📄 rfc2590.txt
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6 | "DLCI" |
+ +
7 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
Fig.1 Frame Relay Pseudo-Interface Identifier
The Duplicate Address Detection specified in [AUTOCONF] is used
repeatedly during the interface identifier and local-link address
generation process, until the generated identifier and consequently
the link-local address on the link -- VC -- are unique.
4.1 Generating the "Mid" field.
The "Mid" can be generated in multiple ways. This specification
suggests two mechanisms:
(b.1) "Use of Local Administrative Numbers"
The "Mid" is filled with the result of merging:
(b.1.1) A random number of 6 bits in length (Fig.2).
(b.1.2) The Frame Relay Node Identifier -- 16 bits -- is a user
administered value used to locally identify a Frame Relay
node (Fig.2).
(b.1.3) The Frame Relay Link Identifier -- 16 bits -- is a numerical
representation of the Frame Relay interface or link (Fig.2).
Conta, et al. Standards Track [Page 7]
RFC 2590 IPv6 over Frame Relay Networks May 1999
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
(Octets) 0 | Random Number | MBZ |
+-----------------------------------+-----+-----+
1 | |
+ Frame Relay Node Identifier +
2 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
3 | |
+ Frame Relay Link Identifier +
4 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
5 | |
+ +
6 | "DLCI" |
+ +
7 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
Fig.2 Frame Relay Pseudo-Interface Identifier
or,
(b.2) "Use of The Frame Relay address - E.164 [E164], X.121
[X25] numbers, or NSAP [NSAP] address"
If a Frame Relay interface has an E.164 or a X.121 number, or an
NSAP address, the "Mid" field MUST be filled in with a number
resulted from it as follows: the number represented by the BCD
encoding of the E.164 or X.121 number, or the binary encoding of
the NSAP address is truncated to 38 bits (Fig.3). Since the Frame
Relay interface identifier has a "local" significance, the use of
such a value has no real practical purposes other than adding to
the uniqueness of the interface identifier on the link. Therefore
the truncation can be performed on the high order or low order
bits. If the high order bits truncation does not provide
uniqueness on the link -- perhaps the DLCI value is not unique --
this most likely means that the VC spans more for instance than a
national and/or international destination area for an E.164
number, and therefore the truncation of the low order bits should
be performed next, which most likely will provide the desired
uniqueness.
Conta, et al. Standards Track [Page 8]
RFC 2590 IPv6 over Frame Relay Networks May 1999
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
(Octets) 0 | | MBZ |
+ +-----+-----+
1 | |
+ E.164, X.121 (BCD encoding) +
2 | or NSAP Address |
+ +
3 | (truncated to 38 bits) |
+ +
4 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
5 | |
+ +
6 | "DLCI" |
+ +
7 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
Fig.3 Frame Relay (Pseudo) Interface Identifier
5. Link-Local Addresses
The IPv6 link-local address [AARCH] for an IPv6 Frame Relay interface
is formed by appending the interface identifier, formed as defined
above, to the prefix FE80::/64 [AARCH].
10 bits 54 bits 64 bits
+----------+-----------------------+----------------------------+
|1111111010| (zeros) |Frame Relay Interface Ident.|
+----------+-----------------------+----------------------------+
6. Address Mapping -- Unicast, Multicast
The procedure for mapping IPv6 addresses to link-layer addresses is
described in [IPv6-ND]. Additionally, extensions to Neighbor
Discovery (ND) that allow the mapping of link-layer addresses to IPv6
addresses are defined as Inverse Neighbor Discovery (IND) in [IND].
This document defines the formats of the link-layer address fields
used by ND and IND. This specification does not define an algorithmic
mapping of IPv6 multicast addresses to Frame Relay link-layer
addresses.
The Source/Target Link-layer Address option used in Neighbor
Discovery and Inverse Neighbor Discovery messages for a Frame Relay
link follows the general rules defined by [IPv6-ND]. IPv6 addresses
can map two type of identifiers equivalent to link-layer addresses:
Conta, et al. Standards Track [Page 9]
RFC 2590 IPv6 over Frame Relay Networks May 1999
DLCIs, and Frame Relay Addresses. Therefore, for Frame Relay, this
document defines two distinct formats for the ND and IND messages
Link-Layer Address field:
(a) DLCI Format -- used in ND and/or IND messages on VCs that were
established prior to the ND or IND message exchange -- mostly
PVCs. The use on SVCs makes sense with Inverse Neighbor
Discovery [IND] messages if IND is employed after the successful
establishing of an SVC to gather information about other IPv6
addresses assigned to the remote node and that SVC.
(b) Frame Relay Address Format -- used mostly prior to establishing
a new SVC, to get the Frame Relay remote node identifier
(link-layer address) mapping to a certain IPv6 address.
Note: An implementation may hold both types of link layer
identifiers in the Neighbor Discovery cache. Additionally, in
case of multiple VCs between two nodes, one node's Neighbor
Discovery cache may hold a mapping of one of the remote node's
IPv6 addresses to each and every DLCI identifying the VCs.
The mechanisms which in such an implementation would make the
distinction between the Neighbor Discovery Cache mapping of an
IPv6 address to a "Frame Relay Address Format" and a "DLCI
Format" link-layer address, or among several mappings to a "DLCI
Format" addresses are beyond the scope of this specification.
The use of the override "O" bit in the advertisement messages
that contain the above Link-Layer Address formats SHOULD be
consistent with the [ND] specifications. Additionally, there
should be consistency related to the type of Link-Layer Address
format: an implementation should override one address format in
its Neighbor Discovery cache with the same type of address
format.
The "DLCI Format" is defined as follows:
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
0 | Type |
+-----+-----+-----+-----+-----+-----+-----+-----+
1 | Length |
+-----+-----+-----+-----+-----+-----+-----+-----+
Conta, et al. Standards Track [Page 10]
RFC 2590 IPv6 over Frame Relay Networks May 1999
with a DLCI (Q.922 address) encoded as option value:
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
2 | | 1 | 1 |
+ unused +-----+-----+
3 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
4 | DLCI(high order) | 0 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
5 | DLCI(low order) | 0 | 0 | 0 | 1 |
+-----+-----+-----+-----+-----+-----+-----+-----+
6 | |
+ Padding +
7 | (zeros) |
+-----+-----+-----+-----+-----+-----+-----+-----+
10 bits DLCI
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
2 | | 1 | 1 |
+ unused +-----+-----+
3 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
4 | DLCI(high order) | 0 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
5 | DLCI | 0 | 0 | 0 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
6 | DLCI(low order) | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
7 | unused (set to 0) | 1 | 1 |
+-----+-----+-----+-----+-----+-----+-----+-----+
17 bits DLCI
Conta, et al. Standards Track [Page 11]
RFC 2590 IPv6 over Frame Relay Networks May 1999
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
2 | | 1 | 1 |
+ unused +-----+-----+
3 | |
+-----+-----+-----+-----+-----+-----+-----+-----+
4 | DLCI(high order) | 0 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----
5 | DLCI | 0 | 0 | 0 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
6 | DLCI | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
7 | DLCI (low order) | 0 | 1 |
+-----+-----+-----+-----+-----+-----+-----+-----+
23 bits DLCI
Option fields:
Type 1 for Source Link-layer address.
2 for Target Link-layer address.
Length The Length of the Option (including the Type
and Length fields) in units of 8 octets.
It has the value 1.
Link-Layer Address The DLCI encoded as a Q.922 address.
Description
The "DLCI Format" option value field has two components:
(a) Address Type -- encoded in the first two bits of the first
two octets. Both bits are set to 1 to indicate the DLCI
format. The rest of the bits in the two first octets are
not used -- they MUST be set to zero on transmit and MUST
be ignored by the receiver.
(b) DLCI -- encoded as a Q.922 address padded with zeros to the
last octet of the 6 octets available for the entire Link-
Layer Address field of this format.
Conta, et al. Standards Track [Page 12]
RFC 2590 IPv6 over Frame Relay Networks May 1999
The "Frame Relay Address Format" is defined as follows:
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
0 | Type |
+-----+-----+-----+-----+-----+-----+-----+-----+
1 | Length |
+-----+-----+-----+-----+-----+-----+-----+-----+
with an E.164, X.121, number or NSAP address encoded as option
value:
7 6 5 4 3 2 1 0 (bit order)
+-----+-----+-----+-----+-----+-----+-----+-----+
2 | size | 1 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
3 | E.164 or X.121, or NSAP |
+--- Address Family Number ---+
4 | (Assigned Number) |
+-----+-----+-----+-----+-----+-----+-----+-----+
5 | |
/ E.164, or X.121 number (BCD encoded) /
/ or NSAP address /
4+size | |
+-----+-----+-----+-----+-----+-----+-----+-----+
5+size | |
/ Padding /
/ (zeros) /
8*Length-1| |
+-----+-----+-----+-----+-----+-----+-----+-----+
Option fields:
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