must
be
unique on the virtual link represented by the virtual circuit
i.e.,
the circuit's end-point nodes must have distinct interface
tokens.
This applies regardless the virtual circuit is a
point-to-point,
point-to-multipoint, or multipoint-to-multipoint circuit, and
regard-
less the timing of the node joining a multi-point ended circuit.
The interface token is locally generated by the Frame Relay
device,
and it can have as seed any combination of 64 bits, as long as
the
result is a unique token on the link.
A method to construct the Frame Relay Interface Token is as follows:
0 1 2 3 4 5 6 7 (Bits)
+-----+-----+-----+-----+-----+-----+-----+-----+
(Ootets) 0 | | MBZ |
+ Any value +-----+-----+
1 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
2 | Frame Relay Node Identifier |
+-----+-----+-----+-----+-----+-----+-----+-----+
3 | |
+- Frame Relay Link Identifier -+
4 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
5 | |
+- -+
6 | Frame Relay DLCI |
+- -+
7 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
The EUI-64 "universal/local" bit is set to zero to reflect that
the
64 bit interface identifier value has local significance. The
"indi-
vidual/group" bit is set to 0 to reflect the unicast address.
There-
fore bits 6, and 7 of the first octet Must Be Zero (MBZ).
The rest of the first two octets can be any combination of bit
val-
ues.
The Frame Relay Node Identifier is a user administered value used
to
Locally identify this Frame Relay Switching Node.
The Frame Relay link identifier is a numerical representation of
the
link over which the Frame Relay VC is configured.
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The DLCI value is normalized to a 24 bit representation. This
handles
all combinations of 10, 17, and 24 bit DLCIs.
Note that other mechanisms to generate the interface token can
be
used, such as random number generators, etc... In either case,
in
conformance to {AARCH] the bit 6 and 7 MUST be 0 to reflect
the
EUI-64 local significance, respectively the unicast address.
Addi-
tionally, octet 5, 6, and 7, MUST be the normalized value of
the
DLCI. This ensures that the Frame Relay "solicited-node
multicast
address" derived from the IPv6 address built with this
interface
token contains the DLCI. It also allows building a valid
IPv6
"solicited-node multicast" address knowing a DLCI of an interface.
0 1 2 3 4 5 6 7 (Bits)
+-----+-----+-----+-----+-----+-----+-----+-----+
0 | | MBZ |
+ +-----+-----+
1 | |
+- -+
2 | Random Generated Number |
+- -+
3 | |
+- -+
4 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
5 | |
+- -+
6 | Frame Relay DLCI |
+- -+
7 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
The Duplicate Address Detection specified in [CONF] is
used
repeatedly during the interface token and local-link address
gen-
eration process, until the generated token and the
link-local
address on the link is unique.
Since DLCI values are local to a Frame Relay node, it is
possible
to have Frame Relay nodes within a Frame Relay network with
the
same interface token and link-local address on distinct
virtual
circuits (links).
5. Link-Local Addresses
The IPv6 link-local address [AARCH] for an IPv6 Frame Relay
interface
is formed by appending the interface token, as defined above, to
the
prefix FE80::/64.
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10 bits 54 bits 64 bits
+----------+-----------------------+----------------------------+
|1111111010| (zeros) |Frame Relay Interface Token |
+----------+-----------------------+----------------------------+
6. Address Mapping - Unicast
The procedure for mapping IPv6 addresses to Frame Relay
link-layer
addresses is described in [ND] and [IND].
The Source/Target Link-layer Address option used in Neighbor
Discov-
ery and Inverse Neighbor Discovery messages has the following
format
for a Frame Relay link:
0 1 2 3 4 5 6 7
+----+----+----+----+----+----+----+----+
0 | Type |
+----+----+----+----+----+----+----+----+
1 | Length |
+----+----+----+----+----+----+----+----+
with the following option values:
+----+----+----+----+----+----+----+----+
2 |EA=3D0| C/R| DLCI(high order) |
+----+----+----+----+----+----+----+----+
3 |EA=3D1| DE |BECN|FECN| DLCI(low order) |
+----+----+----+----+----+----+----+----+
4 | |
+ +
5 | |
+ Padding +
6 | (zeros) |
+ +
7 | |
+----+----+----+----+----+----+----+----+
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0 1 2 3 4 5 6 7
+----+----+----+----+----+----+----+----+
2 |EA=3D0| C/R| DLCI (high order) |
+----+----+----+----+----+----+----+----+
3 |EA=3D0| DLCI |
+----+----+----+----+----+----+----+----+
4 |EA=3D1| DE |BECN|FECN| DLCI(low order) |
+----+----+----+----+----+----+----+----+
5 | |
+ +
6 | Padding |
+ +
7 | |
+----+----+----+----+----+----+----+----+
0 1 2 3 4 5 6 7
+----+----+----+----+----+----+----+----+
2 |EA=3D0| C/R| DLCI (high order) |
+----+----+----+----+----+----+----+----+
3 |EA=3D0| DLCI |
+----+----+----+----+----+----+----+----+
4 |EA=3D0| DLCI |
+----+----+----+----+----+----+----+----+
5 |EA=3D1| DE |BECN|FECN| DLCI(low order) |
+----+----+----+----+----+----+----+----+
6 | |
+ Padding +
7 | |
+----+----+----+----+----+----+----+----+
Option fields:
Type 1 for Source Link-layer address.
2 for Target Link-layer address.
Length 1 (in units of 8 octets) for a 10, 17, or 24 bit
DLCI
DLCI The 10, 17, or 24 bit DLCI. The C/R, DE, BECN, FECN
bits
have no addressing significance. The EA bit signals
the
end of a DLCI.
6. Address Mapping - Solicited-Node Multicast Address
A Frame Relay interface token contains the 24 bit normalized value
of
the DLCI. An IPv6 packet with an IPv6 Solicited-Node Multicast
des-
tination address consisting of the sixteen octets DST[1]
through
DST[16], is transmitted to the Frame Relay DLCI derived from
DST[14],
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DST[15], and DST[16] - 24 bit normalized 10, 17, or 24 bit
DLCI
value.
Conversely, an IPv6 "solicited-node multicast" address built based
on
an interface's known DLCI is a valid multicast address for
that
interface.
0 1 2 3 4 5 6 7
+----+----+----+----+----+----+----+----+
0 |EA=3D0| C/R| DLCI(high order) |
+----+----+----+----+----+----+----+----+
1 |EA=3D1| DE |BECN|FECN| DLCI(low order) |
+----+----+----+----+----+----+----+----+
0 1 2 3 4 5 6 7
+----+----+----+----+----+----+----+----+
0 |EA=3D0| C/R| DLCI (high order) |
+----+----+----+----+----+----+----+----+
1 |EA=3D0| DLCI |
+----+----+----+----+----+----+----+----+
2 |EA=3D1| DE |BECN|FECN| DLCI(low order) |
+----+----+----+----+----+----+----+----+
0 1 2 3 4 5 6 7
+----+----+----+----+----+----+----+----+
0 |EA=3D0| C/R| DLCI (high order) |
+----+----+----+----+----+----+----+----+
1 |EA=3D0| DLCI |
+----+----+----+----+----+----+----+----+
2 |EA=3D0| DLCI |
+----+----+----+----+----+----+----+----+
3 |EA=3D1| DE |BECN|FECN| DLCI(low order) |
+----+----+----+----+----+----+----+----+
7. Security Considerations
The mechanisms defined in this document for generating IPv6
Frame
Relay address tokens are intended to provide local link
uniqueness.
There is no security protection from duplication through forgery
or
accident.
8. Acknowledgments
Thanks to Dan Harrington and Milan Merhar for reviewing this
document
and providing useful suggestions.
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9. References
[RFC-1883] S. Deering, R. Hinden, "Internet Protocol Version 6
Speci-
fication"
[AARCH]R. Hinden, S. Deering "IPv6 Addressing Architecture"
[ND] RFC 1970, T. Narten, E. Nordmark, W.Simpson "Neighbor
Discovery
for IP Version 6 (IPv6)"
[CONF] RFC 1971, S. Thomson, T. Narten "IPv6 Stateless
Autoconfigura-
tion"
[ENCAPS]RFC 1490, T. Bradley, C. Brown, A. Malis,
"Multiprotocol
Interconnect
over Frame Relay".
[IND] A. Conta "IPv6 ND Extensions for Inverse Neighbor Discovery".
Authors' Addresses
Alex Conta
Lucent Technologies Inc.
300 Baker Ave, Suite 100
Concord, MA 01742
+1-508-287-2842
email: aconta@lucent.com
Martin Mueller
Lucent Technologies Inc.
300 Baker Ave, Suite 100
Concord, MA 01742
+1-508-287-2833
email: memueller@lucent.com
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