Internet DRAFT - draft-ietf-sipp16-sdrp-format
draft-ietf-sipp16-sdrp-format
Network Working Group Peter Ford
INTERNET DRAFT LANL
Tony Li
cisco Systems
Yakov Rekhter
T.J. Watson Research Center, IBM Corp.
July 1994
SDRP Routing Header Format for SIPP-16
<draft-ford-sdrp-sipp16-format-00.txt>
Status of this Memo
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1. Introduction
This document specifies the format of a SIPP extended routing header
to provide forwarding functionality comparable to SDRP [SDRP]. The
reader should be familiar with [SIPP-16].
2. Acknowledgements
This document is based on "Source Demand Routing: Packet Format and
Forwarding Specification (Version 1)" [SDRP].
3. Model of Operation
An Internet can be viewed as a collection of routing domains
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interconnected by means of common subnetworks, and Border Routers
(BRs) attached to these subnetworks. A routing domain itself may be
composed of further subnetworks, routers interconnecting these
subnetworks, and hosts. This document assumes that there is some
type of routing present within the routing domain, but it does not
assume that this intra-domain routing is coordinated or even
consistent.
For the purposes of this discussion, a BR belongs to only one domain.
A pair of BRs, each belonging to a different domain, but attached to
a common subnetwork, form an inter-domain connection. By definition,
packets that traverse multiple domains must traverse BRs of these
domains. Note that a single physical router may act as multiple BRs
for the purposes of this model.
A pair of domains is said to be adjacent if there is at least one
pair of BRs, one in each domain, that form an inter-domain
connection.
Each domain has a globally unique identifier, called a Domain
Identifier (DI). All the BRs within a domain need to know the DI
assigned to the domain. Management of the DI space is outside the
scope of this document. This document assumes that DIs are expressed
as SIPP-16 cluster addresses. A domain path (or simply path) refers
to a list of DIs such as might be taken from an IDRP RD path.
A component in an SDRP route is either a DI (expressed as a cluster
address) or a router (expressed as a unicast address). Thus, an SDRP
route is defined as a sequence of domains and routers, syntactically
expressed as a sequence of cluster and unicast addresses. Thus an
SDRP route is a collection of source routed hops.
An SDRP hop can either be a "strict" source routed hop, or a "loose"
source routed hop. A strict source route hop is one in which, if the
next hop specified is a DI, and the DI refers to a domain immediately
adjacent to the current domain, then the packet will be forwarded
directly along a route within the domain; if the next hop specified
is an IP address, then it must refer to an immediately adjacent
system on a common subnetwork to the current router. Any other kind
of a source route hop is a loose source route hop.
A route is a "strict source route" if the current hop being executed
is processed as a strict source route hop. Likewise, a route is a
"loose source route" if the current hop being executed is processed
as a loose source route hop.
In the common case of unicast source routing, the last element of a
source route will be the unicast address of the destination host. A
source route with components consisting of a list of DIs terminated
by a unicast destination address would be used for implementing
provider selection to a destination.
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This document specifies SDRP operations when that common network
layer protocol is [SIPP-16].
4. SDRP Routing Header format
A SDRP Routing Header is a type of a SIPP Routing Header. The value
of the Routing Type field of the SIPP Routing Header is set to 1 for
a SDRP Routing Header. A SDRP SIPP-16 Routing header has the
following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header |Routing Type=1 |M|F| Reserved | SrcRouteLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NextHopPtr | Strict/Loose Bit Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Route, a list of SIPP addresses |
| (integral multiple of 128 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header - 8-bit selector. Identifies the type of the header
immediately following the Routing header. Uses the same values as
the IPv4 Protocol field [RFC-1340] plus new types defined for
SIPP.
Routing Type - 1.
Flags (2 bits):
MRE, Must Report Errors (bit 0).
If this bit is set to 1, and a router can not further
forward a packet (with an incompletely traversed source
route), as specified in the Source Route, the router must
generate an ICMP error message. If this bit is set to 0,
and a router can not further forward a packet (with an
incompletely traversed source route), as specified in the
Source Route, the router should not generate an ICMP error
message.
Failure of Source Route Behavior(bit 1).
If this bit it set to 1, it indicates that if a router can
not further forward a packet (with an incompletely
traversed source route), as specified in the Source Route,
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the router must set the value of the Next Hop Pointer
field to the value of the Source Route Length field, so
that the subsequent forwarding will be based solely on the
destination address. If this bit is set to 0, it indicates
that if a router can not further forward a packet (with an
incompletely traversed source route), as specified in the
Source Route, the router must discard the packet.
Reserved (6 bits).
Must be sent as zero and ignored on receipt.
Source Route Length- 8 bit unsigned integer. Number of source
route elements/hops in the SDRP Routing header. Length of SDRP
routing header can be calculated from this value (length =
SrcRouteLen * 16 + 8) This field may not exceed a value of 24.
Next Hop Pointer- 8 bit unsigned integer. Index of next
element/hop to be processed; initialized to 0 to point to first
element/hop in the source route. When Next Hop Pointer is equal
to Source Route Length then the Source Route is completed.
Strict/Loose Bit Mask (24 bits).
The Strict/Loose Bit Mask is used when making a forwarding
decision. If the value of the Next Hop Pointer field is N,
and the N-th bit in the Strict/Loose Bit Mask field is set
to 1, it indicates that the next hop is a Strict Source
Route Hop. If this bit is set to 0, it indicates that the
next hop is a Loose Source Route Hop.
Source Route (variable length, multiple of 16 octets).
The components of the source route are syntactically
SIPP-16 addresses[SIPP-16]. A Source Route can contain an
arbitrary intermix of unicast and cluster addresses.
5. Forwarding Behavior
The forwarding behavior is defined in [SRFSS].
6. Authors' Address
Peter Ford
Los Alamos National Laboratory
Los Alamos
Phone: (505) 665-0058
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e-mail: peter@goshawk.lanl.gov
Tony Li
cisco Systems, Inc.
1525 O'Brien Drive
Menlo Park, CA 94025
email: tli@cisco.com
Yakov Rekhter
T.J. Watson Research Center IBM Corporation
P.O. Box 218
Yorktown Heights, NY 10598
Phone: (914) 945-3896
email: yakov@watson.ibm.com
7. References
[RFC-1340] Reynolds, J. and Postel, J. "Assigned Numbers". July 1992.
RFC 1340.
[SDRP] Estrin, D., Li, T. , Rekhter, Y., and Varadhan K., "Source Demand
Routing: Packet Format and Forwarding Specification (Version 1)" 22
March, 1994. Internet Draft.
[SIPP-16] Deering, S., "Simple Internet Protocol Plus (SIPP)
Specification (128 bit address version)". 17 July 1994. Internet Draft.
[SRFSS] Li, T., Rekhter, Y. and Ford, P. "Source Routing Forwarding
Specification for SIPP". Work in Progress.
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