Internet DRAFT - draft-ietf-trill-active-active-connection-prob
draft-ietf-trill-active-active-connection-prob
TRILL Working Group Yizhou Li
INTERNET-DRAFT Weiguo Hao
Intended Status: Informational Huawei Technologies
Radia Perlman
EMC
Jon Hudson
Brocade
Hongjun Zhai
ZTE
Expires: Feb 26, 2015 August 25, 2014
Problem Statement and Goals for Active-Active TRILL Edge
draft-ietf-trill-active-active-connection-prob-07
Abstract
The IETF TRILL (Transparent Interconnection of Lots of Links)
protocol provides support for flow level multi-pathing with rapid
failover for both unicast and multi-destination traffic in networks
with arbitrary topology. Active-active at the TRILL edge is the
extension of these characteristics to end stations that are multiply
connected to a TRILL campus. This informational document discusses
the high level problems and goals when providing active-active
connection at the TRILL edge.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2014 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
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Target Scenario . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 LAALP and Edge Group Characteristics . . . . . . . . . . . . 6
3. Problems in Active-Active at the TRILL Edge . . . . . . . . . . 7
3.1 Frame Duplications . . . . . . . . . . . . . . . . . . . . . 7
3.2 Loop Back . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3 Address Flip-Flop . . . . . . . . . . . . . . . . . . . . . 8
3.4 Unsynchronized Information Among Member RBridges . . . . . . 8
4. High Level Requirements and Goals for Solutions . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1 Normative References . . . . . . . . . . . . . . . . . . . 10
8.2 Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
The IETF TRILL (Transparent Interconnection of Lots of Links)
[RFC6325] protocol provides loop free and per hop based multipath
data forwarding with minimum configuration. TRILL uses [IS-IS]
[RFC6165] [RFC7176] as its control plane routing protocol and defines
a TRILL specific header for user data. In a TRILL campus,
communications between TRILL switches can
(1) use multiple parallel links and/or paths,
(2) spread load over different links and/or paths at a fine grained
flow level through equal cost multipathing of unicast traffic and
multiple distribution trees for multi-destination traffic, and
(3) rapidly re-configure to accommodate link or node failures or
additions.
"Active-active" is the extension, to the extent practical, of similar
load spreading and robustness to the connections between end stations
and the TRILL campus. Such end stations may have multiple ports and
will be connected, directly or via bridges, to multiple edge TRILL
switches. It must be possible, except in some failure conditions, to
spread end station traffic load at the granularity of flows across
links to such multiple edge TRILL switches and rapidly re-configure
to accommodate topology changes.
1.1 Terminology
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].
The acronyms and terminology in [RFC6325] are used herein with the
following additions:
CE - Customer Equipment (end station or bridge).
Data Label - VLAN or FGL (Fine Grained Label [RFC7172]).
LAALP - Local Active-Active Link Protocol. Any protocol similar to
MC-LAG that runs in a distributed fashions on a CE, the links from
that CE to a set of edge group RBridges, and on those RBridges.
MC-LAG - Multi-Chassis Link Aggregation. Proprietary extensions to
IEEE Std 802.1AX-2011 [802.1AX] standard so that the aggregated links
can, at one end of the aggregation, attach to different switches.
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Edge group - a group of edge RBridges to which at least one CE is
multiply attached using an LAALP. When multiple CEs attach to the
exact same set of edge RBridges, those edge RBridges can be
considered as a single edge group. An RBridge can be in more than one
edge group.
RBridge - Routing Bridge - an alternative name for a TRILL switch.
TRILL - Transparent Interconnection of Lots of Links.
TRILL switch -- a device the implements the TRILL protocol; an
alternative term for an RBridge.
2. Target Scenario
This section presents a typical scenario of active-active connections
to a TRILL campus via multiple edge RBridges where the current TRILL
appointed forwarder mechanism does not work as expected.
The TRILL appointed forwarder mechanism [RFC6439] can handle fail
over (active-standby), provides loop avoidance and, with
administrative configuration, provides load spreading based on VLAN.
One and only one appointed RBridge can ingress/egress native frames
into/from the TRILL campus for a given VLAN among all edge RBridges
connecting a legacy network to the TRILL campus. This is true whether
the legacy network is a simple point-to-point link or a complex
bridged LAN or anything in between. By carefully selecting different
RBridges as appointed forwarder for different sets of VLANs, load
spreading over different edge RBidges across different Data Labels
can be achieved.
The appointed forwarder mechanism [RFC6439] requires all of the edge
group RBridges to exchange TRILL IS-IS Hello packets through their
access ports. As Figure 1 shows, when multiple access links of
multiple edge RBridges are connected to a CE by an LAALP, Hello
messages sent by RB1 via access port to CE1 will not be forwarded to
RB2 by CE1. RB2 (and other members of LAALP1) will not see that Hello
from RB1 via the LAALP1. Every member RBridge of LAALP1 thinks of
itself as appointed forwarder on an LAALP1 link for all VLANs and
will ingress/egress frames. Hence the appointed forwarder mechanism
cannot provide active-active or even active-standby service across
the edge group in such a scenario.
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----------------------
| |
| TRILL Campus |
| |
----------------------
| | |
----- | --------
| | |
+------+ +------+ +------+
| | | | | |
|(RB1) | |(RB2) | | (RBk)|
+------+ +------+ +------+
|..| |..| |..|
| +----+ | | | |
| +---|-----|--|----------+ |
| +-|---|-----+ +-----------+ |
| | | +------------------+ | |
LAALP1--->(| | |) (| | |) <---LAALPn
+-------+ . . . +-------+
| CE1 | | CEn |
| | | |
+-------+ +-------+
Figure 1 Active-Active connection to TRILL edge RBridges
Active-Active connection is useful when we want to achieve the
following two goals:
- Flow rather than VLAN based load balancing is desired.
- More rapid failure recovery is desired. The current appointed
forwarder mechanism relies on the TRILL Hello timer expiration to
detect the unreachability of another edge RBridge connecting to the
same local link. Then re-appointing the forwarder for specific VLANs
may be required. Such procedures take time on the scale of seconds
although this can be improved with TRILL use of BFD [RFC7175].
Active-Active connection usually has a faster built-in mechanism for
member node and/or link failure detection. Faster detection of
failures minimizes the frame loss and recovery time.
Today LAALP is usually a proprietary facility whose implementation
varies by vendor. So, to be sure the LAALP operations successfully
across a group of edge RBridges, those edge RBridges will almost
always have to be from the same vendor. In the case where the LAALP
is an MC-LAG, the CE normally implements standard [802.1AX] logic so
proprietary elements would only be at the edge group end. There is
also a revision of [802.1AX] underway (802.1X-REV) to remove the
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restriction in [802.1AX] that there be one box at each end of the
aggregation. So it is possible that in the future an LAALP could be
implemented through such a revised [802.1AX] with standards
conformant logic at both the CE and edge group ends. In order to have
a common understanding of active-active connection scenarios, the
assumptions in Section 2.1 are made about the characteristics of the
LAALP and edge group of RBridges.
2.1 LAALP and Edge Group Characteristics
For a CE connecting to multiple edge RBridges via an LAALP (active-
active connection), the following characteristics apply:
a) The LAALP will deliver a frame from an endnode to TRILL at exactly
one edge group RBridge.
b) The LAALP will never forward frames it receives from one up-link
to another.
c) The LAALP will attempt to send all frames for a given flow on the
same uplink. To do this, it has some unknown rule for which frames
get sent to which uplinks (typically based on a simple hash function
of Layer 2 through 4 header fields).
d) Frames are accepted from any of the uplinks and passed down to
endnodes (if any exist).
e) The LAALP cannot be assumed to send useful control information to
the up-link such as "this is the set of other RBridges to which this
CE is attached", or "these are all the MAC addresses attached".
For an edge group of RBridges to which a CE is multiply attached with
an LAALP:
a) Any two RBridges in the edge group are reachable from each other
via the TRILL campus.
b) Each RBridge in the edge group knows an ID for each LAALP instance
multiply attached to that group. The ID will be consistent across
the edge group and globally unique across the TRILL campus. For
example, if CE1 attaches to RB1, RB2, ... RBn using an LAALP, then
each of RBs will know, for the port to CE1, that it is has some label
such as "LAALP1"
c) Each RB in the edge group can be configured with the set of
acceptable VLANs for the ports to any CE. The acceptable VLANs
configured for those ports should include all the VLANs the CE has
joined and be consistent for all the member RBridges of the edge
group.
d) When a RBridge fails, all the other RBridges having formed any
LAALP instance with it know the information in a timely fashion.
e) When a down-link of an edge group RBridge to an LAALP instance
fails, that RBridge and all the other RBridges participating in the
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LAALP instance including that down-link know of the failure in a
timely fashion.
f) The RBridges in the edge group have some mechanism to exchange
information with each other, including the set of CEs they are
connecting to or the IDs of the LAALP instances their down-links are
part of.
Other than the applicable characteristics above, the internals of an
LAALP are out of scope for TRILL.
3. Problems in Active-Active at the TRILL Edge
This section presents the problems that need to be addressed in
active-active connection scenarios. The topology in Figure 1 is used
in the following sub-sections as the example scenario for
illustration purposes.
3.1 Frame Duplications
When a remote RBridge ingresses a multi-destination TRILL Data packet
in VLAN x, all edge group RBridges of LAALP1 will receive the frame
if any local CE1 joins VLAN x. As each of them thinks it is the
appointed forwarder for VLAN x, without changes made for active-
active connection support, they would all forward the frame to CE1.
The bad consequence is that CE1 receives multiple copies of that
multi-destination frame from the remote end host source.
Frame duplication may also occur when an ingress RBridge is non-
remote, say ingress and egress are two RBridges belonging to the same
edge group. Assume LAALP m connects to an edge group g and the edge
group g consists of RB1, RB2 and RB3. The multi-destination frames
ingressed from a port not connected to LAALP m by RB1 can be locally
replicated to other ports on RB1 and also TRILL encapsulated and
forwarded to RB2 and RB3. CE1 will receive duplicate copies from RB1,
RB2 and RB3.
Note that frame duplication is only a problem in multi-destination
frame forwarding. Unicast forwarding does not have this issue as
there is only ever one copy of the packet.
3.2 Loop Back
As shown in Figure 1, CE1 may send a native multi-destination frame
to the TRILL campus via a member of the LAALP1 edge group (say RB1).
This frame will be TRILL encapsulated and then forwarded through the
campus to the multi-destination receivers. Other members (say RB2) of
the same LAALP edge group will receive this multicast packet as well.
In this case, without changes made for active-active connection
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support, RB2 will decapsulate the frame and egress it. The frame
loops back to CE1.
3.3 Address Flip-Flop
Consider RB1 and RB2 using their own nickname as ingress nickname for
data into a TRILL campus. As shown by Figure 1, CE1 may send a data
frame with the same VLAN and source MAC address to any member of the
edge group LAALP1. If some egress RBridge receives TRILL data packets
from different ingress RBridges but with same source Data Label and
MAC address, it learns different Data Label and MAC to nickname
address correspondences when decapsulating the data frames. Address
correspondence may keep flip-flopping among nicknames of the member
RBridges of the LAALP for the same Data Label and MAC address.
Existing hardware does not support data plane learning of multiple
nicknames for the same MAC address and data label -- when data plane
learning indicates attachment of the MAC to a new nickname, it
overwrites the old attachment nickname.
Implementers have stated that most current TRILL switch hardware,
when doing data plane learning, behaves badly under these
circumstances and, for example, interpret address flip-flopping as a
severe network problem. It may also cause the returning traffic to go
through different paths to reach the destination resulting in
persistent re-ordering of the frames.
3.4 Unsynchronized Information Among Member RBridges
A local RBridge, say RB1 connected to LAALP1, may have learned a Data
Label and MAC to nickname correspondence for a remote host h1 when h1
sends a packet to CE1. The returning traffic from CE1 may go to any
other member RBridge of LAALP1, for example RB2. RB2 may not have
h1's Data Label and MAC to nickname correspondence stored. Therefore
it has to do the flooding for unknown unicast [RFC6325]. Such
flooding is unnecessary since the returning traffic is almost always
expected and RB1 had learned the address correspondence. It is
desirable to avoid flooding; it imposes a greater burden on the
network than known destination unicast traffic because the flooded
traffic is sent over more links.
Synchronization of the Data Label and MAC to nickname correspondence
information among member RBridges will reduce such unnecessary
flooding.
4. High Level Requirements and Goals for Solutions
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The problems identified in section 3 should be solved in any solution
for active-active connection to edge RBridges. The following high-
level requirements and goals should be met.
Data plane:
1) All up-links of CE MUST be active: the LAALP is free to choose any
up-link on which to send packets and the CE is able to receive
packets from any up-link of an edge group.
2) Looping back and frame duplication MUST be prevented.
3) Learning of Data Label and MAC to nickname correspondence by a
remote RBridge MUST NOT flip-flop between the local multiply attached
edge RBridges.
4) Packets for a flow SHOULD stay in order.
5) The Reverse Path Forwarding Check MUST work properly as per
[RFC6325].
6) Single up-link failure on CE to an edge group MUST NOT cause
persistent packet delivery failure between TRILL campus and CE.
Control plane:
1) No requirement for new information to be passed between edge
RBridges and CE or between edge RBridges and endnodes.
2) If there is any TRILL specific information required to be
exchanged between RBridges in an edge group, for example data labels
and MAC addresses binding to nicknames, a solution MUST specify the
mechanism to perform such exchange unless this is handled internal to
the LAALP.
3) RBridges SHOULD be able to discover other members in the same edge
group by exchanging their LAALP attachment information.
Configuration, incremental deployment, and others:
1) Solution SHOULD require minimal configuration.
2) Solution SHOULD automatically detect misconfiguration of edge
RBridge group.
3) Solution SHOULD support incremental deployment, that is, not
require campus wide upgrading for all RBridges, only changes to the
edge group RBridges.
4) Solution SHOULD be able to support from 2 up to at least 4 active-
active up-links on a multiply attached CE.
5) Solution SHOULD NOT assume there is a dedicated physical link
between any two of the edge RBridges in an edge group.
5. Security Considerations
As an informational overview, this draft does not introduce any extra
security risks. Security risks introduced by any particular LAALP or
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other elements of solutions to the problems presented here will be
discussed in the separate document(s) describing such LAALP or
solutions.
End station links in TRILL are Ethernet links and consideration
should be given to securing them with [802.1AE] link security for the
protection of end station data and link level control messages
including any LAALP control messages.
For general TRILL Security Considerations, see [RFC6325].
6. IANA Considerations
No IANA action is required. RFC Editor: please delete this section
before publication.
7. Acknowledgments
Special acknowledgments to Donald Eastlake, Adrian Farrel and Mingui
Zhang for their valuable comments.
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.
[IS-IS] ISO/IEC 10589:2002, Second Edition, "Intermediate System to
Intermediate System Intra-Domain Routing Exchange Protocol
for use in Conjunction with the Protocol for Providing the
Connectionless-mode Network Service (ISO 8473)", 2002.
[RFC6165] Banerjee, A. and D. Ward, "Extensions to IS-IS for Layer-2
Systems", RFC 6165, April 2011.
[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011
[RFC6439] Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F. Hu,
"Routing Bridges (RBridges): Appointed Forwarders", RFC
6439, November 2011
[RFC7172] Eastlake, D., M. Zhang, P. Agarwal, R. Perlman, D. Dutt,
"Transparent Interconnection of Lots of Links (TRILL):
Fine-Grained Labeling", RFC7172, May 2014.
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[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.
8.2 Informative References
[RFC7175] Manral, V., D. Eastlake, D. Ward, A. Banerjee, "Transparent
Interconnetion of Lots of Links (TRILL): Bidirectional
Forwarding Detection (BFD) Support", RFC7175, May 2014.
[802.1AX] IEEE, "Link Aggregration", 802.1AX-2008, 3 November 2008.
[802.1Q] IEEE, "Media Access Control (MAC) Bridges and Virtual
Bridged Local Area Networks", IEEE Std 802.1Q-2011, 31
August 2011.
[802.1AE] IEEE, "Media Access Control (MAC) Security", IEEE Std
802.1AE-2006, 18 August 2006.
Authors' Addresses
Yizhou Li
Huawei Technologies
101 Software Avenue,
Nanjing 210012
China
Phone: +86-25-56625409
EMail: liyizhou@huawei.com
Weiguo Hao
Huawei Technologies
101 Software Avenue,
Nanjing 210012
China
Phone: +86-25-56623144
EMail: haoweiguo@huawei.com
Radia Perlman
EMC
2010 256th Avenue NE, #200
Bellevue, WA 98007 USA
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Email: Radia@alum.mit.edu
Jon Hudson
Brocade
130 Holger Way
San Jose, CA 95134 USA
Phone: +1-408-333-4062
jon.hudson@gmail.com
Hongjun Zhai
ZTE
68 Zijinghua Road, Yuhuatai District
Nanjing, Jiangsu 210012
China
Phone: +86 25 52877345
Email: zhai.hongjun@zte.com.cn
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