wdiff rfc7968.original rfc7968.txt

TRILL Working Group
Internet Engineering Task Force (IETF) Y. Li
INTERNET-DRAFT
Request for Comments: 7968 D. Eastlake
Intended Status: Standard 3rd
Category: Standards Track W. Hao
ISSN: 2070-1721 H. Chen
Huawei Technologies
S. Chatterjee
Cisco
Expires: January 1, 2017 June 30,
August 2016

TRILL:

Transparent Interconnection of Lots of Links (TRILL):
Using Data Label based Labels for Tree Selection for Multi-destination Multi-Destination Data
draft-ietf-trill-tree-selection-05

Abstract

TRILL (Transparent Interconnection of Lots of Links) uses
distribution trees to deliver multi-destination frames. Multiple
trees can be used by an ingress RBridge Routing Bridge (RBridge) for flows flows,
regardless of the VLAN, Fine Grained Fine-Grained Label (FGL), and/or multicast
group of the flow. Different ingress RBridges may choose different
distribution trees for TRILL Data packets in the same VLAN, FGL,
and/or multicast group. To avoid unnecessary link utilization,
distribution trees should be pruned based on VLAN and/or FGL and/or one or more of the
following: VLAN, FGL, or multicast destination address. If any VLAN,
FGL, or multicast group can be sent on any tree, for typical fast fast-
path hardware, the amount of pruning information is multiplied by the
number of trees, but there is a limited hardware capacity for such
pruning information.

This document specifies an optional facility to restrict the TRILL
Data packets sent on particular distribution trees by VLAN, FGL,
and/or multicast group groups, thus reducing the total amount of pruning
information so that it can more easily be accommodated by fast path fast-path
hardware.

Status of this This Memo

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 ....................................................3
1.1. Background Description . . . . . . . . . . . . . . . . . . 4 .....................................3
1.2. Terminology Used in This Document . . . . . . . . . . . . . 4 ..........................4
2. Motivations . . . . . . . . . . . . . . . . . . . . . . . . . 5 .....................................................5
3. Data Label based Tree Selection . . . . . . . . . . . . . . . 8 Based on Data Labels .............................9
3.1. Overview of the Mechanism . . . . . . . . . . . . . . . . . 8 ..................................9
3.2. APPsub-TLVs Supporting Tree Selection . . . . . . . . . . . 9 .....................10
3.2.1. The Tree and VLANs APPsub-TLV . . . . . . . . . . . . . 10 ......................11
3.2.2. The Tree and VLANs Used APPsub-TLV . . . . . . . . . . 11 .................12
3.2.3. The Tree and FGLs APPsub-TLV . . . . . . . . . . . . . 11 .......................12
3.2.4. The Tree and FGLs Used APPsub-TLV . . . . . . . . . . . 12 ..................13
3.2.5. The Tree and Groups APPsub-TLV . . . . . . . . . . . . 13 .....................13
3.2.6. The Tree and Groups Used APPsub-TLV . . . . . . . . . . 13 ................14
3.3. Detailed Processing . . . . . . . . . . . . . . . . . . . . 14 .......................................14
3.4. Failure Handling . . . . . . . . . . . . . . . . . . . . . 15 ..........................................15
4. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 16 .........................................17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17 ........................................18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 ............................................19
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 .....................................................19
7.1. Normative References . . . . . . . . . . . . . . . . . . . 18 ......................................19
7.2. Informative References . . . . . . . . . . . . . . . . . . 18
8. ....................................20
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 19 ...................................................21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 ................................................21

1. Introduction

1.1. Background Description

One or more distribution trees, identified by their root nickname, nicknames,
are used to distribute multi-destination data in a TRILL (Transparent
Interconnection of Lots of Links) (TRILL) campus [RFC6325]. The RBridge
Routing Bridge (RBridge) having the highest tree root priority
announces the total number of trees that should be computed for the
campus. It may also specify the list of trees that RBridges need to
compute using the Tree Identifiers (TREE-RT-IDs) sub-TLV [RFC7176].
Every RBridge can specify the trees it will use for multi-destination
TRILL data Data packets it originates in the Trees Used Identifiers (TREE-
USE-IDs)
(TREE-USE-IDs) sub-TLV [RFC7176], and the VLANs or fine grained labels (FGLs
[RFC7172]) Fine-Grained
Labels (FGLs) [RFC7172] it is interested in are specified in
Interested VLANs and/or Interested Labels sub-TLVs [RFC7176]. It is
suggested that, that by
default, default the ingress RBridge uses the distribution
tree whose root is the closest [RFC6325]. Trees Used Identifiers sub-TLVs are The TREE-USE-IDs sub-TLV
is used to build the RPF (Reverse Path Forwarding) Check check table that
is used for
reverse path forwarding check, RPF checking. Interested VLANs and Interested Labels
sub-TLVs are used for distribution tree pruning pruning, and the multi-
destination
multi-destination forwarding table with pruning info information is built
based on that RPF Check Table. check table. To reduce unnecessary link loads,
each distribution tree should be pruned per VLAN/FGL, eliminating
branches that have no potential receivers downstream as specified in
[RFC6325]. Further pruning based on Layer 2 or Layer 3 multicast address
addresses is also possible.

Defaults are provided provided, but it depends on the implementation how many trees are calculated, where the
tree roots are located, and which
tree(s) tree or trees are to be used by an
ingress RBridge. RBridge are implementation dependent. With the increasing
demand to use TRILL in data center networks, there are some features
we can explore for multi-destination frames in the data center use
case. In order to achieve non-blocking data forwarding, a fat tree
structure is often used. Figure 1 shows a typical fat tree structure
based data center network.
network based on the fat tree structure. RB1 and RB2 are aggregation switches
switches, and RB11 to through RB14 are access switches. It is a common
practice to configure the tree roots to be at the aggregation
switches for efficient traffic transportation. Then all All the ingress
RBridges that are access switches have the same distance to will then be equally distant from
all the tree roots.

1.2. Terminology Used in This Document

This document uses the terminology from [RFC6325] and [RFC7172], some
of which is repeated below for

+-----+ +-----+
| RB1 | | RB2 |
+-----+ +-----+
/ | \\ / /|\
/ | \ \ / / | \
/ | \ \ / | \-----+
/ | \/ \ | |
/ | /\/ \| |
/ /---+---/ /\ |\ |
/ / | / \ | \ |
/ / | / \ | \ |
/ / | / \ | \ |
+-----+ +-----+ +-----+ +-----+
| RB11| | RB12| | RB13| | RB14|
+-----+ +-----+ +-----+ +-----+

Figure 1: TRILL Network Based on Fat Tree Structure

1.2. Terminology Used in This Document

This document uses the terminology from [RFC6325] and [RFC7172], some
of which is repeated below for convenience, along with some
additional terms listed below:

Campus: Name The name for a network using the TRILL network, like protocol in the same
sense that a "bridged LAN" is a the name for a
bridged network. It does not have any network using
bridging. In TRILL, the word "campus" has no academic
implication.

Data Label: VLAN or FGL.

ECMP: Equal Cost Multi-Path Equal-Cost Multipath [RFC6325].

FGL: Fine Grained Fine-Grained Label [RFC7172].

Interested Labels sub-TLV: Short for "Interested Labels and Spanning
Tree Roots sub-TLV" [RFC7176].

Interested VLANs sub-TLV: Short for "Interested VLANs and Spanning
Tree Roots sub-TLV" [RFC7176].

IPTV: "Television" (video) over IP.

RBridge: An alternative name for a TRILL switch.

RPF: Reverse Path Forwarding.

TRILL: Transparent Interconnection of Lots of Links (or Tunneled
Routing in the Link Layer).

TRILL switch: A device implementing the TRILL protocol. Sometimes
called an RBridge.

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 RFC 2119 [RFC2119].

Figure 1. Fat Tree Structure based TRILL network

2. Motivations

In the structure of Figure 1, if we choose to put the tree roots at
RB1 and RB2, the ingress RBridge (e.g. (e.g., RB11) would find more than
one
equal cost equal-cost closest tree root (i.e. (i.e., RB1 & and RB2). An ingress
RBridge has two options to select the tree root for multi-destination
frames: choose one and only one as the distribution tree root root, or use
an ECMP-like algorithm to balance the traffic among the multiple
trees whose roots are at the same distance. distance from the RBridge.

- For the former (one distribution tree root), a single tree used by
each ingress RBridge, RBridge can have the problem of uneven or inefficient
link usage. For example, if RB11 chooses the tree1 tree that is rooted
at RB1 as the distribution tree, the link between RB11 and RB2
will not be used for multi-destination frames ingressed by RB11.

- For the latter (ECMP-Like (an ECMP-like algorithm), ECMP based ECMP-based tree selection
results in a linear increase in multicast forwarding table size
with the number of trees trees, as explained in the next paragraph.

A multicast forwarding table at an RBridge is normally used to map
the key of (distribution tree nickname + VLAN) to an index to a list
of ports for multicast packet replication. The key used for mapping
is simply the tree nickname when the RBridge does not prune the tree.

The key could be the distribution tree nickname augmented by the Fine
Grained Label (FGL) FGL
and/or Layer 2 or 3 multicast address when the RBridge supports FGL
and/or Layer 2 or 3 pruning information.

For any RBridge RBn, for each VLAN x, if RBn is in a distribution
tree t used by traffic in VLAN x, there will be an entry of (t, x,
port list) in the multicast forwarding table on RBn. Typically Typically, each
entry contains a distinct combination of (tree nickname, VLAN) as the
lookup key. If there are n such trees and m such VLANs, the
multicast forwarding table size on RBn is n*m entries. If a fine-grained label an FGL is
used [RFC7172] and/or finer pruning is used (for example, VLAN +
multicast group address is used for pruning), the value of m
increases. In the larger scale larger-scale data center, more trees would be
necessary for purposes of better load balancing purpose and load-balancing; this results in an
increased value for n. In either case, the number of table entries
n*m
(i.e., n*m) will increase dramatically.

The left hand left-hand table in Figure 2 shows an example of the multicast
forwarding table on RB11 in the Figure 1 topology, with two
distribution trees in a campus using typical fast-path hardware.

Before VLAN-Based After VLAN-Based
Tree Selection Tree Selection
+--------------+-----+---------+ +--------------+-----+---------+
|tree nickname |VLAN |port list| |tree nickname |VLAN |port list|
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 1 | | | tree 1 | 1 | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 2 | | | tree 1 | 2 | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | ... | | | tree 1 | ... | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | ... | | | tree 1 | 1999| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | ... | | | tree 1 | 2000| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 4093| | | tree 2 shows an example of the multicast
forwarding table on RB11 in the Figure | 2001| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 topology with | 4094| | | tree 2 distribution
trees in a campus using typical fast path hardware. | 2002| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | 1 | | | tree 2 | ... | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | 2 | | | tree 2 | 4093| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | ... | | | tree 2 | 4094| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | ... | |
+--------------+-----+---------+
| tree 2 | ... | |
+--------------+-----+---------+
| tree 2 | ... | |
+--------------+-----+---------+
| tree 2 | 4093| |
+--------------+-----+---------+
| tree 2 | 4094| |
+--------------+-----+---------+

Figure 2: Multicast Forwarding Table
before and after Using VLAN-Based Tree Selection

The number of entries is approximately 2 * 4K 2*4K in this case. If 4 four
distribution trees are used in a TRILL campus and RBn has 4K VLANs
with downstream receivers, it consumes 16K table entries. Fast path The size
of fast-path TRILL multicast forwarding tables is typically have a size limited
by hardware. The hardware; therefore, the table entries are a precious resource.

In some implementations, the table is shared with Layer 3 IP
multicast for a total of 16K or 8K table entries. Therefore Therefore, we want
to reduce the table size consumed for TRILL distribution trees as
much as possible and at the same time maintain the load balancing load-balancing among
the trees.

In cases where blocks of consecutive VLANs or FGLs can be assigned to
a tree, the multicast forwarding table could be greatly compressed if
entries could have a Data Label value and mask mask, with the fast path fast-path
hardware doing the longest prefix matching. But few few, if any fast path any,
fast-path implementations provide such logic.

A straightforward way to alleviate the problem of limited table
entries problem is not to prune the distribution tree. However However, this can
only be used in restricted scenarios scenarios, for the following reasons:

- Not pruning wastes bandwidth for multi-destination packets. There
is normally broadcast traffic, like ARP and unknown unicast, that
can be pruned on a VLAN (or FGL) so that it is not sent down
branches of a distribution tree where it is not needed. In
addition, if there is a lot of Layer 3 multicast traffic, no
pruning may result in the worse
consequence of a worst-case scenario where that user data
is unnecessarily flooded all over the campus. The volume of
flooded data could be very large if certain applications like such as
IPTV ("Television" (video) over IP) are supported. More precise pruning, such as pruning based
on multicast group, groups, may be desirable in this case.

- Not pruning is only useful at pure transit nodes. Edge nodes
always need to maintain the multicast forwarding table with the
key of (tree nickname + VLAN (or FGL)) FGL)), since the edge node needs
to decide whether and how to replicate the frame to local access
ports. It is likely that edge nodes are relatively low end low-end
switches with a smaller shared table size, say 4K, available.

- Security concerns. VLAN Due to security concerns, VLAN-based (or FGL) based FGL-based) traffic
isolation is a basic requirement in some scenarios. No pruning
may increase the risk of leakage of the traffic. Misbehaved Misbehaving
RBridges may take advantage of this leakage of traffic.

In addition to the concern regarding multicast table size concern, size, some
silicon does not currently support hashing-based tree nickname
selection at the ingress RBridge but commonly uses VLAN based VLAN-based tree
selection. If the control plane of the ingress RBridge maps the
incoming VLAN x to a tree nickname t. Then t, the data plane will always use
tree t for VLAN x multi-destination frames. Such an ingress RBridge
may choose multiple trees to be used for load sharing, load-sharing; it can use one
and only one tree for each VLAN. If we make sure that all ingress
RBridges campus-
wide campus-wide send VLAN x multi-destination packets only using use
tree t, then there would be no need to store the multicast table
entry with the key of (tree-other-than-t, x) on any RBridge.

This document describes the TRILL control plane control-plane support for
distribution tree selection based on a VLAN, FGL, and/or multicast
address to reduce the multicast forwarding table size. It is
compatible with the silicon implementations mentioned in the previous
paragraph.

3. Data Label based Tree Selection Based on Data Labels

Data Label (VLAN (VLAN-based or FGL) based FGL-based) tree selection can be used as a
distribution tree selection mechanism, especially when the multicast
forwarding table size is a concern. This section specifies that
mechanism and how to extend it so that tree selection can be based on
multicast group. groups.

3.1. Overview of the Mechanism

The RBridge that has the highest priority to be a tree root announces
the tree nicknames and the Data Labels allowed on each tree. Such
announcements of correspondence of tree to Data Label correspondence announcements can be based on
static configuration or some predefined algorithm beyond the scope of
this document. An ingress RBridge selects the tree-VLAN
correspondence that it wishes to use from the list announced by the
highest priority
highest-priority tree root. It SHOULD NOT transmit VLAN x frame frames on
tree y if the highest priority highest-priority tree root does not say that VLAN x is
allowed on tree y.

If we make sure that a particular VLAN is allowed on one and only one
tree, we can keep the number of multicast forwarding table entries on
any RBridge fixed at 4K maximum (or up to 16M in the case of fine grained
label). an FGL).
Take Figure 1 as an example, where two trees are rooted at RB1 and RB2
RB2, respectively. The highest priority highest-priority tree root appoints the tree1 tree 1 to
carry VLAN 1-2000 and tree2 tree 2 to carry VLAN 2001-4094. With such an
announcement by the highest priority highest-priority tree root, every RBridge which that
understands the announcement will not send VLAN 2001-4094 traffic on
tree1
tree 1 and will not send VLAN 1-2000 traffic on tree2. Then tree 2. That way, no
RBridge would need to store the entries for tree1/VLAN2001-4094 tree 1 / VLAN 2001-4094
or
tree2/VLAN1-2000. tree 2 / VLAN 1-2000. Figure 2 shows the multicast forwarding
table on an RBridge before and after we use VLAN based VLAN-based tree
selection. The number of entries is reduced by a factor f, where f being
is the number of trees used in the campus. In this example, it is
reduced from 2*4094 to 4094. This affects both transit nodes and
edge nodes. The data plane data-plane encoding does not change.

+--------------+-----+---------+ +--------------+-----+---------+
|tree nickname |VLAN |port list| |tree nickname |VLAN |port list|
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 1 | | | tree 1 | 1 | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 2 | | | tree 1 | 2 | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | ... | | | tree 1 | ... | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | ... | | | tree 1 | 1999| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | ... | | | tree 1 | 2000| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 4093| | | tree 2 | 2001| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 4094| | | tree 2 | 2002| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | 1 | | | tree 2 | ... | |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | 2 | | | tree 2 | 4093| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | ... | | | tree 2 | 4094| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 2 | ... | |
+--------------+-----+---------+
| tree 2 | ... | |
+--------------+-----+---------+
| tree 2 | ... | |
+--------------+-----+---------+
| tree 2 | 4093| |
+--------------+-----+---------+
| tree 2 | 4094| |
+--------------+-----+---------+

Figure 2. Multicast forwarding table before (left) & after (right)

3.2. APPsub-TLVs Supporting Tree Selection

Six new APPsub-TLVs that can be carried in the TRILL GENINFO TLV
[RFC7357] in E-L1FS FS-LSPs [rfc7780] Extended Level 1 Flooding Scope (E-L1FS) FS-Link State
Protocol Data Units (FS-LSPs) [RFC7780] are defined below. The first
four can be considered analogous to finer granularity finer-granularity versions of the
Tree Identifiers Sub-TLV
TREE-RT-IDs sub-TLV and the Trees Used Identifiers Sub-TLV in TREE-USE-IDs sub-TLV [RFC7176]. Two
APPsub-TLVs supporting VLAN based VLAN-based tree selection are specified in
Sections 3.2.1 and 3.2.2. They are used by the highest
priority highest-priority tree
root to announce the allowed VLANs on each tree in the campus and by
an ingress RBridge to announce the tree-VLAN correspondence that it
selects from the list announced by the highest
priority highest-priority tree root.
Two APPsub-TLVs supporting FGL based FGL-based tree selection are specified in Section
Sections 3.2.3 and 3.2.4 for the same purpose. Sections 3.2.5 and
3.2.6 define two APPsub-TLVs to support finer granularity in
selecting trees based on multicast group groups rather than Data Label. Labels.

New APPSubTLVs APPsub-TLVs Description
======================= =============
Tree and VLANS VLANs announcement by the highest priority highest-priority
tree root of the VLANs allowed per tree

Tree and VLANS VLANs Used tree-VLAN correspondence that an
ingress RBridge selects

Tree and FGLs announcement by the highest priority highest-priority
tree root of the FGLs allowed per tree

Tree and FGLs Used tree-FGL correspondence that an
ingress RBridge selects

Tree and GROUPs Groups announcement by the highest priority highest-priority
tree root of the multicast groups
allowed on each tree

Tree and GROUPs Groups Used tree and multicast group correspondence
that an ingress RBridge selects

3.2.1. The Tree and VLANs APPsub-TLV

The RBridge that is the highest priority highest-priority tree root announces the
VLANs allowed on each tree with the Tree and VLANs (TREE-VLANS) (TREE-VLANs)
APPsub-TLV. Multiple instances of this sub-TLV APPsub-TLV may be carried.
The same tree nicknames may occur in multiple Tree-VLAN RECORDs
within the same APPsub-TLV or across multiple sub-TLVs. APPsub-TLVs. The sub-TLV
APPsub-TLV format is as follows:

where each Tree-VLAN RECORD is of the form:

o Type: TRILL GENINFO APPsub-TLV type, type; set to tbd1 (TREE-VLANS). 11 (TREE-VLANs).

o Length: 6*n bytes, where there are n Tree-VLAN RECORDs. Thus Thus, the
value of Length can be used to determine n. If Length is not a
multiple of 6, the sub-TLV APPsub-TLV is corrupt and MUST be ignored.

o Nickname: The nickname identifying the distribution tree by its
root.

o RESV: 4 bits that MUST be sent as zero and ignored on receipt.

o Start.VLAN, End.VLAN: These fields are the VLAN IDs of the allowed
VLAN range on the tree, inclusive. To specify a single VLAN, the
VLAN's ID appears as both the start and end VLAN. If End.VLAN is
less than Start.VLAN Start.VLAN, the Tree-VLAN RECORD MUST be ignored.

3.2.2. The Tree and VLANs Used APPsub-TLV

This APPsub-TLV has the same structure as the Tree and VLANs APPsub-
TLV (TREE-VLANS) TREE-VLANs APPsub-TLV
specified in Section 3.2.1. The differences are that its APPsub-TLV
type is set to tbd2 (TREE-VLANS-USE) 12 (TREE-VLAN-USE) and the
Tree-VLAN tree-VLAN correspondences
in the Tree-VLAN RECORDs listed are those correspondences that the
originating RBridge wants to use for multi-destination packets. This
APPsub-TLV is used by an ingress RBridge to distribute the tree-
VLAN tree-VLAN
correspondence that it selects from the list announced by the highest
priority
highest-priority tree root.

3.2.3. The Tree and FGLs APPsub-TLV

The RBridge that is the highest priority highest-priority tree root can use the Tree
and FGLs (TREE-FGLS) (TREE-FGLs) APPsub-TLV to announce the FGLs allowed on each
tree. Multiple instances of this APPsub-TLV may be carried. The
same tree nicknames may occur in the multiple Tree-FGL RECORDs within
the same APPsub-TLV or across multiple APPsub-TLVs. Its format is as
follows:

where each Tree-VLAN Tree-FGL RECORD is of the form:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nickname | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
| Start.FGL | (3 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
| End.FGL | (3 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
o Type: TRILL GENINFO APPsub-TLV type, type; set to tbd3 (TREE-FGLS). 13 (TREE-FGLs).

o Length: 8*n bytes, where there are n Tree-FGL RECORDs. Thus Thus, the
value of Length can be used to determine n. If Length is not a
multiple of 8, the sub-TLV APPsub-TLV is corrupt and MUST be ignored.

o Nickname: The nickname identifying the distribution tree by
its root.

o RESV: 4 bits that MUST be sent as zero and ignored on receipt.

o Start.FGL, End.FGL: These fields are the FGL IDs of the allowed
FGL range on the tree, inclusive. To specify a single FGL, the
FGL's ID appears as both the start and end FGL. If End.FGL is
less than
Start.FGL Start.FGL, the Tree-FGL RECORD MUST be ignored.

3.2.4. The Tree and FGLs Used APPsub-TLV

This APPsub-TLV has the same structure as the Tree and FGLs APPsub-
TLV (TREE-FGLS) TREE-FGLs APPsub-TLV
specified in Section 3.2.3. The only difference is differences are that its APPsub-TLV
type is set to tbd4 (TREE-FGLS-USE), 14 (TREE-FGL-USE) and the Tree-FGL correspondences in
the Tree-FGL RECORDs listed are those that the originating RBridge
wants to use for multi-destination packets. This APPsub-TLV is used
by an ingress RBridge to distribute the tree-FGL correspondence that
it selects from the list announced by the highest priority highest-priority tree root.

3.2.5. The Tree and Groups APPsub-TLV

Data Label based tree

Tree selection based on Data Labels is easily extended to (Data tree
selection based on Data Label + Layer 2 or 3 multicast group) based tree selection. groups. We
can appoint multicast group 1 in VLAN 10 to tree1 tree 1 and appoint
group 2 in VLAN 10 to tree2 tree 2 for better load sharing. load-sharing.

The RBridge that is the highest priority highest-priority tree root can announce the
multicast groups allowed on each tree for each data label Data Label with the
Tree and Groups (TREE-GROUPS) (TREE-GROUPs) APPsub-TLV. Multiple instances of this
sub-TLV
APPsub-TLV may be carried. The sub-TLV APPsub-TLV format is as follows:

o Type: TRILL GENINFO APPsub-TLV type, type; set to tbd5 (TREE-GROUPS). 15 (TREE-GROUPs).

o Length: 2 + the length of the Group Sub-Sub TLVs included that are
included.

o Nickname: The nickname identifying the distribution tree by its
root.

o Group Sub-Sub-TLVs: Zero or more of the TLV structures that are
allowed as sub-TLVs of the GADDR Group Address (GADDR) TLV [RFC7176].
Each such TLV structure specifies a multicast group and either a
VLAN or FGL. Although these TLV structure structures are considered
sub-TLVs when they appear inside a GADDR TLV, they are technically
sub-sub-TLVs when they appear inside a TREE-GROUPs APPsub-TLV which that
is in turn inside a TRILL GENINFO TLV [RFC7357].

3.2.6. The Tree and Groups Used APPsub-TLV

This

The Tree and Groups Used (TREE-GROUPs-USE) APPsub-TLV has the same
structure as the Tree and GROUPs APPsub-
TLV (TREE-GROUPS) TREE-GROUPs APPsub-TLV specified in Section 3.2.5.
The only difference is differences are that its APPsub-TLV type is set to tbd6 (TREE-GROUPS-USE), 16
(TREE-GROUPs-USE) and the
tree Tree Nickname and multicast groups Group sub-sub-TLVs listed
in this sub-TLV APPsub-TLV are those that the originating RBridge wants to
use for multi-destination packets. This APPsub-TLV is used by an
ingress RBridge to distribute the tree-group correspondence that it
selects from the list announced by the highest
priority highest-priority tree root.

3.3. Detailed Processing

The highest priority highest-priority tree root RBridge MUST include all the necessary
tree related
tree-related sub-TLVs defined in [RFC7176] as usual in its E-L1FS FS-
LSP
FS-LSP and MAY include the Tree and VLANs Sub-TLV (TREE-VLANs) TREE-VLANs APPsub-TLV and/or
Tree and FGLs Sub-TLV (TREE-FGLs) the TREE-FGLs
APPsub-TLV in its E-L1FS FS-LSP [RFC7780]. In this way way, it MAY
indicate that each VLAN and/or FGL is only allowed on one or some
other number of trees less than the number of trees being calculated
in the campus in order to save table space in the fast
path fast-path
forwarding hardware.

An ingress RBridge that understands the TREE-VLANs APPsub-TLV SHOULD
select the tree-VLAN correspondences that it wishes to use and put
them in TREE-VLAN-USE APPsub-TLVs. If there are multiple tree
nicknames announced in a TREE-VLANs Sub-TLV APPsub-TLV for a VLAN x, the
ingress RBridge chooses one of them if it supports this feature. For
example, the ingress RBridge may choose the closest (minimum cost) (minimum-cost)
root among them. How to make such a choice is out of the scope of for this
document. It may be desirable to have some fixed algorithm to
make sure that all ingress RBs RBridges choose the same tree for VLAN x
in this case. Any single Data Label that the ingress RBridge is
interested in should be related to only one tree ID in a
TREE-VLAN-USE APPsub-TLV to minimize the multicast forwarding table
size on other RBridges RBridges, but as long as the Data Label is related to
less than all the trees being calculated, it will reduce the burden
on the forwarding table size.

When an ingress RBridge encapsulates a multi-destination frame for
Data Label x, it SHOULD use a tree nickname that it selected
previously in a TREE-VLAN-USE or TREE-FGL-USE APPsub-TLV for
Data Label x. However, that may not be possible because either
(1) the RBridge may not have advertised such TREE-VLAN-USE or
TREE-FGL-USE APPsub-TLVs, in which case it can use any tree that has
been advertised as permitted for the Data Label by the highest priority
highest-priority tree root RBridge, or (2) the tree or trees it
advertised might be unavailable due to failures.

If RBridge RBn does not perform pruning, it builds the multicast
forwarding table as specified in [RFC6325].

If RBn prunes the distribution tree based on VLANs, RBn uses the
information received in TREE-VLAN-USE APPsub-TLVs to mark the set of
VLANs reachable downstream for each adjacency and for each related
tree. If RBn prunes the distribution tree based on FGLs, RBn uses
the information received in TRILL-FGL-USE APPsub-TLVs to mark the
set of
FLGs FGLs reachable downstream for each adjacency and for each
related tree.

Logically, an ingress RBridge that does not support VLAN/FGL based VLAN-based or
FGL-based tree selection is equivalent to the one that supports it and
but uses it in such a way as to gain no advantage; for example, it
announces all the combination pair use of tree-id-used all trees for all VLANs and interested-
vlan/interested-fgl as TREE-VLAN-USE. FGLs.

3.4. Failure Handling

This section discusses failure of scenarios for a distribution tree root
for the
cases case where that tree root is not the highest priority highest-priority root
and the case where it is the highest priority highest-priority root. It This section
also discusses some other transient error conditions.

Failure of a tree root that is not the highest priority: highest-priority tree root:
It is the responsibility of the highest priority highest-priority tree root to
inform other RBridges of any change in the allowed tree-VLAN
correspondence. When the highest priority highest-priority tree root learns that
the root of tree t has failed, it should re-assign reassign the VLANs
allowed on tree t to other trees or to a tree replacing the
failed one.

Failure of the highest priority highest-priority tree root: It is suggested that the
second highest priority
tree root of second-highest priority be pre-configured with the
proper knowledge of the tree-VLAN correspondence allowed when the highest
priority
highest-priority tree root fails. The information announced by
the second RBridge that has the second-highest priority to be a tree root
would be in the link state of all RBridges but would not take
effect unless the RBridge noticed the failure of the
highest priority
highest-priority tree root. When the highest priority the highest-priority tree root
fails, the former second priority tree root that formerly had second-highest priority
will become the highest
priority highest-priority tree root of the campus. When an
RBridge notices the failure of the original highest priority highest-priority tree
root, it can immediately use the stored information announced by
the original second priority tree
root. root that originally had second-highest priority. It is
suggested that the tree-VLAN correspondence information be
pre-configured on the second highest priority tree root of second-highest priority to be
the same as that on the highest priority highest-priority tree root for the trees
other than the highest priority highest-priority tree itself. This can minimize
the change to multicast forwarding tables in the case of highest priority
highest-priority tree root failure. For a large campus, it may
make sense to pre-configure this information in a similar way on
the third, fourth, third-priority, fourth-priority, or even lower
priority lower-priority tree
root RBridges.

In some transient conditions conditions, or in the case of misbehavior by the highest
priority a misbehaving
highest-priority tree root, an ingress RBridge may encounter the
following scenarios:

- No tree has been announced for which VLAN x frames are allowed.

- An ingress RBridge is supposed to transmit VLAN x frames on
tree t, but the root of tree t is no longer reachable.

For the second case, an ingress RBridge may choose another reachable
tree root which that allows VLAN x frames according to the highest priority highest-priority
tree root announcement. If there is no such tree available, then it
is the same as the first case above. Then the The ingress RBridge should then
be
'downgraded' "downgraded" to a conventional RBridge with behavior as specified
in [RFC6325]. A timer should be set to allow the temporary transient
stage to complete before the change of the responsive tree or 'downgrade' the
downgrade takes effect. The value of the timer should be set to at
least the LSP flooding time of the campus.

4. Backward Compatibility

RBridges MUST include the TREE-USE-IDs and INT-VLAN sub-TLVs in their
LSPs when required by [RFC6325] whether or not they support the new
TREE-VLAN-USE or TREE-FGL-USE sub-TLVs APPsub-TLVs specified by this draft. document.

RBridges that understand the new TREE-VLAN-USE sub-TLV APPsub-TLV sent from
another RBridge RBn should use it to build the multicast forwarding
table and ignore the TREE-USE-IDs and INT-VLAN sub-TLVs sent from the
same RBridge. TREE-USE-IDs and INT-VLAN sub-TLVs are still useful
for some purposes other than building the multicast forwarding table (E.g.
(e.g., building an RPF table building, table, spanning tree root notification, etc.) notification). If
the RBridge does not receive TREE-VLAN-USE sub-TLVs APPsub-TLVs from RBn, it
uses the conventional way described in [RFC6325] to build the
multicast forwarding table.

For example, there are two distribution trees, tree1 tree 1 and tree2, tree 2, in
the campus. RB1 and RB2 are RBridges that use the new APPsub-TLVs
described in this document. RB3 is an old RBridge that is compatible
with [RFC6325]. Assume that RB2 is interested in VLANs 10 and 11 and
RB3 is interested in VLANs 100 and 101. Hence Hence, RB1 receives ((tree1,
VLAN10), (tree2, VLAN11))
((tree 1, VLAN 10), (tree 2, VLAN 11)) as a TREE-VLAN-USE sub-TLV APPsub-TLV
and (tree1,
tree2) (tree 1, tree 2) as a TREE-USE-IDs sub-TLV from RB2 on port x. And
Also, RB1 receives
(tree1) (tree 1) as a TREE-USE-IDs sub-TLV and no
TREE-VLAN-USE sub-TLV APPsub-TLV from RB3 on port y. RB2 and RB3 announce
their interested VLANs in an INT-
VLAN INT-VLAN sub-TLV as usual. Then RB1 will
then build the entry of (tree1,
VLAN10, (tree 1, VLAN 10, port x) and (tree2, VLAN11,
(tree 2, VLAN 11, port x) based on RB2's LSP and the mechanism
specified in this document. RB1 also builds entries of
(tree1, VLAN100,
(tree 1, VLAN 100, port y), (tree1, VLAN101, (tree 1, VLAN 101, port y), (tree2, VLAN100,
(tree 2, VLAN 100, port y), (tree2, VLAN101, and (tree 2, VLAN 101, port y) based on
RB3's LSP in the conventional way.

The multicast forwarding table on RB1 with a merged entry would be
like the following. following:

+--------------+-----+---------+
|tree nickname |VLAN |port list|
+--------------+-----+---------+
| tree 1 | 10 | x |
+--------------+-----+---------+
| tree 1 | 100 | y |
+--------------+-----+---------+
| tree 1 | 101 | y |
+--------------+-----+---------+
| tree 2 | 11 | x |
+--------------+-----+---------+
| tree 2 | 100 | y |
+--------------+-----+---------+
| tree 2 | 101 | y |
+--------------+-----+---------+

As expected, that table is not as small as the one where every
RBridge supports the new TREE-VLAN-USE sub-TLVs. The worst case in APPsub-TLVs. In a hybrid campus is
campus, the worst case would be where the number of entries is equal
to the number in of entries required by the current practice which that does
not support VLAN based VLAN-based tree selection. Such an extreme case happens
when the interested VLAN set of interested VLANs from the new RBridges is a subset of
the interested VLAN set of interested VLANs from the old RBridges.

Tree selection based on the Data Label and multicast group based tree selection is
compatible with the current practice. Its effectiveness increases
with more
RBridge RBridges supporting this feature in the TRILL campus.

5. Security Considerations

This document does not change the general RBridge security
considerations of the TRILL base protocol. The APPsub-TLVs specified
can be secured using the IS-IS authentication feature [RFC5310]. See
Section 6 of [RFC6325] for general TRILL security considerations.

6. IANA Considerations

IANA is requested to assign has assigned six new TRILL APPsub-TLV type codes types from the range less
than 255 255, as specified in Section 3 3, and update updated the "TRILL
APPsub-TLV Types under IS-IS TLV 251 Application Identifier 1"
Registry
registry on the IANA TRILL Parameters web page
<http://www.iana.org/assignments/trill-parameters/>, as shown below.

Type Name of APPsub-TLV code Reference
---- ----------------------- ---------

tbd1 -------------------------
11 Tree and VLANs [this document 3.2.1]
tbd2 Section 3.2.1 of RFC 7968
12 Tree and VLANs Used [this document 3.2.2]
tbd3 Section 3.2.2 of RFC 7968
13 Tree and FGLs [this document 3.2.3]
tbd4 Section 3.2.3 of RFC 7968
14 Tree and FGLs Used [this document 3.2.4]
tbd5 Section 3.2.4 of RFC 7968
15 Tree and Groups [this document 3.2.5]
tbd6 Section 3.2.5 of RFC 7968
16 Tree and Groups Used [this document 3.2.6] Section 3.2.6 of RFC 7968

7. References

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011, <http://www.rfc-
editor.org/info/rfc6325>.
<http://www.rfc-editor.org/info/rfc6325>.

[RFC7172] Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
D. Dutt, "Transparent Interconnection of Lots of Links
(TRILL): Fine-Grained Labeling", RFC 7172,
DOI 10.17487/RFC7172, May 2014,
<http://www.rfc-editor.org/info/rfc7172>.

[RFC7176] Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
D., and A. Banerjee, "Transparent Interconnection of Lots
of Links (TRILL) Use of IS-IS", RFC 7176,
DOI 10.17487/RFC7176, May 2014,
<http://www.rfc-editor.org/info/rfc7176>.

[RFC7357] Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
Stokes, "Transparent Interconnection of Lots of Links
(TRILL): End Station Address Distribution Information
(ESADI) Protocol", RFC 7357, DOI 10.17487/RFC7357,
September 2014,
<http://www.rfc-editor.org/info/rfc7357>

[RFC7176] Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt, D.,
and A. Banerjee, "Transparent Interconnection of Lots of
Links (TRILL) Use of IS-IS", RFC 7176, May 2014,
<http://www.rfc-editor.org/info/rfc7176>. <http://www.rfc-editor.org/info/rfc7357>.

[RFC7780] Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
Ghanwani, A. A., and S. Gupta, S., "Transparent Interconnection
of Lots of Links (TRILL): Clarifications, Corrections, and
Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016. 2016,
<http://www.rfc-editor.org/info/rfc7780>.

7.2. Informative References

[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310,
February 2009, <http://www.rfc-
editor.org/info/rfc5310>.

8. <http://www.rfc-editor.org/info/rfc5310>.

Acknowledgments

Authors

The authors wish to thank David M. Bond, Liangliang Ma, Naveen Nimmu,
Radia Perlman, Rakesh Kumar, Robert Sparks, Daniele Ceccarelli Ceccarelli, and
Sunny Rajagopalan for their valuable comments and contributions.

Authors' Addresses

Yizhou Li
Huawei Technologies
101 Software Avenue, Avenue
Nanjing 210012
China

Phone: +86-25-56624629
Email: liyizhou@huawei.com

Donald Eastlake 3rd
Huawei R&D USA Technologies
155 Beaver Street
Milford, MA 01757 USA
United States of America

Phone: +1-508-333-2270
Email: d3e3e3@gmail.com

Weiguo Hao
Huawei Technologies
101 Software Avenue, Avenue
Nanjing 210012
China

Phone: +86-25-56623144
Email: haoweiguo@huawei.com
Hao Chen
Huawei Technologies
101 Software Avenue, Avenue
Nanjing 210012
China

Email: philips.chenhao@huawei.com

Somnath Chatterjee
Cisco Systems, Systems
SEZ Unit, Cessna Business Park, Park
Outer ring road, Ring Road
Bangalore - 560087
India

Email: somnath.chatterjee01@gmail.com