Документ взят из кэша поисковой машины. Адрес оригинального документа : http://mirror.msu.net/pub/rfc-editor/internet-drafts/draft-hao-bier-active-active-00.txt Дата изменения: Mon Jan 11 06:53:07 2016 Дата индексирования: Sun Apr 10 07:12:18 2016 Кодировка: Поисковые слова: horizon

BIER Working Group W. Hao
INTERNET-DRAFT Y. Li
S. Zhuang
Intended Status: Standard Track Huawei
Expires: July 11, 2016 January 11, 2016



BIER Split-horizon mechanism for active-active access
draft-hao-bier-active-active-00.txt

Abstract

This document proposes a BIER split-horizon mechanism for active-
active access. Both data plane and control plane extension are
included.

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Table of Contents


1. Introduction ................................................ 2
2. Conventions used in this document............................ 4
3. Solution overview ........................................... 4
4. Data plane format ........................................... 5
5. Discovery of Multi-homing BFRs............................... 5
5.1. IS-IS extension......................................... 6
5.2. OSPF extension ......................................... 6
6. Security Considerations...................................... 7
7. Normative References......................................... 7
Acknowledgments ................................................ 7
Authors' Addresses ............................................. 7

1. Introduction

Bit Index Explicit Replication (BIER) ([BIER-ARCH]) is an
architecture that provides optimal multicast forwarding through a
"multicast domain", without requiring intermediate routers to
maintain any per-flow state. BIER doesn't engage in any explicit
tree-building protocols, it can be thought of implicitly created
P2MP tunnels from each "Bit Forwarding Ingress Router" (BFIR) to all
the "Bit Forwarding Egress Routers" (BFERs) in the BIER domain. BIER
is potentially applicable to many services where Multicast is used,
especially as P-Tunnel for MVPN, EVPN, etc.
+------+
| CE4 |
+------+
|
+-----------+
| BFR4 |
+-----------+

| | |
-------- | --------
| | |
+------+ +------+ +------+
| BFR1 | | BFR2 | | BFR3 |
+------+ +------+ +------+
* | * | * | ^
* | * | * | ^


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* ----------*-------------*-- ^
***************************** | ^
MC-LAG1 * MC-LAG2 | ^
+------+ +------+ +------+
| CE1 | | CE2 | | CE3 |
+------+ +------+ +------+
Figure 1 BIER Active-active access

As illustrated in figure 1, to provide redundant connectivity, a CE
is normally connected to multiple BFRs through an Ethernet Link
Aggregation Group with LACP [802.1AX], the CE can be a multicast
source or receiver. The BFRs offering multi-homing is called Active-
Active BFR (AABFR) group. In Active-Active case, the following two
problems for multicast packet forwarding should be solved:



1.Duplicated delivery of flooding traffic

The issue occurs on the multi-homed BFERs connecting to one or more
multicast receivers. If more than one BRER out of the AABFR group
egress a copy of a multicast packet from BIER domain, the Multicast
receiver will see packet duplication. Therefore, it is REQUIRED that
a unique BFER is appointed as the multicast egress BFR. This unique
multicast egress NVE can be appointed according to a unanimous
agreed designated forwarder (DF) election algorithm by all BRRs in a
AABFR group. The election algorithm should be used to ensure service
carving balance among different BFRs in a redundant group, the
service carving factor can be based on VPN instance, multicast group,
access VLAN, etc, so it is carried service dependant rather than
service agnostic. The DF election process defined in [EVPN] is an
example for DF PE determination.



2.Loop & Echo Forwarding among multi-homed PEs.

The issue occurs on the multi-homed BFIRs connecting to one or more
multicast sources. Assuming a multicast source S1 is multi-homed to
BFIR1 and BFIR2 using an Ethernet Link Aggregation Group with LACP
[802.1AX], when S1 sends a multicast packet to BFIR1, the BFIR1 will
inject the packet to BIER domain and the packet will be received by
BFIR2 from the BIER domain, then BFIR2 will perform BIER
decapsulation and send the packet to S1 again. Split-horizon
filtering mechanism should be used to prevent the loop between BFIR1
and BFIR2. The split-horizon mechanism relies on the packet from
ingress device carrying origin identification to identify the
segment from which the frame entered the BIER network, the egress


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device performs filtering function based on the origin
identification. The split-horizon mechanism should be service
agnostic and should be maintained in transport layer, i.e, BIER
should provide the Split-horizon capability.

In summary, BIER as a transport layer technology, it should provide
split-horizon capability for active-active access and can be shared
by all multicast services. As for DF election mechanism, it should
be provided in each multicast service. This document will define the
data plane and control plane extension respectively for BIER split-
horizon mechanism.

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 terms and acronyms in [RFC6325] are used with the following
additions:

o Ethernet Segment (ES): When a customer site (device or network)
is connected to one or more PEs via a set of Ethernet links, then
that set of links is referred to as an 'Ethernet segment'.

o Ethernet Segment Identifier (ESI): A unique non-zero
identifier that identifies an Ethernet segment is called an
'Ethernet Segment Identifier'.

o MVPN: Multicast Virtual Private Network -- a VPN [RFC4364] in
which multicast service is offered.

o P-tunnel. A multicast tunnel through the network of one or
more SPs. P-tunnels are used to transport MVPN multicast data.

3. Solution overview

Every BFR track the BFID(es) associated with the other BFR(s) with
which it has shared multi-homed Ethernet Segments. When the BFIR
receives a multi-destination frame from the BEIR domain, it examines
the source BFID in the BIER header (which corresponds to the BFIR)
and filters out the frame on all local interfaces connected to
Ethernet Segments that are shared with the ingress BFR.

Each BFIR performs replication locally to all directly attached
Ethernet Segments for all flooded traffic ingress from the access



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interfaces (i.e. from the multicast source). This approach is
referred to as "Local Bias".

4. Data plane format

In [BIER-MPLS], the BIER header format is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 0 1| Ver | Len | Entropy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (first 32 bits) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ BitString (last 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|OAM| Reserved | Proto | BFIR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BIER Header

BFIR-id field is the BFR-id of the BFIR, it can be used for split-
horizon filtering.

5. Discovery of Multi-homing BFRs

Each Ethernet segment is assigned a global ESI as Ethernet segment
identification. The ESI can be manually configured or automatically
derived.

A couple of different mechanisms are available to derive the ESI
automatically, such as snooping LACP packets or LLDP packets. Once
the ESI for an Ethernet segment is assigned for a multi-homed CE, it
is advertised by the BFRs through IS-IS or OSPF extension.

The following two ESI values are reserved:

- ESI 0 denotes a single-homed site.

- ESI {0xFF} (repeated 10 times) is known as MAX-ESI and is
reserved.

In general, an Ethernet segment SHOULD have a non-reserved ESI
that is unique network wide (i.e., across all EVPN instances on all
the PEs).





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5.1. IS-IS extension

BIER Info sub-TLV (Section 6.1 [BIER-ISIS])carries the information
for the BIER sub-domains that the router participates in as BFR. A
newly defined BIER ESI sub-sub-TLV carries the information of local
ESIs and is carried within the BIER Info sub-TLV that the router
participates in as BFR. The BIER ESI sub-sub-TLV format is as
follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type(1 octet) |Length(1 octet)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ethernet Segment Identifier (1) (10 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ethernet Segment Identifiern (N) (10 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Type: TBD

Length: 1 byte

Ethernet Segment Identifier: It is encoded as a 10-octet integer in
line format with the most significant octet sent first.



5.2. OSPF extension

BIER ESI Sub-TLV is a sub-TLV of the BIER Sub-TLV [BIER-OSPF].
BIER ESI Sub-TLV is used in order to advertise local connecting ESI
used for BIER. The BIER ESI sub-TLV format is as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type(2 octet) |Length(2 octet)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ethernet Segment Identifier (1) (10 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ethernet Segment Identifiern (N) (10 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: TBD

Length: 1 byte

Ethernet Segment Identifier: It is encoded as a 10-octet integer in
line format with the most significant octet sent first.


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6. Security Considerations

Implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors which cause hard protocol
failures.

7. Normative References

1. [BIER-ARCH] Wijnands et al., IJ., "Stateless Multicast using
Bit Index Explicit Replication Architecture", internet-draft
draft-ietf-bier-architecture-02.txt, July 2015.

2. [BIER-MPLS] Wijnands et al., IJ., "Bit Index Explicit
Replication using MPLS encapsulation", internet-draft draft-
ietf-bier-mpls-encapsulation-02.txt, Aug 2015.

3. [BIER-OSPF] Psenak et al., P., "OSPF Extensions For BIER",
internet-draft draft-ietf-bier-ospf-bier-extensions-01.txt,
October 2015.

4. [BIER-ISIS] L. Ginsberg et al.,"BIER support via ISIS",
internet-draft draft-ietf-bier-isis-extensions-01.txt, October
2015.

5. [EVPN] A. Sajassi et al., "BGP MPLS-Based Ethernet VPN",
RFC7432, February 2015.

Acknowledgments

The authors wish to acknowledge the important contributions of
Eric Wu.

Authors' Addresses

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









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

Shunwan Zhuang
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: zhuangshunwan@huawei.com



































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