INTERNET-DRAFT Mingui Zhang
Intended Status: Proposed Standard Huafeng Wen
Expires: April 25, 2015 Huawei
Jie Hu
China Telecom
October 22, 2014
STP Application of ICCP
draft-ietf-pwe3-iccp-stp-02.txt
Abstract
Inter-Chassis Communication Protocol (ICCP) supports the inter-
chassis redundancy mechanism which achieves high network
availability.
In this document, the PEs in a Redundant Group (RG) running ICCP are
used to offer multi-homed connectivity to Spanning Tree Protocol
(STP) networks. The ICCP TLVs for the STP application are defined,
therefore PEs from the RG can make use of these TLVs to synchronize
the state and configuration data of the STP network. The operation
logic of the application and the usage of these ICCP TLVs are
specified.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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Copyright and License Notice
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Copyright (c) 2014 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
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Conventions used in this document . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2. The Use Case Scenario . . . . . . . . . . . . . . . . . . . . . 4
2.1. STP as an Application of ICCP . . . . . . . . . . . . . . . 5
2.2. The BPDU Tunneling Model . . . . . . . . . . . . . . . . . 6
3. Spanning Tree Protocol Application TLVs . . . . . . . . . . . . 7
3.1. STP Connect TLV . . . . . . . . . . . . . . . . . . . . . . 7
3.2. STP Disconnect TLV . . . . . . . . . . . . . . . . . . . . 8
3.2.1. STP Disconnect Cause TLV . . . . . . . . . . . . . . . 9
3.3. STP Config TLVs . . . . . . . . . . . . . . . . . . . . . . 9
3.3.1. STP System Config . . . . . . . . . . . . . . . . . . . 10
3.3.2. STP Region Name . . . . . . . . . . . . . . . . . . . . 10
3.3.3. STP Revision Level . . . . . . . . . . . . . . . . . . 11
3.3.4. STP Instance Priority . . . . . . . . . . . . . . . . . 12
3.3.5. STP Configuration Digest . . . . . . . . . . . . . . . 12
3.4. STP State TLVs . . . . . . . . . . . . . . . . . . . . . . 13
3.4.1. STP Topology Changed Instances . . . . . . . . . . . . 13
3.4.2. STP CIST Root Time . . . . . . . . . . . . . . . . . . 14
3.4.3. STP MSTI Root Time . . . . . . . . . . . . . . . . . . 15
3.5. STP Synchronization Request TLV . . . . . . . . . . . . . . 16
3.6. STP Synchronization Data TLV . . . . . . . . . . . . . . . 17
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1. Common AC Procedures . . . . . . . . . . . . . . . . . . . 18
4.1.1. Remote PE Node Failure or Isolation . . . . . . . . . . 18
4.1.2. Local PE Isolation . . . . . . . . . . . . . . . . . . 18
4.2. STP Application Procedures . . . . . . . . . . . . . . . . 18
4.2.1. Initial Setup . . . . . . . . . . . . . . . . . . . . . 19
4.2.2. Configuration Synchronization . . . . . . . . . . . . . 19
4.2.3. Status Synchronization . . . . . . . . . . . . . . . . 20
4.2.4. Failure and Recovery . . . . . . . . . . . . . . . . . 21
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 22
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6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 22
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 22
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1. Normative References . . . . . . . . . . . . . . . . . . . 22
7.2. Informative References . . . . . . . . . . . . . . . . . . 23
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
Inter-Chassis Communication Protocol (ICCP [RFC7257]) specifies a
multi-chassis redundant mechanism, which enables PEs located in
multi-chassis to act as a single Redundant Group (RG).
This document introduces Spanning Tree Protocol (STP) as a new
application of ICCP. When a bridge network running STP is connected
to an RG, the RG members pretend to be a single root bridge to
participate the operations of the STP. STP relevant information need
be exchanged and synchronized among the RG members. ICCP TLVs for the
STP application are specified for this purpose.
From the point of view of the customers, ISPs are still providing
Virtual Private LAN Service (VPLS). Familiarity with [RFC4762] is
assumed in this document.
1.1. 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].
1.2. Terminology
ICCP: Inter-Chassis Communication Protocol
VPLS: Virtual Private LAN Service
STP: Spanning Tree Protocol
MSTP: Multiple Spanning Tree Protocol
DSLAM: Digital Subscriber Line Access Multiplexer
MST: Multiple Spanning Trees
CIST: Common and Internal Spanning Tree
MSTI: Multiple Spanning Tree Instance
BPDU: Bridge Protocol Data Unit
In this document, unless otherwise explicitly noted, when the term
STP is used, it also covers MSTP.
2. The Use Case Scenario
In customers' broadband networks, bridged DSLAMs are usually
geographically dispersed. ISPs provides these customers with VPLS.
It's common that one customer broadband network has multiple DSLAMs
connected to a carrier's network at different locations for the sake
of reliability. Requirements from customers for this use case are
listed as follows.
o These DSLAMs are running STP.
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o These DSLAMs are not geographically close to each other. Multiple
DSLAMs are connected to the carrier network at different
locations.
o When one connection to the carrier network fails, customers wish a
connection in another location can continue to work after the re-
convergence of the STP rather than compromising the whole STP
network. The failure of the connection may be due to the failure
of the PE, the AC or even the CE (a DSLAM) itself.
o Customers want to balance the load among those connections to the
carrier's network, therefore all those connections need be
active.
In order to meet these requirements, the 'ICCP-STP' model is proposed
in Section 2.1. It introduces STP as a new application of ICCP. In
Section 2.2, a counter-part solution based on the BPDU tunneling
technique is addressed as a contrast. Its issues are analyzed.
2.1. STP as an Application of ICCP
+--------------+ +=============+
| | | |
| | | |
| +---+ | | +-----+|<--|--Pseudowire-->|
| +---+CE1+<6>-------<5>+ PE1 || | |
| <1> +---+ | | +-----+|<--|--Pseudowire-->|
| +-+-+ | | || |
| |CE3| | | ||ICCP |--> Towards Core
| +-+-+ | | || |
| <2> +---+ | | +-----+|<--|--Pseudowire-->|
| +---+CE2+<3>-------<4>+ PE2 || | |
| +---+ | | +-----+|<--|--Pseudowire-->|
| | | |
| Multi-homed | | Redundancy |
| STP Network | | Group |
+--------------+ +=============+
Figure 2.1: A STP network is multi-homed to an RG running ICCP.
Figure 2.1 shows an example topology of this model. With ICCP, the
whole RG will be virtualized to be a single bridge. Each RG member
has its BridgeIdentifier (the MAC address). The least significant one
is used as the BridgeIdentifier of the 'virtualized root bridge'. The
RG pretends that the ports connected to the STP network (port <4>,
<5>) are from the same root bridge. All these ports emit the
configuration BPDU with the highest root priority to trigger the
construction of the spanning tree. The link between the peering PEs
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is not visible to the STP network. In this way, the STP will always
break a loop within the multi-homed STP network. As if the whole
network is broken into separate islands that each is attached to one
PE. It forces all PEs in the RG to be active. This is different from
a generic VPLS per [RFC4762] where the root bridge resides in the
customer network and the multi-homed PEs usually act in the active-
standby mode. Note that the specification of VPLS should remain
unchanged other than this operation. For instance, a full-mesh of PWs
is established between PEs, split-horizon is still used to perform
the loop-free protection through the core, etc.
2.2. The BPDU Tunneling Model
+--------------+ +=============+
| | | |
| | | |
| +---+ | | +-----+|<--|--Pseudowire-->|
| +---+CE1+<6>-------<5>+ PE1 || | |
| <1> +---+ | | +-----+|<--|--Pseudowire-->|
| +-+-+ | | ||BUDU |
| |CE3| | | PW||tunnel|--> Towards Core
| +-+-+ | | || |
| <2> +---+ | | +-----+|<--|--Pseudowire-->|
| +---+CE2+<3>-------<4>+ PE2 || | |
| +---+ | | +-----+|<--|--Pseudowire-->|
| | | |
| Multi-homed | | Redundancy |
| STP Network | | Group |
+--------------+ +=============+
Figure 2.2: The BPDU Tunneling Model
Figure 2.2 shows an example network of the 'BPDU tunneling' model.
Two PEs tunnel customer traffic and BPDUs of the STP network over a
PW. The OAM designed in [RFC7023] can be adopted for the interworking
between MPLS and Ethernet.
In this model, the ports connected to the STP network at the PEs'
side are non-bridge ports (e.g., port <4>, <5>). The tunnel between
PE1 and PE2 is a transparent tunnel of BPDUs. For CE1 and CE2, they
regard that there is a direct link between them. Issues of this model
are listed as follows.
o Assume port <1> was blocked according to the STP calculation. Now,
suppose link CE3-CE2 fails, port <2> is blocked while port <1> is
unblocked. Since the BPDUs is just tunneled, PE2 is unaware of
this change. Consider the remote traffic from PEx to PE2 then to
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CE3. PE2 continues to send traffic to CE3 via CE2 where a black-
hole happens.
In order to handle this issue, PEs need to snoop the Topology
Change (TC) message of the STP network so the tunnel is not
"transparent" to BPDUs anymore. When the TC event is sensed, these
PEs should withdraw MAC addresses of those instances affected by
the TC event across the carrier's network.
o When port <4> fails, CE1 is unaware. Suppose CE2 is the root
bridge, port <6> has to wait for 3 STP HELLO Intervals (3*2s) and
2 Forwarding Delays (2*15s). The STP network takes at least 36
seconds to complete the convergence. The convergence process of
the STP network is greatly slowed down. This actually changes the
behavior of customers' STP networks.
In order to speed up the convergence, CE1 has to sense the state
of the link between CE2 and PE2. The interworking PEs and CEs have
to cope with various combinations of failures. There is no
standard solution yet.
Compared with this 'BPDU tunneling' model, the advantage point of the
"ICCP-STP" model is that PEs "participate" in the STP calculation,
therefore we need not design the complex interworking mechanism.
3. Spanning Tree Protocol Application TLVs
This section specifies the ICCP TLVs for the STP application.
3.1. STP Connect TLV
This TLV is included in the RG Connect message to signal the
establishment of STP application connection.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0040 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Version |A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Sub-TLVs |
~ ~
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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- U and F Bits
Both are set to 0.
- Type
set to 0x0040 for "STP Connect TLV"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- Protocol Version
The version of this particular protocol for the purposes of
ICCP. This is set to 0x0001.
- A bit
Acknowledgement Bit. Set to 1 if the sender has received a STP
Connect TLV from the recipient. Otherwise, set to 0.
- Reserved
Reserved for future use.
- Optional Sub-TLVs
There are no optional Sub-TLVs defined for this version of the
protocol.
3.2. STP Disconnect TLV
This TLV is used in an RG Disconnect Message to indicate that the
connection for the STP application is to be terminated.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0041 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Sub-TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
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- Type
set to 0x0041 for "STP Disconnect TLV"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- Optional Sub-TLVs
The only optional Sub-TLV defined for this version of the
protocol is the "STP Disconnect Cause" TLV defined next:
3.2.1. STP Disconnect Cause TLV
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x004C | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Disconnect Cause String |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x004C for "STP Disconnect Cause TLV"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- Disconnect Cause String
Variable length string specifying the reason for the disconnect.
Used for network management.
3.3. STP Config TLVs
The STP Config TLVs are sent in the RG Application Data message. When
a STP Config TLV is received by a peering RG member, it MUST
synchronize the configuration information contained in the TLV. TLVs
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specified from Section 3.3.1 through Section 3.3.5 contains such kind
of configuration information.
3.3.1. STP System Config
This TLV announces the local node's STP System Parameters to the RG
peers.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0042 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ROID |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x0042 for "STP System Config"
- Length
Length of the MAC address, which is 6 octets.
-ROID
As defined in Section 6.1.3 of [RFC7257].
- MAC Address
The MAC address of the sender. This MAC address is set to the
BridgeIdentifier of the sender, as defined in [802.1q] Section
13.23.2. The the least significant unsigned BridgeIdentifier is
used as the MAC address of the Virtual Root Bridge mentioned in
Section 2.1.
3.3.2. STP Region Name
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This TLV is used to report the Value of Region Name to other members
in the RG.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0046 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Region Name |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x0046 for "STP Region Name"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- Region Name
The Name of the MST Region.
3.3.3. STP Revision Level
This TLV is used to report the Value of Revision Level to other
members in the RG.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0047 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Revision Level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x0047 for "STP Revision Level"
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- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- Revision Level
The Revision Level as specified in [802.1q] Section 3.21;
3.3.4. STP Instance Priority
This TLV is used to report the Value of Instance Priority to other
members in the RG.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0048 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pri | InstanceID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x0048 for "STP Instance Priority"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- Pri
The Instance Priority
- InstanceID
The instance identification number of the MSTI.
3.3.5. STP Configuration Digest
This TLV is used to report the Value of STP VLAN Instance Mapping to
other members in the RG.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0049 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Configuration Digest |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x0049 for "STP Configuration Digest"
- Length
Length of the STP Configuration Digest which is 16 octets.
- Configuration Digest
As specified in [802.1q] Section 13.7.
3.4. STP State TLVs
The STP State TLVs are sent in the RG Application Data message. They
are used by a PE to report its STP status to other members in the RG.
Such TLVs are specified in the following subsections.
3.4.1. STP Topology Changed Instances
This TLV is used to report the Topology Changed Instances to other
members in the RG. The receiver RG member SHOULD enforce the Topology
Change event, including sending a BPDU with the Topology Change flag
set to 1 out of the designated port(s) connected to the STP network,
the flushing out of MAC addresses relevant to the instances listed in
this TLV, etc.
If the PE supports the MAC Address Withdrawal (see Section 6.2 of
[RFC4762]), it SHOULD send an LDP Address Withdraw Message with the
list of MAC addresses to be removed to all remote peering PEs over
the corresponding LDP sessions. It's unnecessary to send such a
message to PEs in the same RG since the flushing of their MAC address
tables should have been performed upon the STP Topology Changed
Instances TLV is received.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0043 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| InstanceID List |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x0043 for "STP Topology Changed Instances"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- InstanceID List
The list of the instances whose topology is changed as indicated
by the Topology Change Notification (TCN) Messages as specified
in [802.1q] Section 13.14.
3.4.2. STP CIST Root Time
This TLV is used to report the Value of CIST Root Time to other
members in the RG.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0044 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MaxAge | MessageAge | FwdDelay | HelloTime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RemainingHops |
+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
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set to 0x0044 for "STP CIST Root Time"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- MaxAge
The Maximum Age of this TLV.
- MessageAge
The actual age of this TLV.
- FwdDelay
The delay before the port enters the forwarding status.
- HelloTime
The interval between two continuous configuration BPDUs.
- RemainingHops
The remaining hops of this TLV
3.4.3. STP MSTI Root Time
This TLV is used to report the Value of MSTI Root Time to other
members in the RG.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x0045 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| InstanceID | RemainingHops |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x0045 for "STP MSTI Root Time"
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- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- InstanceID
The instance identification number of the MSTI.
- remainingHops
The remaining hops of this TLV
3.5. STP Synchronization Request TLV
The STP Synchronization Request TLV is used in the RG Application
Data message. This TLV is used by a device to request from its peer
to re-transmit configuration or operational state. The following
information can be requested:
- system configuration and/or state
- configuration and/or state for a specific port
The format of the TLV is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x004A | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request Number | Request Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x004A for "STP Synchronization Request TLV"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
- Request Number
2 octets. Unsigned integer uniquely identifying the request.
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Used to match the request with a response. The value of 0 is
reserved for unsolicited synchronization, and MUST NOT be used
in the STP Synchronization Request TLV.
- Request Type
14-bits specifying the request type, encoded as follows:
0x00 Request Configuration Data
0x01 Request State Data
0x3FFF Request All Data
3.6. STP Synchronization Data TLV
The STP Synchronization Data TLV is used in the RG Application Data
message. A pair of these TLVs is used by a device to delimit a set of
TLVs that are being transmitted in response to an STP Synchronization
Request TLV. The delimiting TLVs signal the start and end of the
synchronization data, and associate the response with its
corresponding request via the 'Request Number' field.
The STP Synchronization Data TLVs are also used for unsolicited
advertisements of complete STP configuration and operational state
data. The 'Request Number' field MUST be set to 0 in this case.
This TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type=0x004B | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request Number | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- U and F Bits
Both are set to 0.
- Type
set to 0x004B for "STP Synchronization Data TLV"
- Length
Length of the TLV in octets excluding the U-bit, F-bit, Type,
and Length fields.
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- Request Number
2 octets. Unsigned integer identifying the Request Number from
the "STP Synchronization Request TLV" which solicited this
synchronization data response.
- Flags
2 octets, response flags encoded as follows:
0x00 Synchronization Data Start
0x01 Synchronization Data End
4. Operations
Operation procedures for AC redundancy applications have been
specified in Section 9.2 of [RFC7257]. As an AC redundancy
application, the operation procedures of the STP application should
follow most of these procedures except the changes presented in this
section.
4.1. Common AC Procedures
For the generic procedures of AC redundancy applications defined in
Section 9.2.1 of [RFC7257], the following changes are introduced.
4.1.1. Remote PE Node Failure or Isolation
When a PE node detects that a remote PE that is a member of the same
RG is no longer reachable (using the mechanisms described in Section
5 of [RFC7257]), the local PE determines if it has redundant ACs for
the affected services. If the local PE has the highest priority
(after the failed PE), then it becomes the virtual root bridge.
4.1.2. Local PE Isolation
When a PE node detects that it has been isolated from the core
network (i.e., all core-facing interfaces/links are not operational),
then it should ensure that its AC redundancy mechanism will change
the status of any active ACs to standby. The AC redundancy
application SHOULD then send ICCP "Application Data" messages in
order to trigger failover to another active PE in the RG. Note that
this works only in the case of dedicated interconnect (Sections 3.2.1
and 3.2.3), since ICCP will still have a path to the peer, even
though the PE is isolated from the MPLS core network.
4.2. STP Application Procedures
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This section defines the procedures that are specific to the STP
application, which is applicable for Ethernet ACs.
4.2.1. Initial Setup
When an RG is configured on a system to support the STP application,
the system MUST send an "RG Connect" message with "STP Connect TLV"
to each PE that is member of the same RG. The sending PE MUST set the
A bit to 1 in the said TLV if it has received a corresponding "STP
Connect TLV" from its peer PE; otherwise, the sending PE MUST set the
A bit to 0. If a PE receives an "STP Connect TLV" from its peer after
sending the said TLV with the A bit set to 0, it MUST resend the TLV
with the A bit set to 1. A system considers the STP application
connection to be operational when it has sent and received "STP
Connect TLVs" with the A bit set to 1. When the STP application
connection between a pair of PEs is operational, the two devices can
start exchanging "RG Application Data" messages for the STP
application. This involves having each PE advertise its STP
configuration and operational state in an unsolicited manner. A PE
SHOULD subscribe to the following order when advertising its STP
state upon initial application connection setup:
- Advertise system configuration TLV
- Advertise remaining configuration TLVs
- Advertise state TLVs
A PE MUST use a pair of "STP Synchronization Data TLVs" to delimit
the entire set of TLVs that are being sent as part of this
unsolicited advertisement.
If a system receives an "RG Connect" message with "STP Connect TLV"
that has a differing Protocol Version, it MUST follow the procedures
outlined in the "Application Versioning" Section of [RFC7257].
After the STP application connection has been established, every PE
MUST communicate its system level configuration to its peers via the
use of "STP System Config TLV".
When the STP application is disabled on the device, or is
unconfigured for the RG in question, the system MUST send an "RG
Disconnect" message with "STP Disconnect TLV".
4.2.2. Configuration Synchronization
A system that support the STP application MUST synchronize the
configuration with other RG members. This is achieved via the use of
"STP Config TLVs". The PEs in an RG MUST all agree on the MAC address
to be associated with the virtual root bridge. It is possible to
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achieve this via consistent configuration on member PEs. However, in
order to protect against possible misconfiguration, a system MUST
use, for the virtual root bridge, the MAC address supplied by the PE
with the numerically least significant BridgeIdentifier (i.e., the
MAC address of the bridge) in the RG.
Furthermore, for a given STP application, an implementation MUST
advertise the configuration prior to advertising its state. If a PE
receives any STP State TLV that it had not learned of before via an
appropriate STP Config TLV, then the PE MUST request synchronization
of the configuration and state from its respective peer. If during a
synchronization, a PE receives a State TLV that it has not learned of
before, then the PE MUST send a NAK TLV for the offending TLV. The PE
MUST NOT request re-synchronization in this case.
4.2.3. Status Synchronization
PEs within an RG need to synchronize their state-machines for proper
STP operation. This is achieved by having each system advertise its
running state in STP State TLVs. Whenever any STP parameter, whether
on the CE or PE side, is changed a system MUST transmit an updated
TLV. Moreover, when the administrative or operational state changes,
the system MUST transmit an updated state TLV to its peers.
A PE MAY request that its peer retransmit previously advertised
state. This is useful for example when the PE is recovering from a
soft failure and attempting to relearn state. To request such
retransmissions, a PE MUST send a set of one or more "STP
Synchronization Request TLVs".
A PE MUST respond to a "STP Synchronization Request TLV" by sending
the requested data in a set of one or more STP configuration or state
TLVs delimited by a pair of "STP Synchronization Data TLVs". The TLVs
comprising the response MUST be ordered in the RG Application Data
message(s) such that the Synchronization Response TLV with the
"Synchronization Data Start" flag precedes the various other STP
configuration of state TLVs encoding the requested data. These, in
turn, MUST precede the Synchronization Data TLV with the
"Synchronization Data End" flag.
Note that the response may span across multiple RG Application Data
messages, for example when MTU limits are exceeded; however, the
above ordering MUST be retained across messages, and only a single
pair of Synchronization Data TLVs MUST be used to delimit the
response across all Application Data Messages.
A PE device MAY re-advertise its STP state in an unsolicited manner.
This is done by sending the appropriate Config and State TLVs
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delimited by a pair of "STP Synchronization Data TLVs" and using a
'Request Number' of 0.
While a PE has a pending synchronization request for a system, it
SHOULD silently ignore all TLVs for said system, that are received
prior to the synchronization response and which carry the same type
of information being requested. This saves the system from the
burden of updating state that will ultimately be overwritten by the
synchronization response. Note that TLVs pertaining to other systems,
are to continue to be processed per normal in this case.
If a PE receives a synchronization request that doesn't exist or is
not known to the PE, then it MUST trigger an unsolicited
synchronization of all system information (i.e. replay the
initialization sequence).
If a PE learns, as part of a synchronization operation from its peer,
that the latter is advertising a Node ID value which is different
from the value previously advertised, then the PE MUST purge all
state data previously learnt from that peer prior to the last
synchronization.
4.2.4. Failure and Recovery
When a PE that is active for a STP application encounters a core
isolation fault [RFC7257], it SHOULD attempt to fail-over to a peer
PE which hosts the same RO. The default fail-over procedure is to
have the failed PE bring down the link(s) towards the multi-homed STP
network (e.g. by bringing down the line-protocol). This will cause
the STP network reconverges and uses the other links that are
connected to the other PE(s) in the RG. Other procedures for
triggering fail-over are possible, and are outside the scope of this
document.
If the isolated PE is the one that has the lowest BridgeIdentifier,
PEs in the RG MUST synchronize STP configuration and state TLVs and
determine a new virtual root bridge as specified in Section 4.2.2
(i.e., the PE with the least significant BridgeIdentifier will become
the virtual root bridge.).
Upon recovery from a previous fault, a PE MAY reclaim the role of the
virtual root for the STP network if it has the lowest
BridgeIdentifier among the RG. PEs in the RG MUST synchronize the STP
configuration and state TLVs.
Whenever the virtual root bridge changes, the STP Topology Changed
Instances TLV lists the instances that are affected by the change.
These instances MUST undergo a STP reconvergence procedure when this
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TLV is received as defined in Section 3.4.1.
5. Security Considerations
This document specifies an application running on the channel
provided by ICCP. See security considerations of [RFC7257].
6. IANA Considerations
The ICC RG parameter types used by the application TLVs defined in
Section 3 of this document should be assigned. ICC RG parameter types
are 14-bit values. Parameter Type values 1 through 0x003A are
specified in [RFC7257]. This document adds the specification of
values 0x003B through 0x004C. Parameter Type values 0x004D through
0x1FFF are to be assigned by IANA, using the "Expert Review" policy
defined in [RFC5226]. Suggested parameter type space value
allocations for the STP application are specified below:
Parameter Type Description
-------------- ---------------------------------
0x003B-0x003F Reserved
0x0040 STP Connect TLV
0x0041 STP Disconnect TLV
0x0042 STP System Config TLV
0x0043 STP Region Name TLV
0x0044 STP Revision Level TLV
0x0045 STP Instance Priority TLV
0x0046 STP Configuration Digest TLV
0x0047 STP Topology Changed Instances TLV
0x0048 STP STP CIST Root Time TLV
0x0049 STP MSTI Root Time TLV
0x004A STP Synchronization Request TLV
0x004B STP Synchronization Data TLV
0x004C STP Disconnect Cause TLV
Acknowledgements
Authors would like to thank the comments and suggestions from Gregory
Mirsky and Alexander Vainshtein.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private
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LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, January 2007.
[RFC7257] L. Martini, S. Salam, et al, "Inter-Chassis Communication
Protocol for L2VPN PE Redundancy", draft-ietf-pwe3-iccp-16.txt,
in RFC Ed Queue.
[802.1q] "IEEE Standard for Local and Metropolitan Area Networks---
Virtual Bridged Local Area Networks.". IEEE Std 802.1 Q-2005,
May 19, 2006.
7.2. Informative References
[RFC7023] D. Mohan, Ed., N. Bitar, Ed., A. Sajassi, Ed., S. DeLord,
P. Niger, R. Qiu., "MPLS and Ethernet Operations,
Administration, and Maintenance (OAM) Interworking", RFC 7023,
October 2013.
[RFC6310] Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations,
Administration, and Maintenance (OAM) Message Mapping", RFC
6310, July 2011.
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Author's Addresses
Mingui Zhang
Huawei Technologies
No. 156 Beiqing Rd. Haidian District,
Beijing 100095
P.R. China
EMail: zhangmingui@huawei.com
Huafeng Wen
Huawei Technologies
101 Software Avenue,
Nanjing 210012
P.R. China
EMail: wenhuafeng@huawei.com
Jie Hu
China Telecom
EMail: hujie@ctbri.com.cn
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