TRILL (Transparent Interconnection of Lots of Links): Edge Directory Assistance Framework
draft-ietf-trill-directory-framework-04
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (trill WG) | |
|---|---|---|---|
| Authors | Linda Dunbar , Donald E. Eastlake 3rd , Radia Perlman , Igor Gashinsky | ||
| Last updated | 2013-02-25 | ||
| Replaces | draft-dunbar-trill-directory-assisted-edge | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-trill-directory-framework-04
INTERNET-DRAFT Linda Dunbar
Intended Status: Informational Donald Eastlake
Huawei
Radia Perlman
Intel
Igor Gashinsky
Yahoo
Expires: August 22, 2012 February 23, 2013
TRILL (Transparent Interconnection of Lots of Links):
Edge Directory Assistance Framework
<draft-ietf-trill-directory-framework-04.txt>
Abstract
Edge RBridges currently learn the mapping between MAC addresses and
their egress RBridges by observing the data packets they ingress or
egress or by the TRILL ESADI protocol. When an ingress RBridge
receives a data frame whose destination address (MAC&VLAN) that
RBridge does not know, the data frame is flooded within the VLAN
across the TRILL campus.
This document describes the framework for using directory services to
assist edge RBridges in reducing multi-destination frames,
particularly unknown unicast frames flooding, and ARP/ND, thus
improving TRILL (Transparent Interconnection of Lots of Links)
network scalability.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Distribution of this document is unlimited. Comments should be sent
to the TRILL working group mailing list.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
L. Dunbar, et al [Page 1]
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
L. Dunbar, et al [Page 2]
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Table of Contents
1. Introduction............................................4
2. Terminology.............................................5
3. Impact of Massive Number of End Stations................6
3.1 Issues of Flooding Based Learning in Data Centers......6
3.2 Two Examples...........................................7
4. Benefits of Directory Assisted Edge RBridge.............8
5. Generic operation of Directory Assistance..............10
5.1 Information in Directory for Edge RBridges............10
5.2 Push Model and Requirements...........................10
5.3 Pull Model and Requirements...........................12
6. Recommendation.........................................14
7. Security Considerations................................14
8. IANA Considerations....................................14
9. Acknowledgements.......................................14
10. References............................................15
10.1 Normative References.................................15
10.2 Informative References...............................15
Authors' Addresses........................................16
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1. Introduction
Edge RBridges (devices implementing [RFC6325], also known as TRILL
Switches) currently learn the mapping between destination MAC
addresses and their egress RBridges by observing data packets or by
the ESADI (End Station Address Distribution Information) protocol.
When an ingress RBridge receives a data frame for a destination
address (MAC&VLAN) that RBridge does not know, the data frame is
flooded within that VLAN across the TRILL campus.
This document describes a framework for using directory services to
assist edge RBridges by reducing multi-destination frames,
particularly ARP [RFC826], ND [RFC4861], and unknown unicast,
improving TRILL network scalability in environments where a directory
can be available, such as data centers.
Data center networks differ from enterprise campus networks in
several ways that make them attractive for the use of directory
assistance, in particular:
1. Data centers, especially Internet and/or multi-tenant data centers
tend to have a large number of end stations with a wide variety of
applications.
2. Topology is often based on racks and rows. Furthermore, guest
operating system assignment to Servers, Racks, and Rows is
orchestrated by a Server/VM (virtual machine) Management system,
not done at random. So the information necessary for a directory
is normally available.
3. Rapid workload shifting in data centers can accelerate the
frequency of the physical servers being re-loaded with different
applications. Sometimes, the applications loaded into one physical
server at different times can belong to different subnets. When a
VM is moved to a new location or a server is loaded with a new
application with different IP/MAC addresses, it is more likely
that the destination address of data packets sent out from those
VMs are unknown to their attached edge RBridges.
4. With server virtualization, there is an increasing trend to
dynamically create or delete VMs when demand for resource changes,
to move VMs from overloaded servers to less loaded servers, or to
aggregate VMs onto fewer servers when demand is light. This
results in the more common occurrence of multiple subnets on the
same port at the same time and a higher change rate for VMs than
for physical servers.
Both items 3 and 4 above can lead to applications in one subnet being
placed in different locations (racks or rows) or one rack having
applications belonging to different subnets.
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2. Terminology
The terms "Subnet" and "VLAN" are used interchangeably in this
document because it is common to map one subnet to one VLAN.
Bridge: IEEE Std 802.1Q-2011 compliant device [802.1Q]. In this
document, Bridge is used interchangeably with Layer 2
switch.
EoR: End of Row switches in data center. Also known as
aggregation switches.
End Station: Guest OS running on a physical server or on a virtual
machine. An end station in this document has at least one IP
address and at least one MAC address.
IS-IS: Intermediate System to Intermediate System. TRILL uses IS-IS
[IS-IS] [RFC6326].
RBridge: "Routing Bridge", an alternative name for a TRILL switch.
Station: A node, or a virtual node, with IP and/or MAC addresses.
ToR: Top of Rack Switch in data center. It is also known as
access switches in some data centers.
TRILL: Transparent Interconnection of Lots of Links [RFC6325]
TRILL switch: A device implementing the TRILL protocol [RFC6325]
VM: Virtual Machine
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3. Impact of Massive Number of End Stations
This section discusses the impact of a massive number of end stations
in a TRILL campus using Data Centers as an example.
3.1 Issues of Flooding Based Learning in Data Centers
It is common for Data Center networks to have multiple tiers of
switches, for example, one or two Access Switches for each server
rack (ToR), aggregation switches for some rows (or EoR switches), and
some core switches to interconnect the aggregation switches. Many
aggregation switches deployed in data centers have high port density.
It is not uncommon to see aggregation switches interconnecting
hundreds of ToR switches.
+-------+ +------+
+/------+ | +/-----+ |
| Aggr11| + ----- |AggrN1| + EoR Switches
+---+---+/ +------+/
/ \ / \
/ \ / \
+---+ +---+ +---+ +---+
|T11|... |T1x| |T21| .. |T2y| ToR switches
+---+ +---+ +---+ +---+
| | | |
+-|-+ +-|-+ +-|-+ +-|-+
| |... | | | | .. | |
+---+ +---+ +---+ +---+Server racks
| |... | | | | .. | |
+---+ +---+ +---+ +---+
| |... | | | | .. | |
+---+ +---+ +---+ +---+
Figure 1: Typical Data Center Network Design
The following problems could occur when TRILL is deployed in a data
center with large number of end stations and the end stations in one
subnet/VLAN could be placed under multiple edge RBridges:
- Unnecessary filling of slots in the MAC address learning table
of edge RBridges, e.g. RBridge T11, due to T11 receiving
broadcast / multicast traffic (e.g. ARP/ND, cluster multicast,
etc.) from end stations under other edge RBridges that are not
actually communicating with any end stations attached to T11.
- Packets being flooded across TRILL campus when their destination
MAC addresses are not in ingress RBridge's MAC address to egress
RBridge cache.
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- In an environment where VMs migrates, there is higher chance of
cached information becoming invalid, causing traffic to be
black-holed by the ingress RBridge, that is, persistently sent
to the wrong egress RBridge. If VMs do not flood gratuitous
ARP/ND or VDP [802.1Qbg] messages upon arriving at new
locations, the ingress nodes might not have MAC entries for the
MAC of the newly arrived VMs, causing unknown address flooding.
3.2 Two Examples
Consider a data center with 1600 server racks. Each server rack has
at least one ToR switch. The ToR switches are further divided into 8
groups, with each group being connected by a set of aggregation
switches. There could be 4 to 8 aggregation switches in each set to
achieve load sharing for traffic to/from server racks. If TRILL is
deployed in this data center environment, let's consider the
following two scenarios for the TRILL campus boundary:
- Scenario #1: TRILL campus boundary starts at ToR switches:
If each server rack has one ToR, there are 1600 edge RBridges.
If each rack has two ToR switches, then there will be 3200 edge
RBridges
In this scenario, the TRILL domain will have more than 1600 (or
3200) + 8*4 (or 8*8) nodes, which is a large IS-IS domain. Even
though a mesh IS-IS domain can scale up to thousands of nodes,
it is challenging for aggregation switches to handle IS-IS link
state advertisement among hundreds of parallel ports.
- Scenario #2: TRILL campus boundary starts at the aggregation
switches:
With the same assumptions as before, the number of nodes in the
TRILL campus will be less than 100, and aggregation switches
don't have to handle IS-IS link state advisements among hundreds
of parallel ports.
However, the number of MAC&VLAN<->Egress RBridge Mapping entries
to be learned and managed by RBridge edge node can be very
large. In the example above, each edge RBridge has 200 edge
ports facing the ToR switches. If each ToR has 40 downstream
ports facing servers and each server has 10 VMs, there could be
200*40*10 = 80000 end stations attached. If all those end
stations belong to 1600 VLANs (i.e. 50 per VLAN) and each VLAN
has 200 end stations, then under the worst-case scenario, the
total number of MAC&VLAN entries to be learned by the edge
RBridge can be 1600*200=320000, which is very large.
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4. Benefits of Directory Assisted Edge RBridge
In some environments, particularly data centers, the assignment of
applications to servers, including rack and row selection, is
orchestrated by Server (or VM) Management System(s). That is, there
is a database or multiple databases (distributed model) that have the
knowledge of where each application is placed. If the application
location information can be fed to RBridge edge nodes, in some form
of Directory Service, then there is much less chance of RBridge edge
nodes receiving unknown MAC destination address, therefore less
chance of flooding.
Avoiding unknown unicast address flooding to the TRILL campus is
especially valuable in the data center environment because there is a
higher chance of an edge RBridge receiving packets with unknown
unicast destination address and broadcast / multicast messages due to
VM migration and servers being loaded with different applications.
When a VM is moved to a new location or a server is loaded with a new
application with a different IP/MAC addresses, it is more likely that
the destination address of data packets sent out from those VMs are
unknown to their attached edge RBridges. In addition, gratuitous ARP
(IPv4, [RFC826]) or Unsolicited Neighbor Advertisement (IPv6,
[RFC4861]) sent out from those newly migrated or activated VMs have
to be flooded to other edge RBridges that have VMs in the same
subnets.
The benefits of using directory assistance include:
- Avoid flooding unknown unicast destination address across TRILL
campus. The Directory enforced MAC&VLAN <-> Egress RBridge
mapping table can determine if a data packet needs to be
forwarded across TRILL campus.
When multiple RBridge edge ports are connected via a bridged LAN
to end stations (servers/VMs), a directory assisted edge RBridge
won't need to flood unknown unicast destination data frames to
all ports of the edge RBridges in the frame's VLAN when it
ingresses a frame. It can depend on the directory to tell it
where the destination is. When the directory doesn't have the
needed information, the frames can be dropped or flooded
depending on the policy configured.
- Reduce flooding of decapsulated Ethernet frames with unknown MAC
destination address to a bridged LAN connected to RBridge edge
ports.
When an RBridge receives a TRILL data packet whose destination
Nickname matches with its own, the normal procedure is for the
RBridge to decapsulate it and forward the decapsulated Ethernet
frame to the directly attached bridged LAN. If the destination
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MAC is unknown, the RBridge floods the decapsulated Ethernet
frame out all ports in the fame's VLAN. With directory
assistance, the egress RBridge can determine if the MAC
destination address in a frame matches any end stations attached
via the bridged LAN. Frames can be discarded if their
destination addresses do not match.
- Reduce the amount of MAC&VLAN <-> Egress RBridge mapping
maintained by edge RBridges. There is no need for an edge
RBridge to keep MAC entries of remote end stations that don't
communicate with the end stations locally attached.
- Eliminate ARP/ND being broadcasted or multi-casted through the
TRILL core.
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5. Generic operation of Directory Assistance
5.1 Information in Directory for Edge RBridges
To achieve the benefits of directory assistance for TRILL, the
corresponding directory server entries will need, at a minimum, the
following logical attributes:
[{IP, MAC/VLAN, {list of attached RBridge nicknames}, {list of
interested RBridges}]
The {list of attached RBridges} are the edge RBridges to which the
host (or VM) specified by the [IP or MAC/VLAN] in the entry is
attached. The {list of interested RBridges} are the remote RBridges
that might have attached hosts to communicate with the host in this
entry.
When a host has multiple IP addresses, there will be multiple
entries.
The {list of interested RBridges} could get populated when an RBridge
queries for information, or pushed down from management systems. The
list is used to notify those RBridges when the host (specified by the
IP/MAC/VLAN) in the entry connectivity to its attached RBridges
changes. An explicit list in the directory is not needed as long as
the interested RBridges can be determined.
There are two different models for Directory assistance to edge
RBridges: Push Model and Pull Model.
5.2 Push Model and Requirements
Under this model, Directory Server(s) push down the MAC&VLAN <->
Egress RBridge mapping for all the end stations that might
communicate with end stations attached to an RBridge edge node. If
the packet's destination address can't be found in the
MAC&VLAN<->Egress RBridge table, the ingress RBridge could be
configured to:
simply drop a data packet,
flood it to TRILL campus, or
start the pull process to get information from directory
server(s)
It may not be necessary for every edge RBridge to get the entire
mapping table for all the end stations in a campus. There are many
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ways to narrow the full set down to a smaller set of remote end
stations that communicate with end stations attached to an edge
RBridge. A simple approach is to only pushing down the mapping for
the VLANs that have active end stations under an edge RBridge. This
approach can reduce the number of mapping entries being pushed down.
However, the Push Model usually will push down more entries of
MAC&VLAN<->Egress RBridge mapping to edge RBridges than needed.
Under the normal process of edge RBridge cache aging and unknown
destination address flooding, rarely used mapping entries would have
been removed. But it can be difficult for Directory Servers to
predict the communication patterns among applications within one
VLAN. Therefore, it is likely that the Directory Servers will push
down all the MAC&VLAN entries if there are end stations in the VLAN
being attached to the edge RBridge. This is a disadvantage of the
Push Model compared with the Pull Model described below.
In the Push Model, it is necessary to have a way for an RBridge node
to request directory server(s) to start pushing down the mapping
entries. This method should at least include the VLANs enabled on the
RBridge, so that directory server doesn't need to push down the
entire mapping entries for all the end stations in the campus. An
RBridge must be able to get mapping entries when it is initialized or
restarted.
The Push Model's detailed method and any handshake mechanism between
RBridge and Directory Server(s) is beyond the scope of this framework
document.
When a directory server needs to push down a large number of entries
to edge RBridges, efficient data organization should be considered.
For example, with one edge RBridge Nickname being associated with all
attached end stations' MAC addresses and VLANs as shown below:
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+------------+-------+--------------------------------+
| Nickname1 |VID-1 | IP/MAC1, IP/MAC2, ,, IP/MACn |
| |------ +--------------------------------+
| |VID-2 | IP/MAC1, IP/MAC2, ,, IP/MACn |
| |------ +--------------------------------+
| | .... | IP/MAC1, IP/MAC2, ,, IP/MACn |
+------------+------ +--------------------------------+
| Nickname2 |VID-1 | IP/MAC1, IP/MAC2, ,, IP/MACn |
| |------ +--------------------------------+
| |VID-2 | IP/MAC1, IP/MAC2, ,,IP/MACn |
| |------ +--------------------------------+
| | | IP/MAC1, IP/MAC2, ,, IP/MACn |
+------------+------ +--------------------------------+
| ------- |------ +--------------------------------+
| | | IP/MAC1, IP/MAC2, ,, IP/MACn |
+------------+------ +--------------------------------+
Table 1: Summarized table pushed down from directory
Whenever there is any change in MAC&VLAN <-> Egress RBridge mapping,
that can be triggered by end stations being added, moved, or de-
commissioned, an incremental update can be sent to the edge RBridges
which are impacted by the change. Therefore, something like a
sequence number has to be maintained by directory servers and
RBridges. Detailed mechanisms will be specified in a separate
document.
5.3 Pull Model and Requirements
Under this model, an RBridge pulls the MAC&VLAN<->Egress RBridge
mapping entry from the directory server when its cache doesn't have
the entry. There are several possibilities to trigger the pulling
process:
- The RBridge edge node can send a pull request whenever it
receives an unknown MAC destination, or
- The RBridge edge node can intercept all ARP/ND requests and
forward them or appropriate requests to the Directory Server(s)
that has the information on where the target stations are
located.
- The Pull Directory response could indicate that the address
being queried is unknown or that the requestor is
administratively prohibited from getting an informative
response.
By using a Pull Directory, the frame with unknown MAC destination
address doesn't have to be flooded across TRILL domain and the ARP/ND
requests don't have to be broadcast or multicast across the TRILL
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domain.
The ingress RBridge can cache the response pulled down from the
directory. The timer for cache should be short in an environment
where VMs move frequently. The cache timer could be configured by
management system or could be sent down along with the Pulled reply
by the directory server(s). It is important that the cached
information be kept consistant with the actual placement of addresses
in the campus; therefore, there needs to be some mechanism by which
RBridges that have pulled information that has not expired can be
informed when that information changes or the like.
One advantage of the Pull Model is that edge RBridges can age out
MAC&VLAN entries if they haven't been used for a certain configured
period of time or a period of time provided by the Directory.
Therefore, each edge RBridge will only keep the entries that are
frequently used, so mapping table size will be smaller. Edge RBridges
would query the Directory Server(s) for unknown MAC destination
addresses in data frames or ARP/ND and cache the response. When end
stations attached to remote edge RBridges rarely communicate with the
locally attached end stations, the corresponding MAC&VLAN entries
would be aged out from the RBridge's cache.
An RBridge waiting for response from Directory Servers upon receiving
a data frame with an unknown destination address is similar to an
L2/L3 boundary router waiting for ARP/ND response upon receiving an
IP data packet whose destination IP is not in the router's IP/MAC
cache table. Most deployed routers today do hold the packet and send
ARP/ND requests to the target upon receiving a packet with
destination IP not in its IP to MAC cache. When ARP/ND replies are
received, the router will send the data packet to the target. This
practice minimizes flooding when targets don't exist in the subnet.
When the target doesn't exist in the subnet, routers generally re-
send an ARP/ND request a few more times before dropping the packets.
So, the holding time by routers to wait for ARP/ND response can be
longer than the time taken by the Pull Model to get IP to MAC mapping
from a directory if target doesn't exist in the subnet.
For RBridges with mapping entries being pushed down from directory
server, they can be configured to use Pull model for targets which
don't exist in the mapping data pushed down.
A separate document will specify the detailed messages and mechanism
for edge RBridges to pull information from directory server(s).
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6. Recommendation
TRILL should provide a directory assisted approach. This document
describes a basic framework of using a directory assisted approach
for RBridge edge nodes. More detailed mechanisms will be described in
a separate document or documents.
7. Security Considerations
Accurate mapping of IP addresses into MAC addresses and of MAC
addresses to the RBridge from which they are reachable is important
to the correct delivery of information. The security of specific
directory assisted mechanisms will be discussed in the document or
documents specifying those mechanisms.
For general TRILL security considerations, see [RFC6325].
8. IANA Considerations
This document requires no IANA actions. RFC Editor: please delete
this section before publication.
9. Acknowledgements
Thanks for comments and review from the following:
David Black, Erik Nordmark
The document was prepared in raw nroff. All macros used were defined
within the source file.
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10. References
10.1 Normative References
As an Informational document, this draft has no Normative References.
10.2 Informative References
[802.1Q] - IEEE Std 802.1Q-2011, "IEEE Standard for Local and
metropolitan area networks - Virtual Bridged Local Area
Networks", May 2011.
[802.1Qbg] - IEEE Std 802.1Qbg-2012, ''Media Access Control (MAC)
Bridges and Virtual Bridged Local Area Networks --- Edge
Virtual Bridging'', July 2012.
[IS-IS] - ISO/IEC, "Intermediate system to Intermediate system
routeing information exchange protocol for use in conjunction
with the Protocol for providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002.
[RFC826] - Plummer, D., "An Ethernet Address Resolution Protocol",
RFC 826, November 1982.
[RFC4861] - Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC6326] - Eastlake, D., Banerjee, A., Dutt, D., Perlman, R., and A.
Ghanwani, "Transparent Interconnection of Lots of Links (TRILL)
Use of IS-IS", RFC 6326, July 2011.
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Authors' Addresses
Linda Dunbar
Huawei Technologies
5430 Legacy Drive, Suite #175
Plano, TX 75024, USA
Phone: +1-469-277-5840
Email: ldunbar@huawei.com
Donald Eastlake
Huawei Technologies
155 Beaver Street
Milford, MA 01757 USA
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
Radia Perlman
Intel Labs
2200 Mission College Blvd.
Santa Clara, CA 95054-1549 USA
Phone: +1-408-765-8080
Email: Radia@alum.mit.edu
Igor Gashinsky
Yahoo
45 West 18th Street 6th floor
New York, NY 10011 USA
Email: igor@yahoo-inc.com
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