Internet DRAFT - draft-tissa-trill-multilevel
draft-tissa-trill-multilevel
TRILL Working Group Tissa Senevirathne
Internet Draft Les Ginsberg
Intended status: Standard Track CISCO
Sam Aldrin
HuaWei
Ayan Banerjee
CISCO
May 28, 2013
Expires: November 2013
Default Nickname Based Approach for Multilevel TRILL
draft-tissa-trill-multilevel-02.txt
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Abstract
Multilevel TRILL allows the interconnection of multiple TRILL
networks to form a larger TRILL network without proportionally
increasing the size of the IS-IS LSP DB. In this document, an
approach based on default route concept is presented. Also,
presented in the document is a novel method of constructing multi-
destination trees using partial nickname space. Methods presented in
this document are compatible with the RFC6325 specified data plane
operations.
Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................4
3. Solution Overview..............................................4
4. Operational Overview...........................................5
4.1. Unicast Forwarding........................................5
4.2. IS-IS Protocol changes for unicast forwarding.............5
4.3. MAC Address Learning......................................5
4.4. Multicast.................................................6
4.5. Life of Multicast frame...................................9
5. Area Affinity sub-TLV.........................................10
6. Nickname acquisition and conflict resolution..................11
6.1. Nickname Management sub-TLV..............................13
7. Further optimizations.........................................14
7.1. Leaking of TRILL IS-IS sub-TLV within areas..............14
7.2. Identification of Global Trees...........................15
7.2.1. Global Tree capability sub-TLV......................17
7.2.2. Global Tree proposal sub-TLV........................17
7.2.3. Global Tree Identifier sub-TLV......................18
7.3. Announcing Group Addresses...............................18
8. Architecture Elements of Multi-level Multicast framework......21
8.1. Bootstrap RBridge........................................21
8.2. Rendezvous Point (RP)....................................22
8.3. Default Affinity sub-TLV.................................22
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8.4. Area Affinity sub-TLV....................................22
8.5. TRILL BSR Protocol.......................................22
9. Security Considerations.......................................22
10. IANA Considerations..........................................23
11. References...................................................23
11.1. Normative References....................................23
11.2. Informative References..................................23
12. Acknowledgments..............................................24
1. Introduction
The TRILL Base Protocol Specification [RFC6325] provides a method
for forwarding Layer 2 data frames over multiple active links,
thereby optimizing network bandwidth and resiliency. TRILL requires
native Layer 2 frames to be encapsulated with the TRILL header.
TRILL devices (RBridges) are identified with a 16 bit identifier
called a nickname. The TRILL header contains egress and ingress
RBridge nicknames. Intermediate RBridges performs forwarding based
on the egress nickname. TRILL utilize the IS-IS protocol to
distribute RBridge nicknames.
TRILL Base Protocol Specification [RFC6325] specifies a tree based
paradigm to forward broadcast and multicast traffic as well as
unknown unicast traffic.
Traditional Layer 2 devices perform forwarding based on MAC
addresses. As a result, in theory, all of the devices in the network
are required to learn all of the MAC addresses in the Layer 2
domain. This leads to very large forwarding table sizes in the
devices which limits the size of the layer 2 domain. Forwarding
within the TRILL network occurs not based on MAC addresses but based
on the RBridge nicknames. Hence, TRILL based networks have
significant potential to be the core forwarding plane of very large
datacenters.
Large datacenters are often multisite in nature and contain a large
number of RBridges. TRILL is designed to be a single IS-IS area. As
the size of the TRILL network grows, the size of the IS-IS LSP
database grows, leading to network convergence delays and increased
volatility during transient conditions such as link flaps.
As mentioned above TRILL utilizes a tree based forwarding paradigm
for multi-destination traffic. In large TRILL networks this may lead
to sub-optimal forwarding. Additionally, entire network wide
multicasting may lead to network bandwidth inefficiencies and have a
negative impact on performance.
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In order to support scaling and performance of large TRILL networks,
it is important to have methods to:
1. Limit the size of the IS-IS LSP database
2. Optimize multicast forwarding
3. Limit the scope of flooding and broadcast traffic
In this document we propose methods that allow implementing multi-
level TRILL without any data plane changes as well as meet the above
design goals.
Also presented in this document is a novel method of constructing
multi-destination trees using partial nickname space.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. Solution Overview
Herein we present a high level view of the proposed solution;
differing the details of the solution to subsequent sections.
The TRILL campus is divided in to multiple IS-IS L1 Areas
interconnected by L2 backbone area. The backbone area may be inter-
connected by an IS-IS K2 area or by some other means. For example,
one does not preclude a configuration based approach for the L2
backbone.
Area border RBridges indicate their ability to reach other areas by
setting the Attach bit in IS-IS Link State PDU.
RBridges forward frames destined to RBridges in the area using the
exact match of nicknames. Frames destined to RBridges outside of the
L1 area are forwarded using the default route advertised by the area
border RBridges.
Campus wide Multi-destination trees are partitioned in to two parts.
A backbone tree rooted on the L2 backbone and local trees rooted
within each L1 area. For campus wide trees the local trees and the
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backbone tree have the same nickname. This avoids the need for
egress RBridge nickname translation at the border RBridges).
One of the border RBridges performs connecting its local tree to the
corresponding backbone tree. The Affinity sub-TLV and Area Affinity
sub-TLV information facilitate constructing proper RPF states.
4. Operational Overview
4.1. Unicast Forwarding
The TRILL campus is divided in to multiple IS-IS L1 Areas with a
Layer 2 backbone. (Figure 1).
The "Attached" bit in IS-IS PDU is used to indicate the advertising
IS connected to other areas. In this document we propose to leverage
the "Attached" bit to identify the border RBRidges and forward
traffic for all un-resolved nicknames to the border RBridges.
Border RBridges possess the complete nickname space of the TRILL
campus. Utilizing this information, ingress area border RBRidge
forward TRILL frames to the egress area border RBridge via the L2
backbone.
Egress area border RBridges, forward the frame normally to the
intended destination in the given L1 Area.
4.2. IS-IS Protocol changes for unicast forwarding
Support for non zero IS-IS areas for TRILL.
No new TLV or sub-TLV required.
Border RBridges advertise LSP with the "Attached" bit set
L1 Area RBridges are required to advertise TRILL related sub-TLV
defined in [RFC 6326] with the router capability bit "S" set. The
capability bit "D" MUST be set to zero (0). This allows leaking L1
PDU to the L2 backbone area but not to other L1 areas [RFC4971].
4.3. MAC Address Learning
Egress RBridge learn remote MAC addresses against the actual
nickname of the ingress RBRidge.
As an example: Let's Assume MAC address A is attached to RB1 and MAC
address B is attached to RB7.
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RB1 receives a frame destined to MAC B. RB1 does not know the
location of MAC B. However, local policy such as, port or VLAN
indicates that the frame is of global scope. RB1 transmits the frame
on global tree "t" as an unknown unicast frame.
RB7 receives the frame and learn MAC A is associated with RB1. RB7
programs its forwarding tables such that MAC-A is associated with
RB1. It also forwards the frame to MAC-B.
MAC-B responds. RB7 has the association of MAC-A to RB1. Hence, RB7
forwards the frame to RB1 as a unicast frame, with egress RBridge
nickname as RB1 and ingress RBridge nickname as RB7.
The frame follows the normal uicast forwarding process explained
above and arrives at RB1. RB1, learns the MAC-B association to RB7
and updates its forwarding tables accordingly. Also, RB1 forwards
the frame to MAC-A.
4.4. Multicast
Multicast forwarding has two parts: 1. Construction of the multicast
trees 2. RPF (Reverse Path Forwarding) check.
In most of the real world deployments, not all of the traffic is
required or desired to span across the entire TRILL campus. The
majority of the traffic tends to have a local scope and some subset
of traffic to have a global scope.
The scope of global traffic may be identified either through VLAN or
via finegrain label that spans across the entire TRILL campus.
In this document we propose to classify TRILL multi-destination
trees into two types:
1. Local trees (trees that have a scope within the local area)
2. Global trees (trees that have a scope throughout the TRILL campus)
Multi-destination traffic of local scope is forwarded using Local
trees. Multi-destination traffic of global scope is forwarded using
global trees.
Construction of global multi-destination trees and performing RPF
check for such trees requires knowledge of all of the RBridges in
the entire TRILL campus. In a large TRILL campus, construction of
such global trees that need information of all RBridges may not only
lack scalability but also may run in to instabilities during network
changes. Additionally, when the TRILL campus is divided into
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multiple IS-IS L1 areas, RBridges within an L1 areas do not possess
reachability information for other areas. Thus, constructing such
global trees may not be possible.
In this document we propose an [RFC6325] compatible approach of
building multicast trees to address the issues mentioned above.
In the proposed method, global trees (campus wide trees) are
partitioned in to two instances; a backbone tree instance and set of
local tree instance per each area.
Backbone tree - An instance of the tree rooted in the L2 backbone.
The Backbone tree is represented by the same nickname as the global
tree.
Local tree - An instance of a tree per area, per campus wide tree,
rooted within each area. Each instance of the tree in each area is
represented by the same nickname as the global tree. (This is
important to avoid the need for tree translation at the border
RBridges)
L2 LSPs advertise the backbone tree.
L1 LSPs advertise the corresponding local-tree within each area.
One of the L1-L2 area border RBridges in an given area is assigned
the role of Rendezvous Point (RP) for the specific local tree (more
details are presented in section 8. ).
Each RP functions as the plumb between the global tree and local
tree. Both the trees have exactly the same nickname.
RP An RP advertises affinity to the rest of the campus for the
specified tree by using the Affinity sub-TLV [trillcmt]. In the
Affinity TLV associated nickname MUST be specified as zero to
indicate the Affinity is related to default route. We refer to this
usage of Affinity TLV as the default Affinity sub-TLV in the rest of
the document.
Each RBridge in the local L1 area builds its multi-destination SPF
tree as specified in [RFC6325] and [trillcmt]. RPF checks are
performed as specified in [RFC6325] and [trillcmt]. Additionally,
RPF checks for default nicknames (i.e. all unknown nicknames to the
local L1 area) are performed per the association specified by the
default Affinity sub-TLV.
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Additionally, each RP on behalf of the local Area it is representing
for multi-cast tree Tx, advertises Area Affinity-TLV towards the L2
backbone area. The Area Affinity TLV, include the L1 Area ID of the
associated area. The Area Affinity TLV, notifies RBridges in the L2
area to enable the RPF check to accept nicknames in the associated
L1 area from the announcing RP. The Area Affinity TLV allows greater
scaling of the IS-IS LSP DB. If Affinity TLV contains all of the
nicknames the IS-IS PDU size increases. Use of the Area Affinity
sub-TLV to summarize the entire area in a single sub-TLV, limits the
size of the LSP DB as well as PDU size. (Please see below for the
structure of the Area Affinity sub-TLV).
L1 Area A1 L2 Backbone L1 Area A2
+------------------+ +----------------+ +-----------------+
| RB2 | | RB5 |
| +---+ | | +---+ |
| o---o o---o o--o o--o |
| RB1 | | | | | | RB7 |
| +---+ +---+ | | +---+ +---+ |
|o-o | | | | | | |
| | o--o +---+ | | +---+ o--o o-o |
| +---+ | | | | | | +---+ |
| o---o o---o o--o o--o |
| +---+ | | +---+ |
| RB3 +----------------+ RB6 |
+-----------------+ +-----------------+
Figure 1 Sample Topology
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L1 Area A1 L2 Backbone L1 Area A2
+-------------------+ +----------------+ +-----------------+
| - t - | | - t - | | t |
| | \ \ | | / | \ | | - |- |
| | \ \ | | / | \ / | \ |
| | \ ----o RB2 o---- /|\ ----o RB5 o-- | \ |
| | \ (RP) | / \ | (RP) / \ |
| o \ | | / \ | | / o |
| \- | | / \ | | / RB7 |
| RB1 ---o RB3 | / \ | / |
| X---o \ t----- |
| | | ----X RB6 |
+-------------------+ +----------------+ +----------------+
-t- Tree root for tree t
--o Port that accept multicast traffic for the tree "t"
--X Ports that do not accept multicast traffic for the tree "t"
Figure 2 Logical Topology
Above Figure 1 depicts a sample Topology, Figure 2 depicts the
corresponding logical topology. Local multicast trees and the global
multicast trees have the same nickname "t". "X" denote the branches
of the multicast tree that are not used for multicast traffic
reception or transmission. L1 RBridges, RB1, RB7 install RPF check
based on the default Affinity TLV. L1 area border RBridges MUST not
install the default RPF check on L2 interfaces, instead they MUST
honor the Area Affinity TLV and install explicit RPF checks. Strict
RPF check on area border RBridges are mandatory to prevent transient
loops during topology changes.
4.5. Life of Multicast frame.
RB1 ingresses multicast frames of global scope to global tree "t".
The multicast frame traverses the tree "t" and arrives at RBridges
RB2 and RB3. RB2 is the Rendezvous Point (RP) for tree "t" for Area
A1. RB2 forward the frame to backbone multicast tree "t" as well as
to the other local ports. RB3 is not the RP for tree "t" for area
A1. Hence, it forwards the frame to local ports but does not forward
along the backbone multicast tree "t".
The multicast frame traverses along the backbone tree "t" and
arrives at Area A2 border RBridges RB5 and RB6. The RB6, which is
not the Rendezvous Point (RP) for backbone tree "t" for Area A2,
accepts multi-destination frames arriving on L2 interface and only
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forwards to other applicable L2 interfaces. Non RP RBridges do not
forward multi-destination frames arriving on global tree on L1 area
interface. RB5, the RP for the Area A2 for the multicast tree "t",
contains the RPF check to accept frames from others areas on tree
"t" on its L2 area interface. Hence, RB5, accept the multicast frame
from tree "t" and forward along the local tree "t" and its local
ports.
The multicast packet traverses along the local tree "t" in Area A2
and arrive at RB7. RB7 contains RPF check installed based on the
Default Affinity TLV for tree "t", to receive multicast traffic for
tree "t" that arrives from the RP facing interface. RB7 accepts the
multicast frame arriving on local tree "t" with ingress RBridge
nickname RB1 and performs applicable forwarding as specified in
[RFC6325].
RB6 is an Area border RBRidge for Area A2, but not RP for the area.
RB6 receives the multicast frame through the local tree "t". Non RP
area border RBridges for RPF and multi-destination forwarding
purposes function like a L1 area RBridge. RB6, honors the default
Affinity TLV received from RB5 for local multicast tree "t". Hence,
it installs RPF check to accept all nicknames (default nickname) for
tree "t" from the L1 Area interface pointing towards RB5.
RB6 accepts the incoming multicast frame along tree "t" with the
ingress RBridge nickname RB1 and performs applicable forwarding to
locally attached ports. RB6, which is a non RP for tree "t" for area
A2, MUST not forward the multicast frame to the global tree "t".
5. Area Affinity sub-TLV
Area Affinity sub-TLV is a sub-TLV under IS-IS Router capability TLV
and contains the following structure.
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+-+-+-+-+-+-+-+-+
|Type=AREA-AFF | (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+---------------+
| Area-ID-Length| (1 byte)
+---------------+---------------+
| Area ID | (variable 1..13)
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| number of trees | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|tree-num of 1st preferred root | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|tree-num of 2nd preferred root | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
+-------------------------------+
|tree-num of Nth preferred root | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 Area Affinity TLV structure
o Type: AREA-AFF, (TBD).
o Length: variable. Length is 1 + length of Area ID + 2*n, where
n is the number listed tree numbers.
o Area-ID : (variable length) Is the IS-IS Area ID. Length can be
1-13 bytes long.
o Number of trees : number of trees for which association
(affinity) being announced.
o Tree-num of preferred root: The tree Number of the multicast
tree.
Area-affinity conflicts MUST be resolved using methods specified
in [trillcmt].
6. Nickname acquisition and conflict resolution
In the proposed method, nicknames of RBridges in remote L1 areas are
not advertised into the local L1 area by area border RBridges.
However, L2 backbone RBridges and L1-L2 border RBridges contain the
nicknames used by all the RBridges in the campus. We propose to
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introduce a new IS-IS sub-TLV under Router capability TLV to
distribute available nickname space. New IS-IS sub TLV is Nickname
Management sub-TLV.
Nickname Management sub-TLV is announced by the area border RBridges
in to the local L1 area with Router capability bits D set to one and
S set to one. Nickname Management sub-TLV is announced in to L2 area
by the area border RBridges with S and D bit clear. These settings
ensure Nickname Management TLV is confined to the local L1 area L2
area and does not leak to other L1 areas.
Nickname Management sub-TLV instance announced in to the local area,
contains two sets of ranges. Local nickname ranges and dynamic
nickname ranges. Local nickname ranges are one or more sets of
ranges that network administrator has configured on the border
RBridges. Multiple local nickname ranges allow network administrator
to configure multiple sets of non contiguous nickname ranges.
L1 area RBridges SHOULD, first, select a nickname or nicknames from
the local ranges.
If entire local nickname space has exhausted (i.e. taken up by other
RBridges), then L1 are RBridges SHOULD select a nickname or
nicknames from the dynamic ranges.
It is recommended that RBridges use different nickname priorities to
differentiate nickname acquired by different methods. Nickname
priorities are assigned based on the acquisition method such that
configured nicknames have highest priority, followed by nicknames
derived from the local range, followed by nicknames derived from the
dynamic range.
Dynamic ranges are derived by the area border RBridges based on the
local nickname ranges of its and other areas. As an example let's
assume area A1 has local nickname range of 100-200, A2 has a local
nickname range of 201-300. Then the dynamic range is from 1-99 and
301 to 65471 (0xFFBF). Nickname values 0 and 0xFFC0 to 0xFFFF are
reserved and MUST not be included in the dynamic nickname ranges.
Nickname Management sub-TLV instance announced in to the L2 backbone
area, contains only the local nickname ranges. Local nickname ranges
of each area allow other areas to derive applicable dynamic ranges
to announce in to the corresponding L1 area.
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6.1. Nickname Management sub-TLV
+-+-+-+-+-+-+-+-+
|Type=NICK-MGMT | (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+---------------+
| Area-ID-Length| (1 byte)
+---------------+---------------+
| Area ID | (variable 1..13)
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NL | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|starting nickname for l-range 1| (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|end nickname for l-range 1 | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|starting nickname for l-range n| (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|end nickname for l-range n | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ND | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|starting nickname for d-range 1| (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|end nickname for d-range 1 | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|starting nickname for d-range n| (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|end nickname for d-range n | (2 bytes)
+-------------------------------+
Figure 4 Nickname Management sub-TLV structure
o Type: NICK-MGMT, (TBD).
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o Length: variable. Length is 1 + length of Area ID + 1+2*2*NL +
1 + 2*2*ND, where NL is the number local ranges and ND is
number of dynamic ranges.
o Area-ID : (variable length) Is the IS-IS Area ID. Length can be
1-13 bytes long.
o NL : number of local nickname ranges.
o ND : number of dynamic ranges.
o Starting nickname for l-range n: starting nickname of the local
range n.
o End nickname for l-range n: End nickname of the local range n.
o Starting nickname for d-range n: starting nickname of the
dynamic range n.
o End nickname for d-range n: End nickname of the dynamic range
n.
NOTE: Multiple instances of the nickname management sub-TLV MAY be
included. Nickname management sub-TLV has usage in non multi-level
deployments as well. Nickname management sub-TLV allows
administrator to control nickname acquisition by RBridges.
7. Further optimizations
RFC6325 allows multiple instance of nickname sub-TLV. If more
specific forwarding is required, for some critical RBridges, such
nicknames MAY be advertised in a separate Router capability TLV,
with S bit set. So it leaks to all L1 areas.
7.1. Leaking of TRILL IS-IS sub-TLV within areas
At the boundary nodes, the following information needs to be leaked
from the Level-1 database to the Level-2 database. The nickname TLVs
that are learned from all nodes within the same site needs to be
redistributed to the Level-2 database. All such redistributed
nickname TLVs will have the root priority set to 0. Note, that all
border area nodes will announce this TLV into the Level-2 database.
As a result, all Level-2 nodes will be able to see the reachability
of all other nodes. This enables unicast traffic flow. With respect
to multicast, redistributed nicknames are not to be used in the root
election for global trees. The roots of the global trees will be
from the set of nicknames that are in the Level-2 database. Once the
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roots have been identified, these nicknames need to be leaked back
to the Level-1 areas. Calculation of multi-destination trees are
presented in section 7.2.
7.2. Identification of Global Trees
It is expected only a sub-set of traffic requires a global reach
(inter Area). Majority of the traffic will be of local scope (intra
area). Scope of the traffic can be identified either based on VLAN
or fine-grain label. Traffic of global scope is forwarded using
global trees. The trees of global scope may be indentified:
1. By means of configuration
2. By means of multi-destination tree announcements sub-TLV.
Point number 2 above requires further clarifications. We propose to
introduce 3 new sub-TLV under IS-IS router capability TLV to
advertise global multi-destination trees. These new sub-TLV are
listed below. Format of the new sub-TLVs are presented in section
7.2.1. to 7.2.3.
o The Global Tree capability sub-TLV
o The Global Tree proposal sub-TLV
o The Global Tree identifier sub-TLV
Each RBridge announces two sets of capabilities; global tree
capabilities and local tree capabilities. It announces, maximum
number of global distributions trees it can compute. RBridges
utilize Global Tree sub-TLV for the purpose of announcing its global
tree capability. RBridges announce local tree capabilities using The
Tree sub-TLV [RFC6326]. Global tree space is disjoint from the local
tree space and MUST not have any effect on each other. Please refer
to [RFC6325] for the process of how local trees are derived. In this
section we present how the total number of global trees needed is
calculated and identification of nickname of each tree root.
Each area border RBridge, using the global tree sub-TLV received
from RBRidges in its local area, derives the number of trees the
area can support. The number of global trees "s", a local area can
support is the fewest number of global trees that an RBridge in
local area can support. Area border RBridges advertise in to the
backbone, using the global Tree capability sub-TLV, the number of
trees "s" that the given area can calculate. Global Tree capability
sub-TLV announced in to the L2 backbone are advertised with "S" and
"D" flags of Router Capability TLV set to 0. This prevent them
leaking to L1 areas.
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Rbridges in the L2 backbone calculate the number of global trees the
campus can calculate. This number "i" is the fewest number of global
trees among all areas.
Each RBridge in the L2 backbone using Global Tree proposal sub-TLV
advertise the number of trees it want other RBridges in the L2
backbone to calculate. RBridges in the L2 backbone identifies number
of global trees they need to calculate based on the number of trees
"k" advertised by the highest priority RBridge in the L2 backbone.
The L2 area RBridge with the highest priority advertises set of
nicknames for the global tree roots. These tree roots are selected
based on tree root priority announced by L2 backbone RBridges.
Global Tree Identifier sub-TLV is used for the purpose.
BSR RBRidge of each L1 area advertises nicknames of global tree
roots using Global Tree Identifier sub-TLV in to the corresponding
local area. BSR also advertises the number of Global trees k the
local area needs to calculate using Global tree proposal sub-TLV.
RBridges in the local area contain only nicknames of the local area.
Global Tree Identifier sub-TLV announced by the BSR contains
nicknames that are unknown to the local L1 area RBridges. How do
local RBridges calculate it SPF ?
Global Tree Identifier sub_TLV contain nickname of the global trees
ordered in ascending order. Default Affinity TLV announced by RP
RBridge contains the tree-id(s) that it is an RP. Tree-id k in the
Default affinity TLV corresponds to nickname k in the Global Tree
Identifier. RBRidges in the local L1 area calculate its SPF tree
assuming the tree-k is rooted at the RP RBridge announcing the
Default affinity sub-TLV for that tree.
Global Tree proposal sub-TLV and Global Tree Identifier sub-TLV MUST
only be advertised by BSR. Sub-TLV from highest priority RBRidge is
chosen, in the event of multiple RBridges advertising conflicting
sub-TLVs.
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7.2.1. Global Tree capability sub-TLV
+-+-+-+-+-+-+-+-+
|Type = GL-TREES| (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum trees able to compute | (2 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 Global Tree Capability sub-TLV
Type: Router Capability sub-TLV type, TBD
Length: 2.
Maximum trees able to compute: An unsigned 16-bit integer indicates
maximum number of global trees the announcing RBridge able to
compute.
7.2.2. Global Tree proposal sub-TLV
+-+-+-+-+-+-+-+-+
|Type = GL-TR-PR| (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum trees to compute | (2 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 Global Tree Proposal sub-TLV
Type: Router Capability sub-TLV type, TBD (GL-TR-PR)
Length: 2.
Maximum trees to compute: An unsigned 16-bit integer indicates
maximum number of global trees the announcing RBridge wants area
RBRidges to calculate.
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7.2.3. Global Tree Identifier sub-TLV
+-+-+-+-+-+-+-+-+
|Type=GLTR-RT-IDs| (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Starting Tree Number | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nickname (K-th root) | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nickname (K+1 - th root) | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nickname (...) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 Global Tree Identifier sub-TLV
Type: Router Capability sub-TLV type, set to TBD (GLTR-RT-IDs).
Length: 2 + 2*n, where n is the number of nicknames listed.
Starting Tree Number: This identifies the starting tree number ofthe
nicknames that are trees for the domain. This is set to 1 for the sub-
TLV containing the first list. Other Tree-Identifiers sub-TLVs will
have the number of the starting list they contain. In the event a tree
identifier can be computed from two such sub-TLVs and they are
different, then it is assumed that this is a transient condition that
will get cleared. During this transient time, such a tree SHOULD NOT
be computed unless such computation is indicated by all relevant sub-
TLVs present.
Nickname: The nickname at which a distribution tree is rooted.
7.3. Announcing Group Addresses
Group Address announcements facilitate optimization of multicast
forwarding. [RFC6326] and [rfc6326bis], define series of sub-TLV to
announce various flavors of Group addresses. These sub-TLVs are
encapsulated in Group Address TLV (142). We propose to define new
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set of sub-TLV under Group Address TLV to carry Group Address
announcements applicable to Global trees. IS-IS Group Address TLV
(142) does not have flags to control the scope of the TLV. Hence,
explicit, sub-TLV definitions are required to indentify group
announcements that have global scope.
New sub-TLV numbers are required for the following.
o Group MAC Address Sub-TLV
o Group IPv4 Address Sub-TLV
o Group IPv6 Address Sub-TLV
o Group Labeled MAC Address Sub-TLV
o Group Labeled IPv4 Address Sub-TLV
o Group Labeled IPv6 Address Sub-TLV
Above sub-TLVs as defined in [RFC6326] and [rfc6326bis] applies to
all trees within the TRILL campus. New sub-TLV definitions include
flexibility to define the applicable multicast trees. This
flexibility allows applications to further optimize multicast
pruning per multicast tree basis.
New group address sub-TLV will be named as below and they have
common TLV header as defined in Figure 8.
o Group MAC Address-multicast tree Sub-TLV
o Group IPv4 Address-multicast tree Sub-TLV
o Group IPv6 Address-multicast tree Sub-TLV
o Group Labeled MAC Address-multicast tree Sub-TLV
o Group Labeled IPv4 Address-multicast tree Sub-TLV
o Group Labeled IPv6 Address-multicast tree Sub-TLV
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+-+-+-+-+-+-+-+-+
|Type=G-ADDR-TR | (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESV | Topology-ID | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| number of trees | (2 bytes)
+-------------------------------+
| nickname of kth tree | (2 bytes)
+-------------------------------+
| nickname of k+1 tree | (2 bytes)
+-------------------------------+
. .
| |
+-------------------------------+
| nickname of (k+n) tree | (2 bytes)
+-------------------------------+
| RESV | VLAN ID/Label | (2 or 3 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Num Group Recs | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GROUP RECORDS (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GROUP RECORDS (m) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 Common structure of Group-Address-multicast tree sub-TLVs
o Type: G-ADDR-TR, (TBD). Defines sub-TLV for
o Group MAC Address-multicast tree Sub-TLV
o Group IPv4 Address-multicast tree Sub-TLV
o Group IPv6 Address-multicast tree Sub-TLV
o Group Labeled MAC Address-multicast tree Sub-TLV
o Length: Applicable length of the sub-TLV in bytes. Excludes
length of G-ADDR-TR and Length fields.
o Topology ID: 2 byte identifier of the topology instance id.
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o Number of trees: Number of tree nicknames included in the sub-
TLV. The nicknames included in the sub-TLV MUST be sorted in
ascending order.
o Nickname of kth tree: 2 byte nickname of the kth tree to which
this Group address-tree announcement applies.
o VLAN ID/Label: Either 4bit reserved followed by 12bit VLAN ID
or 24bit finegrain label. Please see [rfc6326bis] for details.
o Num Grp Recs: Number of Group Records to follow.
o Group Record: Contents of the Group Records depend on the G-
ADDR-TR definition and identical to their counterparts defined
in [rfc6326bis].
8. Architecture Elements of Multi-level Multicast framework
o Bootstrap RBridge
o Rendezvous Point (RP)
o Default Affinity sub-TLV
o Area Affinity sub-TLV
o RP Election Protocol
Five main elements of the multi-level multicast framework are listed
above. Functional overviews of the elements are discussed below.
Details, such as state machines, PDU format, etc, will be presented
in later versions of this document.
8.1. Bootstrap RBridge
Each Area has one more area border RBridges between the Area and the
L2 backbone area. For each area one of its area border RBridges is
elected as the Bootstrap RBridge.
Border RBridges communicate with each other using the TRILL BSR
protocol. Each border RBridge has a configured priority to be a
Bootstrap RBridge with system-ID as the tie breaker. The RBridge
with the highest priority become the bootstrap RBridge for the area.
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Bootstrap RBRidge selects the Rendezvous Point (RP) RBridges and
assign each RP a set of trees for which RP will function as the
gateway between the local and global multicast trees. To avoid loops
and/or packet duplication the set of trees MUST only be allocated to
one and only one RP.
8.2. Rendezvous Point (RP)
Rendezvous Point (RP) RBridge performs the function of gateway (or
acts as a point of plumbing) between the local multicast tree and
the corresponding global multicast tree rooted in the L2 backbone
area.
Bootstrap RBridge designates one of the border RBridges (including
itself) as the RP for a set of (mutually exclusive) trees.
Each border RBridge, using TRILL BSR protocol, announces its desire
to be an RP. The desire to be an RP is a configurable option and
enabled by default to be an RP.
8.3. Default Affinity sub-TLV
Default Affinity sub-TLV is announced by each RP to inform the
RBridges in the L1 Area the association of the default nickname to a
set of trees through the announcing RP [trillcmt].
RBridges in the L1 area, based on the Default Affinity sub-TLV
installs the RPF check for default nickname for the specified tree
"t" on an interface facing towards the announcing RP.
8.4. Area Affinity sub-TLV
The Area Affinity sub-TLV announced by each RP to inform the
RBridges in L2 backbone Area the association of local L1 Area
nicknames to a set of trees through the announcing RP (Figure 3).
RBridges in the L2 backbone area or has interfaces to the L2
backbone area, based on the Area Affinity sub-TLV, installs the RPF
check for the nicknames in the indicated L1 Area, for the specified
tree "t", on an interface facing towards the announcing RP.
8.5. TRILL BSR Protocol
9. Security Considerations
TBD
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10. IANA Considerations
IANA is requested to add the Area Affinity sub-TLV, Nickname
Management sub-TLV, Global Tree capability sub-TLV, Global tree
proposal sub-TLV, Global tree Identfier sub-TLV as sub-TLVs under
Router capability TLV.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, Internet Mail
Consortium and Demon Internet Ltd., November 1997.
[RFC4971] Vasseur, JP, et.al, "Intermediate System to Intermediate
System (IS-IS) Extensions for Advertising Router
Information ", RFC 4971, July 2007.
[RFC6325] Perlma, R., et.al, "Routing Bridges (RBridges): Base
Protocol Specification", RFC 6325, July 2011.
[trillcmt]Senevirathne, T., et.al, "Coordinated Multicast Trees
(CMT)for TRILL", Work in Progress, January 2012.
[RFC4971] Vasseur, JP, et.al, "Intermediate System to Intermediate
System (IS-IS) Extensions for Advertising Router
Information", RFC 4971, July 2007.
11.2. Informative References
[RFC6326] Eastlake, D, et.al, "Transparent Interconnection of Lots
of Links (TRILL) Use of IS-IS", RFC 6326, July 2011.
[rfc6326bis] Eastlake, D, et.al, "Transparent Interconnection of
Lots of Links (TRILL) Use of IS-IS", Work in Progress,
draft-eastlake-isis-rfc6326bis-04.txt, January 2012.
[trillml] Perlman, R., et.al, "RBridges: Multilevel TRILL", Work in
Progress, draft-perlman-trill-rbridge-multilevel-03.txt,
October 2011.
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12. Acknowledgments
We wish to thank Leonard Tracy, Dinesh Dutt and Ashok Ganesan for
reviewing and providing constructive feedback.
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Tissa Senevirathne
CISCO Systems
375 East Tasman Drive
San Jose CA 95134
Phone: 408-853-2291
Email: tsenevir@cisco.com
Les Ginsberg
CISCO Systems
510 McCarthy Blvd.
Milpitas CA 95035
Phone: 408-527-7729
Email:ginsberg@cisco.com
Sam Aldrin
Huawei Technologies
2330 Central Express Way
Santa Clara, CA 95951
Email: aldrin.ietf@gmail.com
Ayan Banerjee
CISCO Systems
425 East Tasman Drive
San Jose CA 95134
Phone: 408-527-0539
Email: ayabaner@cisco.com
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