draft-ietf-opsawg-large-flow-load-balancing-09.txt   draft-ietf-opsawg-large-flow-load-balancing-10.txt 
OPSAWG R. Krishnan OPSAWG R. Krishnan
Internet Draft Brocade Communications Internet Draft Brocade Communications
Intended status: Informational L. Yong Intended status: Informational L. Yong
Expires: October 5, 2014 Huawei USA Expires: October 8, 2014 Huawei USA
A. Ghanwani A. Ghanwani
Dell Dell
Ning So Ning So
Tata Communications Tata Communications
B. Khasnabish B. Khasnabish
ZTE Corporation ZTE Corporation
April 6, 2014 April 8, 2014
Mechanisms for Optimizing LAG/ECMP Component Link Utilization in Mechanisms for Optimizing LAG/ECMP Component Link Utilization in
Networks Networks
draft-ietf-opsawg-large-flow-load-balancing-09.txt draft-ietf-opsawg-large-flow-load-balancing-10.txt
Status of this Memo Status of this Memo
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as an RFC and to translate it into languages other than English. as an RFC and to translate it into languages other than English.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on October 6, 2014. This Internet-Draft will expire on October 8, 2014.
Copyright Notice Copyright Notice
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This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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publication of this document. Please review these documents publication of this document. Please review these documents
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o The presence of 2 large flows causes congestion on this o The presence of 2 large flows causes congestion on this
component link. component link.
+-----------+ -> +-----------+ +-----------+ -> +-----------+
| | -> | | | | -> | |
| | ===> | | | | ===> | |
| (1)|--------|(1) | | (1)|--------|(1) |
| | -> | | | | -> | |
| | -> | | | | -> | |
| (R1) | -> | (R2) | | (R1) | -> | (R2) |
| (2)|--------|(2) | | (2)|--------|(2) |
| | -> | | | | -> | |
| | -> | | | | -> | |
| | ===> | | | | ===> | |
| | ===> | | | | ===> | |
| (3)|--------|(3) | | (3)|--------|(3) |
| | | | | | | |
+-----------+ +-----------+ +-----------+ +-----------+
Where: -> small flow Where: -> small flow
skipping to change at page 8, line 47 skipping to change at page 8, line 47
+-----+ +-----+ +-----+ +-----+
/ \ \ / /\ / \ \ / /\
/ +---------+ / \ / +---------+ / \
/ / \ \ / \ / / \ \ / \
/ / \ +------+ \ / / \ +------+ \
/ / \ / \ \ / / \ / \ \
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
| L1 | | L2 | | L3 | | L1 | | L2 | | L3 |
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
Figure 3: Two-level fat tree Figure 3: Two-level Fat Tree
To demonstrate the limitations of local optimization, consider a two- To demonstrate the limitations of local optimization, consider a two-
level fat-tree topology with three leaf nodes (L1, L2, L3) and two level fat-tree topology with three leaf nodes (L1, L2, L3) and two
spine nodes (S1, S2) and assume all of the links are 10 Gbps. spine nodes (S1, S2) and assume all of the links are 10 Gbps.
Let L1 have two flows of 4 Gbps each towards L3, and let L2 have one Let L1 have two flows of 4 Gbps each towards L3, and let L2 have one
flow of 7 Gbps also towards L3. If L1 balances the load optimally flow of 7 Gbps also towards L3. If L1 balances the load optimally
between S1 and S2, and L2 sends the flow via S1, then the downlink between S1 and S2, and L2 sends the flow via S1, then the downlink
from S1 to L3 would get congested resulting in packet discards. On from S1 to L3 would get congested resulting in packet discards. On
the other hand, if L1 had sent both its flows towards S1 and L2 had the other hand, if L1 had sent both its flows towards S1 and L2 had
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flow -- and the link utilization is normal now. flow -- and the link utilization is normal now.
+-----------+ -> +-----------+ +-----------+ -> +-----------+
| | -> | | | | -> | |
| | ===> | | | | ===> | |
| (1)|--------|(1) | | (1)|--------|(1) |
| | | | | | | |
| | ===> | | | | ===> | |
| | -> | | | | -> | |
| | -> | | | | -> | |
| (R1) | -> | (R2) | | (R1) | -> | (R2) |
| (2)|--------|(2) | | (2)|--------|(2) |
| | | | | | | |
| | -> | | | | -> | |
| | -> | | | | -> | |
| | ===> | | | | ===> | |
| (3)|--------|(3) | | (3)|--------|(3) |
| | | | | | | |
+-----------+ +-----------+ +-----------+ +-----------+
Where: -> small flow Where: -> small flow
===> large flow ===> large flow
Figure 4: Evenly utilized Composite Links Figure 4: Evenly Utilized Composite Links
Basically, the use of the mechanisms described in Section 4.4.1 Basically, the use of the mechanisms described in Section 4.4.1
resulted in a rebalancing of flows where one of the large flows on resulted in a rebalancing of flows where one of the large flows on
component link (3) which was previously congested was moved to component link (3) which was previously congested was moved to
component link (2) which was previously under-utilized. component link (2) which was previously under-utilized.
5. Information Model for Flow Rebalancing 5. Information Model for Flow Rebalancing
In order to support flow rebalancing in a router from an external In order to support flow rebalancing in a router from an external
system, the exchange of some information is necessary between the system, the exchange of some information is necessary between the
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