TRILL Working Group Sam Aldrin
INTERNET-DRAFT Donald Eastlake
Intended Status: Proposed Standard Huawei Technologies
Tissa Senevirathne
Ayan Banerjee
Santiago Alvarez
CISCO
Xiaolan Wan
XiaoPeng Yang
Hangzhou H3C Tech. Co. Ltd
Expires: January 10, 2013 July 9, 2012
TRILL Campus Extension
draft-aldrin-trill-campus-extension-00
Abstract
This document presents a solution suite for TRILL campuses to be
connected over WAN networks. TRILL protocol is primarily designed to
work within intra-data centers. Connecting different sites over WAN
using overlay tunnel protocols is the primary method employed at
present. Though this presents a simple mechanisms to extend TRILL
campuses over WAN networks, it also brings in the problem of
scalability for TRILL nicknames exchanged between sites, latency,
duplication of traffic etc. This draft proposes a way to extend the
TRILL sites without having the WAN network aware of TRILL campus
network and its topology. This document details on how to extend
TRILL campus sites and to establish connections between various sites
without having to exchange entire TRILL campus information, thus
reducing the information flow to the required sites only. This
document do not add or define datacenter interconnect protocol.
Status of this Memo
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Contributors . . . . . . . . . . . . . . . . . . . . . . . 5
2. Solution overview . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Site inter-connection . . . . . . . . . . . . . . . . . . . 6
2.2 Requirements overview . . . . . . . . . . . . . . . . . . . 6
2.2 TRILL campus extension . . . . . . . . . . . . . . . . . . 7
2.3 TRILL nickname exhaustion . . . . . . . . . . . . . . . . . 7
3. Solution analysis and comparison . . . . . . . . . . . . . . . 7
3.1 TRILL campus extension . . . . . . . . . . . . . . . . . . 8
3.2 TRILL campus extension over IP . . . . . . . . . . . . . . 9
3.3 TRILL campus interconnection with TRILL-EVPN . . . . . . . 10
3.4 TRILL campus interconnection over VPN's . . . . . . . . . . 11
4. Operational Overview . . . . . . . . . . . . . . . . . . . . . 12
4.1 Campus and Backbone Areas . . . . . . . . . . . . . . . . . 12
4.2 Unicast forwarding . . . . . . . . . . . . . . . . . . . . . 12
4.3 Multicast Forwarding . . . . . . . . . . . . . . . . . . . . 13
4.4 MAC learning . . . . . . . . . . . . . . . . . . . . . . . . 14
4.5 TRILL nickname aggregation . . . . . . . . . . . . . . . . . 15
5. TRILL campus inter-connectivity . . . . . . . . . . . . . . . . 15
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5.1 Border RBridges interconnection . . . . . . . . . . . . . . 16
5.2 Inter-site nickname exchange . . . . . . . . . . . . . . . . 16
5.3 Border RBridge capability exchange . . . . . . . . . . . . . 16
5.4 TRILL adjacency resolution . . . . . . . . . . . . . . . . . 17
5.5 Forwarding of data frames . . . . . . . . . . . . . . . . . 17
6. Proposed additions and extensions . . . . . . . . . . . . . . . 17
6.1 Border RBridge capability TLV . . . . . . . . . . . . . . . 18
6.2 TRILL nickname aggregation sub-TLV . . . . . . . . . . . . . 18
7. TRILL campus extension over IP . . . . . . . . . . . . . . . . 19
7.1 Underlying Network . . . . . . . . . . . . . . . . . . . . . 19
7.2 Overlay Control Plane . . . . . . . . . . . . . . . . . . . 19
7.2.1 BRbridge discovery and adjacency setup . . . . . . . . . 19
7.2.2 Control plane packet encapsulation . . . . . . . . . . . 19
7.3 Overlay Data Plane . . . . . . . . . . . . . . . . . . . . . 20
7.3.1 Encapsulation . . . . . . . . . . . . . . . . . . . . . 20
7.4 Forwarding Process . . . . . . . . . . . . . . . . . . . . . 22
7.4.1. Forwarding from an Internal Link to the Overlay . . . 22
7.4.2. Forwarding from the Overlay Link to an Internal Link . 22
7.4.5. Mac Address Learning . . . . . . . . . . . . . . . . . 22
7.4.6. Multi-homing . . . . . . . . . . . . . . . . . . . . . 23
7.5 Control plane termination . . . . . . . . . . . . . . . . . 23
7.6 Control plane termination and Data plane de-capsulation . . 24
8 Security Considerations . . . . . . . . . . . . . . . . . . . . 24
9 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 24
10 References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
10.1 Normative References . . . . . . . . . . . . . . . . . . . 24
9.2 Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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1 Introduction
TRILL protocol is primarily designed as an intra-datacenter protocol
by leveraging the routing functionality to interconnect bridges.
Traditional Ethernet networks provided a single path for forwarding
the traffic, which is usually derived using protocols like Spanning
Tree. TRILL provided a way to utilize multiple links for forwarding,
thus utilizing the resources effectively. Even though TRILL is new
protocol, it seamlessly integrates with legacy bridging networks
without having to forklift upgrade of all the bridges to support
TRILL. By not having to learn the MAC addresses of end stations by
intermediate devices, provided a powerful way to interconnect bridges
within a datacenter and maximizing the resource usage and providing
multipath usage option.
TRILL enabled network creates efficiency by having reduced forwarding
table size. By doing TRILL nickname based forwarding created a layer
of abstraction and much easier to implement the protocol. This
enabled to address the scalability of a L2 domain, where thousands of
RBridges could exist to meet the needs of a datacenter. By leveraging
IS-IS protocol, the information exchange and leveraging the path
computation technology brought forth a new paradigm into bridging
technology. TRILL Base Protocol Specification [RFC6325] specifies a
tree based paradigm to forward broadcast and multicast traffic as
well as unknown unicast traffic.
Even though the TRILL is enabled within a campus network or a
datacenter, it is not primarily designed to work over WAN. There is a
need to interconnect various TRILL campuses to extend beyond a single
LAN domain. Some enterprise or campus networks could be having
multiple TRILL sites and these TRILL enabled sites could run
independently or could share resources in order to cater to the needs
of customers or users. As such, there exist few proposals based on
overlay technologies which interconnect these sites but those
solutions require MAC learning at the edge RBridges and stripping of
TRILL nickname on the frame. Another option is to interconnect these
TRILL sites transparently over Pseudowires and making a huge TRILL
campus site. This is useful option but the downside of this is when
provider would like to maintain independent sites and exchange only
the required data to be shared across sites, it becomes complicated
to maintain the networks.
[TRILL-EVPN] draft details the data center protocol in interconnect
different LAN domains, including TRILL sites, over VPN's. This
requires establishing VPN's over WAN using BGP protocol, thus
requiring WAN service provider involvement in establishing
interconnection between different sites.
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This draft solves a specific problem where a TRILL campus needs to be
extended, be it a different geographical location or network
administrative domain. Though the primary goal is effective extension
of TRILL campuses, this draft is not a replacement for datacenter
interconnect protocols like PBB_EVPN. All the extensions are limited
to TRILL protocol, without any extensions to WAN protocols for
interconnect, such that, effective unicast and multicast traffic
could be sent over WAN links and keeping core network agnostic of the
TRILL network.
1.1 Terminology
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 [RFC2119].
1.2 Contributors
In addition to the authors listed above the following individuals
also contributed to this document:
Xiaopeng Yan
Hangzhou H3C Tech. Co., Ltd.
Vishwas Manral
Alvaro Retana
Dave Tucker
Hewlett-Packard
2. Solution overview
This section provides the high-level overview of the solution to the
problems in various scenarios. More detailed representation of the
solution is covered in the later sections of the draft.
TRILL site or TRILL campus uses IS-IS to setup the RBridge
interconnection. A RBridge knows how to reach another RBridge within
the campus. When two TRILL campuses are interconnected, one could
visualize it in two different perspectives. First one is a merger of
two TRILL campuses into one. This requires each RBridge to know about
the other and the IS-IS should be able to compute the shortest paths
from one to another. The downside of this model is that information
exchange explosion and the size of IS-IS db and number of PDU's being
exchanged could increase exponentially.
The second perspective is to have these two TRILL campuses being
interconnected over a WAN, but their functioning nature is
independent to each other. The two campuses exchange only the
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required information between border RBridges of the campuses. This
will be more optimal and leads to interconnecting multiple campuses
without having to redesign the whole network to ensure uniqueness and
identity of RBridges.
Solution being proposed is in line with second option, which
maintains site independency with a simplified solution and modeled
around the existing and proven technologies. Some of the enhancements
were already proposed in other drafts like multilevel TRILL [TISSA-
MLEVEL] and the solution leverages by extending those definitions as
necessary. The solution addresses the following areas described in
the following sections
2.1 Site inter-connection
Each TRILL campus is considered as an independent site or an L1 IS-IS
domain. These TRILL campus sites are interconnected over WAN. Each
area will have an appointed border RBridges. These RBridges exchange
the information of other border RBridges of different TRILL campus
sites to establish connection with each other. When a TRILL campus is
extended by interconnecting two or more campuses, the interconnection
could be over L2 or L3 WAN connection. A frame from an RBridge in
campus, to reach other RBridge in other campus, should be aware of
the path it should take. When a frame is sent from the border RBridge
to another Border RBridge in the other campus, it traverses the WAN
network. This is transparent to the source RBridge in order to reach
the destination RBridge. The WAN connection established between the
campuses is not aware of the traffic it is carrying and is not
established based on the TRILL campuses.
2.2 Requirements overview
There are various requirements necessary to be met in order to
provide a seamless TRILL campus extension. Some of the important
requirements are as follows
o Extend TRILL technology over interconnect
o Ability to provide the same fast convergence for mobility as it
does in intra-TRILL campus
o Ability to work transparent with various WAN technologies
o Option for dynamic establishment of connectivity across sites
o Minimal changes to TRILL protocol and definitions
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o Backward compatible to existing networks and their functions.
In some scenarios it may be required for TRILL to be extended over an
IP network, for example a case where the network administrator does
not have control over the wide area network configuration. The TRILL
over IP solution should meet the requirements outlined above and
additionally:
o Require only unciast reachability between RBridges and multicast
support from the WAN provider
o Provide Auto-discovery of Border Rbridges
2.2 TRILL campus extension
By interconnecting TRILL campus sites over WAN, one could extend the
L1 area, but that would cause other issues as detailed in the earlier
section. When two campuses merge, there will be a possibility for
nickname collision. The ideal situation is to keep the ability for
each campus nicknames overlapped with the other campus. The other
option is to provide a mechanism to do the nickname resolution. This
version of the document details the solution of the later option. In
the subsequent version, the former option for retaining nicknames
will be addressed.
2.3 TRILL nickname exhaustion
Though this draft is not meant to provide solution for TRILL nickname
exhaustion, it enables provider to deal with the problem effectively
and not having to re-design the network, every time a new campus is
interconnected. The proposed solution has RBridges which are not
required to be exposed outside of the campus and there are other
RBridges which are also known as border RBridges. This version the
document assumes global uniqueness of TRILL nicknames across various
campuses. When a frame has to be forwarded to an RBridge which
resides in another campus, the originating RBridge knows how to get
to the borderRBridge. This border RBridge should have the list of
RBridges of other campus sites and thus could select the appropriate
link connecting to the destination campus and encapsulate the TRILL
frame and forward over that. More details are covered in the unicast
and multicast sections of the detailed solution.
3. Solution analysis and comparison
As eluded to in the earlier sections, there are various methods on
interconnecting different TRILL campus sites. Before going into the
details of proposed solution a close examination of some of the
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proposed solutions, provides better perspective of this solution.
3.1 TRILL campus extension
In this model TRILL campuses are connected over WAN using
technologies like PW. This is the most simple way of interconnecting
the sites. When campuses are interconnected, the TRILL campus will
get expanded and each RBridge could reach each other. The main
criteria for this will be to maintain unique nickname for RBridges.
-------------- ------------ --------------
| | | | | |
|TRILL Campus | | WAN | | TRILL Campus |
| | | | | |
| BRB1===| |====BRB2 |
RB1 | | | | RB2
| | | | | |
| | | | | |
-------------- ------------ --------------
As shown in the figure above, two TRILL campuses are interconnected
over WAN. Border RBridges establish connection over WAN using PW or
other WAN technologies. All the nicknames within each campus sites
have to be unique. The WAN in this case is transparent to the TRILL
campuses and the path computation doesn't involve WAN component,
instead it will be like one TRILL campus. When RB1 originates a TRILL
frame destined to RB2, it traverses over BRB1 and BRB2 and reaches
RB2.
This solution is workable when the campuses are small and do NOT need
to change or requires interconnecting more TRILL campuses. The other
downside for this model is, when two campuses are interconnected and
there is overlap of nicknames, the network has to be re-designed to
eliminate the duplicate nicknames and make each RBrige to have a
unique nickname.
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3.2 TRILL campus extension over IP
The TRILL campus could be extended by encapsulating TRILL inside an
IP Tunnel. By using this method the WAN becomes completely
transparent and is only required to provide unicast reachability
between BRbridges and establish the multicast trees.
+---+ +---+IPA --------- IPB +---+ +---+
|S10|-----|S1 |----/ IP Core \----|S2 |-----|S20|
+---+ ^ +---+ \ Network / +---+ ^ +---+
| --------- |
| |
| +------------+ |
| | DA=IPB | |
| +------------+ |
| | SA=IPA | |
+------------+ +------------+ +------------+
|Outer Eth. | |Outer Eth. | |Outer Eth. |
|Header | |Header | |Header |
+------------+ +------------+ +------------+
|TRILL Header| |TRILL Header| |TRILL Header|
+------------+ +------------+ +------------+
|Inner Eth. | |Inner Eth. | |Inner Eth. |
|Frame | |Frame | |Frame |
+------------+ +------------+ +------------+
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Each BRbridge maintains a mapping table between the egress nickname
and an IP address. When a BRbridge receives a frame destined for a
remote BRBridge it looks up the egress nickname in the mapping table
and applies an outer IP header where the destination address is equal
to the Remote BRBridge IP.
+---+ L11+---+IPA --------- IPB +---+ L21+---+
|S10|----|S1 |----/ IP Core \----| S2|----|S20|
+---+ +---+ \ Network / +---+ +---+
---------
S1 S2
+----------------------+ +-------------------+
|Nickname |Interface | |Nickname |Interface|
+----------------------+ +-------------------+
| S10 | L11 | | S10 | IPA |
+----------------------+ +-------------------+
| S20 | IPB | | S20 | L21 |
+----------------------+ +-------------------+
| S1 | self | | S1 | IPA |
+----------------------+ +-------------------+
| S2 | IPB | | S2 | self |
+----------------------+ +-------------------+
3.3 TRILL campus interconnection with TRILL-EVPN
TRILL campuses could be extended over WAN using TRILL-EVPN.
BEB +--------------+ BEB
|| | | ||
\/ | | \/
+----+ AC1 +----+ | | +----+ +----+
| CE1|-----| | | | | |---| CE2|
+----+\ |MES1| | IP/MPLS | |MES3| +----+
\ +----+ | Network | +----+
\ | |
AC2\ +----+ | |
\| | | |
|MES2| | |
+----+ | |
/\ +--------------+
||
The [TRILL-EVPN] draft proposes interconnection details on how two
TRILL campuses could be interconnected using the E-VPN technology. In
this a new BGP route is advertised for reachability of TRILL
RBridges. This technique leverages the PBB technology and also
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enables to retain TRILL header. In this solution, the edge RBridges
should be TRILL aware as well as to be able to speak WAN protocols
like BGP. When a TRILL frame arrives at border RBridge, based on the
nickname it will be forwarded onto a right VPN link setup for the
destination nickname.
3.4 TRILL campus interconnection over VPN's
In this method, TRILL campus sites could be interconnected over
VPN's.
-------------- ------------ --------------
| | | | | |
|TRILL Campus | | WAN | | TRILL Campus |
| | | | | |
| BRB1===| |====BRB2 |
RB1 | | | | RB2
| | | | | |
| | | | | |
-------------- ------------ --------------
||
||
||BRB3
------------
| |
|TRILL Campus|
| |
| |
| |
| |
| |
-----RB3----
These VPN's could be established statically or dynamically. In order
to establish dynamically, the border RBridges needs to exchange
information of the nicknames and connect different sites. The
hierarchical model like H-VPLS could be established as well. One
other option which is much similar to the first model where campuses
exchange TRILL nicknames with other campuses over VPN's. Though this
model groups different sites according to the way VPN's are
configured, avoiding flooding of TRILL nicknames or site independency
cannot be achieved.
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4. Operational Overview
4.1 Campus and Backbone Areas
Each TRILL campus will be assigned a border RBridge. This is
identified using the 'Attached' bit in the IS-IS PDU. The border
RBridge has list of the RBridges of each campus site. These list of
bridges are exchanged using the TRILL nickname aggregation sub-TLV.
Details of the sub-TLV are detailed in the below section.
Every TRILL campus campus need not exchange all the RBridge nicknames
with other campuses. Let us take the scenario of campus A to be
interconnected with campus B. In campus A, there are RBridges
RB1...RB10, which are interconnected in L1. These nicknames are not
tunneled or exchanged with other L1 campus sites. Similarly campus B
has RB11...RB20 and need not be distinct from campus A RBridge
nicknames. So, if a new campus is connected to the domain, there is
a conflict of nicknames. As described in the earlier section, when
nicknames have to be uniquely maintained, the draft describes a
solution. Solution with keeping same nickname across different TRILL
campuses will be addressed in the later versions of the draft.
When campuses are interconnected over WAN links, there are two
possible terminations of the WAN links, the border RBridge and an
edge PE device. If the RBridge is connected to PE device, the TRILL
frames could be sent over the link connecting to the PE device to be
transported across WAN. This process is transparent to the TRILL
network and the RBridge doesn't remove the TRILL encapsulation,
rather tunnel the frames over the WAN to the far end RBridge.
There are many ways the WAN connections could be provided from
RBridge. GRE tunnels, IP tunnels, MPLS LSP's etc. Details of these is
outside the scope of this draft as it is transparent to RBridge.
The border RBridges will have the complete information of its campus
RBridges. Not all of the RBridges nicknames need to be advertised
globally. So, the globally exchanged nicknames of RBridges should be
unique across campuses. Depending on the policy established, these
Border RBridges will exchange the TRILL information with other campus
border Bridges, between different campuses. In IS-IS domain the
equivalent of this is the L2 backbone area, which in this case, is
established over WAN.
4.2 Unicast forwarding
If the destination TRILL nickname is not known, the originating or
transit RBridges forwards it to border RBridge. As the border RBridge
has all the nicknames of each campus, it forwards the frame to the
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right campus border RBridge, which in turn could forward within its
campus as per base protocol specification [RFC6325]. In the case
where the destination is unknown, the frame is flooded to each
campus. Using the MAC learning procedures, the associated RBridge
will be learnt for the subsequent frames to be forwarded as unicast,
instead of flooding. Flooding into various campuses or TRILL data
sites happen only if the the frame is of global ID based on VLAN
identification.
4.3 Multicast Forwarding
Whether the traffic scope is local or global across campuses is
identified by VLAN or port or fine-grain label. If the traffic is to
be forwarded within campus, it is done using the local tree. But if
the forwarding has to be done globally, it needs to use the global
tree. When the frame has global context, it will be flooded into
other TRILL sites as well.
Multicast networks are established within the core networks. In the
case of RBridges, which are part of the customer networks and do not
participate in the core networks and their topologies, the multicast
tree could be built using IP multicast or leverage MVPN services
offered by the core network service provider. The global trees are
established between border RBridges with the help of information
exchanges between border RBridges. As the IS-IS is limited to
individual campus sites, the information for the backbone tree over
WAN has to be exchanged between border RBridges either as a IP
multicast PIM message or specific TLV indented for other campus
border RBridges. More details on this will be added in the later
versions of the draft.
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-------------- ------------ --------------
| | | | | |
|TRILL Campus1 | | WAN | | TRILL Campus2|
| | | | | |
| BRB1===| |====BRB2 |
RB1 | | | | RB2
| | | | | |
| | | | | |
-------------- ------------ --------------
||
||
||BRB3
------------
| |
|TRILL Campus|
| 3 |
| |
| |
| |
| |
-----RB3----
In the above figure when the multicast frame has to be sent from
campus 1 to campus 2 and 3, the frame arrives at border RBridge BRB1.
With the default global tree between border RBridges of different
campuses, the forwarding is setup to egress the frame or replicated
over multicast trees to all other campus sites. If the frame is
destined for non-default global tree, the frame is forwarded
according to the forwarding information established for the tree.
Once the frame is reached on the border router of the campuses, the
frame is locally multicast forwarded. The same technique as employed
in the multilevel draft [TISSA-MLEVEL] is used here as well.
If mVPN services are deployed interconnecting campus sites, the
multicast tree is built over these services based on the customer
VLANs.
4.4 MAC learning
When a frame is to be forwarded from customer MAC A to customer MAC
B, the frame is set as unknown unicast frame over TRILL networks. If
the MAC A and MAC B are connected over WAN, the frame is transmitted
over WAN to the other campus. When the frame is reached at the
RBridge connecting to MAC B, it will learn about the originator
RBridge for MAC A. While responding, the egress RBridge know the
originating RBridge, it will unicast the frame to the originator.
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4.5 TRILL nickname aggregation
Nicknames are allocated or assigned to RBridges in a given campuses
using various methods. It could be OSS, CLI or could be a dynamic
control protocol which configures the nicknames. As the nicknames are
confined to each L1 area, the nickname management, when sites are
connected over WAN, it is essential to optimize the name allocation
in order to use the name space effectively. Name allocation is not in
the scope of this draft. If there is a necessity, the topic could be
considered in the later revisions of the draft. For this version we
do recommend some of the optimization techniques for nickname
allocation defined in the multilevel draft [TISSA-MLEVEL].
Each border RBridges needs to exchange the nicknames of each campuses
with other border RBridges. As the border RBridges are connected over
various types of WAN networks, mandating enhancement to a specific
protocol is deemed not the right approach. As the information
exchange has to be done, certain characteristics for the data
exchange have to be met.
o The amount of data exchange has to be minimal and optimized.
o the information exchange has to be quick.
o Conflicts and duplicate information flow has to be avoided
This draft proposes a generic TLV, which is to be exchanged between
border RBridges. If the nickname allocation is done in terms of
ranges, the same could be exchanged between border RBridges,
seamlessly. As the TLV has to be terminated at the border RBridges,
it is better suited to be sent as a unicast message to the
neighboring border RBridge. This could be sent as an IP message with
TRILL header containing the target border RBridge. More details on
how to encapsulate and process the frame should be in the later
versions of the draft.
5. TRILL campus inter-connectivity
The primary reason to interconnect TRILL campuses is to maintain
geographically distant, segmented sites and customer specific
segregation possible by interconnecting and not having to redo the
network and campus redesign for every change and need. With customers
being mobile or services offered by service providers could be re-
located depending on the time-zones and resource availability,
restricting to a specific site is a thing of the past.
These constraints brought forth the need to have different sites
interconnected over the WAN, be it MPLS or VPLS or IP and to provide
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the services on demand to meet the needs of customers and their data
center needs. As TRILL has proven to be an effective protocol by
bringing routing technologies into bridges or L2 forwarding, the
short coming of TRILL interconnect is to be overcome. As eluded to in
the earlier sections on different kinds of solutions, meeting all the
needs of the TRILL campus extension as laid out in the requirements
section, is the primary goal of this draft.
5.1 Border RBridges interconnection
Border RBridges only participate in interconnecting various TRILL
campuses. These border RBridges are elected or identified as
described in the earlier section i.e. using IS-IS protocol
advertisement. These border RBridges, when required to interconnect
with other campuses, over WAN, depending on configuration of choice,
an overlay tunnels like GRE could be established between the border
RBridges. advertise the route to other site border RBridges using the
BGP enhancement. The connectivity between different campuses over WAN
is already established. When two RBridges needs to be connected over,
a GRE or IP tunnel is established between those two. Detailed
mechanisms on this establishments will be addressed in the later
versions of the draft.
If L2 connectivity is to be used with protocols like VPLS, a similar
method could be employed, where the PWE3 could be established between
border RBridges. More details to be added in the later versions of
the draft.
5.2 Inter-site nickname exchange
There are three types of nicknames which are exchanged between border
RBridges.
o Nickname of border RBridges
o Nicknames of RBridges for each campus
o Nicknames of RBridges which are part of a specific customer VLAN or
VPN
The nickname aggregation TLV is used as payload to be exchanged
between border RBridges. This information is used to establish inter-
connectivity between TRILL sites per customer VLAN or default global
tree. There exchange of information could be done with existing
protocols and is not restricted to any specific protocol.
5.3 Border RBridge capability exchange
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An additional capability TLV is defined to exchange info on what each
of the border RBridge is capable of. This is very essential for
forward and backward capability . Capability information not only
indicates the capability version but could also force the
interconnection to be restricted as per the policy set by the
customer. Some of the capability advertisements are as follows.
o Version.
o default nick name resolution
o connect more campuses
o active-active link support
o Ability to support multicast forwarding
5.4 TRILL adjacency resolution
When a frame is to be forwarded from one campus to another, the
adjacency resolution has to be done on the border RBridge. When TRILL
nicknames are advertised from one border RBridge to another, the
border RBridge keeps the database of all the nicknames.
Once the frame is received on the border RBridge, it will look in the
forwarding table to identify the next hop. The adjacency information
could indicate the outgoing WAN encapsulation. For VPN, there could
be additional encapsulation depending on the network configuration.
The TRILL frame is encapsulated, without removing the TRILL header
and is forwarded over the WAN link.
5.5 Forwarding of data frames
The TRILL frames are forwarded as per the base protocol [RFC6325]
within a campus site. The forwarding of the frames from TRILL campus
to campus over WAN connection is pre-established between border
RBridges. The encapsulation of the Frame with WAN header is based on
the adjacency resolution made in the forwarding on the border
RBridge.
6. Proposed additions and extensions
There are certain extensions being proposed in this draft to
interconnect TRILL campuses or datacenters. These include new
additions to routing and also new TLV's to exchange information
between border RBridges. There are few references to the extensions
proposed in other drafts which are used in this draft as well.
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6.1 Border RBridge capability TLV
This TLV as defined in earlier section, defines the capability of a
border RBridge, to be exchanged with other border RBridges for
seamless inter-working across campus sites.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = <TBD> | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Definition of flag bits will be identified and defined later.
6.2 TRILL nickname aggregation sub-TLV
The nickname aggregation TLV defined in multilevel draft [TISSA-
MLEVEL] is used in advertising the nicknames into other border
Routers. Some new additions or changes will be proposed in later
versions of the draft.
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7. TRILL campus extension over IP
7.1 Underlying Network
The underlying network in the TRILL campus extension over IP solution
could be Wide Area Network. As changes to this network are not in the
administrative control of the TRILL campus, TRILL over IP extends the
campus network by having unicast reach ability between BRbridges and
the ability to establish IP multicast trees over it. There are three
ways the TRILL campus could be extended over IP.
1. TRILL frames, both control and data frames are transparently
tunneled over IP. This is also known as overlay model.
2. TRILL and IS-IS control frames are terminated at the campus edge
and data frames are tunneled transparently.
3. TRILL and IS-IS control frames are terminated at the campus edge
and data frames are stripped off the TRILL header
7.2 Overlay Control Plane The TRILL over IP overlay control plane is
responsible for the auto-discovery of the BRbridges within the same
domain. The TRILL control plane traffic between BRbridges will be
carried over the virtual link. There is no termination of either
TRILL control plane or data plane frames at the edge of the TRILL
campus networks.
7.2.1 BRbridge discovery and adjacency setup BRbridges become part of
the domain when the join the multicast group on the underlying
network associated with the domain. The auto-discovery mechanism
happens when BRbridges peer with each other as if they were directly
connected at layer-2. This peering is possible as all the traffic
for the BRbridge is encapsulated with the underlying network
multicast group address and sent into the core.
7.2.2 Control plane packet encapsulation
Any BRbridge in a TRILL over IP domain should encapsulate the ISIS
routing information of its campus and then relay it to the other
BRbridges in the domain. The control frames are tunnel through the IP
connection established between BRbridges.
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7.3 Overlay Data Plane
7.3.1 Encapsulation
The encapsulation format is TRILL frame encapsulated in UDP inside of
IPv4 or IPv6.
The format of the UDP IPv4 encapsulation is as follows:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol = 17 | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source-site TRILL Joint Device IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination-site TRILL Joint Device (or multicast) Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port = xxxx | Dest Port = TBD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP length | UDP Checksum = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|R|R|R|I|R|R|R| Overlay ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Ethernet Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| TRILL Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Ethernet Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Payload |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format of the UDP IPv6 encapsulation is as follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header=17| Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source-site TRILL Joint Device IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination-site TRILL Joint Device (or multicast) Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port = xxxx | Dest Port = TBD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|R|R|R|I|R|R|R| Overlay ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Ethernet Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| TRILL Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Ethernet Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Payload |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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7.4 Forwarding Process
7.4.1. Forwarding from an Internal Link to the Overlay
The forwarding within a campus is as defined in the base protocol of
TRILL. This section here describes the forwarding from an Internal
link to the Overlay Link, or vice versa. A Joint Device is a transit
Rbridge from TRILL point of view. When a TRILL packet is received
from the internal interface, egress Nickname is used to lookup the
Nickname table which will yield a next-hop IP address entry pointing
to a remote Joint Device. Then the packet is encapsulated with
UDP/IP header and sent over the overlay interface to destination
Joint Device at Layer-3 as a regular IP packet.
7.4.2. Forwarding from the Overlay Link to an Internal Link When a
packet is received on the overlay interface, it will be IP de-
capsulated to reveal the inner TRILL(including the outer MAC) header
for forwarding. The egress Nickname will used for forwarding, the
forwarding action is same as a transit RBridge.
7.4.5. Mac Address Learning
The TRILL edge devices learn remote MAC addresses(including the MAC
addresses in other data centers) in data plane by hardware. In most
cases, the Joint device is like a transit RBridge, and doesn't learn
end host's MAC addresses. From campus extension perspective, the
border device is DCI device at the same time, so TRILL over WAN can
relieve the pressure of MAC addresses table capability in DCI device.
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7.4.6. Multi-homing
In the situation of multi-homing shown as Figure 3, all the BRbridges
can be active by the nature of TRILL. Figure 4 shows what the
resulting forwarding tables would look like in the multi-homing
example.
+---+ L1 +---+ IPA -------- IPD +---+ +---+
|S10|----| S1|-------- / \ ---------|S4 |----|S21|
+---+ +---+ / \ +---+ +---+
\/L2 | IP Core | \/
/\ | Network | /\
+---+ +---+ IPB \ / IPC +---+ +---+
|S11|----|S2 |-------- \ / ---------|S3 |----|S20|
+---+ +---+ -------- +---+ +---+
S1
+----------------------+
|Nickname |Interface |
+----------------------+
| S1 | self |
+----------------------+
| S2 | - |
+----------------------+
| S3 | IPC |
+----------------------+
| S4 | IPD |
+----------------------+
| S10 | L1 |
+----------------------+
| S11 | L2 |
+----------------------+
| S20 | IPC/IPD |
+----------------------+
| S21 | IPC/IPD |
+----------------------+
In S1 device, the traffic destined to S10 and S21 have two next hops,
IPC and IPD. In forwarding process, hashing of TRILL packet inner
information will be used to determine which next hop IP address to
use. Thus, the ingress traffic will be load balanced between
multiple Joint Devices within a site.
7.5 Control plane termination
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When TRILL campuses are extended by interconnecting them, the
administrative domain for control plane could be independent, where
as the data plane could be transparently interconnected. This
requires the campus border RBridges to terminate the control plane.
The IS-IS control frames do not get encapsulated and sent over to the
the IP connection. Border RBridges exchange the campus information
over IP in order to program the forwarding table and adjacency
resolution.
Data frames when arrived at the border RBridges, destined for the
other campus, will be looked for adjacency and encapsulated with IP
and sent over the IP. In the case of multicast, the TRILL frame is
encapsulated and sent over IP multicast network.
7.6 Control plane termination and Data plane de-capsulation
When two campuses are interconnected but no control plane or data
plane is extended over the WAN, the TRILL frames are stripped off the
TRILL header at the border RBridge of the campus. The payload is then
encapsulated as a regular IP packet and sent over the IP network to
the other campus. This requires the border RBridges to learn the host
MAC address to properly encapsulate as IP packet and routed across
the WAN link.
8 Security Considerations
<TBD>
9 IANA Considerations
It is requested that the IANA allocate the following UDP Ports for
the TRILL IS-IS and Data channels:
UDP Port Protocol
TBD TRILL IS-IS Channel
TBD TRILL Data Channel
10 References
10.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, November 1997.
[RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
"Intermediate System to Intermediate System (IS-IS)
Extensions for Advertising Router Information", RFC 4971,
July 2007.
[RFC6325] Perlman, R., et.al, "Routing Bridges (RBridges): Base
Protocol Specification", RFC 6325, July 2011.
[trillcmt]Senevirathne, T., et.al, "Coordinated Multicast Trees
(CMT)for TRILL", Work in Progress, January 2012.
9.2 Informative References
[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.
[RFC6326] Eastlake, D, et.al, "Transparent Interconnection of Lots of
Links (TRILL) Use of IS-IS", RFC 6326, July 2011.
[rfc6326bis] Eastlake, D, et.al, "Transparent Interconnection of Lots
of Links (TRILL) Use of IS-IS", Work in Progress, draft-
eastlake-isis-rfc6326bis-04.txt, January 2012.
[TISSA-MLEVEL] Senevirathne, "RBridges: Multilevel TRILL", Work in
Progress, draft-tissa-trill-multilevel-00.txt, February
2012.
[PBB-EVPN] Sajassi, et.al, "PBB-EVPN", Work in Progress, draft-ietf-
l2vpn-pbb-evpn-03, June 2012.
[TRILL-EVPN] Sajassi, et.al, "TRILL-EVPN", Work in Progress, draft-
ietf-l2vpn-trill-evpn-00, June 2012.
Authors' Addresses
Sam Aldrin
Huawei Technologies
2330 Central Express Way
Santa Clara, CA 95951
Email: aldrin.ietf@gmail.com
Tissa Senevirathne
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CISCO Systems
375 East Tasman Drive
San Jose CA 95134
Phone: 408-853-2291
Email: tsenevir@cisco.com
Ayan Banerjee
CISCO Systems
425 East Tasman Drive
San Jose CA 95134
Phone: 408-527-0539
Email: ayabaner@cisco.com
Donald Eastlake
Huawei Technologies
155 Beaver Street
Milford, MA 01757 USA
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
Santiago Alvarez
CISCO systems
Email: saalvare@cisco.com
Xiaolan Wan
HangZhou H3C Tech. Co. Limited
No. 2 ChuangYe Road, HaiDian District
Beijing
P.R. China
Phone: +86 10 82774971
Email: wxlan@h3c.com
Xiaopeng Yang
HangZhou H3C Co. Limited
No. 2 ChuangYe Road, HaiDian District
Beijing
P.R. China
Phone: +86 10 82774963
Email: yxp@h3c.com
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