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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