Internet DRAFT - draft-ietf-trill-tree-selection
draft-ietf-trill-tree-selection
TRILL Working Group Y. Li
INTERNET-DRAFT D. Eastlake
Intended Status: Standard Track W. Hao
H. Chen
Huawei Technologies
S. Chatterjee
Cisco
Expires: October 14, 2016 April 12, 2016
TRILL: Data Label based Tree Selection for Multi-destination Data
draft-ietf-trill-tree-selection-04
Abstract
TRILL uses distribution trees to deliver multi-destination frames.
Multiple trees can be used by an ingress RBridge for flows regardless
of the VLAN, 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 multicast
destination address. If any VLAN, FGL, or multicast group can be sent
on any tree, for typical 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 thus reducing the total amount of pruning
information so that it can more easily be accommodated by fast path
hardware.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at
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Copyright and License Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Background Description . . . . . . . . . . . . . . . . . . 4
1.2. Motivations . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology Used in This Document . . . . . . . . . . . . . . 7
3. Data Label based Tree Selection . . . . . . . . . . . . . . . 8
3.1. Overview of the Mechanism . . . . . . . . . . . . . . . . . 8
3.2. Sub-TLVs for the Router Capability TLV . . . . . . . . . . 9
3.2.1. The Tree and VLANs APPsub-TLV . . . . . . . . . . . . . 10
3.2.2. The Tree and VLANs Used APPsub-TLV . . . . . . . . . . 11
3.2.3. The Tree and FGLs APPsub-TLV . . . . . . . . . . . . . 11
3.2.4. The Tree and FGLs Used APPsub-TLV . . . . . . . . . . . 12
3.2.5. The Tree and Groups APPsub-TLV . . . . . . . . . . . . 13
3.2.6. The Tree and Groups Used APPsub-TLV . . . . . . . . . . 13
3.3. Detailed Processing . . . . . . . . . . . . . . . . . . . . 14
3.4. Failure Handling . . . . . . . . . . . . . . . . . . . . . 14
4. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
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7.1. Normative References . . . . . . . . . . . . . . . . . . . 18
7.2. Informative References . . . . . . . . . . . . . . . . . . 18
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
1.1. Background Description
One or more distribution trees, identified by their root nickname,
are used to distribute multi-destination data in a TRILL campus
[RFC6325]. The 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-destiantion
TRILL data packets it originates in the Trees Used Identifiers (TREE-
USE-IDs) sub-TLV and the VLANs or 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, by
default, the ingress RBridge uses the distribution tree whose root is
the closest [RFC6325]. Trees Used Identifiers sub-TLVs are used to
build the RPF Check table that is used for reverse path forwarding
check, Interested VLANs and Interested Labels sub-TLVs are used for
distribution tree pruning and the multi-destination forwarding table
with pruning info is built based on that RPF Check Table. Each
distribution tree SHOULD be pruned per VLAN/FGL, eliminating branches
that have no potential receivers downstream [RFC6325]. Further
pruning based on Layer 2 or Layer 3 multicast address is also
possible.
Defaults are provided but it depends on the implementation how many
trees are calculated, where the tree roots are located, and which
tree(s) are to be used by an ingress RBridge. 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. RB1 and RB2 are aggregation switches and
RB11 to 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 the ingress RBridges that
are access switches have the same distance to all the tree roots.
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+-----+ +-----+
| RB1 | | RB2 |
+-----+ +-----+
/ | \\ / /|\
/ | \ \ / / | \
/ | \ \ / | \-----+
/ | \/ \ | |
/ | /\/ \| |
/ /---+---/ /\ |\ |
/ / | / \ | \ |
/ / | / \ | \ |
/ / | / \ | \ |
+-----+ +-----+ +-----+ +-----+
| RB11| | RB12| | RB13| | RB14|
+-----+ +-----+ +-----+ +-----+
Figure 1. Fat Tree Structure based TRILL network
1.2. Motivations
In the structure of figure 1, if we choose to put the tree roots at
RB1 and RB2, the ingress RBridge (e.g. RB11) would find more than one
equal cost closest tree root (i.e. RB1 & RB2). An ingress RBridge has
two options to select the tree root for multi-destination frames:
choose one and only one as distribution tree root or use ECMP-like
algorithm to balance the traffic among the multiple trees whose roots
are at the same distance.
- For the former (one distribution tree root), a single tree used by
each ingress RBridge, can have the problem of uneven or inefficient
link usage. For example, if RB11 chooses the tree1 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 algorithm), ECMP based tree selection
results in a linear increase in multicast forwarding table size with
the number of 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) 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,
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port list) in the multicast forwarding table on RBn. 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
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 data center, more trees would be
necessary for better load balancing purpose and this results in an
increased value for n. In either case, the number of table entries
n*m will increase dramatically.
The left hand table in Figure 2 shows an example of the multicast
forwarding table on RB11 in the Figure 1 topology with 2 distribution
trees in a campus using typical fast path hardware. The number of
entries is approximately 2 * 4K in this case. If 4 distribution trees
are used in a TRILL campus and RBn has 4K VLANs with downstream
receivers, it consumes 16K table entries. Fast path TRILL multicast
forwarding tables typically have a size limited by hardware. 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 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 among trees.
In cases where blocks of consecutive VLANs or FGLs can be assigned to
a tree, it would be very helpful, in compressing the multicast
forwarding table, if entries could have a Data Label value and mask
and the fast path hardware could do longest prefix matching. But few
if any fast path implementations provide such logic.
A straightforward way to alleviate the limited table entries problem
is not to prune the distribution tree. However this can only be used
in restricted 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 VLAN (or FGL) so 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 that user data unnecessarily flooded all over the
campus. The volume could be very large if certain applications like
IPTV ("Television" (video) over IP) are supported. More precise
pruning, such as pruning based on multicast group, 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)) since the edge node needs to decide whether
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and how to replicate the frame to local access ports. It is likely
that edge nodes are relatively low end switches with a smaller shared
table size, say 4K, available.
- Security concerns. VLAN (or FGL) based traffic isolation is a basic
requirement in some scenarios. No pruning may increase the risk of
leakage of the traffic. Misbehaved RBridges may take advantage of
this leakage of traffic.
In addition to the multicast table size concern, some silicon does
not currently support hashing-based tree nickname selection at the
ingress RBridge but commonly uses VLAN based tree selection. If the
control plane of the ingress RBridge maps the incoming VLAN x to a
tree nickname t. Then 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, it can use one and only
one tree for each VLAN. If we make sure all ingress RBridges campus-
wide send VLAN x multi-destination packets only using 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 support for
distribution tree selection based on 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.
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 for a TRILL network, like "bridged LAN" is a name for a
bridged network. It does not have any academic implication.
Data Label: VLAN or FGL.
ECMP: Equal Cost Multi-Path [RFC6325].
FGL: Finge Grainge Lable [RFC7172].
IPTV: "Television" (video) over IP.
RBridge: An alternative name for a TRILL switch.
TRILL: Transparent Interconnection of Lots of Links (or Tunneled
Routing in the Link Layer).
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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 [RFC2119].
3. Data Label based Tree Selection
Data Label (VLAN or 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.
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
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 it wishes to use from the list announced by the
highest priority tree root. It SHOULD NOT transmit VLAN x frame on
tree y if the highest priority tree root does not say VLAN x is
allowed on tree y.
If we make sure 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 case of fine grained
label). Take Figure 1 as example, two trees rooted at RB1 and RB2
respectively. The highest priority tree root appoints the tree1 to
carry VLAN 1-2000 and tree2 to carry VLAN 2001-4094. With such
announcement by the highest priority tree root, every RBridge which
understands the announcement will not send VLAN 2001-4094 traffic on
tree1 and not send VLAN 1-2000 traffic on tree2. Then no RBridge
would need to store the entries for tree1/VLAN2001-4094 or
tree2/VLAN1-2000. Figure 2 shows the multicast forwarding table on an
RBridge before and after we use VLAN based tree selection. The number
of entries is reduced by a factor f, f being 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
encoding does not change.
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+--------------+-----+---------+ +--------------+-----+---------+
|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 | 4094| | | tree 2 | 2001| |
+--------------+-----+---------+ +--------------+-----+---------+
| tree 1 | 4095| | | 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. Sub-TLVs for the Router Capability TLV
Five new APPsub-TLVs that can be carried in the TRILL GENINFO TLV
[RFC7357] in E-L1FS FS-LSPs [rfc7780] are defined below. First four
can be considered analogous to finer granularity versions of the Tree
Identifiers Sub-TLV and the Trees Used Identifiers Sub-TLV in
[RFC7176]. Two APPsub-TLVs supporting VLAN based tree selection are
specified in Sections 3.2.1 and 3.2.2. They are used by the 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 it selects from the list announced by the highest
priority tree root. Two APPsub-TLVs supporting FGL based tree
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selection are specified in Section 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
the finer granularity in selecting trees on multicast group base
rather than data label base.
Proposed new APPSubTLVs Description
======================= =============
Tree and VLANS announcement by the highest priority
tree root of the VLANs allowed per tree
Tree and VLANS Used tree-VLAN correspondence an ingress
RBridge selects
Tree and FGLs announcement by the highest priority
tree root of the FGLs allowed per tree
Tree and FGLs Used tree-FGL correspondence an ingress
RBridge selects
Tree and GROUPs announcement by the highest priority
tree root of the multicast groups
allowed on each tree
Tree and GROUPs Used tree and multicast group correspondence
an ingress RBridge selects
3.2.1. The Tree and VLANs APPsub-TLV
The RBridge that is the highest priority tree root announces the
VLANs allowed on each tree with the Tree and VLANs (TREE-VLANS)
APPsub-TLV. Multiple instances of this sub-TLV may be carried. The
same tree nicknames may occur in multiple Tree-VLAN RECORDs within
the same or across multiple sub-TLVs. The sub-TLV format is as
follows:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = tbd1 | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
| Tree-VLAN RECORD (1) | (6 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
| ................. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
| Tree-VLAN RECORD (N) | (6 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
where each Tree-VLAN RECORD is of the form:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nickname | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESV | Start.VLAN | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESV | End.VLAN | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TRILL GENINFO APPsub-TLV type, set to tbd1 (TREE-VLANS).
o Length: 6*n bytes, where there are n Tree-VLAN RECORDs. Thus the
value of Length can be used to determine n. If Length is not a
multiple of 6, the sub-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 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) specified in Section 3.2.1. The differences are
that its APPsub-TLV type is set to tbd2 (TREE-VLANS-USE) and the
Tree-VLAN correspondences in the Tree-VLAN RECORDs listed are those
the originating RBridge wants to use for multi-destination packets.
This APPsub-TLV is used by an ingress RBridge to distribute the tree-
VLAN correspondence it selects from the list announced by the highest
priority tree root.
3.2.3. The Tree and FGLs APPsub-TLV
The RBridge that is the highest priority tree root can use the Tree
and 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 or across multiple APPsub-TLVs. Its format is as follows:
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1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = tbd3 | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
| Tree-FGL RECORD (1) | (8 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
| ................. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
| Tree-FGL RECORD (N) | (8 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
where each Tree-VLAN RECORD is of the form:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nickname | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
| Start.FGL | (3 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
| End.FGL | (3 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
o Type: TRILL GENINFO APPsub-TLV type, set to tbd3 (TREE-FGLS).
o Length: 8*n bytes, where there are n Tree-FGL RECORDs. Thus the
value of Length can be used to determine n. If Length is not a
multiple of 8, the sub-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 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) specified in Section 3.2.3. The only difference is
that its APPsub-TLV type is set to tbd4 (TREE-FGLS-USE), and the
Tree-FGL RECORDs listed are those 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 it selects
from the list announced by the highest priority tree root.
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3.2.5. The Tree and Groups APPsub-TLV
Data Label based tree selection is easily extended to (Data Label +
Layer 2 or 3 multicast group) based tree selection. We can appoint
multicast group 1 in VLAN 10 to tree1 and appoint group 2 in VLAN 10
to tree2 for better load sharing.
The RBridge that is the highest priority tree root can announce the
multicast groups allowed on each tree for each data label with the
Tree and Groups (TREE-GROUPS) APPsub-TLV. Multiple instances of this
sub-TLV may be carried. The sub-TLV format is as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = tbd5 | (2 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | (2 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tree Nickname | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Sub-Sub-TLVs (variable)
+-+-+-+-+-+-+-+-+-+....
o Type: TRILL GENINFO APPsub-TLV type, set to tbd5 (TREE-GROUPS).
o Length: 2 + the length of the Group Sub-Sub TLVs 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 TLV [RFC7176]. Each such TLV
structure specifies a multicast group and either a VLAN or FGL.
Although these TLV structure 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 is in turn inside a
TRILL GENINFO TLV [RFC7357].
3.2.6. The Tree and Groups Used APPsub-TLV
This APPsub-TLV has the same structure as the Tree and GROUPs APPsub-
TLV (TREE-GROUPS) specified in Section 3.2.5. The only difference is
that its APPsub-TLV type is set to tbd6 (TREE-GROUPS-USE), and the
tree and multicast groups listed in this sub-TLV are those 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 it selects from the list announced by the highest
priority tree root.
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3.3. Detailed Processing
The highest priority tree root RBridge MUST include all the necessary
tree related sub-TLVs defined in [RFC7176] as usual in its E-L1FS FS-
LSP and MAY include the Tree and VLANs Sub-TLV (TREE-VLANs) and/or
Tree and FGLs Sub-TLV (TREE-FGLs) in its E-L1FS FS-LSP [RFC7780]. In
this 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 forwarding hardware.
An ingress RBridge that understands the TREE-VLANs APPsub-TLV SHOULD
select the tree-VLAN correspondences it wishes to use and put them in
TREE-VLAN-USE APPsub-TLVs. If there were multiple tree nicknames
announced in TREE-VLANs Sub-TLV for a VLAN x, ingress RBridge choose
one of them if it supports this feature. For example, the ingress
RBridge may choose the closest (minimum cost) root among them. How to
make such a choice is out of the scope of this document. It may be
desirable to have some fixed algorithm to make sure all ingress RBs
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 TREE-VLAN-USE to minimize the multicast forwarding
table size on other 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 the tree nickname that it selected
previously in TREE-VLAN-USE or TREE-FGL-USE for Data Label x.
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 reachable downstream for each adjacency and for each related
tree.
Logically, an ingress RBridge that does not support VLAN/FGL based
tree selection is equivalent to the one that supports it and
announces all the combination pair of tree-id-used and interested-
vlan/interested-fgl as TREE-VLAN-USE.
3.4. Failure Handling
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This section discusses failure of a distribution tree root for the
cases where that is not the highest priority root and the case where
it is the highest priority root. It also discusses some other
transient error conditions.
Failure of a tree root that is not the highest priority: It is the
responsibility of the highest priority tree root to inform other
RBridges of any change in the allowed tree-VLAN correspondence. When
the highest priority tree root learns the root of tree t has failed,
it should re-assign the VLANs allowed on tree t to other trees or to
a tree replacing the failed one.
Failure of the highest priority tree root: It is RECOMMENDED that the
second highest priority tree root be pre-configured with the proper
knowledge of the tree-VLAN correspondence allowed when the highest
priority tree root fails. The information announced by the second
priority 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 tree root. When the highest priority tree root
fails, the former second priority tree root will become the highest
priority tree root of the campus. When an RBridge notices the failure
of the original highest priority tree root, it can immediately use
the stored information announced by the original second priority tree
root. It is REOMMENDED that the tree-VLAN correspondence information
be pre-configured on the second highest priority tree root to be the
same as that on the highest priority tree root for the trees other
than the highest priority tree itself. This can minimize the change
to multicast forwarding tables in the case of 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, or even lower
priority tree root RBridges.
In some transient conditions or in case of misbehavior by the 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 root of tree t is no longer reachable.
For the second case, an ingress RBridge may choose another reachable
tree root which allows VLAN x according to the highest priority tree
root announcement. If there is no such tree available, then it is the
same as the first case above. Then the ingress RBridge should be
'downgraded' to a conventional BRridge with behavior as specified in
[RFC6325]. A timer should be set to allow the temporary transient
stage to complete before the change of responsive tree or 'downgrade'
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takes effect. The value of 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 specified by this draft.
RBridges that understand the new TREE-VLAN-USE sub-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 multicast forwarding table (E.g.
RPF table building, spanning tree root notification, etc.) If the
RBridge does not receive TREE-VLAN-USE sub-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 and tree2, 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 RB2 is interested in VLANs 10 and 11 and RB3
is interested in VLANs 100 and 101. Hence RB1 receives ((tree1,
VLAN10), (tree2, VLAN11)) as a TREE-VLAN-USE sub-TLV and (tree1,
tree2) as a TREE-USE-IDs sub-TLV from RB2 on port x. And RB1 receives
(tree1) as a TREE-USE-IDs sub-TLV and no TREE-VLAN-USE sub-TLV from
RB3 on port y. RB2 and RB3 announce their interested VLANs in an INT-
VLAN sub-TLV as usual. Then RB1 will build the entry of (tree1,
VLAN10, port x) and (tree2, VLAN11, port x) based on RB2's LSP and
the mechanism specified in this document. RB1 also builds entries of
(tree1, VLAN100, port y), (tree1, VLAN101, port y), (tree2, VLAN100,
port y), (tree2, VLAN101, port y) based on RB3's LSP in conventional
way. The multicast forwarding table on RB1 with merged entry would be
like the following.
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+--------------+-----+---------+
|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 a
hybrid campus is the number of entries equal to the number in current
practice which does not support VLAN based tree selection. Such an
extreme case happens when the interested VLAN set from the new
RBridges is a subset of the interested VLAN set from the old
RBridges.
Data Label and multicast group based tree selection is compatible
with the current practice. Its effectiveness increases with more
RBridge 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 assigne five new TRILL APPsub-TLV type codes
from the range less than 255 as specified in Section 3 and update the
TRILL Parameters registry as shown below.
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Type Name of APPSub TLV code Reference
---- ----------------------- ---------
tbd1 Tree and VLANs [this document 3.2.1]
tbd2 Tree and VLANs Used [this document 3.2.2]
tbd3 Tree and FGLs [this document 3.2.3]
tbd4 Tree and FGLs Used [this document 3.2.4]
tbd5 Tree and Groups [this document 3.2.5]
tbd6 Tree and Groups Used [this document 3.2.6]
7. References
7.1. Normative References
[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011, <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, May 2014,
<http://www.rfc-editor.org/info/rfc7172>.
[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, 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>.
[RFC7780] Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
Ghanwani, A. and Gupta, S., "Transparent Interconnection of
Lots of Links (TRILL): Clarifications, Corrections, and
Updates", RFC 7780, February 2016.
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, February 2009, <http://www.rfc-
editor.org/info/rfc5310>.
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8. Acknowledgments
Authors wish to thank David M. Bond, Liangliang Ma, Naveen Nimmu,
Radia Perlman, Rakesh Kumar and Sunny Rajagopalan for the valuable
comments and contributions (names in alphabet order).
Authors' Addresses
Yizhou Li
Huawei Technologies
101 Software Avenue,
Nanjing 210012
China
Phone: +86-25-56624629
Email: liyizhou@huawei.com
Donald Eastlake
Huawei R&D USA
155 Beaver Street
Milford, MA 01757 USA
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
Weiguo Hao
Huawei Technologies
101 Software Avenue,
Nanjing 210012
China
Phone: +86-25-56623144
Email: haoweiguo@huawei.com
Hao Chen
Huawei Technologies
101 Software Avenue,
Nanjing 210012
China
Email: philips.chenhao@huawei.com
Somnath Chatterjee
Cisco Systems,
SEZ Unit, Cessna Business Park,
Outer ring road,
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Bangalore - 560087
India
Email: somnath.chatterjee01@gmail.com
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