One document matched: draft-ietf-trill-rbridge-arch-03.txt
Differences from draft-ietf-trill-rbridge-arch-02.txt
Network Working Group Eric Gray, Editor
Internet Draft Ericsson
Expires: January, 2008
Intended Status: Informational
July 9, 2007
The Architecture of an RBridge Solution to TRILL
draft-ietf-trill-rbridge-arch-03.txt
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Abstract
RBridges are link layer (L2) devices that use routing protocols
as a control plane. They combine several of the benefits of the
link layer with network layer routing benefits. RBridges use
existing link state routing (without requiring configuration) to
improve RBridge to RBridge aggregate throughput. RBridges also
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provide support for IP multicast and IP address resolution
optimizations. They are intended to be applicable to similar L2
network sizes as conventional bridges and are intended to be
backward compatible with those bridges as both ingress/egress
and transit. They also support VLANs (although this generally
requires configuration) and otherwise attempt to retain as much
'plug and play' as is already available in existing bridges.
This document proposes an RBridge system as a solution to the
TRILL problem. It also defines the RBridge architecture, defines
its terminology, and describes basic components and desired
behavior. One or more separate documents specify the protocols
and mechanisms that satisfy the architecture presented herein.
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Table of Contents
1. Introduction................................................4
2. Background..................................................6
2.1. Existing Terminology...................................6
2.2. RBridge Terminology...................................10
3. Components.................................................12
3.1. RBridge Device........................................12
3.2. RBridge Data Model....................................13
3.2.1. Unicast TRILL Forwarding Database................13
3.2.2. Multi-destination TRILL Forwarding Database......13
3.2.3. Ingress TRILL Forwarding Database................15
4. Functional Description.....................................16
4.1. TRILL Campus Auto-configuration.......................16
4.2. RBridge Peer Discovery................................18
4.3. Tunneling.............................................19
4.4. RBridge General Operation.............................20
4.5. Ingress/Egress Operations.............................21
4.6. Transit Forwarding Operations.........................23
4.6.1. Unicast..........................................23
4.6.2. Broadcast, Multicast and Flooding................23
4.6.2-1. Broadcast...................................24
4.6.2-2. Multicast...................................25
4.6.2-3. Flooding....................................26
4.7. Routing Protocol Operation............................28
4.8. Other Bridging and Ethernet Protocol Operations.......28
4.8.1. Wiring Closet Problem............................29
5. How RBridges Address the TRILL Problem Space...............30
6. Conclusions................................................30
7. Security Considerations....................................31
8. IANA Considerations........................................32
9. Acknowledgments............................................32
10. References................................................32
10.1. Normative References.................................32
10.2. Informative References...............................32
Author's Addresses............................................33
Intellectual Property Statement...............................34
Disclaimer of Validity........................................34
Copyright Statement...........................................34
Acknowledgment................................................35
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1. Introduction
This document describes an architecture that addresses the TRILL
problem and applicability statement [2]. This architecture
describes a solution that is composed of a set of devices called
RBridges. RBridges cooperate together within an Ethernet
network to provide a layer two delivery service that makes
efficient use of available links using a link state routing
protocol. The service provided is analogous to creation of a
single, virtual device composed of an overlay of tunnels,
constructed between RBridge devices, using link state routing.
RBridges thus support increased RBridge to RBridge bandwidth and
fault tolerance, when compared to conventional Ethernet bridges
(which forward frames via a spanning tree), while still being
compatible with bridges and hubs.
The principal objectives of this architecture is to provide an
overview of the use of these RBridges in meeting the following
goals:
1) Provide a form of optimized layer two delivery service.
2) Use existing technology as much as possible.
3) Allow for configuration free deployment.
In providing a (optimized) layer two (L2) service, key factors
we want to maintain are: transparency to higher layer (layer 3
and above) delivery services and mechanisms, and use of location
independent addressing. Optimization of the L2 delivery service
consists of: use of an optimized subset of all available paths
and support for optimization of ARP/ND and pruning of multicast
traffic delivery paths.
To accomplish the goal of using existing technologies as much as
possible, we intend to specify minimal extensions (if required)
to one or more existing link-state routing protocols, as well as
defining the specific sub-set of existing bridging technologies
this architecture is intended to makes use of.
The extent to which routing protocol extensions may be required
depends on the closeness of the "fit" of any chosen routing
protocol to RBridge protocol requirements. See [6] for further
information on these requirements. The use of a specific routing
protocol - along with appropriate extensions and enhancements -
will be defined in corresponding RBridge protocol specifications
(see [3] for example).
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Specific protocol specifications will also describe the details
of interactions between the RBridge protocol and specific L2
technologies - i.e. - Virtual Local Area Networking (VLAN), L2
Multicast, etc. This document describes the general nature of
the RBridge solution without restricting related specifications.
As an overview, however, the intention is to use a link-state
routing protocol to accomplish the following:
1) Discover RBridge peers.
2) Determine RBridge link topology.
3) Advertise L2 reachability information.
4) Establish L2 delivery using shortest path (verses STP).
There are additional RBridge protocol requirements - above and
beyond those addressed by any existing routing protocol - that
are identified in this document and need to be addressed in
corresponding RBridge protocol specifications.
To allow for configuration free deployment, specific protocol
specifications should explicitly define the conditions under
which RBridges may - and may not - be deployed as-is (plug and
play), and the mechanisms that are required to allow this. For
example, the first requirement any RBridge protocol must meet is
to derive information required by link-state routing protocol(s)
for protocol start-up and communications between peers - such as
higher-layer addressing and/or identifiers, encapsulation header
information, etc.
At the abstract level, RBridges need to maintain the following
information:
1) Peer information,
2) Topology information,
3) Forwarding information -
a. unicast,
b. flooded, and
c. multicast.
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In addition, RBridge specifications may suggest (or require) the
maintenance of other information as needed to support ARP/ND and
multicast optimizations.
Peer information may be acquired via the routing protocol, or
may be discovered as a result of RBridge-specific peer discovery
mechanisms. Topology information is expected to be acquired via
the link-state routing protocol.
Forwarding information is derived from the combination of
attached MAC address learning, snooping of multicast-related
protocols (e.g. - IGMP), and routing advertisements and path
computations using the link-state routing protocol.
Other information - such as the mapping of MAC and IP addresses,
or multicast pruning information - may be learned using snooping
of ARP/ND or IGMP (for example) and it is possible that RBridges
may need to participate actively in these protocols.
The remainder of this document outlines the TRILL architecture
of an RBridge-based solution and describes RBridge components,
interactions and functions. Note that this document is not
intended to represent the only solution to the TRILL problem
statement, nor does it specify the protocols that instantiate
this architecture - or that only one such set of protocols is
prescribed. The former may be contained in other architecture
documents and the latter would be contained in separate
specification documents (see - e.g. - [3]).
2. Background
This architecture is based on the RBridge system described in an
Infocom paper [1]. That paper describes the RBridge system as a
specific instance; this document abstracts architectural
features only. The remainder of this section describes the
terminology of this document, which may differ from that of the
original paper.
2.1. Existing Terminology
The following terminology is defined in other documents. A brief
definition is included in this section for convenience and - in
some cases - to remove any ambiguity in how the term may be used
in this document, as well as in derivative documents intended to
specify components, protocol, behavior and encapsulation
relative to the architecture described in this document.
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o IEEE 802.1D and IEEE 802.1Q: IEEE documents which include
specification for bridged Ethernet, including Media Access
Control (MAC) bridges and the BPDUs used in spanning tree
protocol (STP) [5], [11].
o ARP: Address Resolution Protocol - a protocol used to find an
address of form X, given a corresponding address of form Y.
In this document, ARP refers to the well-known protocol used
to find L2 (MAC) addresses, using a given L3 (IP) address.
See [10] for further information on IP ARP.
o Bridge: an Ethernet (L2, 802.1D) device with multiple ports
that receives incoming frames on a port and transmits them on
zero or more of the other ports; bridges support both bridge
learning and STP. Transparent bridges do not modify the L2
PDU being forwarded.
o Bridge Learning: process by which a bridge determines on
which single outgoing port to transmit (forward or copy) an
incoming unicast frame. This process depends on consistent
forwarding as "learning" uses the source MAC address of
frames received on each interface. Layer 2 (L2) forwarding
devices "learn" the location of L2 destinations by peeking at
layer 2 source addresses during frame forwarding, and store
the association of source address and receiving interface.
L2 forwarding devices use this information to create
"filtering database" entries and - gradually - eliminate the
need for flooding.
o Bridge Protocol Data Unit (BPDU): the frame type associated
with bridge control functions (for example: STP/RSTP).
o Bridged LAN: see IEEE 802.1Q-2005, Section 3.3 [11].
o Broadcast Domain: the set of (layer 2) devices that must be
reached (or reachable) by (layer 2) broadcast traffic
injected into the domain.
o Broadcast Traffic: traffic intended for receipt by all
devices in a broadcast domain.
o Ethernet: a common layer 2 networking technology that
includes, and is often equated with, 802.3.
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o Filtering Database: database containing association
information of (source layer 2 address, arrival interface).
The interface that is associated with a specific layer 2
source address, is the same interface which is used to
forward frames having that address as a destination. When a
layer 2 forwarding device has no entry for the destination
layer 2 address of any frame it receives, the frame is
"flooded".
o Flooded Traffic: traffic that is subject to flooding - i.e. -
being forwarded on all interfaces, except the one on which it
was received, within a LAN or VLAN.
o Flooding: the process of forwarding traffic to ensure that
frames reach all possible destinations when the destination
location is not known. In "flooding", an 802.1D forwarding
device forwards a frame for any destination not "known" (i.e.
- not in the filtering or forwarding database) on every
active interface except that one on which it was received.
See also VLAN flooding and flooded traffic.
o Frame: in this document, frame refers to an Ethernet (L2)
unit of transmission (PDU), including header, data, and
trailer (or payload and envelope).
o Hub: an Ethernet device with multiple ports which
transparently transmits frames arriving on any port to all
other ports. This is a functional definition, as there are
devices that combine this function with certain bridge-like
functions that may - under certain conditions - be referred
to as "hubs".
o IS-IS: Intermediate System to Intermediate System routing
protocol. See [8] for further information on IS-IS.
o LAN: Local Area Network, is a computer network covering a
small geographic area, like a home, office, or group of
buildings, e.g., as based on IEEE 802.3 technology, see also
IEEE 802.1Q-2005, Section 3.11 [11].
o MAC: Media Access Control - mechanisms and addressing for L2
frame forwarding.
o Multicast Forwarding: forwarding methods that apply to frames
with broadcast or multicast destination MAC addresses.
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o Node: a device with an L2 (MAC) address that sources and/or
sinks L2 frames.
o OSPF: Open Shortest Path First routing protocol. See [7] and
[9] for further information on OSPF.
o Packet: in this document, packet refers to L3 (or above) data
transmission units (PDU - e.g. - an IP Packet (RFC791 [4]),
including header and data.
o PDU: Protocol Data Unit - unit of data to be transmitted by a
protocol. To distinguish L2 and L3 PDUs, we refer to L2 PDUs
as "frames" and L3 PDUs as "packets" in this (and related)
document(s).
o Router: a device that performs forwarding of IP (L3) packets,
based on L3 addressing and forwarding information. Routers
forward packets from one L2 broadcast domain to another (one,
or more in the IP multicast case) - distinct - L2 broadcast
domain(s). A router terminates an L2 broadcast domain.
o Spanning Tree Protocol (STP): an Ethernet (802.1D) protocol
for establishing and maintaining a single spanning tree among
all the bridges on a local Ethernet segment. Also, Rapid
Spanning Tree Protocol (RSTP). In this document, STP and RSTP
are considered to be the same.
o SPF: Shortest Path First - an algorithm name associated with
routing, used to determine a shortest path graph traversal.
o TRILL: Transparent Interconnect over Lots of Links - the
working group and working name for the problem domain to be
addressed in this document.
o Unicast Forwarding: forwarding methods that apply to frames
with unicast destination MAC addresses.
o Unknown Destination - a destination for which a receiving
device has no filtering database entry. Destination (layer
2) addresses are typically "learned" by (layer 2) forwarding
devices via a process commonly referred to as "bridge
learning".
o VLAN: Virtual Local Area Network, see IEEE 802.1Q-2005 [11].
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o VLAN Flooding: flooding as described previously, except that
frames are only forwarded on those interfaces configured for
participation in the applicable VLAN.
2.2. RBridge Terminology
The following terms are defined in this document and intended
for use in derivative documents intended to specify components,
protocol, behavior and encapsulation relative to the
architecture specified in this document.
o Adjacent RBridges: RBridges that communicate directly with
each other without relay through other RBridges.
o Cooperating RBridges: a set of communicating RBridges that
will share a consistent set of forwarding information.
o Designated RBridge (DR): the RBridge that is elected to
handle ingress and egress traffic to a particular Ethernet
link having shared access among multiple RBridges; that
RBridge is such a link's "Designated RBridge". The Designated
RBridge is determined by an election process among those
RBridges having shared access via a single LAN.
o Edge RBridge (edge of a TRILL Campus): describes RBridges
that serve to ingress frames into the TRILL Campus and egress
frames from the TRILL Campus. L2 frames transiting an TRILL
Campus enter, and leave, it via an edge RBridge.
o Egress RBridge: for any specific frame, the RBridge through
which that frame leaves the TRILL Campus. For frames
transiting a TRILL Campus, the egress RBridge is an edge
RBridge where RBridge encapsulation is removed from the
transit frames prior to exiting the TRILL Campus.
o Encapsulation database: in the TRILL context, the database
that the Designated RBridge (ingress) uses to map the layer 2
destination address in the received frame to the egress
Rbridge.
o Forwarding Tunnels: in this document, Campus Forwarding
Tunnels (or Forwarding Tunnels) is used to refer to the paths
for forwarding transit frames, encapsulated at an RBridge
ingress and decapsulated at an RBridge egress.
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o Ingress RBridge: for any specific frame, the RBridge through
which that frame enters the TRILL Campus. For frames
transiting a TRILL Campus, the ingress RBridge is the edge
RBridge where RBridge encapsulation is added to the transit
traffic entering the TRILL Campus.
o Multi-Destination Frames: Broadcast or Multicast frames, or
Unicast frames destined to a MAC DA that is unknown i.e. -
flooded frames (see flooded traffic). Frames that need to be
delivered to multiple egress RBridges, via the RBridge
Distribution Tree.
o Peer RBridge: The term "Peer RBridge", or (where usage is not
ambiguous) the term "Peer", are used in the RBridge context
to refer to any of the RBridges that make up a TRILL campus.
o RBridge: a logical device as described in this document,
which incorporate both routing and bridging features, thus
allowing for the achievement of TRILL Architecture goals. A
single RBridge device which can cooperate with other RBridge
devices to create a TRILL Campus.
o RBridge Distribution Tree: a tree used by RBridges to deliver
multi-destination frames. An RDT is computed using a specific
RBridge as the root. May also be referred to as an R-tree..
o TRILL Campus: this term, or the term "Campus" (where usage is
not ambiguous) is used in the RBridge context to refer to the
set of cooperating RBridges and TRILL Links that connect them
to each other.
o TRILL Forwarding Database: this term, or the term "forwarding
database" (where not ambiguous) is used in an RBridge context
to refer to the database that maps the egress TRILL address
to the next hop TRILL link.
o TRILL Header: a 'shim' header that encapsulates the ingress
L2 frame and persists throughout the transit of a TRILL
Campus, which may be further encapsulated within a hop-by-hop
L2 header (and trailer). The hop-by-hop L2 encapsulation in
this case includes the source MAC address of the immediate
upstream RBridge transmitting the frame and destination MAC
address of the receiving RBridge - at least in the unicast
forwarding case.
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o TRILL Link: this term, or the term "Link" (where its usage is
not ambiguous) is used in the RBridge context to refer to the
Layer 2 connection that exists either between RBridges, or
between an RBridge and Ethernet end stations.
3. Components
A TRILL Campus is composed of RBridge devices and the forwarding
tunnels that connect them; all other Ethernet devices, such as
bridges, hubs, and nodes, operate conventionally in the presence
of an RBridge.
3.1. RBridge Device
An RBridge is a device - having some of the characteristics of
both bridges and routers - that forwards frames on an Ethernet
link segment. It has one or more Ethernet ports which may be
wired or wireless; the particular physical layer is not
relevant. An RBridge is defined more by its behavior than its
structure, although it contains three tables which distinguish
it from conventional bridges.
Conventional bridges contain a learned filtering (or forwarding)
database, and a spanning tree port state information. The bridge
learns which nodes are accessible from a particular port by
assuming bi-directional consistency: the source addresses of
incoming frames indicate that the incoming port is to be used as
output for frames destined to that address. Incoming frames are
checked against the learned filtering (forwarding) database and
forwarded to the particular port if a match occurs, otherwise
they are flooded out all active ports (except the incoming
port).
Spanning tree port state information indicates the ports that
are active in the spanning tree. Details of STP operation are
out of scope for this document, however the result of STP is to
disable ports which would otherwise result in more than one path
traversal of the spanning tree.
RBridges, by comparison, have a TRILL forwarding database, used
for forwarding of RBridge encapsulated frames across the TRILL
Campus and by the ingress RBridge to determine the encapsulation
to use for frames received as un-encapsulated from non-RBridge
devices. The TRILL forwarding database is described in the
following sections.
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3.2. RBridge Data Model
The following tables represent the logical model of the data
required by RBridges in forwarding unicast and multicast data
across a TRILL Campus.
3.2.1. Unicast TRILL Forwarding Database
The Unicast TRILL Forwarding Database is a forwarding table for
unicast traffic within the TRILL Campus, allowing tunneled
traffic to transit the TRILL Campus from ingress to egress. The
size of a fully populated Unicast TRILL Forwarding Database at
each RBridge is maximally bounded by the product of the number
of directly connected RBridge peers (where "directly connected"
in this context refers to RBridges connected to each other
without transiting one or more additional RBridges) and VLANs.
RBridges may have separate Unicast TRILL Forwarding Databases
for each VLAN, if this is supported by configuration. The
Unicast TRILL Forwarding Database is continually maintained by
RBridge routing protocols and/or MAC learning. (see Section
4.7).
The Unicast TRILL Forwarding Database contains data specific to
RBridge forwarding for unicast traffic. The specific fields
contained in this table are to be defined in RBridge protocol
specifications. In the abstract, however, the table should
contain forwarding direction and encapsulation associated with
an RBridge encapsulated frame received - determined by the TRILL
"shim" header destination and VLAN (if applicable).
3.2.2. Multi-destination TRILL Forwarding Database
The Multi-destination TRILL Forwarding Database consists of a
set of forwarding entries used for support of RBridge
Distribution Trees (RDT). Multi-destination TRILL Forwarding
Database entries are distinct from typical Unicast TRILL
Forwarding Database entries because there may be zero or more of
them that match for any incoming frame.
The Multi-destination TRILL Forwarding Database may overlap the
Unicast TRILL Forwarding Database, or instantiated as a separate
table, in implementations.
In discussing entries to be included in the Multi-destination
TRILL Forwarding Database, the following entities are
temporarily defined, or further qualified:
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o Root RBridge - the RBridge that is the head end of an RDT.
All RBridges within a TRILL Campus are potential Root
RBridges.
o Egress RBridge - an RBridge that is the tail end of a path
corresponding to a specific Multi-destination TRILL
Forwarding Database entry. All RBridges within a TRILL Campus
are potential egress RBridges. Not all RBridges within a
TRILL Campus will be on the shortest path between any ingress
RBridge and any other egress RBridge.
o Local RBridge - the RBridge that forms and maintains the
Multi-destination TRILL Forwarding Database entry (or
entries) under discussion. The local RBridge may be a root
RBridge, or an egress RBridge with respect to any set of
entries in the Multi-destination TRILL Forwarding Database.
o RBridge TRILL Campus Egress Interface - an interface on any
RBridge where a transit RBridge encapsulated frame would be
decapsulated prior to forwarding. With respect to such an
interface, the local RBridge is the egress RBridge.
Each local RBridge will maintain a set of entries for at least
the following - corresponding to a subset of all possible
forwarding paths:
o Zero or more entries grouped for each root RBridge - keyed by
the root RBridge identifier - used to determine forwarding of
broadcast, multicast, and flooded frames originally RBridge
encapsulated by that ingress within the TRILL Campus.
o Corresponding to each of these entry groups, one entry for
each of zero or more egress RBridge - where the local RBridge
is on the shortest path toward that egress RBridge.
o Corresponding to each of these entry groups, one entry for
each of zero or more TRILL Campus egress interfaces.
Each entry would contain an indication of which single interface
a broadcast, multicast or flooded frame would be forwarded for
each (root RBridge, egress RBridge) pair. Entries would also
contain any required encapsulation information, etc. required
for forwarding on a given interface, and toward a corresponding
specific egress RBridge.
A local RBridge could maintain a full set of entries from every
RBridge to every other RBridge, however - depending on topology
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- only a subset of these entries would ever be used. In
addition, a topology change that changed selection of shortest
paths would also very likely change other elements of the
entries, negating possible benefits from having pre-computed
Multi-destination TRILL Forwarding Database entries.
Multi-destination TRILL Forwarding Database entries should also
include VLAN identification information relative to each set of
Root RBridges, to allow scoping of broadcast, multicast and
flooding forwarding by configured VLANs.
Multi-destination TRILL Forwarding Database entries should also
include Multicast-Group Address specific information relative to
each egress RBridge that is a member of a given well-known
multicast group, to allow scoping of multicast forwarding by
multicast group.
Implicit in this data model is the assumption that the TRILL
"shim" header encapsulation will contain information that
explicitly identifies the TRILL Campus ingress RBridge for any
broadcast, multicast or flooded frame.
How the Multi-destination TRILL Forwarding Database is
maintained will be defined in appropriate protocol
specifications used to instantiate this architecture. The
protocol specification needs to include mechanisms and
procedures required to establish and maintain the Multi-
destination TRILL Forwarding Database in consideration of
potential SPF recomputations resulting from network topology
changes.
3.2.3. Ingress TRILL Forwarding Database
The Ingress TRILL Forwarding Database determines how arriving
traffic will be encapsulated, for forwarding to the egress
RBridge, via the TRILL Campus. The Ingress TRILL Forwarding
Database can be considered a version of the learned filtering
(forwarding) database that treats the TRILL Campus, as a whole,
as another port. It becomes configured in much the same way: by
snooping incoming traffic, and assuming bi-directional
consistency. The information may be learned at the egress
RBridge and propagated to all other RBridges in the TRILL Campus
via the RBridge routing protocol, as an alternative to direct
MAC learning from data frames. The Ingress TRILL Forwarding
Database may be as large as the number of nodes on the Ethernet
LAN, across all VLANs. RBridges may have separate Ingress TRILL
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Forwarding Databases for each VLAN, if separate VLANs are
supported by configuration.
The Ingress TRILL Forwarding Database essentially determines the
tunnel encapsulation used to transport each specific frame
across the TRILL Campus.
4. Functional Description
The RBridge Architecture is largely defined by RBridge behavior;
the logical components are minimal, as outlined in Section 3.
4.1. TRILL Campus Auto-configuration
Cooperating RBridges self-organize to compose a single TRILL
Campus system. Consider first a set of bridges on a single
Ethernet LAN (Figure 1). Here bridges are shown as 'b', hubs as
'h', and nodes as 'N'; bridges and hubs are numbered. Note that
the figure does not distinguish between types of nodes, i.e.,
hosts and routers; both are end nodes at the link layer, and are
otherwise indistinguishable to L2 forwarding devices. Bridges in
this topology organize into a single spanning tree, as shown by
double lines ('=', '||', and '//') in the figure.
N N---b3---N
| ||
| ||
N---h1--b4===b5==h2==b6
| // | ||
| // N ||
| // ||
N---b7====b8-----b9-----N
| |\
| | \
N N N
Figure 1 Conventionally bridged Ethernet LAN
It is useful to note that hubs are relatively transparent to
bridges, both for traffic from nodes to bridges (h1) and for
traffic between bridges (h2). Also note that the same hub can
support traffic between bridges and from a host to a bridge
(h2), but that the spanning tree is exclusively between bridges.
Bridges are thus compatible with hubs, both as transits and
ingress/egress.
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A TRILL Campus operates similarly, and can be viewed as a
variant of the way bridges self-organize. Figure 2 shows the
same topology where some of the bridges are replaced by RBridges
(shown as 'r' in the figure). In this figure, stars ('*')
represent the paths the RBridge is capable of utilizing, due to
the use of link state routing. RBridges can tunnel directly to
each other (r4-r5), or through hubs (h2) or bridges (b8).
Note that the former b8-b9 path, which is b8-r9 in Figure 2 and
had been disable by the hypothetical spanning tree in Figure 1,
is now usable.
N N---b3---N
| ||
| ||
N---h1--r4***r5**h2**r6
* * | *
* * N *
* * *
N---r7****b8*****r9-----N
| |\
| | \
N N N
Figure 2 RBridged Ethernet LAN
Every node in a TRILL Campus is considered to have a primary
point of attachment to the TRILL Campus, as defined by the
Designated RBridge. Each Ethernet link segment attached to a
TRILL Campus has a single Designated RBridge; that RBridge is
where all traffic that transits the TRILL Campus enters and
exits. In Figure 2, it is easy to see that the nodes off of h1
must attach at r4; the nodes off of b3, however, attach at
either r5 or r6, depending on which is the Designated RBridge.
Without loss of generality, an RBridge topology can be
reorganized (ignoring link length) such that all nodes, hubs,
and bridges are arranged around the periphery, and all RBridges
are considered directly connected by their tunnels (Figure 3).
Note that this view ignores the ways in which hubs and bridges
may serve both on the ingress/egress and for transit, hence this
view is not useful for traffic analysis. Using this view, it is
easy to distinguish between RBridge to RBridge traffic and other
traffic on shared devices, such as h2 and b8, because RBridge to
RBridge traffic content is hidden from non RBridge devices by
the RBridge encapsulation.
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N N---b3---N
| ||
| ||
| h2
| /| \
| / N \
| / \
N---h1--r4***r5******r6
* * *
* * *
* * *
N---r7***********r9-----N
\ /|\
\ / | \
\ / N N
\ /
\ /
b8
|
N
Figure 3 Reorganized RBridge Ethernet LAN
4.2. RBridge Peer Discovery
Proper operation of the TRILL solution using RBridges depends on
the existence of a mechanism for discovering peer RBridges and
the RBridge topology. An accurate determination of RBridge
topology is required in order to determine how traffic frames
will flow in the topology and thus avoid the establishment of
persistent loops in frame forwarding.
The discovery mechanisms must use protocol messages which will
be propagated throughout a LAN (or broadcast domain) until they
are consumed by another RBridge. This must happen in order to
ensure that RBridges in the same broadcast domain are discovered
by their peers as required to allow for accurate determination
of RBridge topology.
These protocol messages should be distinguished in a manner that
is consistent with the chosen RBridge routing protocol, or any
other discovery mechanism used. It is very likely that peer
discovery will actually be done as part of the RBridge routing
protocol's peer discovery; however this is to be determined by
specific RBridge protocol specification(s).
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An RBridge intercepts protocol messages that it recognizes as
being of this type (peer discovery), performs any processing
required and forwards these messages as required by the
discovery protocol. For example, a receiving RBridge may first
determine if it has seen this message before and insert itself
in a list of RBridges traversed by this message prior to
forwarding the message on at least all interfaces other than the
one on which it was received.
Note that forwarding the modified message on all interfaces in
the example above is safe, if somewhat wasteful.
RBridges must forward all other protocol messages in a manner
consistent with L2 addressing and forwarding - as would be done
by a typical 802.1D bridge.
Handling of 802.1D BPDUs is as determined in section 4.8.
4.3. Tunneling
RBridges pass encapsulated frame traffic to each other
effectively using tunnels. These tunnels use an Ethernet link
layer header, together with a TRILL header.
Specifics of encapsulation are to be defined in appropriate
protocol/encapsulation specifications.
It is the combination of the encapsulation that distinguishes
RBridge to RBridge traffic from other traffic. The link header
includes source and destination addresses, which typically
identify the ingress and egress RBridges. For incoming multicast
and broadcast traffic, one of these addresses may represent the
multicast group or broadcast address. Additionally, these
addresses may be VLAN-specific, i.e., such that each ingress and
egress address have per-VLAN addresses.
The additional TRILL header is required to support loop
mediation for traffic within the TRILL Campus; traffic loops in
forwarding between RBridges and non-RBridge nodes, as well as
across non-RBridge devices between RBridges, is limited by loop
mediation and/or prevention mechanisms that are beyond the scope
of this document (but may include a TTL-like mechanism,
mechanisms to establish a loop free topology - such as
STP/RSTP/MSTP - or both) on the applicable LAN links.
The TRILL header and encapsulation:
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o must clearly identify the traffic as RBridge traffic - the
outer Ethernet header may, for instance, use an Ethertype
number unique to RBridges;
o should also identify a specific (egress) RBridge - the TRILL
header may, for example, include an identifier unique to the
egress RBridge;
o should include the RBridge transit route, a hopcount, or a
timestamp to prevent indefinite looping of a frame.
4.4. RBridge General Operation
Operations that apply to all RBridges include peer and topology
discovery (which may include negotiation of RBridge
identifiers), Designated RBridge election, link-state routing,
SPF computation and advertising reach-ability for specific L2
(MAC Ethernet destination) addresses within a broadcast domain.
In addition, all RBridges will compute RBridge Distribution
Trees for delivery of (potentially VLAN scoped) broadcast,
multicast and flooded frames to each peer RBridge. Setting up
these trees early is important as there is otherwise no means
for frame delivery across the TRILL Campus during the learning
phase. Because it is very likely to be impossible (at an early
stage) for RBridges to determine which RBridges are edge
RBridges, it is preferable that each RBridge compute these trees
for all RBridges as early as possible - even if some entries
will not be used.
The initial phase is the peer and topology discovery phase. This
should continue for a sufficient amount of time to reduce the
amount of re-negotiation (Designated RBridge and - possibly -
identifiers) and re-computation that will be triggered by
discovery of new peers. The timer values selected for delaying
the next phase should take into account the time required for
local STP and availability of segment connectivity between
RBridge peers.
The next phase is election of Designated RBridges for all shared
access segments. This phase cannot complete before completion of
peer and topology discovery. In parallel, RBridge routing
protocol should begin the process of building the link-state
information - assuming this was not done during the peer and
topology discovery phase.
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At about this time, RBridges should establish RBridge
Distribution Trees.
Once RBridges have established RBridge Distribution Trees, the
learning and forwarding phase may begin. In this phase, RBridges
initially forward frames by flooding via RBridge Distribution
Tree(s). Also during this phase, RBridges begin "learning" MAC
address locations from local segments and propagating L2 reach-
ability information via the RBridge routing protocol to all
other RBridges. Gradually, the Unicast TRILL Forwarding
Database will be built up for all RBridges, and fewer frames
will require flooding via the RBridge Distribution Tree(s).
ARP/ND optimization may occur during this phase as information
learned from ARP/ND queries may be propagated across the TRILL
Campus - potentially significantly reducing the impact of at
least one source of broadcast traffic.
The learning phase typically does not complete as new MAC
attachment information continues to be learned and old
information may be timed out and discarded. Consequently, the
learning phase is also the operational phase. During the
combined learning and operational phase, all RBridges maintain
both RBridge Distribution Trees and a Unicast TRILL Forwarding
Database. RBridges not elected as the Designated RBridge may be
required to become one in the event that the DR goes off-line.
4.5. Ingress/Egress Operations
Operation specific to edge RBridges involves RBridge learning,
advertisement, encapsulation (at ingress RBridges) and
decapsulation (at egress RBridges).
As described elsewhere, RBridge learning is similar to typical
bridge learning - i.e. - all RBridges listen promiscuously to L2
Frames on a local LAN segment and acquire location information
associated with source MAC addresses in L2 frames they observe.
By convention, a Designated RBridge election always occurs. In
the degenerate case - where only one RBridge is connected to a
specific Ethernet segment - obviously that RBridge will "win"
the election and become the designated RBridge.
With this convention, only the Designated RBridge performs
RBridge learning for interface(s) connected to that segment.
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As each RBridge learns segment-local MAC source addresses, it
creates an entry in its learned filtering/forwarding database
that associates that MAC source address with the interface on
which it was learned.
Similarly - for ARP/ND optimization - IP-to-MAC association
information may also be learned by snooping corresponding
protocol messages. Protocol specifications may include either
optional or required behaviors to support ARP/ND, or multicast,
learning and distribution methods.
Periodically, as determined by RBridge protocol specification,
each RBridge advertises this learned information to its RBridge
peers.
These advertisements propagate to all edge RBridges (as
potentially scoped by associated VLAN information for each
advertisement). Each edge RBridge incorporates this information
in the form of a Unicast TRILL Forwarding Database entry.
RBridges also discover that they are an edge RBridge as a result
of receiving un-encapsulated frames that require forwarding. If
an RBridge is the Designated RBridge for a segment, and it has
not previously learned that the MAC destination for a frame is
local (this will be the case - for instance - for the very first
frame it observes), then the RBridge would be required to
forward (or flood) the frame via the TRILL Campus to all other
RBridges (potentially within a VLAN scope).
The RBridge in this case would flood the frame unless it has
already created a Unicast TRILL Forwarding Database entry for
the frame's MAC destination address. If it has a corresponding
Unicast TRILL Forwarding Database, then it would use that. This
RBridge would be an ingress RBridge with respect to the frame
being forwarded.
The encapsulation used by this ingress RBridge would be
determined by the Unicast TRILL Forwarding Database - if one
exists - or the Unicast TRILL Forwarding Database-equivalent
entry for the RBridge Distribution Tree. The encapsulation - as
discussed elsewhere - should include (in the TRILL header)
information to identify the egress RBridge (for example, the
RBridge identifier negotiated previously during the peer and
topology discovery phase).
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When the encapsulated frame arrives at egress RBridge(s), it is
decapsulated and forwarded via the egress interface(s) onto the
local segment.
Note that an egress RBridge will be the Designated RBridge on
the local segment accessed via its egress interface(s). If the
received frame does not correspond to a learned MAC destination
address at an egress interface, it will forward the frame on all
interfaces for which it is either the designated - or only -
RBridge. If the received frame does correspond to a learned MAC
destination address at an egress interface, the RBridge will
forward the frame via that interface only.
4.6. Transit Forwarding Operations
There two models for transit forwarding within a TRILL Campus:
unicast frame forwarding for known destinations, and everything
else. The difference between the two is in how the
encapsulation is determined. Exactly one of these models will be
selected - in any instantiation of this architecture- for each
of the following forwarding modes:
o Unicast frame forwarding
o Forwarding of non-unicast frames
o Broadcast frame forwarding
o Multicast frame forwarding
o Frame flooding
4.6.1. Unicast
In unicast forwarding, the TRILL header is specific to the
egress RBridge and MAC destination in the outer Ethernet
encapsulation is specific to the next hop RBridge.
As the frame is prepared for transmission at each RBridge, the
next hop MAC destination information is determined at that local
RBridge using a corresponding Unicast TRILL Forwarding Database
entry based on the TRILL "shim" header.
4.6.2. Broadcast, Multicast and Flooding
RBridge Distribution Trees are used for forwarding of broadcast,
multicast and unknown destination frames across the TRILL
Campus. In a simple implementation, it is possible to use the
Multi-destination TRILL Forwarding Database entries for all
frames of these types.
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However, this approach results in potentially extreme
inefficiencies in the multicast and unknown destination flooding
cases.
As a consequence, instantiations of this architecture should
allow for local optimizations on a hop by hop basis.
Examples of such optimizations are included in the sections
below.
4.6.2-1. Broadcast
The path followed in transit forwarding of broadcast frames will
have been established through actions initiated by each RBridge
(as any RBridge is eligible to subsequently become an ingress
RBridge) in the process of computing Multi-destination TRILL
Forwarding Database entries. Each RBridge assumes that it may be
a transit as well as an ingress and egress RBridge and will
establish forwarding information relative to itself and each of
its peer RBridges, and stored in the Multi-destination TRILL
Forwarding Database. Multi-destination TRILL Forwarding Database
entries are computed at each RBridge for paths going toward all
other RBridges - at least in cases where the RBridge performing
Multi-destination TRILL Forwarding Database computations is on
the shortest path.
Forwarding information is in two forms: transit encapsulation
information for interfaces over which the RBridge will forward a
broadcast frame to one or more peer RBridges and a decapsulation
indication for each interface over which the RBridge may egress
frames from the TRILL Campus. In each case, the Multi-
destination TRILL Forwarding Database includes some
identification of the interface on which a frame is forwarded
toward any specific egress RBridge for frames received from any
specific ingress RBridge.
Note that an interface over which an RBridge may egress frames
is any interface for which the RBridge is a Designated RBridge.
RBridges must not wait to determine that one (or more) non-
RBridge Ethernet nodes is present in an interface before
deciding to forward decapsulated broadcast frames on that
interface.
Forwarding information is selected for each broadcast frame
received by any RBridge (based on identifying the ingress
RBridge for the frame) for all corresponding Multi-destination
TRILL Forwarding Database entries. Each RBridge is thus required
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to replicate one RBridge encapsulated broadcast frame for each
interface that is determined from Multi-destination TRILL
Forwarding Database entries corresponding to the frame's ingress
RBridge. This includes decapsulated broadcast frames for each
interface for which it is the designated RBridge.
Note that frame replication and forwarding should be scoped by
VLAN if VLAN support is provided. Also note that a Designated
RBridge (DR) may be required to transmit a decapsulated frame on
the interface on which it received the RBridge encapsulated
frame.
This approach for broadcast forwarding might be considered to
add complexity because replication occurs at all RBridges along
the ingress RBridge tree, potentially for both RBridge
encapsulated and decapsulated broadcast frames. However, the
replication process is similar to replication of broadcast
traffic in 802.1D bridges with the exception that additional
replication may be required at each interface for egress from
the TRILL Campus.
Note that the additional replication associated with TRILL
Campus egress may be made to exactly conform to 802.1D bridge
broadcast replication in implementations that model a TRILL
Campus egress as a separate logical interface.
Using this approach results in one and only one copy of the
broadcast frame being delivered to each egress RBridge.
4.6.2-2. Multicast
Multicast forwarding is reducible to broadcast forwarding in the
simplest (default) case. However implementations may choose -
using mechanisms that are out of scope for this document - to
optimize multicast forwarding. In order for this to work
effectively, however, support for awareness of multicast
"interest" is required for all RBridges.
Without optimization, multicast frames are injected by the
ingress RBridge onto an RDT by - for instance - encapsulating
the frame with a MAC destination multicast address, and
forwarding it according to its local Multi-destination TRILL
Forwarding Database. Again, without optimization, each RBridge
along the path toward all egress RBridges will similarly forward
the frame according to their local Multi-destination TRILL
Forwarding Database.
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Using this approach results in one and only one copy of the
multicast frame being delivered to appropriate egress RBridges.
However, using this approach, multicast delivery is identical to
broadcast delivery - hence very inefficient.
In any optimization approach, RBridge encapsulated multicast
frames will use either a broadcast or a group MAC destination
address. In either case, the recognizably distinct destination
addressing allows a frame forwarding decision to be made at each
RBridge hop. RBridges may thus be able to take advantage of
local knowledge of multicast distribution requirements to
eliminate the forwarding requirement on interfaces for which
there is no recipient interested in receiving frames associated
with any specific group address.
As stated earlier, in order for RBridges to be able to implement
multicast optimization, distribution of learned multicast group
"interest" information must be provided - and propagated - by
all RBridges. Mechanisms for learning and propagating multicast
group participation by RBridges is out of scope in this document
but may be defined in RBridge protocol specification(s).
Note that, because the multicast optimization would - in
principle - further scope and reduce broadcast traffic, two
things may be said:
o It is not necessary that all implementations in a deployment
implement the optimization (though all must support the data
required to implement it in RBridge peers) in order for any
local multicast optimization (consistent with the above
description) to work;
o Introduction of a multicast optimization will not result in
potential forwarding loops where broadcast forwarding would
not do so.
In the simplest case, the ingress RBridge for a given multicast
frame will re-use the MAC destination group address of a
received multicast frame. However this may not be required as
it is possible that the mechanisms specified to support
multicast will require examination of the decapsulated MAC
destination group address at each RBridge that implements the
optimization.
4.6.2-3. Flooding
Flooding is similarly reducible to broadcast forwarding in the
simplest (default) case - with the exception that a frame being
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flooded across the TRILL Campus is typically a unicast frame for
which no Unicast TRILL Forwarding Database entry exists at the
ingress RBridge. This is not a minor distinction, however,
because it impacts the way that addressing may be used to
accomplish flooding within the TRILL Campus.
An ingress RBridge that does not have a Unicast TRILL Forwarding
Database entry for a received frame MAC destination address,
will inject the frame onto the ingress RBridge Tree by - for
instance - encapsulating the frame with a MAC destination
broadcast address, and forwarding it according to its local
Multi-destination TRILL Forwarding Database. Without
optimization, each RBridge along the path toward all egress
RBridges will similarly forward the frame according to their
local Multi-destination TRILL Forwarding Database.
Using this approach results in one and only one copy of the
flooded frame being delivered to all egress RBridges.
However implementations may choose to optimize flooding. A
Flooding optimization will only work at any specific RBridge if
that RBridge re-evaluates the original (decapsulated) unicast
frame.
Any flooding optimization would operate similarly to the
multicast optimization described above, except that - instead of
requiring local information about multicast distribution - each
RBridge implementing the optimization will need only to lookup
the MAC destination address of the original (decapsulated) frame
in its local Unicast TRILL Forwarding Database. If an entry is
found, the frame could then be forwarded only if the specific
RBridge is on the shortest path between the originating ingress
RBridge and the appropriate egress RBridge. This could be
implemented - for example - as a specialized Multi-destination
TRILL Forwarding Database entry.
Note that, because the flooding optimization would - in
principle - further scope and reduce flooded traffic, two things
may be said:
o It is not necessary that all implementations in a deployment
support the optimization in order for any local flooding
optimization (consistent with the above description) to work
(hence such an optimization is optional);
o Introduction of the flooding optimization will not result in
potential forwarding loops where flooded forwarding would not
do so.
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Because a forwarding decision can be made at each hop, it is
possible to terminate flooding early if a Unicast TRILL
Forwarding Database for the original MAC destination was in the
process of being propagated when flooding for the frame was
started. It is therefore possible to reduce the amount of
flooding to some degree in this case.
4.7. Routing Protocol Operation
The details of routing protocol operation can be determined once
a specific routing protocol has been selected. These details
would be defined in appropriate protocol specification(s).
Protocol specifications should identify means for determining
the content of the Unicast TRILL Forwarding Database and Multi-
destination TRILL Forwarding Database.
4.8. Other Bridging and Ethernet Protocol Operations
In defining this architecture, several interaction models have
been considered for protocol interaction between RBridges and
other L2 forwarding devices - in particular, 802.1D bridges.
Whatever model we adopt for these interactions must allow for
the possibility of other types of L2 forwarding devices. Hence,
a minimal participation model is most likely to be successful
over the long term, assuming that RBridges are used in a L2
topology that would be functional if RBridges were replaced by
other types of L2 forwarding devices.
Toward this end, RBridges - and the TRILL Campus as a whole -
could (in theory) participate in Ethernet link protocols,
notably the spanning tree protocol (STP) on the ingress/egress
links using exactly one of the following interaction models:
o Transparent Participation (Transparent-STP)
o Active Participation (Participate-STP)
o Blocking Participation (Block-STP)
Only one of these variants would be supported by an instance of
this architecture. All RBridges within a single TRILL Campus
must use the same model for interacting with non-RBridge
protocols. Furthermore, it is the explicit intent that only one
of these models is ultimately supported - at least as a default
mode of compliant implementations.
This architecture assumes RBridges block STP.
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4.8.1. Wiring Closet Problem
There is at least one remaining issue with this assumption and
that has been referred to as the "wiring closet problem." The
essential problem is described in this subsection.
Given this configuration of bridges in a wiring closet, and an
RBridge core:
-----> B-1 <----------------> RB-a <-----.
| \
/ > RBridge CORE
| /
-----> B-2 <----------------> RB-b <-----'
The link between (802.1D) bridges B-1 and B-2 is meant to be
disabled by STP. In the RBridge case, however, there is no
indication (from STP) that this link is redundant. Moreover, in
order to avoid breaking bridge learning, either RB-a or RB-b
will be the DR and - as a result, only one of the links (B-
1<=>RB-a, B-2<=>RB-b) will get used.
One solution to this problem is to include - as a configuration
option, for instance - the ability to enable negotiation of (or
use of a pre-defined, or configurable) pseudo-bridge identifier
to be used in any of the variations of STP.
One - (near) zero-configuration - option we've considered would
be to use a well-known bridge identifier that each RBridge would
use as a common pseudo-bridge identifier. Such an ID, used in
combination with other STP configuration parameters, would most
likely have to be guaranteed to win the root bridge election
process in order to be a reasonable and useful default.
However, because this architecture assumes RBridges block STP,
participation in any form of STP is assumed to take place in an
in-line, co-located bridge function. Such a bridge function is
in addition to RBridge architectural functionality described in
this document. Implementations may include such functionality
and will very likely require some minimal configuration to turn
it on, in vendor specific RBridge implementations. An example
of a minimal configuration would be to assign a pseudo-bridge
identifier to (the local in-line co-located bridge associated
with) a specific RBridge port.
For reasons of interoperability, specific protocol proposals to
address the needs of this architecture may specify exactly how a
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co-located bridge will operate in this case (if such co-located
bridge functionality is included in an implementation), as well
as whether or not inclusion of such co-location is required.
As a further note, one of the problems that should be addressed
- assuming that this problem is to be resolved - is how to make
certain the solution is robust against configuration error. In
any solution that requires configuration of a pseudo-bridge ID
that is common across a TRILL Campus, for example, it is
possible to guard against configuration errors by using an
election process (based on the root bridge election process) to
determine which configured ID will be used by all RBridges in
common - assuming that multiple pseudo-bridge IDs are
inadvertently configured.
Finally, note that there is a chicken-and-egg problem associated
with RBridge participation in STP where RBridges may themselves
be connected by spanning trees.
5. How RBridges Address the TRILL Problem Space
The RBridge architecture addresses the following aspects of the
requirements identified in reference [2] through the use of a
link-state routing protocol and defined forwarding behaviors:
o Inefficient Paths
o Robustness to Link Interruption
In addition, using a logical model of "separation of functions"
this architecture allows specifications and implementations to
address existing and developing Ethernet extensions and
enhancements, and provides a background against which protocol
specifications may address: concerns about convergence under
dynamic network changes, and optimizations for VLAN, ARP/ND,
Multicast, etc.
6. Conclusions
This document discusses options considered and factors affecting
any protocol specific choices that may be made in instantiating
the TRILL architecture using RBridges.
Specific architectural and protocol instantiations should take
these into consideration. In particular, protocol, encapsulation
and procedure specifications should allow for potential
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optimizations described in the architectural document to the
maximum extent possible.
Also, this document addresses considerations relative to
interaction with existing technology and "future-proofing"
solutions. For both simplicity in description, and robust long
term implementation of the technology, this document recommends
the use of clear distinction - at all possible points - of
definitions, protocols, procedures, etc. from related (but not
identical) specifications and interactions.
In particular, this document recommends the use of a
"collocation model" in addressing issues with combining RBridge,
Router and 802.1D bridge behavior.
7. Security Considerations
As one stated requirement of this architecture is the need to be
able to provide an L2 delivery mechanism that is potentially
configuration free, the default operation mode for instances of
this architecture should assume a trust model that does not
require configuration of security information. This is - in fact
- an identical trust model to that used by Ethernet devices in
general.
In consequence, the default mode does not require - but also
does not preclude - the use of established security mechanisms
associated with the existing protocols that may be extended or
enhanced to satisfy this document's architectural definitions.
In general, this architecture suggest the use of a link-state
routing protocol - modified as required to support L2 reach-
ability and link state between RBridges. Any mechanisms defined
to support secure protocol exchanges between link-state routing
peers may be extended to support this architecture as well.
This architecture also suggests use of additional encapsulation
mechanisms and - to the extent that any proposed mechanism may
include (or be extended to include) secure transmission - it may
be desirable to provide such (optional) extensions.
To the extent possible, any extensions of protocol or
encapsulation should allow for at least one mode of operation
that doesn't require configuration - if necessary, for limited
use in a physically secure deployment.
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8. IANA Considerations
This document has no direct IANA considerations. It does
suggest, that protocols that instantiate the architecture use a
TRILL header as a wrapper on the payload for RBridge to RBridge
traffic, And this TRILL header may be identified by a new
Ethertype in the tunneled Ethernet link header. This Ethertype,
identified in an Ethernet header, would be allocated by the
IEEE.
9. Acknowledgments
The initial work for this document was largely done by Joe
Touch, based on work he and Radia Perlman completed earlier.
Subsequent changes are not to be blamed on them.
In addition, the current text has been helped substantially by
comments and suggestions from the TRILL working group, working
group chairs, and from Ron Bonica, Stewart Bryant, Joel Halpern,
Guillermo Ibanez and Russ White in particular. Also, a great
deal of work was recently done - by Joe Touch, Radia Perlman,
Dinesh Dutt and Silvano Gai - in an effort to align terminology
and concepts used in this document with those also used in the
other TRILL documents.
10. References
10.1.Normative References
None.
10.2.Informative References
[1] Perlman, R., "RBridges: Transparent Routing", Proc.
Infocom 2005, March 2004.
[2] Touch, J., R. Perlman, (ed.) "Transparent Interconnection
of Lots of Links (TRILL): Problem and Applicability
Statement", work in progress, draft-touch-trill-prob-
00.txt, November, 2005.
[3] Perlman, R., J. Touch, "RBridges: Base Protocol
Specification", work in progress, draft-ietf-trill-
rbridge-protocol-04.txt, January, 2006.
[4] Postel, J., "INTERNET PROTOCOL", RFC 791, September, 1981.
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[5] 802.1D-2004 IEEE Standard for Local and Metropolitan Area
Networks: Media Access Control (MAC) Bridges
[6] Gray, E., (ed.) "TRILL Routing Requirements in Support of
RBridges", work in progress, draft-ietf-trill-routing-
reqs-02.txt, September, 2006
[7] Moy, J., "OSPF Version 2", RFC 2328, April, 1998.
[8] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and
Dual Environments", RFC 1195, December, 1990.
[9] Coltun, R., D. Ferguson & J. Moy, "OSPF for IPv6", RFC
2740, December, 1999.
[10] Plummer, D., "An Ethernet Address Resolution Protocol --
or -- Converting Network Protocol Addresses to 48.bit
Ethernet Address for Transmission on Ethernet Hardware",
RFC 826, November, 1982.
[11] 802.1Q-2005 IEEE Standard for Local and Metropolitan Area
Networks: Virtual Bridged Local Area Networks
(Incorporates IEEE Std 802.1Q-1998, IEEE Std 802.1uT-2001,
IEEE Std 802.1vT-2001, and IEEE 802.1sT-2002)
Author's Addresses
Editor:
Eric Gray
Ericsson
900 Chelmsford Street
Lowell, MA, 01851
Phone: +1 (978) 275-7470
EMail: Eric.Gray@Ericsson.com
Contributors:
Joe Touch
USC/ISI
4676 Admiralty Way
Marina del Rey, CA 90292-6695, U.S.A.
Phone: +1 (310) 448-9151
EMail: touch@isi.edu
URL: http://www.isi.edu/touch
Gray Expires January, 2008 [Page 33]
Internet-Draft RBridge Architecture July 2007
Radia Perlman
Sun Microsystems
EMail: Radia.Perlman@sun.com
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Gray Expires January, 2008 [Page 34]
Internet-Draft RBridge Architecture July 2007
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Acknowledgment
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Gray Expires January, 2008 [Page 35]
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