Connecting Disparate Data Center/PBB/Campus TRILL sites using BGP
draft-balaji-trill-over-ip-multi-level-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
|
|
|---|---|---|---|
| Authors | Bhargav Bhikkaji, Balaji Venkat Venkataswami , Narayana Perumal Swamy | ||
| Last updated | 2012-02-28 | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-balaji-trill-over-ip-multi-level-02
TRILL Working Group Bhargav Bhikkaji
Internet-draft Balaji Venkat Venkataswami
Intended Status: Proposed Standard Narayana Perumal Swamy
Expires: August 2012 DELL-Force10
February 25, 2012
Connecting Disparate Data Center/PBB/Campus TRILL sites using BGP
draft-balaji-trill-over-ip-multi-level-02
Abstract
There is a need to connect (a) TRILL based data centers or (b) TRILL
based networks which provide Provider Backbone like functionalities
or (c) Campus TRILL based networks over the WAN using one or more
ISPs that provide regular IP+GRE or IP+MPLS transport. A few
solutions have been proposed as in [1] in the recent past that have
not looked at the PB-like functionality. These solutions have not
dealt with the details as to how these services could be provided
such that multiple TRILL sites can be inter-connected with issues
like nick-name collisons for unicast (multicast is still TBD) being
taken care of. It has been found that with extensions to BGP the
problem statement which we will define below can be handled. Both
control plane and data plane operations can be driven into the
solution to make it seamlessly look at the entire set of TRILL sites
as a single entity which then can be viewed as one single Layer 2
cloud. MAC moves across TRILL sites and within TRILL sites can be
realized. This document / proposal envisions the use of BGP-MAC-VPN
vrfs both at the IP cloud PE devices and at the peripheral PEs within
a TRILL site providing Provider Backbone like functionality. We deal
in depth with the control plane and data plane particulars for
unicast (multicast is still TBD) with nick-name election being taken
care of as part of the solution.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
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Copyright and License Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Problem Statement . . . . . . . . . . . . . . . . . . . . . 5
1.2.1 TRILL Data Centers requiring connectivity over WAN . . . 5
1.2.2 Provider Backbone remote TRILL cloud requirements . . . 6
1.2.3 Campus TRILL network requirements . . . . . . . . . . . 7
2. Architecture where the solution applies . . . . . . . . . . . 7
2.1 Proposed Solution . . . . . . . . . . . . . . . . . . . . . 7
2.1.1 Control Plane . . . . . . . . . . . . . . . . . . . . . 8
2.1.1.1 Nickname Collision Solution . . . . . . . . . . . . 8
2.1.1.2 U-PE BGP-MAC-VPN VRFs . . . . . . . . . . . . . . . 9
2.1.1.3 Control Plane explained in detail. . . . . . . . . . 11
2.1.2 Corresponding Data plane for the above control plane
example. . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.2.1 Control plane for regular Campus and Data center
sites . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.2.2 Other Data plane particulars. . . . . . . . . . . . 13
2.1.3 Encapsulations . . . . . . . . . . . . . . . . . . . . . 19
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2.1.3.1 IP + GRE . . . . . . . . . . . . . . . . . . . . . . 19
2.1.3.2 IP + MPLS . . . . . . . . . . . . . . . . . . . . . 19
2.2 Other use cases . . . . . . . . . . . . . . . . . . . . . . 19
2.3 Novelty . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4 Uniqueness and advantages . . . . . . . . . . . . . . . . . 20
2.5 Comparison with OTV and VPN4DC and other schemes . . . . . . 21
2.6 Multi-pathing . . . . . . . . . . . . . . . . . . . . . . . 21
2.7 TRILL extensions for BGP . . . . . . . . . . . . . . . . . . 21
2.7.0 Multi-level IS-IS . . . . . . . . . . . . . . . . . . . 21
2.7.1 Format of the MAC-VPN NLRI . . . . . . . . . . . . . . . 22
2.7.2. BGP MAC-VPN MAC Address Advertisement . . . . . . . . . 22
2.7.2.1 Next hop field in MP_REACH_NLRI . . . . . . . . . . 23
2.7.2.2 Route Reflectors for scaling . . . . . . . . . . . . 24
2.7.3 Multicast related ideas . . . . . . . . . . . . . . . . 24
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 25
4 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 25
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.1 Normative References . . . . . . . . . . . . . . . . . . . 25
5.2 Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
A.1 Appendix I . . . . . . . . . . . . . . . . . . . . . . . . . 27
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1 Introduction
There is a need to connect (a) TRILL based data centers or (b) TRILL
based networks which provide Provider Backbone like functionalities
or (c) Campus TRILL based networks over the WAN using one or more
ISPs that provide regular IP+GRE or IP+MPLS transport. A few
solutions have been proposed as in [1] in the recent past that have
not looked at the Provider Backbone-like functionality. These
solutions have not dealt with the details as to how these services
could be provided such that multiple TRILL sites can be inter-
connected with issues like nick-name collisions for unicast
(multicast is still TBD) being taken care of. It has been found that
with extensions to BGP the problem statement which we will define
below can be well handled. Both control plane and data plane
operations can be driven into the solution to make it seamlessly look
at the entire set of TRILL sites as a single entity which then can be
viewed as one single Layer 2 cloud. MAC moves across TRILL sites and
within TRILL sites can be realized. This document / proposal
envisions the use of BGP-MAC-VPN vrfs both at the IP cloud PE devices
and at the peripheral PEs within a TRILL site providing Provider
Backbone like functionality. We deal in depth with the control plane
and data plane particulars for unicast (multicast is still TBD) with
nick-name election being taken care of as part of the solution.
1.1 Acknowledgements
The authors would like to thank Janardhanan Pathangi, Anoop Ghanwani
for their inputs for this proposal.
1.2 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].
Legend :
U-PE : User-near PE device. U-PEs are edge devices in the Customer
site or tier-2 site. This is a Rbridge with BGP capabilities. It has
VRF instances for each tenant it is connected to in the case of
Provider-Backbone functionality use-case.
U-Ps : core devices in the Customer site that do not directly
interact with the Customer's Customer.
N-PE : Network Transport PE device. This is a device with RBridge
capabilities in the non-core facing side. On the core facing side it
is a Layer 3 device supporting IP+GRE and/or IP+MPLS. On the non-core
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facing side it has support for VRFs one for each TRILL site that it
connects to. It runs BGP to convey the BGP-MAC-VPN VRF routes to its
peer N-PEs. It also supports IGP on the core facing side like OSPF or
IS-IS for Layer 3 and supports IP+GRE and/or IP+MPLS if need be. A
pseudo-interface representing the N-PE's connection to the Pseudo
Level 2 area is provided at each N-PE and a forwarding adjacency is
maintained between the near-end N-PE to its remote participating N-
PEs pseudo-interface in the common Pseudo Level 2 area.
N-P : Network Transport core device. This device is IP and/or
IP+MPLS core device that is part of the ISP / ISPs that provide the
transport network that connect the disparate TRILL networks together.
1.2 Problem Statement
1.2.1 TRILL Data Centers requiring connectivity over WAN
____[U-PE]____ ____________ ____[U-PE]____
( ) ( ) ( )
( TRILL Based ) ( IP Core with ) ( TRILL Based )
( Data Center Site) ( IP+GRE Encap ) ( Data Center Site)
[U-PEs] (A) [N-PE] or IP+MPLS [N-PE] (B) [U-PE]
( ) ( Encap Tunnels ) ( )
( ) ( between N-PEs) ( )
(___[U-PE]_____) (____________) (____[U-PE]____)
Figure 1.0 : TRILL based Data Center sites inter-connectivity.
o Providing Layer 2 extension capabilities amongst different
disparate data centers running TRILL.
o Recognizing MAC Moves across data centers and within data centers
to enjoin disparate sites to look and feel as one big Layer 2 cloud.
o Provide a solution agnostic to the technology used in the service
provider network
o Provide a cost effective and simple solution to the above.
o Provide auto-configured tunnels instead of pre-configured ones in
the transport network.
o Provide additional facilities as part of the transport network for
eg., TE, QoS etc
o Routing and forwarding state is to be maintained at the network
edges and not within the site or the core of the transport network.
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This requires minimization of the state explosion required to provide
this solution.
o So connectivity for end-customers is through U-PE onto N-PE onto
remote-N-PE and onto remote U-PE.
1.2.2 Provider Backbone remote TRILL cloud requirements
____[U-PE]____ ____________ ____[U-PE]____
( ) ( ) ( )
( Provider ) ( IP Core with ) ( Provider )
( Backbone TRILL ) ( IP+GRE Encap ) ( Backbone TRILL )
[U-PEs] Site (A) [N-PE] or IP+MPLS [N-PE] Site (B) [U-PE]
( ) ( Encap Tunnels ) ( )
( ) ( Between N-PEs) ( )
(___[U-PE]_____) (____________) (____[U-PE]____)
Figure 2.0 : TRILL based Provider backbone sites inter-connectivity
o Providing Layer 2 extension capabilities amongst different Provider
Backbone Layer 2 clouds that need connectivity with each other.
o Recognizing MAC Moves across Provider Backbone Layer 2 Clouds and
within a single site Layer 2 Cloud to enjoin disparate sites to look
and feel as one big Layer 2 Cloud.
o Provide a solution agnostic to the technology used in the service
provider network
o Provide a cost effective and simple solution to the above.
o Provide auto-configured tunnels instead of pre-configured ones in
the transport network.
o Provide additional facilities as part of the transport network for
eg., TE, QoS etc
o Routing and forwarding state is to be maintained at the network
edges and not within the site or the core of the transport network.
This requires minimization of the state explosion required to provide
this solution.
o These clouds could be part of the same provider but be far away
from each other. The customers of these clouds could demand
connectivity to their sites through these TRILL clouds. These TRILL
clouds could offer Provider Layer 2 VLAN transport for each of their
customers. Hence Provide a seamless connectivity wherever these sites
are placed.
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o So connectivity for end-customers is through U-PE onto N-PE onto
remote-N-PE and onto remote U-PE.
1.2.3 Campus TRILL network requirements
____[U-PE]____ ____________ ____[U-PE]____
( ) ( ) ( )
( Campus ) ( IP Core with ) ( Campus )
( TRILL Based ) ( IP+GRE Encap ) ( TRILL Based )
[U-PEs] Site (A) [N-PE] or IP+MPLS [N-PE] Site (B) [U-PE]
( ) ( Encap Tunnels ) ( )
( ) ( between N-PEs) ( )
(___[U-PE]_____) (____________) (____[U-PE]____)
Figure 3.0 : TRILL based Campus inter-connectivity
o Providing Layer 2 extension capabilities amongst different
disparate distantly located Campus Layer 2 clouds that need
connectivity with each other.
o Recognizing MAC Moves across these Campus Layer 2 clouds and within
a single site Campus cloud to enjoin disparate sites to look and feel
as one Big Layer 2 Cloud.
o Provide a solution agnostic to the technology used in the service
provider network.
o Provide a cost effective and simple solution to the above.
o Provide auto-configured tunnels instead of pre-configured ones in
the transport network.
o Provide additional facilities as part of the transport network for
eg., TE, QoS etc.
o Routing and Forwarding state optimizations as in 1.2.1 and 1.2.2.
o So connectivity for end-customers is through U-PE onto N-PE onto
remote-N-PE and onto remote U-PE.
2. Architecture where the solution applies
2.1 Proposed Solution
The following section outlines (a) Campus TRILL topology or (b) TRILL
Data Center topology or (c) Provider backbone Network topology for
which solution is intended.
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____[U-PE]____ ____________ ____[U-PE]____
( ) ( ) ( )
( TRILL Based ) ( IP Core with ) ( TRILL Based )
( RBridges as U-PEs) ( IP+GRE Encap ) ( RBridges as U-PEs)
[U-PEs]RBridges as [N-PE] or IP+MPLS [N-PE] RBridges as [U-PE]
( U-Ps ) ( Encap Tunnels ) ( U-Ps )
( ) ( between N-PEs) ( )
(___[U-PE]_____) (____________) (____[U-PE]____)
Figure 4.0 : Proposed Architecture
2.1.1 Control Plane
o Site network U-PEs still adopt learning function for source MACs
bridged through their PE-CE links. For Campus TRILL networks (non-
Provider-Backbone networks) the PE-CE links connect the regular hosts
/ servers. In the case of a data center the PE-CE links connect the
servers in a rack to the U-PEs / Top of Rack Switches.
o End customer MACs are placed in BGP-MAC-VPN VRFs in the U-PE to
customer PE-CE links. (at tier 2).
2.1.1.1 Nickname Collision Solution
o The near-end N-PE for a site has a forwarding adjacency for the
Pseudo Level 2 area Pseudo-Interface to obtain trill nicknames of the
next hop far-end N-PE's Level 2 Pseudo-Interface. This forwarding
adjacency is built up during the course of BGP-MAC-VPN exchanges
between the N-PEs. This forwarding adjacency is a kind of targeted
IS-IS adjacency through the IP+GRE or IP+MPLS core. This forwarding
adjacency exchange is accomplished through tweaking BGP to connect
the near-end N-PE with the far-end N-PEs. Nickname election is done
with N-PE Rbridge Pseudo-Interfaces participating in nickname
election in Level 2 Area and their non-core facing interfaces which
are Level 1 interfaces in the sites in the site considered to be a
Level 1 area.
o The Nicknames of each site are made distinct within the site since
the nickname election process PDUs for Level 1 area are NOT tunneled
across the transport network to make sure that each U-P or U-PE or N-
PE's Rbridge interface have knowledge of the nickname election
process only in their respective sites / domains. If a new domain is
connected as a site to an already existing network then the election
process NEED NOT be repeated in the newly added site in order to make
sure the nicknames are distinct as Multi-Level IS-IS takes care of
forwarding from one site / domain to another. It is only the Pseudo-
interface of the N-PE of the newly added site that will have to
partake in an election to generate a new Pseudo Level 2 area Nickname
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for itself.
2.1.1.2 U-PE BGP-MAC-VPN VRFs
o The Customer MACs are placed as routes in the MAC-VPN VRFs with
Nexthops being the area number Nicknames of the U-PEs to which these
customer MAC addresses are connected to. For MAC routes within the
Level 1 area the Nicknames are those of the local U-PE itself while
the MAC routes learnt from other sites have the area number of the
site to which the remote U-PE belongs to. When the source learning
happens the BGP-MAC-VPN-NLRI are communicated to the participating U-
PEs in all the sites of the said customer. Refer to section A.1.1 in
Appendix A.1 for more details on how forwarding takes place between
the sites through the multi-level IS-IS mechanism orchestrated over
the IP core network.
Format of the BGP-MAC-VPN VRF on a U-PE
+---------------------+------------------------+
| MAC address | U-PE Nickname |
+---------------------+------------------------+
| 00:be:ab:ce:fg:9f | <16-bit U-PE Nickname> |
| (local) | |
+---------------------+------------------------+
| 00:ce:cb:fe:fc:0f | <16-bit U-PE Area Num> |
| (Non-local) | |
+---------------------+------------------------+
....
....
o A VRF is allocated for each customer who in turn may have multiple
VLANs in their end customer sites. So in theory a total of 4K VLANs
can be supported per customer. The P-VLAN or the provider VLAN in the
case of a Provider Backbone category can also be 4K VLANs. So in
effect in this scheme upto 4K customers could be supported if P-VLAN
encapsulation is to be used to differentiate between multiple
customers.
o ISIS for Layer 2 is run atop the Rbridges in the site / Tier-2
network
o ISIS for Layer 2 disseminates MACs reachable via the TRILL nexthop
nicknames of site / Tier-2 network Rbridges amongst the Rbridges in
the network site.
o N-PEs have VRFs for each tier-2 access network that gain
connectivity through the IP+GRE or IP+MPLS core.
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____[U-PE]____ ____________ ____[U-PE]____
( ) ( ) ( )
( TRILL Based ) ( IP Core with ) ( TRILL Based )
( RBridges as U-PEs) ( IP+GRE Encap ) ( RBridges as U-PEs)
[U-PEB]RBridges as [N-PE] or IP+MPLS [N-PE] RBridges as [U-PEA]
.( U-Ps / ).( Encap Tunnels ).( \ U-Ps ) .
. ( (X) ) . ( between N-PEs) . ( (Y) ) .
. (___[U-PE]_____) . (____________) . (____[U-PE]____) .
. . . Other remote
Other remote U-PEs ... (BGP-MAC-VPN)... U-PEs known
known through TRILL MP-iBGP session through TRILL
installing site MAC routes
with NextHop as suitable RBridge Nicknames
Legend :
(X) - Customer A Site 1 MAC-VPN-VRF
(Y) - Customer A Site 2 MAC-VPN-VRF
U-PEs are edge devices
U-Ps are core devices that interconnect U-PEs.
Figure 5.0 : BGP-MAC-VPN VRFs amongst N-PEs
o N-PEs re-distribute the MAC routes in their respective VRFs into
the IS-IS Level 1 area after export / import amongst the N-PEs is
done. The reverse re-distribution from IS-IS to BGP is also done at
each N-PE for its tier-2 customer site.
o N-PEs exchange BGP information through route-targets for various
customer sites with other N-PEs. The MAC routes for the various
customer sites are placed in the BGP-MAC-VPN VRF of each N-PE for
each customer site it connects to on the same lines as U-PE MAC-VPN-
VRFs. The MAC routes placed in the VRFs of the N-PEs indicate the MAC
addresses for the various Rbridges of the remote tier-2 customer
sites with the respective next-hops being the Nicknames of the Level
2 pseudo-interface of the far-end N-PE through which these MAC routes
are reachable.
o U-PE and U-P Rbridges MACs and TRILL nicknames are placed in BGP-
MAC-VPN vrf on the N-PEs.
o Routes to various end customer MACs within a tier-2 customer's
sites are exchanged through BGP MAC-VPN sessions between U-PEs. IP
connectivity is provided through IP addresses on same subnet for
participating U-PEs.
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(VRF-CCA)[U-PE]____ ____________ ____[U-PE]____
. ( ) ( ) ( (VRF-CCA)
. ( ) ( IP Core ) ( ) .
.( PBB-CustA-Site 1 ) ( ) ( PBB-CustA-Site 2 ) .
[U-PEA] A1 [N1-PE] [N2-PE] A2 [U-PEB]
.( / ) ( ) ( \ ) .
. ( (X) ) ( ) ( (Y) ) .
. (___[U-PE-B1]__) (____________) (____[U-PE-B2]_) .
. | | .
. H1 H2 .
. Customer's .
Customer's............... (BGP-MAC-VPN)............Customer CCA.
Customer CCA MP-iBGP session Site 1
Site 2 installing Customer's Customer site MAC routes
with NextHop as suitable RBridge Area Nicknames
Legend :
A1, A2 - Area Nicknames of the customer sites in TRILL
N1, N2 - These are the N-PEs connecting A1 and A2 running BGP
sessions
B1, B2 - U-PEs in A1 and A2 respectively running BGP sessions
H1, H2 - Hosts connected to B1 and B2 U-PEs.
Figure 6.0 : BGP-MAC-VPN VRFs between U-PE amongst various sites
2.1.1.3 Control Plane explained in detail.
1) B1 and B2 exchange that MACs of H1 and H2 are reachable via BGP.
Example., H2-MAC is reachable via B2-MAC through area Nickname A2.
2) N1 and N2 exchange that A1 and A2 are reachable through N1
Nickname and N2 Nickname respectively via BGP.
3) N1 and N2 also exchange the MACs of U-PEs B1 and B2.
4) The routes in the N1 and N2 are re-distributed into IS-IS to end
up with the following correlated routing state.
Now the correlated route in B1 is that H2 -> reachable via -> B2 ->
reachable via A2 -> reachable via N1 Nickname.
And the correlated route in B2 is that H1 -> reachable via -> B1 ->
reachable via A1 -> reachable via N2 Nickname.
And the correlated route in N1 is that B2 -> reachable via -> A2 ->
reachable via Nickname N2
And the correlated route in N2 is that B1 -> reachable via -> A1 ->
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reachable via Nickname N1
2.1.2 Corresponding Data plane for the above control plane example.
(VRF-CCA)[U-PE]____ ____________ ____[U-PE]____
. ( ) ( ) ( (VRF-CCA)
. ( ) ( IP Core ) ( ) .
.( PBB-CustA-Site 1 ) ( ) ( PBB-CustA-Site 2 ) .
[U-PEA] A1 [N1-PE] [N2-PE] A2 [U-PEB]
.( / ) ( ) ( \ ) .
. ( (X) ) ( ) ( (Y) ) .
. (___[U-PE-B1]__) (____________) (____[U-PE-B2]_) .
. | | .
. H1 H2 .
. Customer's .
Customer's............... (BGP-MAC-VPN)............Customer CCA.
Customer CCA MP-iBGP session Site 1
Site 2 installing Customer's Customer site MAC routes
with NextHop as suitable RBridge Area Nicknames
Legend :
A1, A2 - Area Nicknames of the customer sites in TRILL
N1, N2 - These are the N-PEs connecting A1 and A2 running BGP
sessions
B1, B2 - U-PEs in A1 and A2 respectively running BGP sessions
H1, H2 - Hosts connected to B1 and B2 U-PEs.
Figure 6.0 : BGP-MAC-VPN VRFs between U-PE amongst various sites
1) H1 sends a packet to B1 with SourceMac as H1-MAC and DestMac as
H2-MAC and C-VLAN as C1. This frame is named F1.
2) B1 encapsulates this packet in a P-VLAN (Provider VLAN) packet
with outer SourceMac as B1-MAC and DestMac as B2-MAC with P-VLAN PV1.
This frame is named F2.
3) B1 being and Rbridge encapsulates a TRILL header on top of F2,
with Ingress Rbridge as B1 and Egress Rbridge as A2.
4) This reaches N1 where N1 decapsulates the TRILL header and sends
frame F2 inside a IP+GRE header with GRE key as Cust-A's VRF id.
5) Packet reaches N2 where N2 looks up the GRE key to identify which
customer / VRF to be looked into.
6) In that VRF table N2 looks up B2 and encapsulates F2 with TRILL
header with Ingress Rbridge as A1 and Egress Rbridge being B2.
7) Finally the packet reaches B2 and is decapsulated and sends F1 to
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the host.
2.1.2.1 Control plane for regular Campus and Data center sites
For non-PBB like environments one could choose the same capabilities
as a PBB like environment with all TORs for e.g in a data center
having BGP sessions through BGP Route Reflectors with other TORs. By
manipulating the Route Targets specific TORs could be tied in
together in the topology within a site or even across sites. The
easier way to go about the initial phase of deployment would be to
restrict the MP-BGP sessions between N-PEs alone within Campus
networks and Data centers and let IS-IS do the job of re-distributing
into BGP. Flexibility however can be achieved by letting the U-PEs in
the Campus or data center networks too to have MP-BGP sessions.
Different logical topologies could be achieved as the result of the
U-PE BGP sessions.
2.1.2.2 Other Data plane particulars.
Default Dtree which is spanning all sites is setup for P-VLAN for
Customer's Customer CCA supported on all Tier-2 sites. Denoted by
===, //.
(VRF-CCA)[U-PE]____ ____________ ____[U-PE]____
. ( ) ( ) ( (VRF-CCA)
. ( TRILL Based ) ( IP Core with ) ( TRILL Based ) .
.( Customer A Site 1) ( IP+GRE Encap ) ( Customer A Site 2) .
[U-PEA]============[N-PE]=============[N-PE]==============[U-PEB]
.( / ) ( Encap Tunnels ) ( \ // ) .
. ( (X) ) ( between N-PEs) ( (Y) // ) .
. (___[U-PE]_____) (____________) (____[U-PEC]....(VRF-CCA)
. Customer's .
Customer's............... (BGP-MAC-VPN)............Customer CCA.
Customer CCA MP-iBGP session Site 1
Site 2 installing Customer's Customer site MAC routes
with NextHop as suitable RBridge Area Nicknames
Legend :
(X) - Customer A Site 1 MAC-VPN-VRF
(Y) - Customer A Site 2 MAC-VPN-VRF
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 1
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 2
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 3
Figure 8.0 : Dtree spanning all U-PEs for unknown floods.
(1) When a packet comes into a U-PE from the near-end the source MAC
is learned and placed in the near-end U-PE BGP-MAC-VPN VRF. This is
done in a sub-table depending on which VLAN they belong to in the
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end-customer's VLANs. The destination MAC if unknown is flooded
through a default Spanning tree (could be a dtree) constructed for
that provider VLAN which is mapped to carry traffic for the end-
customer VLAN in the customer's network sites involved.
Default Dtree which is spanning all sites is setup for P-VLAN for
Customer's Customer CCA supported on all Tier-2 sites.
Denoted by ===, //.
Forwarding for unknown frames using the default Dtree spanning all
customer sites and their respective U-PEs and onto their customers.
(VRF-CCA)[U-PE]____ ____________ ____[U-PE]____
. ( ) ( ) ( (VRF-CCA)
. ( TRILL Based ) ( IP Core with ) ( TRILL Based ) .
.( Customer A Site 1) ( IP+GRE Encap ) ( Customer A Site 2) .
( ............ ) ( ............. ) ( .............. ) .
[U-PEA]============[N-PE]=============[N-PE]==============[U-PEB]
.( / ) ( Encap Tunnels ) ( \ // ) .
. ( (X) ) ( between N-PEs) ( (Y) // ) .
. (___[U-PE]_____) (____________) (____[U-PEC]....(VRF-CCA)
. Customer's .
Customer's............... (BGP-MAC-VPN)............Customer CCA.
Customer CCA MP-iBGP session Site 1
Site 2 installing Customer's Customer site MAC routes
with NextHop as suitable RBridge Area Nicknames
Legend :
(X) - Customer A Site 1 MAC-VPN-VRF
(Y) - Customer A Site 2 MAC-VPN-VRF
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 1
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 2
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 3
Figure 9.0 : Unknown floods through Dtree spanning for that P-VLAN
(2) The Spanning tree (which could be a dtree for that VLAN) carries
that packet through site network switches all the way to N-PEs
bordering that network site. U-PEs can drop the packet if there exist
no ports for that customer VLAN on that U-PE. The Spanning tree
includes auto-configured IP-GRE tunnels or MPLS LSPs across the
IP+GRE and/or IP+MPLS cloud which are constituent parts of that tree
and hence the unknown flood is carried over to the remote N-PEs
participating in the said dtree. The packet then heads to that
remote-end (leaf) U-PEs and on to the end customer sites. For
purposes of connecting multiple N-PE devices for a Dtree that is
being used for unknown floods, a mechanism such as PIM-Bidir in the
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core of the IP network can be used.
(3) BGP-MAC-VPN VRF exchanges between N-PEs carry the routes for MACs
of the near-end Rbridges in the near-end site network to the remote-
end site network. At the remote end U-PE a correlation between near-
end U-PE and the customer MAC is made after BGP-MAC-VPN VRF exchanges
between near-end and far-end U-PEs. The MPLS inner label or the GRE
key indicates which VRF to consult for an incoming encapsulated
packet across the core and the far-end N-PE's Level 1 Area Nickname
of the far-end N-PE is inserted as the Egress Rbridge Nickname in the
TRILL header of the packet traversing the core from the near-end N-
PE.
(4) From thereon the source MAC so learnt at the far end is reachable
just like a Hierarchical VPN case in MPLS Carrier Supporting Carrier.
The only difference is that the nicknames of the far-end U-PEs/U-Ps
may be the same as the nicknames of the near-end U-PEs/U-Ps. In order
to overcome this, the MAC-routes exchanged between the U-PEs have the
next-hops as Area nicknames of the far-end U-PE and then the Area
number nickname is resolved to the near-end N-PE/N-PEs in the local
site that provide connectivity to the far-end U-PE in question.
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<srcMac, DstMac> srcMac is known at U-PEA, so advertize to other U-
PEs through BGP in the other customer sites for Customer A that
srcMAC is reachable via U-PEA. This is received at the BGP-MAC-VPN
VRFs in U-PEB and U-PEC.
(VRF-CCA)[U-PE]____ ____________ ____[U-PE]____
. ( ) ( ) ( (VRF-CCA)
. ( TRILL Based ) ( IP Core with ) ( TRILL Based ) .
.( Customer A Site 1) ( IP+GRE Encap ) ( Customer A Site 2) .
( ............ ) ( ............. ) ( .............. ) .
[U-PEA]============[N-PE]=============[N-PE]==============[U-PEB]
.( / ) ( Encap Tunnels ) ( \ // ) .
. ( (X) ) ( between N-PEs) ( (Y) // ) .
. (___[U-PE]_____) (____________) (____[U-PEC]....(VRF-CCA)
. Customer's .
Customer's............... (BGP-MAC-VPN)............Customer CCA.
Customer CCA MP-iBGP session Site 1
Site 2 installing Customer's Customer site MAC routes
with NextHop as suitable RBridge Area Nicknames
Legend :
(X) - Customer A Site 1 MAC-VPN-VRF
(Y) - Customer A Site 2 MAC-VPN-VRF
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 1
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 2
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 3
Figure 10.0 : Distributing MAC routes through BGP-MAC-VPN
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<srcMac, DstMac>
Flooding when DstMAC is unknown. The flooding reaches all U-PEs and
is forwarded to the customer devices (Customer's customer devices).
(VRF-CCA)[U-PE]____ ____________ ____[U-PE]____
. ( ) ( ) ( (VRF-CCA)
. ( TRILL Based ) ( IP Core with ) ( TRILL Based ) .
.( Customer A Site 1) ( IP+GRE Encap ) ( Customer A Site 2) .
( ............ ) ( ............. ) ( .............. ) .
[U-PEA]============[N-PE]=============[N-PE]==============[U-PEB]
.( / ) ( Encap Tunnels ) ( \ //. ) .
. ( (X) ) ( between N-PEs) ( (Y) //. ) .
. (___[U-PE]_____) (____________) (____[U-PEC]....(VRF-CCA)
. Customer's .
Customer's............... (BGP-MAC-VPN)............Customer CCA.
Customer CCA MP-iBGP session Site 1
Site 2 installing Customer's Customer site MAC routes
with NextHop as suitable RBridge Area Nicknames
Legend :
(X) - Customer A Site 1 MAC-VPN-VRF
(Y) - Customer A Site 2 MAC-VPN-VRF
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 1
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 2
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 3
Figure 11.0 : Forwarding when DstMAC is unknown.
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<srcMac, DstMac>
When DstMAC is known. Payload is carried in the following fashion in
the IP core.
(<Outer Ethernet Header, IP+GRE,VRF in GRE key>,
In PBB like environments / sites interconnected, the payload is P-
VLAN headers encapsulating actual payload.
<Outer Ethernet header, P-VLAN header>
<Payload = Ethernet header, Inner VLAN header>, <Actual Payload>)
In Campus and Data Center environments only the latter is carried.
There is no P-VLAN header required.
(VRF-CCA)[U-PE]____ ____________ ____[U-PE]____
. ( ) ( ) ( (VRF-CCA)
. ( TRILL Based ) ( IP Core with ) ( TRILL Based ) .
.( Customer A Site 1) ( IP+GRE Encap ) ( Customer A Site 2) .
( ............ ) ( ............. ) ( .............. ) .
[U-PEA]============[N-PE]=============[N-PE]==============[U-PEB]
.( / ) ( Encap Tunnels ) ( \ //. ) .
. ( (X) ) ( between N-PEs) ( (Y) //. ) .
. (___[U-PE]_____) (____________) (____[U-PEC]....(VRF-CCA)
. Customer's .
Customer's............... (BGP-MAC-VPN)............Customer CCA.
Customer CCA MP-iBGP session Site 1
Site 2 installing Customer's Customer site MAC routes
with NextHop as suitable RBridge Area Nicknames
Legend :
(X) - Customer A Site 1 MAC-VPN-VRF
(Y) - Customer A Site 2 MAC-VPN-VRF
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 1
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 2
(VRF-CCA) - MAC-VPN-VRF for Customer's Customer A (CCA) Site 3
Figure 12.0 : Forwarding when the DstMAC is known.
(5) The reverse path would do the same for reachability of the
remote-end from the far-end.
(6) Connectivity is thus established between end customer-sites
through site networks and through the IP+GRE and/or IP+MPLS core. One
could deploy also VPLS for access network connectivity after
encapsulating the TRILL header and the outer header.
(7) End customer packets are carried IP+GRE tunnels or IP+MPLS LSPs
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through access network site to near-end N-PE in the near-end. N-PE
encapsulates this in auto-configured MPLS LSPs or IP+GRE tunnels to
far-end N-PEs through the IP+GRE and/or IP+MPLS core. The label is
stripped at the far-end N-PE and the inner frame continues to far-end
U-PE and onto the customer.
2.1.3 Encapsulations
2.1.3.1 IP + GRE
(<Outer Ethernet Header, IP+GRE, VRF in GRE key>,
In PBB like environments...
<Outer Ethernet header, P-VLAN header>,
<Payload = Ethernet header, Inner VLAN header>, <Actual Payload>)
In non-PBB like environments such as Campus and Data Center the
Ethernet header with P-VLAN header is not required.
2.1.3.2 IP + MPLS
(<Outer Ethernet Header, MPLS header, VRF in Inner MPLS label>,
In PBB like environments...
<Outer Ethernet header, P-VLAN header>,
<Payload = Ethernet header, Inner VLAN header>, <Actual Payload>)
In non-PBB like environments such as Campus and Data Center the
Ethernet header with P-VLAN header is not required.
2.2 Other use cases
o Campus to Campus connectivity can also be achieved using this
solution. Multi-homing where multiple U-Pes connect to the same
customer site can also facilitate load-balancing if a site-id (can
use ESI for MAC-VPN-NLRI) is incorporated in the BGP-MAC-VPN NLRI.
Mac Moves can be detected if the site-id of the advertised MAC from
U-Pes is different from the older ones available.
2.3 Novelty
o TRILL MAC routes and their associated nexthops which are TRILL
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nicknames Are re-distributed into BGP from IS-IS
o Thus BGP-MAC-VPNs on N-Pes in the transport network contain MAC
routes with nexthops as TRILL Area nicknames.
o The customer edge Rbridges / Provider bridges too contain MAC
routes with associated nexthops as TRILL nicknames. This proposal is
an extension of BGP-MAC-VPN I-D to include MAC routes with TRILL Area
nicknames as Nexthops.
2.4 Uniqueness and advantages
o Uses existing protocols such as IS-IS for Layer 2 and BGP to
achieve this. No changes to IS-IS except for redistribution into BGP
at the transport core edge and vice-versa.
o Uses BGP-MAC-VPNs for transporting MAC-updates of customer devices
between edge devices only.
o Employs a hierarchical MAC-route hiding within the core Rbridges of
the site. Employs a hierarchical VPN like solution to avoid routing
state of sites within the transport core.
o Multi-tenancy within each data center
o Provider-backbone bridging like customer MAC hiding from the core
of each site.
o Multi-homing where multiple U-Pes connect to the same customer
site can also facilitate load-balancing if a site-id (can use ESI for
MAC-VPN-NLRI) is incorporated in the BGP-MAC-VPN NLRI.
o Mac Moves can be detected if the site-id of the advertised MAC from
U-Pes is different from the older ones available.
o PBB like functionality supported where P-VLAN and C-VLAN are
different spaces.
o Disparate TRILL networks with or without multi-tenancy.
o Uses regular BGP supporting MAC-VPN features. Both between
transport core edge devices and the Tier-2 customer edge devices.
o When new TRILL sites are added then no re-election in the Level 1
area is needed. Only the Pseudo-interface of the N-PE has to be added
to the mix with the transport of the election PDUs being done across
the transport network core.
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2.5 Comparison with OTV and VPN4DC and other schemes
o OTV requires proprietary changes to IS-IS Doesn't seem to have
reached the RFC status yet Its encapsulation could be more
standardized Lot of proprietary changes required compared to this
scheme with regard to IS-IS.
o VPN4DC is just a problem statement.
o [4] deals with Pseudo-wires being setup across the transport core.
The control plane protocols for TRILL seem to be tunneled through the
transport core. The scheme in the proposal we make do NOT require
anything more than Pseudo Level 2 area number exchanges and those for
the Pseudo-interfaces. BGP takes care of the rest of the routing.
Also [4] does not take care of nick-name collision detection since
the control plane TRILL is also tunneled and as a result when a new
site is sought to be brought up into the inter-connection amongst
existing TRILL sites, nick-name re-election may be required.
o [5] does not have a case for TRILL. It was intended for other types
of networks which exclude TRILL.
2.6 Multi-pathing
By using different RDs to export the BGP-MAC routes with their
appropriate Nickname next-hops from more than one N-PE we could
achieve multi-pathing over the transport IP+GRE and/or IP+MPLS core.
2.7 TRILL extensions for BGP
2.7.0 Multi-level IS-IS
Akin to TRILL IS-IS multi-level draft where each N-PE can be
considered as a ABR having one nickname in a customer site which in
turn is a level-1 area and a Pseudo Interface facing the core of the
transport network which belongs to a Level 2 Area, the Pseudo
Interface would do the TRILL header decapsulation for the incoming
packet from the Level 1 Area and throw away the TRILL header within
the Pseudo Level 2 Area and transport the packets across the Layer 3
core (IP+GRE and/or IP+MPLS) after an encapsulation in IP+GRE or
IP+MPLS. Thus we should have to follow a scheme with the NP-E core
facing Pseudo-interface in the Level 2 Pseudo-Area doing the TRILL
encapsulation and decapsulation for outgoing and incoming packets
respectively from and to the transport core. The incoming packets
from the Level 1 area are subject to encapsulation in IP+GRE or
IP+MPLS by the sending N-PE's Pseudo-Interface and the outgoing
packets from the transport core are subject to decapsulation from
their IP+GRE or IP+MPLS headers by the Pseudo-Interface on the
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receiving N-PE.
2.7.1 Format of the MAC-VPN NLRI
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
The Route Type field defines encoding of the rest of MAC-VPN NLRI
(Route Type specific MAC-VPN NLRI).
The Length field indicates the length in octets of the Route Type
specific field of MAC-VPN NLRI.
This document defines the following Route Types:
+ 1 - Ethernet Tag Auto-Discovery (A-D) route
+ 2 - MAC advertisement route
+ 3 - Inclusive Multicast Ethernet Tag Route
+ 4 - Ethernet Segment Route
+ 5 - Selective Multicast Auto-Discovery (A-D) Route
+ 6 - Leaf Auto-Discovery (A-D) Route
+ 7 - MAC Advertisement Route with Nexthop as TRILL Nickname
Here type 7 is used in this proposal.
2.7.2. BGP MAC-VPN MAC Address Advertisement
BGP is extended to advertise these MAC addresses using the MAC
advertisement route type in the MAC-VPN-NLRI.
A MAC advertisement route type specific MAC-VPN NLRI consists of the
following:
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+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
| MAC Address (6 octets) |
+---------------------------------------+
|GRE key / MPLS Label rep. VRF(3 octets)|
+---------------------------------------+
| Originating Rbridge's IP Address |
+---------------------------------------+
| Originating Rbridge's MAC address |
| (8 octets) |
+---------------------------------------+
The RD MUST be the RD of the MAC-VPN instance that is advertising the
NLRI. The procedures for setting the RD for a given MAC VPN are
described in section 8 in [3].
The encoding of a MAC address is the 6-octet MAC address specified by
IEEE 802 documents [802.1D-ORIG] [802.1D-REV].
If using the IP+GRE and/or IP+MPLS core networks the GRE key or MPLS
label MUST be the downstream assigned MAC-VPN GRE key or MPLS label
that is used by the N-PE to forward IP+GRE or IP+MPLS encapsulated
ethernet packets received from remote N-PEs, where the destination
MAC address in the ethernet packet is the MAC address advertised in
the above NLRI. The forwarding procedures are specified in previous
sections of this document. A N-PE may advertise the same MAC-VPN
label for all MAC addresses in a given MAC-VPN instance. Or a N-PE
may advertise a unique MAC-VPN label per MAC address. All of these
methodologies have their tradeoffs.
Per MAC-VPN instance label assignment requires the least number of
MAC-VPN labels, but requires a MAC lookup in addition to a GRE key or
MPLS lookup on an egress N-PE for forwarding. On the other hand a
unique label per MAC allows an egress N-PE to forward a packet that
it receives from another N-PE, to the connected CE, after looking up
only the GRE key or MPLS labels and not having to do a MAC lookup.
The Originating Rbridge's IP address MUST be set to an IP address of
the PE (U-PE or N-PE). This address SHOULD be common for all the
MAC-VPN instances on the PE (e.,g., this address may be PE's loopback
address).
2.7.2.1 Next hop field in MP_REACH_NLRI
The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
be set to the Nickname of the N-PE or in the case of the U-PE the
Area Nickname of the Rbridge one whose MAC address is carried in the
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Originating Rbridge's MAC Address field.
The BGP advertisement that advertises the MAC advertisement route
MUST also carry one or more Route Target (RT) attributes.
It is to be noted that document [3] does not require N-PEs/U-PEs to
create forwarding state for remote MACs when they are learned in the
control plane. When this forwarding state is actually created is a
local implementation matter. However the proposal in this document
requires that forwarding state be established when these MAC routes
are learned in the control plane.
2.7.2.2 Route Reflectors for scaling
It is recommended that Route Reflectors SHOULD be deployed to mesh
the U-PEs in the sites with other U-PEs at other sites (belonging to
the same customer) and the transport network also have RRs to mesh
the N-PEs. This takes care of the scaling issues that may arise if
full mesh is deployed amongst U-PEs or the N-PEs.
2.7.3 Multicast related ideas
For the purpose of multicast it is possible that the IP core can have
a PIM-bidir tree for each customer that will connect all the N-PEs
related to a customer and carry the multicast traffic over the
transport core thus connecting site to site multicast trees. This is
of course out of the scope of this document. The authors intend to
address this issue in future versions of this solution extended for
multicast as well.
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3 Security Considerations
TBD.
4 IANA Considerations
A few IANA considerations need to be considered at this point. A
proper AFI-SAFI indicator would have to be provided to carry MAC
addresses as NLRI with Next-hops as Rbridbge Nicknames. This one AFI-
SAFI indicator could be used for both U-PE MP-iBGP sessions and N-PE
MP-iBGP sessions.
5 References
5.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC1776] Crocker, S., "The Address is the Message", RFC 1776, April
1 1995.
[TRUTHS] Callon, R., "The Twelve Networking Truths", RFC 1925,
April 1 1996.
5.2 Informative References
[1] draft-xl-trill-over-wan-00.txt, XiaoLan. Wan et.al
December 11th ,2011 Work in Progress
[2] draft-perlman-trill-rbridge-multilevel-03.txt, Radia
Perlman et.al October 31, 2011 Work in Progress
[3] draft-raggarwa-mac-vpn-01.txt, Rahul Aggarwal et.al,
June 2010, Work in Progress.
[4] draft-yong-trill-trill-o-mpls, Yong et.al, October
2011, Work in Progress.
[5] draft-raggarwa-sajassi-l2vpn-evpn Rahul Aggarwal
et.al, September 2011, Work in Progress.
[EVILBIT] Bellovin, S., "The Security Flag in the IPv4 Header",
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RFC 3514, April 1 2003.
[RFC5513] Farrel, A., "IANA Considerations for Three Letter
Acronyms", RFC 5513, April 1 2009.
[RFC5514] Vyncke, E., "IPv6 over Social Networks", RFC 5514, April 1
2009.
Authors' Addresses
Bhargav Bhikkaji,
Dell-Force10,
350 Holger Way,
San Jose, CA
U.S.A
Email: Bhargav_Bhikkaji@dell.com
Balaji Venkat Venkataswami,
Dell-Force10,
Olympia Technology Park,
Fortius block, 7th & 8th Floor,
Plot No. 1, SIDCO Industrial Estate,
Guindy, Chennai - 600032.
TamilNadu, India.
Tel: +91 (0) 44 4220 8400
Fax: +91 (0) 44 2836 2446
EMail: BALAJI_VENKAT_VENKAT@dell.com
Narayana Perumal Swamy,
Dell-Force10,
Olympia Technology Park,
Fortius block, 7th & 8th Floor,
Plot No. 1, SIDCO Industrial Estate,
Guindy, Chennai - 600032.
TamilNadu, India.
Tel: +91 (0) 44 4220 8400
Fax: +91 (0) 44 2836 2446
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Email: Narayana_Perumal@dell.com
A.1 Appendix I
A.1.1 Extract from Multi-level IS-IS draft made applicable to scheme
In the following picture, RB2 and RB3 are area border RBridges. A
source S is attached to RB1. The two areas have nicknames 15961 and
15918, respectively. RB1 has a nickname, say 27, and RB4 has a
nickname, say 44 (and in fact, they could even have the same
nickname, since the RBridge nickname will not be visible outside the
area).
Pseudo
Area 15961 level 2 Area 15918
+-------------------+ +-----------------+ +--------------+
| | | IP Core network | | |
| S--RB1---Rx--Rz----RB2--- ----RB3---Rk--RB4---D |
| 27 | | . . | | 44 |
| | |Pseudo-Interface | | |
+-------------------+ +-----------------+ +--------------+
Here RB2 and RB3 are N-PEs. RB4 and RB1 are U-PEs.
This sample topology could apply to Campus and data-center
topologies. For Provider Backbone topologies S would fall outside the
Area 15961 and RB1 would be the U-PE carrying the C-VLANs inside a P-
VLAN for a specific customer.
Let's say that S transmits a frame to destination D, which is
connected to RB4, and let's say that D's location is learned by the
relevant RBridges already. The relevant RBridges have learned the
following:
1) RB1 has learned that D is connected to nickname 15918
2) RB3 has learned that D is attached to nickname 44.
The following sequence of events will occur:
- S transmits an Ethernet frame with source MAC = S and destination
MAC = D.
- RB1 encapsulates with a TRILL header with ingress RBridge = 27,
and egress = 15918.
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- RB2 has announced in the Level 1 IS-IS instance in area 15961,
that it is attached to all the area nicknames, including 15918.
Therefore, IS-IS routes the frame to RB2. (Alternatively, if a
distinguished range of nicknames is used for Level 2, Level 1
RBridges seeing such an egress nickname will know to route to the
nearest border router, which can be indicated by the IS-IS attached
bit.)
In the original draft on multi-level IS-IS the following happens and
QUOTE...
- RB2, when transitioning the frame from Level 1 to Level 2,
replaces the ingress RBridge nickname with the area nickname, so
replaces 27 with 15961. Within Level 2, the ingress RBridge field in
the TRILL header will therefore be 15961, and the egress RBridge
field will be 15918. Also RB2 learns that S is attached to nickname
27 in area 15961 to accommodate return traffic.
- The frame is forwarded through Level 2, to RB3, which has
advertised, in Level 2, reachability to the nickname 15918.
- RB3, when forwarding into area 15918, replaces the egress nickname
in the TRILL header with RB4's nickname (44). So, within the
destination area, the ingress nickname will be 15961 and the egress
nickname will be 44.
- RB4, when decapsulating, learns that S is attached to nickname
15961, which is the area nickname of the ingress.
Now suppose that D's location has not been learned by RB1 and/or RB3.
What will happen, as it would in TRILL today, is that RB1 will
forward the frame as a multi-destination frame, choosing a tree. As
the multi-destination frame transitions into Level 2, RB2 replaces
the ingress nickname with the area nickname. If RB1 does not know the
location of D, the frame must be flooded, subject to possible
pruning, in Level 2 and, subject to possible pruning, from Level 2
into every Level 1 area that it reaches on the Level 2 distribution
tree.
UNQUOTE...
In the current proposal that we outline in this document, the TRILL
header is done away with completely in the IP+GRE or IP+MPLS core. A
re-look into the inner headers after decapsulation gives the
appropriate information to carry the frame from the N-PE towards the
destination U-PE.
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