TRILL (Transparent Interconnection of Lots of Links) Edge Directory Assistance Framework
draft-ietf-trill-directory-framework-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7067.
|
|
|---|---|---|---|
| Authors | Linda Dunbar , Donald E. Eastlake 3rd , Radia Perlman , Igor Gashinsky | ||
| Last updated | 2013-01-14 | ||
| Replaces | draft-dunbar-trill-directory-assisted-edge | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-trill-directory-framework-02
TRILL working group L. Dunbar
Internet Draft D. Eastlake
Category: Informational Huawei
Padia Perlman
Intel
Igor Gashinsky
Yahoo
January 14, 2013
Expires: April 2013
TRILL (Transparent Interconnection of Lots of Links)
Edge Directory Assistance Framework
draft-ietf-trill-directory-framework-02
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
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Dunbar, et al Expires November 2013 [Page 1]
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Abstract
Edge RBridges currently learn the mapping between MAC addresses and
their egress RBridges by observing the data packets ingressed or
egressed and by the TRILL ESADI protocol. When 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 draft describes the framework for using directory services to
assist edge RBridges by reducing multi-destination frames,
particularly unknown unicast frames flooding, and ARP/ND, improving
TRILL (Transparent Interconnection of Lots of Links) network
scalability in environments such as data centers.
Table of Contents
1. Introduction .................................................. 3
2. Terminology ................................................... 3
3. RBridge Campus Impact of Massive Number of End Stations in a DC 4
3.1. Issues of Flooding Based Learning in DCs ................. 4
3.2. Some Examples ............................................ 6
4. Benefits of Directory Assisted Edge RBridge in DC ............. 7
5. Generic operation of Directory Assistance ..................... 8
5.1. Information in Directory for Edge Bridges ................ 8
5.2. Push Model ............................................... 9
5.3. Pull Model .............................................. 10
6. Conclusion and Recommendation ............................... 12
7. Security Considerations ..................................... 12
8. IANA Considerations .......................................... 12
9. Acknowledgements ............................................. 12
10. References .................................................. 12
10.1. Normative References ................................... 12
10.2. Informative References ................................ 13
Authors' Addresses .............................................. 13
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1. Introduction
Edge RBridges (devices implementing [RFC6325], also known as TRILL
(Transparent Interconnection of Lots of Links) Switches) currently
learn the mapping between destination MAC addresses and their egress
RBridges by observing data packets or by ESADI (End Station Address
Distribution Information). 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 draft describes the 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, such as data
centers.
Data center networks are different from enterprise campus networks
in several ways, 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 usually based on racks and rows.
Guest OS assignment to Servers, Racks, and Rows is
orchestrated by a Server/VM Management system, not done at
random.
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.
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.
Both 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.
2. Terminology
The terms "Subnet" and "VLAN" are used interchangeably in this
document because it is common to map one subnet to one VLAN.
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Bridge: IEEE Std 802.1Q-2011 compliant device [802.1Q]. In this
draft, Bridge is used interchangeably with Layer 2 switch.
DA: Destination Address
DC: Data Center
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, which
could be in DA or SA field of a data frame.
RBridge: ''Routing Bridge'', an alternative name for a TRILL switch.
SA: Source Address
Station: A node, or a virtual node, with IP and/or MAC addresses,
which could be in the DA or SA of a data frame.
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 Machines
3. TRILL Campus Impact of Massive Number of End Stations in a DC
3.1. Issues of Flooding Based Learning in DCs
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.
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+-------+ +------+
+/------+ | +/-----+ |
| 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 learning table of edge
RBridges, e.g. RB1 (or T11), due to RB1 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 RB1.
- Some edge RBridge ports being blocked for user traffic when
there are more than one RBridge ports connected to an edge
bridged LAN. When there are multiple RBridge ports connected to
a bridged LAN in each VLAN, only one (the Appointed Forwarder
port) can forward/receive native traffic for that bridged LAN
or VLAN. The rest have to be blocked for forwarding/receiving
native traffic for that VLAN. When servers have dual uplinks to
two different ToR switches (or edge RBridges), some links may
not be fully utilized.
- Packets being flooded across TRILL campus when their DAs are
not in ingress RBridge's cache.
- In an environment where VMs migrates, there is higher chance of
cached entries becoming invalid, causing traffic to be black
holed by the egress RBridge. If VMs send out gratuitous ARP/ND
or [802.1Qbg] VDP messages upon arriving at new locations, the
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ingress nodes might not have the MAC entries for the newly
arrived VMs, causing more unknown flooding.
3.2. Some 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 uplink to one ToR, there are 1600
edge RBridges. If each rack has dual uplinks to 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 assumption 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.
But bridged LANs are formed under the aggregation switches in
this scenario. With aggregation switches being the RBridge
edge nodes, multiple RBridge edge ports could be connected to
one bridged LAN. To avoid potential loops, TRILL requires only
one of multiple RBridge edge ports connected to each VLAN being
designated as Appointed Forwarder [RFC6439], and other ports
being blocked for native frames in that VLAN.
In addition, 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
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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.
4. Benefits of Directory Assisted Edge RBridge in DC
In the data center environment, application placement to servers,
racks, and rows 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-DA, therefore less chance of flooding.
Avoiding unknown unicast MAC-DA 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 DA 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 DA 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 DA 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 DA 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 DA is. When the directory doesn't have the needed
information, the frames can be dropped or flooded depending on
the policy configured.
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- Reduce flooding of decapsulated Ethernet frames with unknown
MAC-DA to a bridged LAN connected to RBridge edge ports.
When an RBridge receives a TRILL frame whose destination
Nickname matches with its own, the normal procedure is for the
RBridge to decapsulate the TRILL header and forward the
decapsulated Ethernet frame to the directly attached bridged
LAN. If the destination MAC is unknown, the normal
Ethernet switch's flooding will occur with the decapsulated
Ethernet frame. With directory assistance, the egress RBridge
can determine if the MAC-DA in a frame matches with any end
stations attached via the bridged LAN. Frames can be discarded
if their DAs 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.
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 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} would 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
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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 RBridge
edge nodes: 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.
Under this model, if the packet's destination address can't be found
in the MAC&VLAN<->Egress RBridge table, the ingress RBridge can be
configured to:
- simply drop a data packet,
- flooding 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 data center. There are
many 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 DA
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 data center.
An RBridge must be able to get mapping entries when it is
initialized or restarted.
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The Push Model's detailed method and any hand-shake mechanism
between RBridge and Directory Server(s) is beyond the scope of this
framework draft.
When directory server needs to push down a very large number of
entries to edge RBridges, summarization should be considered. For
example, with one edge RBridge Nickname being associated with all
attached end stations' MAC addresses and VLANs as shown below:
+------------+-------+--------------------------------+
| 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 options to trigger the pulling process:
- The RBridge edge node can send a pull request whenever it
receives an unknown MAC-DA, or
- The RBridge edge node can simply intercept all ARP/ND requests
and forward them to the Directory Server(s) that has the
information on where the target stations are located.
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- The Pull Directory response could indicate that the MAC-DA
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-DA doesn't
have to be flooded across TRILL domain and the ARP/ND requests don't
have to be broadcast or multicast across TRILL 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).
One advantage of the Pull Model is that edge RBridge 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-DAs 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 DA is similar to a L2/L3
boundary router waiting for ARP/ND response upon receiving an IP
data frame whose DA is not in the router's IP/MAC cache table. Most
deployed routers today do hold the packet and send an ARP/ND
requests to the target upon receiving a packet with IP DA not in its
IP-MAC cache. When ARP/ND replies are received, the router will send
the data frame 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 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-MAC mapping
from 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.
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A separate document will specify the detailed messages and mechanism
for edge RBridges to pull information from directory server(s).
6. Conclusion and Recommendation
The traditional RBridge learning approach of observing data plane
will have difficulty keep pace with the ever growing number of end
stations in Data centers.
Therefore, TRILL should provide a directory assisted approach. This
document describes the basic framework of using a directory assisted
approach for RBridge edge nodes. More detailed mechanisms will be
described in separate drafts.
7. Security Considerations
Accurate mapping of IP addresses into MAC addresses 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
This document was prepared using 2-Word-v2.0.template.dot.
10. References
10.1. Normative References
[RFC6352] Perlman, et, al ''RBridge: Base Protocol Specification'',
https://datatracker.ietf.org/doc/rfc6325/, July, 2011
[RFC6439] Perlman, et, al ''RBridges: Appointed Forwarders'',
https://datatracker.ietf.org/doc/rfc6439/, Nov 2011
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
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.
[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.
Authors' Addresses
Linda Dunbar
Huawei Technologies
5430 Legacy Drive, Suite #175
Plano, TX 75024, USA
Phone: (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
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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
Email: igor@yahoo-inc.com
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