Coordinated Multicast Trees (CMT)for TRILL
draft-tissa-trill-cmt-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Tissa Senevirathne , Jon Hudson | ||
| Last updated | 2012-01-05 | ||
| Replaced by | draft-ietf-trill-cmt, draft-ietf-trill-cmt, RFC 7783 | ||
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| Consensus boilerplate | Unknown | ||
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draft-tissa-trill-cmt-00
TRILL Working Group Tissa Senevirathne
Internet Draft CISCO
Intended status: Standard Track Janardhanan Pathangi
DELL
Jon Hudson
Brocade
January 5, 2012
Expires: July 2012
Coordinated Multicast Trees (CMT)for TRILL
draft-tissa-trill-cmt-00.txt
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carefully, as they describe your rights and restrictions with
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Abstract
TRILL facilitates loop free connectivity to non TRILL legacy
networks via choice of an Appointed Forwarder for set of VLANs.
Appointed Forwarder provides VLAN level load sharing with active-
standby model. Mission critical operations such as High Performance
Data Centers require active-active load sharing model. Active-Active
load sharing model can be accomplished by representing any given non
TRILL legacy network with a single virtual RBridge. Virtual
representation of the non-TRILL legacy network with a single RBridge
poses serious challenges in multi-destination RPF calculations. This
document presents the required enhancements to build Coordinated
Multicast Trees (CMT) within the TRILL campus. CMT provides
flexibility to RBridges to select desired path of association to a
given distribution tree.
Table of Contents
1. Introduction...................................................3
1.1. Contributors..............................................4
2. Conventions used in this document..............................5
3. IS-IS extension................................................5
3.1. AFFINITY TLV..............................................5
4. Multicast Tree Construction and use of Affinity Sub-TLV........7
4.1. Update to RFC 6325........................................8
4.2. Announcing virtual RBridge nickname.......................9
4.3. Affinity Sub-TLV capability...............................9
5. Theory of operation............................................9
5.1. Distribution Tree provisioning............................9
5.2. Affinity Sub-TLV advertisement............................9
5.3. Affinity sub-TLV conflict resolution.....................10
5.4. Ingress Multi-Destination Forwarding.....................10
5.4.1. Forwarding when n < k...............................10
5.5. Egress Multi-Destination Forwarding......................11
5.5.1. Traffic Arriving on an assigned Tree to RBk-RBv.....11
5.5.2. Traffic Arriving on other Trees.....................11
5.6. Failure scenarios........................................11
5.6.1. Edge RBridge RBk failure............................11
5.7. Backward compatibility...................................12
6. Security Considerations.......................................12
7. IANA Considerations...........................................13
8. References....................................................13
8.1. Normative References.....................................13
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8.2. Informative References...................................13
9. Acknowledgments...............................................13
10. Authors' Addresses...........................................14
1. Introduction
TRILL presented in [RFC6325] and other related documents, provide
methods of utilizing all available paths for active forwarding, with
minimum configuration. TRILL utilizes IS-IS as control plane and
encapsulates native frames with a TRILL header.
Legacy networks utilize IEEE 802.1D Spanning Tree Protocol as the
control protocol and utilizes at any given time, a single path among
all available paths for active forwarding. Legacy networks forward
frames in "native" format.
[RFC6325],[RFC6327] and [RFC6439] provide methods for
interoperability between TRILL and Legacy networks. [RFC6439],
provide active-standby solution, where only one of the RBridges is
in active forwarding state for any given VLAN. The RBridge in active
forwarding state for any given VLAN is referred to as the Appointed
Forwarder (AF). All frames ingressing into a TRILL network via the
Appointed Forwarder are encapsulated with the TRILL header with a
nickname held by the ingress AF RBridge. Due to failures, re-
configurations and other network dynamics, Appointed Forwarder for
any set of VLANs may change. RBridges maintain forwarding table that
contain destination MAC address to egress RBridge binding. In the
event of AF change, forwarding tables of remote RBridges may
continue to forward traffic to the previous AF and may get discarded
at the egress, causing traffic disruption.
Mission critical applications such as High Performance Data Centers
require resiliency during failover. The active-active forwarding
model minimizes impact during failures and maximizes the available
network bandwidth. A typical deployment scenario, depicted in Figure
2, which may have either End Stations and/or Legacy bridges attached
to the RBridges. These Legacy devices typically are multi-homed to
several RBridges and treats all of the uplinks as a single Link
Aggregation (LAG) bundle. The Appointed Forwarder designation
presented in [RFC6439] requires each of the edge RBridges to
exchange TRILL hello packets. By design, a LAG does not forward
packets received on one of the member ports of the LAG to other
member ports of the same LAG. As a result AF designation methods
presented in [RFC6439] cannot be applied to deployment scenario
depicted in Figure 2
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An active-active load sharing model can be implemented by
representing the edge of the network connected to a specific group
of RBridges by a single virtual RBridge. In addition to an active-
active forwarding model, there may be other applications that may
requires similar representations.
Sections 4.5.1 and 4.5.2 of [RFC6325] specify distribution tree
calculation and Reverse Path Forwarding Check calculation algorithms
for multi-destination forwarding. The algorithms specified in
[RFC6325], strictly depends on link cost and parent RBridge
priority. As a result, based on the network topology, it may be
possible that a given edge RBridge, if it is forwarding on behalf of
the virtual RBridge, may not have a candidate multicast tree that
the edge RBridge can forward traffic on because there is no tree for
which the virtual RBridge is a leaf node from the edge RBridge.
In this document we present a method that allows RBridges to specify
the path of association to distribution trees. Remote RBridges
calculate the SPF and derive the RPF for distribution trees based on
the distribution tree association advertisements. In the absence of
distribution tree association advertisements, remote RBridges derive
the SPF based on the algorithm specified in section 4.5.1 of [RFC
6325].
Other applications, beside the above mentioned active-active
forwarding model, may utilize the distribution tree association
framework presented in this document to associate to distribution
trees through a preferred path.
This proposal requires presence of multiple multi-destination trees
within the TRILL campus and updating all the RBridges in the network
to support the new Affinity sub-TLV. It is expected that both of
these requirements will be met as they are control plane changes,
and will be common deployment scenario. In case any of the above two
conditions are not met RBridges MUST support a fallback option for
interoperability. Since the fallback is expected to be a temporary
phenomenon till all RBridges are upgraded, this proposal gives
guidelines for such fallbacks, and does not mandate or specify any
specific set of fallback options.
1.1. Contributors
The work in this document is a result of much passionate discussions
and contributions from following individuals. Their names are listed
in alphabetical order and do not in any means intended to be ranked
in any other way.
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Ayan Banerjee, Dinesh Dutt, Donald Eastlake, Mingui Zhang, Radia
Perlman, Shivakumar Sundaram.
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 [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 [RFC2119] significance.
3. IS-IS extension
3.1. AFFINITY TLV
Association of a RBridge to a multicast tree through a specific path
is accomplished by using a new IS-IS sub-TLV, Affinity TLV.
AFFINITY TLV is a sub-TLV under Router capability TLV (242) [RFC
4971]. [RFC6326bis] formally defines the Affinity sub-TLV. The
details of the Affinity sub-TLV are presented for clarity and
readers are encouraged to refer to [RFC6326bis] for latest updates.
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+-+-+-+-+-+-+-+-+
|Type=AFFNITYTLV| (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+---------------+---------------+
| nickname | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 1 Affinity TLV structure
o Type: AFINITYTLV, (TBD).
o Length: 4 + 2*n, where n is the number of nicknames of affinity
trees listed tree numbers.
o Nickname : TRILL 16bit nickname of the RBridge whose
association to the listed multicast trees are through the
announcing RBRidge.
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.
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4. Multicast Tree Construction and use of Affinity Sub-TLV
------------------
/ \
| |
| TRILL Campus |
| |
\ /
---------------------
| | |
| | | ----------
DRB| | |
+------+ +------+ +------+
| | | | | |
|(RB1) | |(RB2) | | (RBk)|
+------+ +------+ +------+
| | |
| | ----------- ----
| | | ------------- |
----- | | ----------- | |
LAG---->(| | | ) (| | |) LAG
+-------+ . . . +-------+
| CE1 | | CEn |
| | | |
+-------+ +-------+
Figure 2 Reference Topology
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------------------ Sample Multicast Tree (T1)
/ \
| | |
| TRILL Campus | o RBn
| | / | \
\ / / | ---\
--------------------- RB1o o o
| | | | RB2 RBk
| | | ---------- |
DRB| | | oRBv
+------+ +------+ +------+
| | | | | |
|(RB1) | |(RB2) | | (RBk)|
+------+ +------+ +------+
ooo|ooooooo|oooooooooooooo|oo
o o
o virtual RBridge RBv o
ooo|ooooooo|ooo|ooooooooooooo ----
| | | ---------- |
----- | | ---------- | |
LAG---->(| | | ) (| | | ) LAG
+-------+ . . . +-------+
| CE1 | | CEn |
| | | |
+-------+ +-------+
Figure 3 Example Logical Topology
4.1. Update to RFC 6325
Section 4.5.1 of [RFC6325], is updated as below:
Each RBridge that desires to be a parent RBridge for a specific
multi-destination distribution tree x for child RBridge RBy or
nickname Ny (in the event of announcing multiple nicknames),
announces the desired association through Affinity sub-TLV.
When such an Affinity sub-TLV is present, the association specified
by the affinity sub-TLV MUST be used when constructing the SPF tree.
In the absence of such Affinity sub-TLV, or if there are RBRidges in
the network that are do not support Affinity sub-TLV, SPF tree is
calculated as specified in the section 4.5.1 of [RFC6325]. Section
4.3. below explains methods of identifying RBridges that support
Affinity sub-TLV capability.
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4.2. Announcing virtual RBridge nickname
Each edge RBridge RB1 to RBk advertise virtual RBridge nickname RBv
using nickname sub-TLV (6), [RFC6326bis], along with their original
nicknames RBi, RBj.
4.3. Affinity Sub-TLV capability.
RBridges that announce the TRILL version sub-TLV [RFC6326bis] and
set the Affinity capability bit (section 7. ) support the Affinity
sub-TLV and calculation of multi-destination distribution trees as
specified herein.
5. Theory of operation
5.1. Distribution Tree provisioning
Let's assume there are n distribution trees and k edge RBridges in
the edge group of interest.
If n >= k
Let's assume edge RBridges are sorted in numerically ascending
order by SystemID such that RB1 < RB2 < RBk. Each Rbridge in the
numerically sorted list is assigned a monotonically increasing
number j such that; RB1=0, RB2=1, RBi=j and RBi+1=j+1.
Assign each tree to RBi such that tree number { (tree_number) %
k}+1 is assigned to RBridge i for tree_number from 1 to n. where n
is the number of trees and k is the number of RBridges considered
for tree allocation.
If n < k
Distribution trees are assigned to RBridges RB1 to RBn, using the
same algorithm as n >= k case. RBridges RBn+1 to RBk do not
participate in active-active forwarding process on behalf of RBv.
5.2. Affinity Sub-TLV advertisement
Each RBridge in the RB1..RBk domain advertises Affinity TLV on
behalf of RBv.
As an example, let's assume that RB1 has chosen Trees t1 and tk+1 on
behalf of RBv.
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RB1 advertises affinity TLV; {RBv, Num of Trees=2, t1, tk+1.
Other RBridges in the RB1..RBk edge group follow the same procedure.
5.3. Affinity sub-TLV conflict resolution
If different RBridges advertise Affinity sub-TLVs that try to
associate the same virtual RBridge as their child in the same tree
or trees, those Affinity sub-TLVs are in conflict for those trees.
The nicknames of the conflicting RBridges are compared to identify
which RBridge holds the nickname that is the highest priority to be
a tree root, with the System ID as the tie breaker
The RBridge with the highest priority to be a tree root will retain
the Affinity association. Other RBridges with lower priority to be a
tree root MUST stop advertising their conflicting Affinity sub-TLV,
re-calculate the multicast tree affinity allocation, and, if
appropriate, advertise a new non-conflict Affinity sub-TLV.
Similarly, remote RBridges MUST honor the Affinity sub-TLV from the
RBridge with the highest priority to be a tree root and ignore the
conflicting Affinity sub-TLV entries advertised by the RBridges with
lower priorities to be tree roots.
5.4. Ingress Multi-Destination Forwarding
If there is at least one tree on which RBv has affinity via RBk ,
then RBk performs the following operations, for multi-destination
frames received from a CE node:
1. Flood to locally attached CE nodes subjected to VLAN and multicast
pruning.
2. Encapsulate in TRILL header and assign ingress RBridge nickname as
RBv. (nickname of the virtual RBridge).
3. Forward to one of the distribution trees, tree x in which RBv is
associated with RBk
5.4.1. Forwarding when n < k
If there is no tree on which RBv can claim affinity via RBk
(Probably because the number of trees n built is less than number
of RBridges k announcing the affinity sub-TLV), then RBk MUST fall
back to one of the following
1. This RBridge should stop forwarding frames from the CE nodes,
and should mark its link as passive. This will prevent CE nodes
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from forwarding data on to this RBridge, and only use those
RBridges which have been assigned a tree -OR-
2. This RBridge tunnels multi-destination frames received from
attached native devices to an RBridge RBy that has an assigned
tree. The tunnel destination should forward it to the TRILL
network, and also to its local access links . (The mechanism
of tunneling and handshake between the tunnel source and
destination are out of scope of this specification and may be
addressed in future documents).
Above fallback options may be very specific to active-active
forwarding scenario. However, as stated above, Affinity sub-TLV may
be used in other applications. In such event the application SHOULD
specify applicable fallback options.
5.5. Egress Multi-Destination Forwarding
5.5.1. Traffic Arriving on an assigned Tree to RBk-RBv
Multi-destination frames arriving at RBk on a Tree x, where RBk has
announced the affinity of RBv via x, MUST be forwarded to CE members
of RBv. Forwarding to other end-nodes and RBridges that are not part
of the network represented by the RBv virtual RBridge MUST follow
the forwarding rules specified in [RFC6325].
5.5.2. Traffic Arriving on other Trees
Multi-destination frames arriving at RBk on a Tree y, where RBk has
not announced the affinity of RBv via y, MUST NOT be forwarded to CE
members of RBv. Forwarding to other end-nodes and RBridges that are
not part of the network represented by the RBv virtual RBridge but
MUST follow the forwarding rules specified in RFC6325.
5.6. Failure scenarios
5.6.1. Edge RBridge RBk failure
Each of the member RBridges of given virtual RBridge edge group is
aware of its member RBridges through configuration or some other
method.
Member RBridges detects nodal failure of a member RBridge through
IS-IS LSP advertisements or lack thereof.
Upon detecting a member failure, each of the member RBridges of the
RBv edge group start recovery timer T_rec for failed RBrdige RBi. If
the previously failed RBridge RBi has not recovered after the expiry
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of timer T_rec, members RBridges perform distribution tree
assignment algorithm specified in section 5.1. Each of the member
RBridges re-advertises the Affinity sub-TLV with new tree
assignment. This action causes the campus to update the tree
calculation with the new assignment.
RBi upon start-up, starts advertising its presence through ISIS LSP
and starts a timer T_i. Member RBridges detecting the presence of RB
start a timer T_j. Timer T_j SHOULD be at least < T_i/2. (Please see
note below)
Upon expiry of timer T_j, member RBridges recalculate the multi-
destination tree assignment and advertised the related trees using
Affinity sub-TLV.
Upon expiry of timer T_i, RBi recalculate the multi-destination tree
assignment and to advertised the related trees using Affinity TLV.
Note: Timers T_i and T_j are designed such that to minimize traffic
down time and avoid multi-destination packet duplication.
Above failure recovery algorithm is presented as a guideline.
Implementations MAY include other failure recover algorithms.
Details of such algorithms are outside the scope of this document.
5.7. Backward compatibility
Implementations MUST support backward compatibility mode to
interoperate with pre Affinity sub-TLV RBRidges in the network. Such
backward compatibility operation MAY include, however is not limited
to, tunneling and/or active-standby modes of operations.
Example:
Step 1. Stop using virtual RBRidge nickname for traffic ingressing
from CE nodes
Step 2. Stop performing active-active forwarding. And fall back to
active standby forwarding, based on locally defined policies.
Definition such policies are outside the scope of this document
and may be addressed in future documents.
6. Security Considerations
Security considerations are similar to RFC 6325,RFC 6326 and RFC
6327. Additional security considerations are being discussed.
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7. IANA Considerations
IANA is requested to allocate a capability bit for "Affinity
Supported" in the TRILL-VER sub-TLV. "Affinity Supported" capability
bit and Affinity sub-TLV are specified and allocated in
[RFC6326bis].
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6325] Perlman, R., et.al. "RBridge: Base Protocol
Specification", RFC 6325, July 2011.
[RFC6327] Eastlake, D. et.al., "RBridge: Adjacency", RFC 6327, July
2011.
[RFC6349] Eastlake, D. et.al., "RBridge: Appointed Forwarder", RFC
6349, November 2011.
[RFC6326bis] Eastlake, D. et.al., "Transparent Interconnection of
Lots of Links (TRILL) Use of IS-IS", draft-eastlake-isis-
rfc6326bis-02.txt, Work in Progress, December 2011.
8.2. Informative References
[RFC6165] Banerjee, A. and Ward, D. "Extensions to IS-IS for Layer-2
Systems", RFC 6165, April 2011.
[RFC4971] Vasseur, JP. et.al "Intermediate System to Intermediate
System (IS-IS) Extensions for Advertising Router
Information", RFC 4971, July 2007.
9. Acknowledgments
Authors wish to extend their appreciations towards individuals who
volunteered to review and comment on the work presented in this
document and provided constructive and critical feedback. Specific
acknowledgements are due for Ronak Desai, Gayatri Ramachandran,
Varun Shah and Anoop Ghanwani.
This document was prepared using 2-Word-v2.0.template.dot.
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10. Authors' Addresses
Tissa Senevirathne
Cisco Systems
375 East Tasman Drive,
San Jose, CA 95134
Phone: 408-853-2291
Email: tsenevir@cisco.com
JanardhananPathangi
Dell/Force10 Networks
Olympia Technology Park,
Guindy Chennai 600 032
Phone: +91 44 4220 8400
Email: Pathangi_Janardhanan@Dell.com
Jon Hudson
Brocade
130 Holger Way
San Jose, CA 95134 USA
Email: jon.hudson@gmail.com
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