TRILL working group L. Dunbar
Internet Draft Huawei
Intended status: Standard Track
Expires: Sept 2011
March 7, 2011

Directory Server Assisted TRILL edge
draft-dunbar-trill-server-assisted-edge-00.txt

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Abstract

TRILL edge nodes currently learn the mapping between MAC address and
its corresponding TRILL edge node address by observing the data
packets traversed through.

This document describes why and how directory based server(s) can
optimize TRILL network in data center environment.

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 RFC-2119 0.

Table of Contents

1. Introduction ................................................ 2
2. Terminology ................................................. 3
3. Impact to TRILL by massive number of hosts ................... 3
4. Directory Server for TRILL in Data Center environment. ........ 4
5. Conclusion and Recommendation ................................ 5
6. Manageability Considerations ................................. 5
7. Security Considerations ...................................... 5
8. IANA Considerations ......................................... 5
9. Acknowledgments ............................................. 5
10. References ................................................. 5
Authors' Addresses ............................................. 6
Intellectual Property Statement ................................. 6
Disclaimer of Validity ......................................... 6

1. Introduction

Data center networks are different from campus networks in several
ways. Main differences include:
VM (host) to server assignment is done by Server (or VM)
Manager, which means that the host location is arranged by
management system(s).
Topology is based on racks and rows;
There could be massive number of virtual machines (hosts), but
relatively small number of switches.

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This draft describes why Data Center TRILL networks can be optimized
by utilizing directory server based approach.
2. Terminology

Bridge: IEEE802.1Q compliant device. In this draft, Bridge is used
interchangeably with Layer 2 switch.

DC: Data Center

EOR: End of Row switches in data center.

FDB: Filtering Database for Bridge or Layer 2 switch

ToR: Top of Rack Switch. It is also known as access switch.

VM: Virtual Machines

3. Impact to TRILL by massive number of hosts

In a virtualized data center, a VM may be placed on any physical
server. A variety of algorithms can be applied to select the location
of a VM. Resource aware algorithms (e.g. energy, bandwidth, etc,)
will use a placement that satisfies the processing requirements of
each VM but require the minimal number of physical servers and
switching devices.
With this, and similar types of assignment algorithm, subnets tend to
extend throughout the network. When this happens, the broadcast
messages within each subnet will be flooded across the TRILL domain,
which not only consumes a lot of bandwidth on links in TRILL domain,
but also causes a TRILL edge port to learn all the hosts belonging to
all the subnets which are enabled on the port. Even though a TRILL
edge port is only supposed to learn the entries which communicate
with hosts underneath, the frequent ARP/ND from all hosts within each
subnet will always refresh the TRILL edge node's MAC<->TRILL-Edge
mapping table.
Consider a data center with 80 rows, 8 racks per row and 40 servers
per rack. There can be 80*8*40=25600 servers. Suppose each server is
virtualized to 20 VMs, there could be 25600*20=512000 hosts in this
data center.
Let's consider a case that the TRILL edge starts at an Ingress port
of a TOR switch. Assuming there are 5 different VLANs enabled on the
TRILL Ingress port (i.e. the 20 VMs in one server belong to 5
different VLANs) and each VLAN has 200 hosts, then the TRILL edge

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port has to learn 5*200=1000 MAC&VLAN entries. Since there are 40
ports on the TOR, the total number of MAC&VLAN entries for the TOR
switch is 1000*40= 40000. Under this scenario, there will be 25600
entries in the TRILL routing domain if protection is not considered.
When protection is considered, the number of ports in TRILL domain
will double. That may be too many nodes for the IS/IS routing domain.
Let's consider another case of TRILL edge starting at the End of Row
switches. With the same assumption as before, there are 40*20 = 800
hosts to attached to each port of an EoR switch and 8*800=6400 hosts
attached to an EoR switch. If all those 6400 hosts belong to 640
VLANs and each VLAN has 200 hosts, then the total number of MAC&VLAN
entries to be learned by the TRILL edge (i.e. EoR) = 640*200=128000.
Under this scenario, there will be 80*8 = 640 EoR ports in the TRILL
routing domain when protection is not considered and 1280 EoR ports
when protection is considered. However, the number of MAC&VLAN
entries to be learnt by the TRILL edge node is very large.

4. Directory Server for TRILL in Data Center environment.

As described in the Section 1, the VM placement to server/rack is
orchestrated by Server (or VM) Management System(s). Therefore, there
is a central location with the information on where each VM is
placed. So it is relatively reliable to build a centralized (or
distributed) directory server(s) who has the knowledge on where each
VM is placed.

Here can be a procedure for TRILL edge node to utilize a Directory
Server

TRILL edge node can simply intercept all ARP requests and
forward them to the Directory Server,

The reply from the Directory Server can be the standard ARP
reply with an extra field showing the TRILL egress node address

TRILL ingress node can cache the mapping

If TRILL edge node receives an unknown MAC-DA, it simply
forwards the packet to the directory server. The directory
server can simply drop the frame if it doesn't have the
information, or forward the frame to the correct egress node and
send down a new mapping to the ingress Trill edge node.

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Another approach is for Directory Server to pass down the MAC&VLAN
mapping for all the hosts belonging to all the VLANs enabled on the
TRILL edge port.

5. Conclusion and Recommendation

The traditional TRILL learning approach of observing data plane can
no longer keep pace with the ever growing number of hosts in Data
center.

Therefore, we suggest TRILL to consider directory assisted
approach(es). This draft only introduces the basic concept of using
directory assisted approach for TRILL edge nodes to learn the MAC to
TRILL mapping. We want to get some working group consensus before
drilling down to detailed steps required for the approach.

6. Manageability Considerations

This document does not add additional manageability considerations.

7. Security Considerations

This document has no additional requirement for security.

8. IANA Considerations

9. Acknowledgments

This document was prepared using 2-Word-v2.0.template.dot.

10. References

[ARMD-Problem] Dunbar, et,al, "Address Resolution for Large Data
Center Problem Statement", Oct 2010.

[ARP reduction] Shah, et. al., "ARP Broadcast Reduction for Large Data
Centers", Oct 2010

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Authors' Addresses

Linda Dunbar
Huawei Technologies
1700 Alma Drive, Suite 500
Plano, TX 75075, USA
Phone: (972) 543 5849
Email: ldunbar@huawei.com

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Acknowledgment

Funding for the RFC Editor function is currently provided by the
Internet Society.

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