Internet DRAFT - draft-ietf-trill-directory-assisted-encap
draft-ietf-trill-directory-assisted-encap
INTERNET-DRAFT Linda Dunbar
Intended status: Proposed Standard Donald Eastlake
Huawei
Radia Perlman
Dell/EMC
Expires: September 7, 2018 March 8, 2018
Directory Assisted TRILL Encapsulation
<draft-ietf-trill-directory-assisted-encap-11.txt>
Abstract
This draft describes how data center networks can benefit from non-
RBridge nodes performing TRILL encapsulation with assistance from a
directory service.
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 authors or the TRILL working group mailing list:
trill@ietf.org
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Table of Contents
1. Introduction............................................3
2. Conventions Used in This Document.......................4
3. Directory Assistance to Non-RBridge.....................5
4. Source Nickname in Encapsulation by Non-RBridge Nodes...8
5. Benefits of Non-RBridge Performing TRILL Encapsulation..9
5.1. Avoid Nickname Exhaustion Issue.......................9
5.2. Reduce MAC Tables for Switches on Bridged LANs........9
6. Manageability Considerations...........................11
7. Security Considerations................................11
8. IANA Considerations....................................13
Normative References......................................14
Informative References....................................14
Acknowledgments...........................................14
Authors' Addresses........................................15
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1. Introduction
This document describes how data center networks can benefit from
non-RBridge nodes performing TRILL encapsulation with assistance from
a directory service and specifies a method for them to do so.
[RFC7067] and [RFC8171] describe the framework and methods for edge
RBridges to get MAC&VLAN <-> Edge RBridge mapping from a directory
service instead of flooding unknown destination MAC addresses across
a TRILL domain. If it has the needed directory information, any node,
even a non-RBridge node, can perform the TRILL data packet
encapsulation. This draft describes the benefits of and a scheme for
non-RBridge nodes performing TRILL encapsulation.
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2. 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 [RFC2119].
AF: Appointed Forwarder RBridge port [RFC8139].
Bridge: An IEEE 802.1Q compliant device. In this draft, Bridge is
used interchangeably with Layer 2 switch.
DA: Destination Address.
ES-IS: End System to Intermediate Systems [RFC8171].
Host: A physical server or a virtual machine running
applications. A host usually has at least one IP address
and at least one MAC address.
IS-IS: Intermediate System to Intermediate System [RFC7176].
SA: Source Address.
TRILL-EN: TRILL Encapsulating node. A node that performs the TRILL
encapsulation but doesn't participate in RBridge's IS-IS
routing.
VM: Virtual Machine.
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3. Directory Assistance to Non-RBridge
With directory assistance [RFC7067] [RFC8171], a non-RBridge node can
learn if a data packet needs to be forwarded across the RBridge
domain and if so the corresponding egress RBridge.
Suppose the RBridge domain boundary starts at network switches (not
virtual switches embedded on servers). (See Figure 1 for a high level
diagram of a typical data center network.) A directory can assist
Virtual Switches embedded on servers to encapsulate with a proper
TRILL header by providing the nickname of the egress RBridge edge to
which the destination is attached. The other information needed to
encapsulate can be either learned by listening to TRILL ES-IS and/or
IS-IS Hellos [RFC7176] [RFC8171], which will indicate the MAC address
and nickname of appropriate local edge RBridges, or by configuration.
If it is not known whether a destination is attached to one or more
RBridge edge nodes, based on the directory, the non-RBridge node can
forward the data frames natively, i.e. not encapsulating with any
TRILL header. Or, if the directory is known to be complete, the non-
RBridge node can discard such data frames.
\ +-------+ +------+ TRILL Domain/
\ +/------+ | +/-----+ | /
\ | Aggr11| + ----- |AggrN1| + /
\ +---+---+/ +------+/ /
\ / \ / \ /
\ / \ / \ /
\ +---+ +---+ +---+ +---+ /
\- |T11|... |T1x| |T21| .. |T2y|---
+---+ +---+ +---+ +---+
| | | |
+-|-+ +-|-+ +-|-+ +-|-+
| |... | V | | V | .. | V |<- vSwitch
+---+ +---+ +---+ +---+
| |... | V | | V | .. | V |
+---+ +---+ +---+ +---+
| |... | V | | V | .. | V |
+---+ +---+ +---+ +---+
Figure 1. TRILL domain in a typical Data Center Network
When a TRILL encapsulated data packet reaches the ingress RBridge,
that RBridge simply performs the usual TRILL processing and forwards
the pre-encapsulated packet to the RBridge that is specified by the
egress nickname field of the TRILL header. When an ingress RBridge
receives a native Ethernet frame in an environment with complete
directory information, the ingress RBridge doesn't flood or forward
the received data frames when the destination MAC address in the
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Ethernet data frames is unknown.
When all end nodes attached to an ingress RBridge pre-encapsulate
with a TRILL header for traffic across the TRILL domain, the ingress
RBridge doesn't need to encapsulate any native Ethernet frames to the
TRILL domain. The attached nodes can be connected to multiple edge
RBridges by having multiple ports or through a bridged LAN. All
RBridge edge ports connected to one bridged LAN can receive and
forward pre-encapsulated traffic, which can greatly improve the
overall network utilization. However, it is still necessary to
designate AF ports to, for example, be sure that multi-destination
packets from the TRILL campus are only egressed through one RBridge.
The TRILL base protocol specification [RFC6325] Section 4.6.2 Bullet
8 specifies that an RBridge port can be configured to accept TRILL
encapsulated frames from a neighbor that is not an RBridge.
When a TRILL frame arrives at an RBridge whose nickname matches the
destination nickname in the TRILL header of the frame, the processing
is exactly as normal: as specified in [RFC6325] the RBridge
decapsulates the received TRILL frame and forwards the decapsulated
frame to the target attached to its edge ports. When the destination
MAC address of the decapsulated Ethernet frame is not in the egress
RBridge's local MAC attachment tables, the egress RBridge floods the
decapsulated frame to all attached links in the frame's VLAN, or
drops the frame (if the egress RBridge is configured with that
policy).
We call a node that, as specified herein, only performs TRILL
encapsulation, but doesn't participate in RBridge's IS-IS routing, a
TRILL Encapsulating node (TRILL-EN). The TRILL Encapsulating Node can
pull MAC&VLAN <-> Edge RBridge mapping from directory servers
[RFC8171]. In order to do this, a TRILL-EN MUST support TRILL ES-IS
[RFC8171].
Upon receiving or locally generating a native Ethernet frame, the
TRILL-EN checks the MAC&VLAN <-> Edge RBridge mapping, and performs
the corresponding TRILL encapsulation if the mapping entry is found
as shown in Figure 2. If the destination MAC address and VLAN of the
received Ethernet frame doesn't exist in the mapping table and there
is no positive reply from pull requests to a directory, the Ethernet
frame is dropped or is forwarded in native form to an edge RBridge,
depending on the TRILL-EN configuration.
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+------------+--------+---------+---------+--+-------+---+
|OuterEtherHd|TRILL HD| InnerDA | InnerSA |..|Payload|FCS|
+------------+--------+---------+---------+--+-------+---+
|
| |<Inner Ether Header> |
|
|
| +-------+ TRILL +------+
| | R1 |-----------| R2 | Decapsulate
| +---+---+ domain +------+ TRILL header
v | |
+---------->| |
| |
+-----+ +-----+
Non-RBridge node: |T12 | | T22 |
Encapsulate TRILL +-----+ +-----+
Header for data
Frames to traverse TRILL domain.
Figure 2. Data frames from a TRILL-EN
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4. Source Nickname in Encapsulation by Non-RBridge Nodes
The TRILL header includes a Source RBridge's Nickname (ingress) and
Destination RBridge's Nickname (egress). When a TRILL header is added
to a data packet by a TRILL-EN, the Ingress RBridge nickname field in
the TRILL header is set to a nickname of the AF for the data packet's
VLAN. The TRILL-EN determines the AF by snooping on IS-IS Hellos from
the edge RBridges on the link with the TRILL-EN in the same way that
the RBridges on the link determine the AF [RFC8139]. A TRILL-EN is
free to send the encapsulated data frame to any of the edge RBridges
on its link.
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5. Benefits of Non-RBridge Performing TRILL Encapsulation
This section summarizing benefits of having a non-RBridge node
perform TRILL encapsulation.
5.1. Avoid Nickname Exhaustion Issue
For a large Data Center with hundreds of thousands of virtualized
servers, setting the TRILL boundary at the servers' virtual switches
will create a TRILL domain with hundreds of thousands of RBridge
nodes, which has issues of TRILL Nickname exhaustion and challenges
to IS-IS. On the other hand, setting the TRILL boundary at
aggregation switches that have many virtualized servers attached can
limit the number of RBridge nodes in a TRILL domain, but introduces
the issue of very large MAC&VLAN <-> Edge RBridge mapping tables to
be maintained by RBridge edge nodes.
Allowing Non-RBridge nodes to pre-encapsulate data frames with TRILL
headers makes it possible to have a TRILL domain with a reasonable
number of RBridge nodes in a large data center. All the TRILL-ENs
attached to one RBridge can be represented by one TRILL nickname,
which can avoid the Nickname exhaustion problem.
5.2. Reduce MAC Tables for Switches on Bridged LANs
When hosts in a VLAN (or subnet) span across multiple RBridge edge
nodes and each RBridge edge has multiple VLANs enabled, the switches
on the bridged LANs attached to the RBridge edge are exposed to all
MAC addresses among all the VLANs enabled.
For example, for an Access Switch with 40 physical servers attached,
where each server has 100 VMs, there are 4000 hosts under the Access
Switch. If indeed hosts/VMs can be moved anywhere, the worst case for
the Access Switch is when all those 4000 VMs belong to different
VLANs, i.e. the access switch has 4000 VLANs enabled. If each VLAN
has 200 hosts, this access switch's MAC table potentially has
200*4000 = 800,000 entries.
If the virtual switches on servers pre-encapsulate the data frames
destined for hosts attached to remote RBridge Edge nodes, the outer
MAC destination address of those TRILL encapsulated data frames will
be the MAC address of a local RBridge edge, i.e. the ingress
RBridge. The switches on the local bridged LAN don't need to keep the
MAC entries for remote hosts attached to other edge RBridges.
But the TRILL traffic from nodes attached to other RBridges is
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decapsulated and has the true source and destination MACs. One simple
way to prevent local bridges from learning remote hosts' MACs and
adding to their MAC tables, if that would be a problem, is to disable
this data plane learning on local bridges. The local bridges can be
pre-configured with MAC addresses of local hosts with the assistance
of a directory. The local bridges can always send frames with
unknown destination MAC addresses to the ingress RBridge. In an
environment where a large number of VMs are instantiated in one
server, the number of remote MAC addresses could be very large. If it
is not feasible to disable learning and pre- configure MAC tables for
local bridges and all important traffic is IP, one effective method
to minimize local bridges' MAC table size is to use the server's MAC
address to hide MAC addresses of the attached VMs. I.e., the server
acting as an edge node uses its own MAC address in the source MAC
address field of the packets originated from a host (or VM) embedded.
When the Ethernet frame arrives at the target edge node (the egress),
the target edge node can send the packet to the corresponding
destination host based on the packet's IP address. Very often, the
target edge node communicates with the embedded VMs via a layer 2
virtual switch. In this case, the target edge node can construct the
proper Ethernet header with the assistance of the directory. The
information from the directory includes the proper host IP to MAC
mapping information.
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6. Manageability Considerations
Directory assistance [RFC8171] is required to make it possible for a
non-TRILL node to pre-encapsulate packets destined towards remote
RBridges. TRILL-ENs have the same configuration options as any pull
directory client. See Section 4 of [RFC8171].
7. Security Considerations
If the TRILL-ENs are not trusted, they can forge arbitrary ingress
and egress nicknames in the TRILL Headers of the TRILL Data packets
they construct. Decapsulating at egress RBridges that believe such a
forged ingress nickname would send future traffic destined for the
inner source MAC address of the TRILL Data frame to the wrong edge
RBridge if data plane learning is in use. Because of this, an
RBridge port should not be configured to accept encapsulated TRILL
data frame on a link were it does not have an RBridge adjacency
unless the end stations on that link are trusted.
As with any end station, TRILL-ENs can forge the outer MAC addresses
of packets they send (See Sectin 6 of [RFC6325].) Because they pre-
encapsulate, they can also forge inner MAC addresses.
The pre-encapsulation performed by TRILL-ENs also means they can send
data in any VLAN which means that must be trusted in order to enforce
a security policy based on VLANs. (See Section 6.1 of [RFC6325].)
Use of directory assisted encapsulation by TRILL-ENs essentially
involves those TRILL-ENs spoofing edge RBridges to which they are
connected, which is another reason that TRILL-ENs should be trusted
nodes. Such spoofing cannot cause persistently looping traffic
because TRILL has a hop count in the TRILL header [RFC6325] so that,
should there be a loop, a TRILL packet caught in that loop (i.e., an
encapsulated frame) will be discarded. (In the potentially more
dangerous case of multi-destination packets, as compared with known
unicast, where copies could multiply due to forks in the distribution
tree, a Reverse Path Forwarding Check is also used [RFC6325] to
discard packets that appear to be on the wrong link or when there is
disagreement about the distribution tree.)
The mechanism described in this document requires TRILL-ENs to be
aware of the MAC address(es) of the TRILL edge RBridge(s) to which
the TRILL-EN is attached and the egress RBridge nickname from which
the destination of the packets is reachable. With that information,
TRILL-ENs can learn a substantial amount about the topology of the
TRILL domain. Therefore, there could be a potential security risk
when the TRILL-ENs are not trusted or are compromised.
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If the path between the directory and the TRILL-ENs is attacked,
false mappings can be sent to the TRILL-EN causing packets from the
TRILL-EN to be sent to wrong destinations, possibly violating
security policy as to which end stations should receive what data.
Therefore, a combination of authentication and encryption is
RECOMMENDED between the Directory and TRILL-EN. The entities involved
will need to properly authenticate with each other, provide session
encryption, maintain security patch levels, and configure their
systems to allow minimal access and running processes to protect
sensitive information.
For added security against the compromise of data due to its mis-
delivery for any reason, including the above, end-to-end encryption
and authentication should be considered; that is, encryption and
authentication from source end station to destination end station.
For Pull Directory and TRILL ES-IS security considerations, see
[RFC8171].
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8. IANA Considerations
This document requires no IANA actions. RFC Editor: please remove
this section before publication.
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Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119,
March 1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
<http://www.rfc-editor.org/info/rfc6325>.
[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, DOI 10.17487/RFC7176, May
2014, <http://www.rfc-editor.org/info/rfc7176>.
[RFC8139] Eastlake 3rd, D., Li, Y., Umair, M., Banerjee, A., and F.
Hu, "Transparent Interconnection of Lots of Links (TRILL):
Appointed Forwarders", RFC 8139, DOI 10.17487/RFC8139, June
2017, <https://www.rfc-editor.org/info/rfc8139>.
[RFC8171] Eastlake 3rd, D., Dunbar, L., Perlman, R., and Y. Li,
"Transparent Interconnection of Lots of Links (TRILL): Edge
Directory Assistance Mechanisms", RFC 8171, DOI
10.17487/RFC8171, June 2017, <https://www.rfc-
editor.org/info/rfc8171>.
Informative References
[RFC7067] Dunbar, L., Eastlake 3rd, D., Perlman, R., and I.
Gashinsky, "Directory Assistance Problem and High-Level Design
Proposal", RFC 7067, DOI 10.17487/RFC7067, November 2013,
<https://www.rfc-editor.org/info/rfc7067>.
Acknowledgments
The following are thanked for their contributions:
Igor Gashinsky
Ben Nevin-Jenkins
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Authors' Addresses
Linda Dunbar
Huawei Technologies
5340 Legacy Drive, Suite 175
Plano, TX 75024, USA
Phone: +1-469-277-5840
Email: linda.dunbar@huawei.com
Donald Eastlake
Huawei Technologies
155 Beaver Street
Milford, MA 01757 USA
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
Radia Perlman
Dell/EMC
2010 256th Avenue NE, #200
Bellevue, WA 98007 USA
Email: Radia@alum.mit.edu
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