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Versions: (draft-hao-trill-centralized-replication) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 8361

TRILL Working Group                                              W. Hao
INTERNET-DRAFT                                                    Y. Li
Intended Status: Standard Track                     Huawei Technologies
                                                             M. Durrani
                                                                  Cisco
                                                               S. Gupta
                                                            IP Infusion
                                                                  A. Qu
                                                               MediaTec
                                                                 T. Han
                                                    Huawei Technologies
Expires: October 2015                                    April 30, 2015




       Centralized Replication for BUM traffic in active-active edge
                                connection
              draft-ietf-trill-centralized-replication-02.txt


Abstract

   In TRILL active-active access scenario, RPF check failure issue may
   occur when pseudo-nickname mechanism in [TRILLPN] is used. This
   draft describes a solution to the RPF check failure issue through
   centralized replication for BUM (Broadcast, Unknown unicast,
   Mutlicast) traffic. The solution has all ingress RBs send BUM
   traffic to a centralized node via unicast TRILL encapsulation. When
   the centralized node receives the BUM traffic, it decapsulates the
   traffic and forwards the BUM traffic to all destination RBs using a
   distribution tree established via the TRILL base protocol. To avoid
   RPF check failure on a RBridge sitting between the ingress RBridge
   and the centralized replication node, some change of RPF calculation
   algorithm is required. RPF calculation on each RBridge should use
   the centralized node as ingress RB instead of the real ingress
   RBridge of RBv to perform the calculation.

Status of this Memo



   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.





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Table of Contents

   1. Introduction ................................................ 3
   2. Conventions used in this document............................ 4
   3. Centralized Replication Solution Overview.................... 4
   4. Frame duplication from remote RB............................. 5
   5. Local forwarding behavior on ingress RBridge................. 6
   6. Loop prevention among RBridges in a edge group............... 7
   7. Centralized replication forwarding process................... 8


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   8. BUM traffic loadbalancing among multiple centralized nodes....9
   9. Co-existing with CMT solution............................... 10
   10. Network Migration Analysis................................. 11
   11. TRILL protocol extension................................... 11
      11.1. "R" and "C" Flag in Nickname Flags APPsub-TLV..........11
   12. Security Considerations.................................... 12
   13. IANA Considerations........................................ 12
   14. References ................................................ 12
      14.1. Normative References ..................................12
      14.2. Informative References ................................12
   15. Acknowledgments ........................................... 13

1. Introduction

   The IETF TRILL (Transparent Interconnection of Lots of Links)
   [RFC6325] protocol provides loop free and per hop based multipath
   data forwarding with minimum configuration. TRILL uses IS-IS
   [RFC6165] [RFC6326bis] as its control plane routing protocol and
   defines a TRILL specific header for user data.

   Classic Ethernet device (CE) devices typically are multi-homed to
   multiple edge RBridges which form an edge group. All of the uplinks
   of CE are bundled as a Multi-Chassis Link Aggregation (MC-LAG). An
   active-active flow-based load sharing mechanism is normally
   implemented to achieve better load balancing and high reliability. A
   CE device can be a layer 3 end system by itself or a bridge switch
   through which layer 3 end systems access to TRILL campus.

   In active-active access scenario, pseudo-nickname solution in
   [TRILLPN] can be used to avoid MAC flip-flop on remote RBs. The
   basic idea is to use a virtual RBridge of RBv with a single pseudo-
   nickname to represent an edge group that MC-LAG connects to. Any
   member RBridge of that edge group should use this pseudo-nickname
   rather than its own nickname as ingress nickname when it injects
   TRILL data frames to TRILL campus. The use of the nickname solves
   the address flip flop issue by making the MAC address learnt by the
   remote RBridge bound to pseudo-nickname. However, it introduces
   another issue, which is incorrect packet drop by RPF check failure.
   When a pseudo-nickname is used by an edge RBridge as the ingress
   nickname to forward BUM traffic, any RBridges sitting between the
   ingress RB and the distribution tree root will treat the traffic as
   it is ingressed from the virtual RBridge RBv. If same distribution
   tree is used by these different edge RBridges, the traffic may
   arrive at RBn from different ports. Then the RPF check fails, and
   some of the traffic receiving from unexpected ports will be dropped
   by RBn.



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   This document proposes a centralized replication solution for
   broadcast, unknown unicast, multicast(BUM) traffic forwarding to
   solve the issue of incorrect packet drop by RPF check failure. The
   basic idea is that all ingress RBs send BUM traffic to a centralized
   node which is recommended to be a distribution tree root using
   unicast TRILL encapsulation. When the centralized node receives that
   traffic, it decapsulates it and then forwards the BUM traffic to all
   destination RBs using a distribution tree established per TRILL base
   protocol.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119
   [RFC2119].The acronyms and terminology in [RFC6325] is used herein
   with the following additions:

   BUM - Broadcast, Unknown unicast, and Multicast

   CE - As in [CMT], Classic Ethernet device (end station or bridge).

      The device can be either physical or virtual equipment.



3. Centralized Replication Solution Overview

   When an edge RB receives BUM traffic from a CE device, it acts as
   ingress RB and uses unicast TRILL encapsulation instead of multicast
   TRILL encapsulation to send the traffic to a centralized node. The
   centralized node is recommended to be a distribution tree root.

   The TRILL header of the unicast TRILL encapsulation contains an
   "ingress RBridge nickname" field and an "egress RBridge nickname"
   field. If ingress RB receives the traffic from the port which is in
   a MC-LAG, it should set the ingress RBridge nickname to be the
   pseudo-nickname rather than its own nickname to avoid MAC flip-flop
   on remote RBs as per [TRILLPN]. The egress RBridge nickname is set
   to the special nickname of the centralized node which is used to
   differentiate the unicast TRILL encapsulation BUM traffic from
   normal unicast TRILL traffic. The special nickname is called R-
   nickname.

   When the centralized node receives the unicast TRILL encapsulated
   BUM traffic from ingress RB, the node decapsulates the packet. Then
   the centralized node replicates and forwards the BUM traffic to all


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   destination RBs using one of the distribution trees established per
   TRILL base protocol, if the centralized node is the root of a
   distribution tree, the recommended distribution tree is the tree
   whose root is the centralized node itself. When the centralized node
   forwards the BUM traffic, ingress nickname remains the same as that
   in frame it received to ensure that the MAC address learnt by all
   egress RBridges bound to pseudo-nickname.

   When the replicated traffic is forwarded on each RBridge along the
   distribution tree starting from the centralized node, RPF check will
   be performed as per RFC6325. For any RBridge sitting between the
   ingress RBridge and the centralized replication node, the traffic
   incoming port should be the centralized node facing port as the
   multicast traffic always comes from the centralized node in this
   solution. However the RPF port as result of distribution tree
   calculation as per RFC 6325 will be the real ingress RB facing port
   as it uses virtual RBridge as ingress RB, so RPF check will fail. To
   solve this problem, some change of RPF calculation algorithm is
   required. RPF calculation on each RBridge should use the centralized
   node as ingress RB instead of the real ingress virtual RBridge to
   perform the calculation. As a result, RPF check will point to the
   centralized node facing port on the RBridge for multi-destination
   traffic. It prevents the incorrect frame discard by RPF check.

   To differentiate the unicast TRILL encapsulation BUM traffic from
   normal unicast TRILL traffic on a centralized node, besides the
   centralized node's own nickname, R-nickname should be introduced for
   centralized replication. Only when the centralized node receives
   unicast TRILL encapsulation traffic with egress nickname equivalent
   to the R-nickname, the node does unicast TRILL decapsulaton and then
   forwards the traffic to all destination RBs through a distribution
   tree. The centralized nodes should announce its R-nickname to all
   TRILL campus through TRILL LSP extension.

4. Frame duplication from remote RB

   Frame duplication may occur when a remote host sends multi-
   destination frame to a local CE which has an active-active
   connection to the TRILL campus. To avoid local CE receiving multiple
   copies from a remote RBridge, the designated forwarder (DF)
   mechanism should be supported for egress direction multicast traffic.

   DF election mechanism allows only one port in one RB of MC-LAG to
   forward multicast traffic from TRILL campus to local access side for
   each VLAN. The basic idea of DF is to elect one RBridge per VLAN
   from an edge group to be responsible for egressing the multicast



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   traffic. [draft-hao-trill-dup-avoidance-active-active-02] describes
   the detail DF mechanism and TRILL protocol extension for DF election.

   If DF-election mechanism is used for frame duplication prevention,
   access ports on an RB are categorized as three types: non mc-lag,
   mc-lag DF port and mc-lag non-DF port. The last two types can be
   called mc-lag port. For each of the mc-lag port, there is a pseudo-
   nickname associated. If consistent nickname allocation per edge
   group RBridges is used, it is possible that same pseudo-nickname
   associated to more than one port on a single RB. A typical scenario
   is that CE1 is connected to RB1 & RB2 by mc-lag1 while CE2 is
   connected to RB1 & RB2 by mc-lag 2. In order to conserve the number
   of pseudo-nickname used, member ports for both mc-lag1 and mc-lag2
   on RB1 & RB2 are all associated to pseudo-nickname pn1.

5. Local forwarding behavior on ingress RBridge

   When a ingress RBridge(RB1) receives BUM traffic from an active-
   active accessing CE(CE1) device, the traffic will be injected to
   TRILL campus through TRILL encapsulation, and it will be replicated
   and forwarded to all destination RBs which include ingress RB itself
   along a TRILL distribution tree. So the traffic will return to the
   ingress RBridge. To avoid the traffic looping back to original
   sender CE, ingress nickname can be used for traffic filtering.

   If there are two local connecting CE(CE1 and CE2) devices on ingress
   RB, the BUM traffic between these two CEs can't be forwarded locally
   and through TRILL campus simultaneously, otherwise duplicated
   traffic will be received by destination CE. Local forwarding
   behavior on ingress RBridge should be carefully designed.

   To avoid duplicated traffic on receiver CE, local replication
   behavior on RB1 is as follows:

   1. Local replication to the ports associated with the same pseudo-
   nickname as that associated to the incoming port.

   2. Do not replicate to mc-lag port associated with different pseudo-
   nickname.

   3. Do not replicate to non mc-lag ports.

   The above local forwarding behavior on the ingress RB of RB1 can be
   called centralized local forwarding behavior A.

   If ingress RB of RB1 itself is the centralized node, BUM traffic
   injected to TRILL campus won't loop back to RB1. In this case, the


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   local forwarding behavior is called centralized local forwarding
   behavior B. The local replication behavior on RB1 is as follows:

   1. Local replication to the ports associated with the same pseudo-
   nickname as that associated to the incoming port.

   2. Local replication to the mc-lag DF port associated with different
   pseudo-nickname. Do not replicate to mc-lag non-DF port associated
   with different pseudo-nickname.

   3. Local replication to non mc-lag ports.

6. Loop prevention among RBridges in a edge group

   If a CE sends a broadcast, unknown unicast, or multicast (BUM)
   packet through DF port to a ingress RB, it will forward that packet
   to all or subset of the other RBs that only have non-DF ports for
   that MC-LAG. Because BUM traffic forwarding to non-DF port isn't
   allowed, in this case the frame won't loop back to the CE.

   If a CE sends a BUM packet through non-DF port to a ingress RB, say
   RB1, then RB1 will forward that packet to other RBridges that have
   DF port for that MC-LAG. In this case the frame will loop back to
   the CE and traffic split-horizon filtering mechanism should be used
   to avoid looping back among RBridges in a edge group.

   Split-horizon mechanism relies on ingress nickname to check if a
   packet's egress port belongs to a same MC-LAG with the packet's
   incoming port to TRILL campus.

   When the ingress RBridge receives BUM traffic from an active-active
   accessing CE device, the traffic will be injected to TRILL campus
   through TRILL encapsulation, and it will be replicated and forwarded
   to all destination RBs which include ingress RB itself through TRILL
   distribution tree. If same pseudo-nickname is used for two active-
   active access CEs as ingress nickname, egress RB can use the
   nickname to filter traffic forwarding to all local CE. In this case,
   the traffic between these two CEs goes through local RB and another
   copy of the traffic from TRILL campus is filtered. If different
   ingress nickname is used for two connecting CE devices, the access
   ports connecting to these two CEs should be isolated with each other.
   The BUM traffic between these two CEs should go through TRILL campus,
   otherwise the destination CE connected to same RB with the sender CE
   will receive two copies of the traffic.

   Do note that the above sections on techniques to avoid frame
   duplication, loop prevention is applicable assuming the Link


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   aggregation technology in use is unaware of the frame duplication
   happening. For example using mechanisms like IEEE802.1AX,
   Distributed Resilient Network Interconnect (DRNI) specs implements
   mechanism similar to DF and also avoids some cases of frame
   duplication & looping.

7. Centralized replication forwarding process

                                   +-----------+
                                   |   (RB5)   |
                                   +-----------+
                                         |
                                   +-----------+
                                   |   (RB4)   |
                                   +-----------+

                                    |     |    |
                            --------      |     --------
                           |              |             |
                         +------+      +------+      +------+
                         |(RB1) |      |(RB2) |      | (RB3)|
                         +------+      +------+      +------+
                           *   |         *  |          * |  ^
                           *   |         *  |          * |   ^
                           *   ----------*-------------*--    ^
                           ***************************** |     ^
                   MC-LAG1 *                     MC-LAG2 |      ^
                       +------+                    +------+    +------+
                       |  CE1 |                    | CE2  |    | CE3  |
                       +------+                    +------+    +------+
                    Figure 1 TRILL Active-active access

   Assuming the centralized replication solution is used in the network
   of above figure 1, RB5 is the distribution tree root and centralized
   replication node, CE1 and CE2 are active-active accessed to RB1,RB2
   and RB3 through MC-LAG1 and MC-LAG2 respectively, CE3 is single
   homed to RB3. The RBridge's own nickname of RB1 to RB5 are nick1 to
   nick5 respectively. RB1,RB2 and RB3 use same pseudo-nickname for MC-
   LAG1 and MC-LAG2, the pseudo-nickname is P-nick. The R-nickname on
   the centralized replication node of RB5 is S-nick.

   The BUM traffic forwarding process from CE1 to CE2,CE3 is as follows:

   1. CE1 sends BUM traffic to RB3.





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   2. RB3 replicates and sends the BUM traffic to CE2 locally. RB2 also
      sends the traffic to RB5 through unicast TRILL encapsulation.
      Ingress nickname is set as P-nick, egress nickname is set as S-
      nick.

   3. RB5 decapsulates the unicast TRILL packet. Then it uses the
      distribution tree whose root is RB5 to forward the packet. The
      egress nickname in the trill header is the nick5. Ingress
      nickname is still P-nick.

   4. RB4 receives multicast TRILL traffic from RB5. Traffic incoming
      port is the up port facing to distribution tree root, RPF check
      will be correct based on the changed RPF port calculation
      algorithm in this document. After RPF check is performed, it
      forwards the traffic to all other egress RBs(RB1,RB2 and RB3).

   5. RB3 receives multicast TRILL traffic from RB4. It decapsulates
      the multicast TRILL packet. Because ingress nickname of P-nick is
      equivalent to the nickname of local MC-LAGs connecting CE1 and
      CE2, it doesn't forward the traffic to CE1 and CE2 to avoid
      duplicated frame. RB3 only forwards the packet to CE3.

   6. RB1 and RB2 receive multicast TRILL traffic from RB4. The
      forwarding process is similar to the process on RB3, i.e, because
      ingress nickname of P-nick is equivalent to the nickname of local
      MC-LAGs connecting CE1 and CE2, they also don't forward the
      traffic to local CE1 and CE2.

8. BUM traffic loadbalancing among multiple centralized nodes

   To support unicast TRILL encapsulation BUM traffic load balancing,
   multiple centralized replication node can be deployed and the
   traffic can be load balanced on these nodes in vlan-based.

   Assuming there are k centralized nodes in TRILL campus, each
   centralized node has different R-nickname, VLAN-based(or FGL-based)
   loadbalancing algorithm used by ingress active-active access RBridge
   is as follows:

      1. All R-nicknames are ordered and numbered from 0 to k-1 in
   ascending order.

      2. For VLAN ID m, choose the R-nickname whose number equals (m
   mod k) as egress nickname for BUM traffic unicast TRILL
   encapsulation.




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   For examples, there are 3 centralized nodes (CN) which has one R-
   nickname respectively, the CN nodes will be ordered based on the
   ordering algorithm for each R-nickname from CN0 to CN2. Assuming
   there are 5 VLANs from 1 to 5 spreading among edge RBridges, the
   traffic in VLAN 1 will go to CN1, VLAN 2 will go to CN2, and so on.

   When an ingress RBridge participating active-active connection
   receives BUM traffic from local CE, the RB decides to send the
   traffic to which centralized node based on the VLAN-based
   loadbalancing algorithm, vlan-based loadbalancing for the BUM
   traffic can be achieved among multiple centralized nodes.

9. Co-existing with CMT solution

                    +------+    +------+
                    |(RB6) |    |(RB7) |
                    +------+    +------+
      ------------------|-----------|----------------------
      |            |              |          |            |
   +------+    +------+       +------+    +------+     +------+
   |(RB1) |    |(RB2) |       |(RB3) |    |(RB4) |     |(RB5) |
   +------+    +------+       +------+    +------+     +------+
       |          |               |          |            |
       ------------               -------------------------
             |                               |
         +------+                         +------+
         |  CE1 |                         |  CE2 |
         +------+                         +------+
       Figure 2 CMT and centralized replication co-existing scenario

   Both the centralized replication solution and CMT solution rely on
   pseudo-nickname concept to avoid MAC flip-flop on remote RBridges,
   these two solutions can co-exist in single TRILL network. Each
   solution can be selected by each edge group RBridges independently.
   As illustrated in figure 2, RB1 and RB2 use CMT for CE1's active-
   active access, RB3,RB4 and RB5 use the centralized replication for
   CE2's active-active access.

   For the centralized replication solution, edge group RBridges should
   announce local pseudo-nickname using Nickname Flags APPsub-TLV with
   C-flag, the nickname with C-flag is called "C-nickname". A transit
   RBridge will perform the centralized replication specific RPF check
   algorithm if it receives TRILL encapsulation traffic with C-nickname
   as ingress nickname.





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10. Network Migration Analysis

   Centralized nodes need software and hardware upgrade to support
   centralized replication process, which stitches TRILL unicast
   traffic decapsulation process and the process of normal TRILL
   multicast traffic forwarding along distribution tree.

   Active-active connection edge RBs need software and hardware upgrade
   to support unicast TRILL encapsulation for BUM traffic, the process
   is similar to normal head-end replication process.

   Transit nodes need software upgrade to support RPF port calculation
   algorithm change.

11. TRILL protocol extension

   Two Flags of "R" and "C" in Nickname Flags APPsub-TLV [RFC7180bis]
   are introduced, the nickname with "R" flag is called R-nickname, the
   nickname with "C" flag is called C-nickname. R-nickname is a
   specialized nickname attached on a centralized node to differentiate
   unicast TRILL encapsulation BUM traffic from normal unicast TRILL
   traffic. C-nickname is set on each edge group RBridge, C-nickname is
   a specialized pseudo-nickname for transit RBridges to perform
   different RPF check algorithm.

   When active-active edge RBridges use centralized replication to
   forward BUM traffic, the R-nickname is used as the egress nickname
   and the C-nickname is used as ingress nickname in TRILL header for
   unicast TRILL encapsulation of BUM traffic.

11.1. "R" and "C" Flag in Nickname Flags APPsub-TLV

            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
            |   Nickname                                    |
            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
            |IN|SE|R | C|    RESV                           |
            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                            NICKFLAG RECORD

         o R. If R flag is one, it indicates that the advertising TRILL
   switch is a centralized replication node, and the nickname is used
   as egress nickname for edge group RBridges to inject traffic to
   TRILL campus when the edge group RBridges use centralized
   replication solution for active-active access. If flag is zero, that
   nickname will not be used for that purpose.




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         o C. If C flag is one, it indicates that the TRILL traffic
   with this nickname as ingress nickname requires special RPF check
   algorithm. If flag is zero, that nickname will not be used for that
   purpose.

12. Security Considerations

   This draft does not introduce any extra security risks. For general
   TRILL Security Considerations, see [RFC6325].

13. IANA Considerations

   This document requires no IANA Actions. RFC Editor: Please remove
   this section before publication.

14. References

14.1. Normative References

   [1]  [RFC6165]  Banerjee, A. and D. Ward, "Extensions to IS-IS for
         Layer-2 Systems", RFC 6165, April 2011.

   [2]  [RFC6325] Perlman, R., et.al. "RBridge: Base Protocol
         Specification", RFC 6325, July 2011.

   [3]  [RFC6326bis] Eastlake, D., Banerjee, A., Dutt, D., Perlman, R.,
         and A. Ghanwani, "TRILL Use of IS-IS", draft-eastlake-isis-
         rfc6326bis, work in progress.

   [4]  [RFC7180bis] Eastlake, D., Zhang, M., Perlman, R., Banerjee, A.
         Ghanwani and Gupta.S, "TRILL: Clarifications, Corrections, and
         Updates", draft-ietf-trill-rfc7180bis-00, work in progress.

14.2. Informative References

   [1]  [TRILLPN] Zhai,H., et.al., "RBridge: Pseduonode nickname",
         draft-hu-trill-pseudonode-nickname, Work in progress, November
         2011.

   [2]  [TRILAA] Li,Y., et.al., " Problem Statement and Goals for
         Active-Active TRILL Edge", draft-ietf-trill-active-active-
         connection-prob-00, Work in progress, July 2013.

   [3]  [CMT] Senevirathne, T., Pathangi, J., and J. Hudson,
         "Coordinated Multicast Trees (CMT)for TRILL", draft-ietf-
         trill-cmt-00.txt Work in Progress, April 2012.



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15. Acknowledgments

   The authors wish to acknowledge the important contributions of
   Hongjun Zhai, Xiaomin Wu, Liang Xia.

Authors' Addresses

   Weiguo Hao
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012
   China
   Email: haoweiguo@huawei.com

   Yizhou Li
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012
   China
   Email: liyizhou@huawei.com

   Muhammad Durrani
   Cisco
   Email: mdurrani@cisco.com

   Sujay Gupta
   IP Infusion
   RMZ Centennial
   Mahadevapura Post
   Bangalore - 560048
   India
   Email: sujay.gupta@ipinfusion.com

    Andrew Qu
   MediaTec
   Email: laodulaodu@gmail.com

   Tao Han
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012
   China
   Email: billow.han@huawei.com






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