MPLS Working Group Liwen Wu
Internet Draft Pierrick Cheval
Expiration Date: August 1999 Christophe Boscher
Alcatel USA
Eric Gray
Lucent
Februray 1999
LDP State Machine
draft-ietf-mpls-ldp-state-00.txt
0. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
1. Abstract
In the current LDP draft [Ref5], there is no state machine specified
for processing the LDP messages. We think that defining a common
state machine is very important for interoperability between
different ldp implementations.
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This draft provides state machine tables for ATM switch LSRs. We
begin in section 2 by defining a list of terminologies. Then in
section 3, we propose two sets of state machine tables for ATM switch
LSRs, one for non-vc merge ATM LSRs and one for the vc merge ATM
LSRs. Finally, in section 4, we outline the possible future working
items.
Even though the state machines in this document are specific for
ATM-LSR, they can be easily adapted for other types of LSRs.
2. Terminologies
- LDP-REQUEST: LDP Label Request message
- LDP-MAPPING: LDP Label Mapping message
- LDP-WITHDRAW: LDP Label Withdraw message
- LDP-RELEASE: LDP Label Release message
- LDP-NAK: It is a LDP notifications which is used to abort a LSP
setup or reject a LSP Label Request message.
3. State Machine
This draft focuses on the LDP state machines and the associated
control blocks. It does not describe the "LDP controller" which is
in charge of LDP session initialization, address mapping messages
management, routing interface, etc.
In this draft, we provide two sets of state machines: one for the ATM
LSR which does not have VC-merge capability, and the other one for
the ATM LSR which does have VC-merge capability.
The state machines cover both independent LSP control and ordered LSP
control.
The loop detection and loop prevention message will be processed in
the way as specified in [Ref5]. The impact of loop detection and loop
prevention messages on a state transition is left for further study.
3.0 An LSR's Behavior in the Case of a Next Hop Change
When there is a topology change and an LSR detects a new better next
hop for an LSP, it may behave in 2 different ways:
1) It tries to do a "local repair". This means that it extends the
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LSP through the new next hop, releases the old path from this LSR
forward and then splices into this newly extended LSP.
2) If the LSP is created with the "pinned" option, the LSR ignores
the new next hop change, and the LSP stays unchanged. The LSR may
decide to send an LDP-MAPPING which contains the attribute about this
New Next Hop (NH) change.
3.1. ATM Switch LSR with NO VC-merge
In an MPLS domain where some ATM LSRs do not have VC-merge
capability, downstream-on-demand mode is required for these ATM
LSRs[Ref1]. Also, "conservative label retention mode" is required in
this case[Ref1].
For each LSP, there are 2 kinds of state machines involves:
1) the LSP Control Block and its state machine which can be used to
handle normal LSP setup. It is created when the LSR receives a new
LDP Request and it is deleted when the LSP of this request is torn
down.
2) the Next Hop Trigger Control Block and its state machine which is
used to handle switching over to a better LSP through a different
next hop. It is created when the LSR decides to switch over to a
better next hop and it is deleted when the LSR finishes switching
over to the better next hop.
3.1.1 LSP Control Block
For each LSP, an LSP_Control_Block is defined which may contain the
following information:
- Upstream Label Request ID(assigned by the upstream LSR), which is
the 'Return Message Id' in the Label Request Message received from
the upstream LSR.
- Downstream Label Request ID (assigned by this LSR itself), which
is 'Return Message Id' in the Label Request Message sent to the
downstrearm LSR.
- Upstream LDP Session Identifier
- Downstream LDP Session Identifier
- State
- FEC
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- Upstream Label(assigned by this LSR)
- Downstream Label(assigned by the downstream LSR)
- Trigger Control Block Pointer, (Only used at the ingress LSR of a
LSP)which points to the control block that triggers setting up this
LSP or tearing down this LSP.
- Next Hop Control Block Pointer, which points to the control block
which is used for switching over to a better LSP.
The following index combinations can be used to locate a unique
LSP_Control_Block:
- Downstream Label and Downstream LDP Session Identifier, or
- Upstream Label and Upstream LDP Session Identifier, or
- Upstream Label Request ID and Upstream LDP Session Identifier
Here is the relationship between different control blocks, the detail
definition of Next Hop Trigger Block is described in section 3.1.6.
For example, an LSP which transit through (LSR-A, LSR-B, LSR-C,LSR-
D):
LSR-A ----> LSR-B ---> LSR-C ---> LSR-D
The control blocks in LSR-A are:
+-----------------------+
| Trigger Control Block |
| (e.g, by config) |
+-----------------------+
^
|(Trigger Control block pointer)
|
|
+-----------------------+
| LSP Control Block |
+-----------------------+
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When LSR-B detects a better next hop to LSR-D through LSR-E, and it
decides to switch over to it, so control blocks in LSR-B are:
+-----------------------+
| LSP Control Block |
| (original LSP) |
+-----------------------+
(LSP ^ |
Control | | (Next Hop Control Block Pointer)
Block | |
Pointer | v
+--------------------------------+
| Next Hop Trigger Control Block |
+--------------------------------+
^ |
(Trigger | | (New Next Hop LSP
Control | | Control Block Pointer)
Block | |
Pointer)| |
| v
+------------------------+
| LSP Control Block |
| (for LSP: LSR-B,LSR-E, |
| LSR-D) |
+------------------------+
3.1.2 States
This section describes the various states that are used in the state
machine for the ATM non VC-merge LSR.
-- IDLE
This is the initial LSP state, when the LSP_Control_Block is created.
-- RESPONSE_AWAITED
This state means that the LSR has received and processed an LDP-
REQUEST from an upstream LSR, or it has received an internal set up
request. It has sent a new LDP-REQUEST towards a downstream LSR. The
LSR is waiting for the LDP-MAPPING message from the downstream LSR.
-- ESTABLISHED
This state means that the LSR has received the LDP-MAPPING message
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from the downstream LSR and the LSP is up and operational.
-- RELEASE_AWAITED
This state means that the LSR has sent a LDP-WITHDRAW message
upstream and is waiting for the LDP-RELEASE before freeing up the
label resource.
3.1.3 Events
-- LDP Request
The LSR receives an LDP-REQUEST from an upstream LSR.
-- LDP Mapping
The LSR receives an LDP-MAPPING from a downstream LSR.
-- LDP Release
The LSR receives an LDP-RELEASE from an upstream LSR.
-- LDP Withdraw
The LSR receives an LDP-WITHDRAW from a downstream LSR.
-- LDP Upstream Nak
The LSR receives an LDP-NAK from an upstream LSR.
-- LDP Downstream Nak
The LSR receives an LDP-NAK from a downstream LSR.
-- Upstream Lost
The LSR loses its LDP session with an upstream LDP peer.
-- Downstream Lost
The LSR loses its LDP session with a downstream LDP peer.
-- Internal SetUp
For some reason, e.g. a configuration request of a traffic
engineering tunnel, or recognizing a new FEC could trigger an
Internal SetUp event to set up a new LSP from this node.
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-- Internal Destroy
The LSR send an Internal Destroy event to tear down an LSP.
-- Internal Cross-Connect
The LSR send an Internal Cross-Connect to splice two LSPs into one
LSP.
-- Internal New NH
The LSR decides to switch over the better next hop.
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3.1.4 State Transitions
The following diagram describes briefly the state transitions.
+-------------------+
| |
+-------->| IDLE |<--------------+
| | | |
| +-------------------+ |(LDP Release)
|(LDP Upstream Nak) | |
|(LDP DownstreamNak)|(LDP Request) |(LDP Upstream Nak)
|(Downstream Lost) |(Internal SetUp) |
| | |
|(Upstream Lost) v |(Upstream Lost)
| +-------------------+ |
| | | |
+---------| RESPONSE_AWAITED | |
| | |
+-------------------+ |
| |
|(LDP Mapping) |
| |
v |
+-------------------+ |
| | |
| ESTABLISHED |------------>--+
| | |
+-------------------+ |
| |
| |
|(LDP Withdraw) |
|(Downstream Lost) |
| |
v |
+-------------------+ |
| | |
| RELEASE_AWAITED |------------>--+
| |
+-------------------+
3.1.5 State Machine
3.1.5.1 State -- "IDLE"
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State: IDLE
Event: LDP Request
New States: Depends upon the action routine
Actions:
If this LSR is the LSP Egress or Proxy Egress [Ref2]
Then:
Choose an upstream label, connect this upstream label to the local
IP forwarding module, allocate the resources, send the LDP-MAPPING
message upstream with the upstream label, and go to the new state
`ESTABLISHED'.
else
Obtain a next hop (or interface) with the FEC specified in the
LDP-REQUEST message, propagate the LDP-REQUEST message towards the
obtained next hop, and go to the new state `RESPONSE_AWAITED'.
If the LSR uses the independent control mode[Ref2], choose an
upstream label, connect this upstream label to the local IP
forwarding module, and send an LDP-MAPPING message upstream with
the upstream label.
If unable to process the request for any reason, issue an LDP-NAK
message to the sender with the appropriate error code and delete the
control block.
State: IDLE
Event: LDP Mapping
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Release
New State: IDLE
Actions:
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Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Withdraw
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Upstream Nak
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Downstream Nak
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Upstream Lost
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Downstream Lost
New State: IDLE
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Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Internal SetUp
New State: RESPONSE_AWAITED
Actions:
Set up the Trigger Control Block pointer,
Obtain a next hop (or interface) with the FEC specified in the
Internal SetUp message, send a LDP-REQUEST towards the obtained next
hop, and go to the new state 'RESPONSE_AWAITED'.
State: IDLE
Event: Internal Destroy
New State: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal Cross-Connect
New State: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal New NH
New State: IDLE
Actions:
Ignore. It is an internal implementaion error.
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3.1.5.2 State -- "RESPONSE_AWAITED"
State: RESPONSE_AWAITED
Event: LDP Request
New State: RESPONSE_AWAITED
Actions:
Ignore the event. It is an internal implementation error. A non VC
merge ATM LSR must create a new LSP control block for a new LDP
request.
State: RESPONSE_AWAITED
Event: LDP Mapping
New State: ESTABLISHED
Actions:
1) If the LSP is triggered by the local router(Trigger Control Block
Pointer is not zero), send event "Internal LSP UP" to the Trigger
control block.
2) Else If the LSR uses the ordered control mode, choose an upstream
label.
3) Connect the upstream label to the downstream label. Allocate the
resources. propagate the LDP-MAPPING message upstream with the
upstream label.
If unable to process the message, disconnect the upstream label from
the downstream label, free the upstream label, release the resources,
send an LDP-RELEASE message downstream and an LDP-Nak upstream, and
delete the LSP_Control_Block.
State: RESPONSE_AWAITED
Event: LDP Release
New State: IDLE
Actions:
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If the LSR uses the independent control mode, free the upstream
label.
Send an LDP-NAK message downstream and delete the LSP_Control_Block.
State: RESPONSE_AWAITED
Event: LDP Withdraw
New State: RESPONSE_AWAITED
Actions:
Ignore the event. It's a protocol error from the downstream LSR.
State: RESPONSE_AWAITED
Event: LDP Upstream Nak
New State: IDLE
Actions:
If the LSR uses the independent control mode, free the upstream
label.
Send an LDP-NAK message downstream.
Delete the LSP_Control_Block.
State: RESPONSE_AWAITED
Event: LDP Downstream Nak
New State: Depends on the action routine
Actions:
1. If the LSP is triggered by the local router(Trigger Control Block
Pointer is not zero), send event "Internal LSP DOWN" to the Trigger
control block.
2. Else If the LSR uses the independent control mode, send an LDP-
WITHDRAW message upstream and go to state 'RELEASE_AWAITED'.
If the LSR uses the ordered control mode, send an LDP-NAK message
upstream. Then delete the control block.
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State: RESPONSE_AWAITED
Event: Upstream Lost
New State: IDLE
Actions:
If the LSR uses the independent control mode, free the upstream
label.
Send an LDP-NAK downstream and delete the LSP_Control_Block.
State: RESPONSE_AWAITED
Event: Downstream Lost
New State: Depends on the action routine
Actions:
1. If the LSP is triggered by the local router(Trigger Control Block
Pointer is not zero), send event "Internal LSP DOWN" to the trigger
control block.
2. Else, If the LSR uses the independent control mode, free the
upstream label and send an LDP-WITHDRAW upstream and go to state
'RELEASE_AWAITED'.
If the LSR uses the ordered control mode, send an LDP-NAK upstream
and then delete the control block.
State: RESPONSE_AWAITED
Event: Internal SetUp
New State: RESPONSE_AWAITED
Actions:
Ignore, it is an internal implementation error.
State: RESPONSE_AWAITED
Event: Internal Destroy
New State: IDLE
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Actions:
Send an LDP-NAK downstream and delete the LSP_Control_Block.
State: RESPONSE_AWAITED
Event: Internal Cross-Connect
New State: RESPONSE_AWAITED
Actions:
Ignore the event. It is an internal implementation error.
State: RESPONSE_AWAITED
Event: Internal New NH
New State: RESPONSE_AWAITED
Actions:
Send LDP-NAK to the old downstream, and send LDP-REQUEST to the new
next hop.
3.1.5.3 State --"ESTABLISHED"
State: ESTABLISHED
Event: LDP Request
New State: ESTABLISHED
Actions:
Ignore the event. It's an internal implementation error. For non VC-
merge ATM LSR, a new LSP control block is always created for each LDP
request.
State: ESTABLISHED
Event: LDP Mapping
New State: ESTABLISHED
Actions:
Process the LDP-MAPPING message, which may contain the new attributes
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of the label mapping and then propagate the LDP-MAPPING message
upstream.
State: ESTABLISHED
Event: LDP Release
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Free the resources.
Send event "Internal Destroy" to the Next Hop Trigger Block if it was
in the middle of switching over to the better next hop.
Propagate the LDP-RELEASE message downstream if the LSR is not the
end of LSP and delete the LSP_Control_Block.
State: ESTABLISHED
Event: LDP Withdraw
New State: Depends on the action routine.
Actions:
1) Free the resources and send LDP-RELEASE downstream.
2) If it is independent control mode, set the state to 'IDLE', create
a internal LDP Request with the information in the LSP_Control_Block,
and pass event 'LDP Request' to its own state machine.
3) Else for the ordered control mode
3.1)If the LSP is triggerd to be setup by itself(e.g it is the
ingress LSR of this LSP), send event "Internal LSP NAK" to the
trigger control block and delete the control block
3.2) else, if it is triggered by the incoming LDP Request,
Disconnect the upstream label from the downstream label. And
Propagate the LDP-WITHDRAW message upstream and go to state
'RELEASE_AWAITED'.
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3.3) If the LSP is in the middle of switching over to a better LSP,
send event 'Internal Destroy' to the state machine of its New Next
Hop LSP Control Block.
State: ESTABLISHED
Event: LDP Upstream Nak
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Send event "Internal Destroy" if the LSR was in the middle of
switching over to the better next hop.
Propagate an LDP-RELEASE message downstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: LDP Downstream Nak
New State: ESTABLISHED
Actions:
Ignore the event. It is a protocol error from the downstream LSR.
The downstream LSR should always LSP-WITHDRAW msg to tear down the
LSP when the LSP is established.
State: ESTABLISHED
Event: Upstream Lost
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label.
Free the upstream label.
Send event "Internal Destroy" to the Next Hop Trigger Control Block
if it was in the middle of switching over to the better next hop.
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Free the resources.
Propagate an LDP-RELEASE message downstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: Downstream Lost
New State: Depends on the actions
Actions:
1) If the LSP is triggered by the local router(Trigger Control Block
Pointer is not zero), send event "Internal LSP NAK" to the Trigger
control block and delete the control block.
2) Else, disconnect the upstream label from the downstream label.
Propagate an LDP-WITHDRAW message upstream and go to state
'RELEASE_AWAITED' state.
3) Send event "Internal Destroy" to the Next Hop Trigger Control
Block if it was in the middle of switching over to the better next
hop.
State: ESTABLISHED
Event: Internal Setup
New State: ESTABLISHED
Actions:
Ignore, it is an internal implementation error.
State: ESTABLISHED
Event: Internal Destroy
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label if it is not
the ingress of the LSP.
Free the resources.
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Send an LDP-RELEASE message downstream and delete the
LSP_Control_Block.
State: ESTABLISHED
Event: Internal Cross-Connect
New State: ESTABLISHED
Actions:
Connect the upstream label to the downstream label
May need to send a new LDP-MAPPING upstream with the attributes from
the new next hop.
Reset Trigger Control Block Pointer to zero.
State: ESTABLISHED
Event: Internal New NH
New State: ESTABLISHED
Actions:
1) If the LSR was in the middle of switching over to a better next
hop(Next Hop Trigger Control Block Pointer is not zero), it send
"Internal New NH" to that control block.
2) Else, create a new Next Hop Trigger Control Block, set Next Hop
Trigger Control Block pointer which points this control block. And
then pass "Internal New NH" to this control block.
State RELEASE_AWAITED
Event LDP Request
New State: RELEASE_AWAITED
Actions:
Ignore the event. It is an internal implementation error.
State RELEASE_AWAITED
Event LDP Mapping
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New State: RELEASE_AWAITED
Actions:
Ignore the event. It is an protocol error from the downstream LDP
peer.
State RELEASE_AWAITED
Event LDP Release
New State: IDLE
Actions:
1) Free the upstream label
2) Delete the control block.
State RELEASE_AWAITED
Event LDP Withdraw
New State: IDLE
Actions:
Ignore the event. It is an protocol error from the downstream LDP
peer.
State RELEASE_AWAITED
Event LDP Upstream Nak
New State: IDLE
Actions:
1) Free the upstream label
2) Delete the control block.
State RELEASE_AWAITED
Event LDP Downstream Nak
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New State: RELEASE_AWAITED
Actions:
Ignore the event. Continue waiting for the LDP-RELEASE from upstream.
State RELEASE_AWAITED
Event Upstream Lost
New State: IDLE
Actions:
1) Free the upstream label
2) Delete the control block.
State RELEASE_AWAITED
Event Downstream Lost
New State: RELEASE_AWAITED
Actions:
Ignore the event. Continue waiting for the LDP-RELEASE from upstream.
State RELEASE_AWAITED
Event Internal SetUp
New State: RELEASE_AWAITED
Actions:
Ignore the event. It is an internal implementation error.
State RELEASE_AWAITED
Event Internal Destroy
New State: RELEASE_AWAITED
Actions:
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Ignore the event. It is an internal implementation error.
State RELEASE_AWAITED
Event Internal Cross-Connect
New State: RELEASE_AWAITED
Actions:
Ignore the event. It is an internal implementation error.
3.1.6 Handling the Next Hop Change
When an LSR detects a better next hop, it may decides to establish a
new LSP through this next hop. For example, an LSR is configured as
"local repair", or the LSR is configured as "global repair" and it is
the ingress end of a LSP. It can then create a Next Hop Trigger
Control Block and use the state machine of Next Hop Trigger Control
Block to establish a new LSP through the better next hop.
3.1.6.1 Next Hop Trigger Control Block
-- LSP Control Block Pointer, which points to the original LSP
control block.
-- New Next Hop LSP Control Block Pointer, which points to the LSP
Control Block that is setting up an LSP through the new next hop.
3.1.6.2 States
-- IDLE
This is the initial LSP state, when the Trigger_Control_Block is
created.
-- NEW_NH_RETRY
This is the state where an LSR waits for a retry timer to expire and
then tries to establish an LSP through a new next hop.
-- NEW_NH_RESPONSE_AWAITED
This is the state where an LSR is in the middle of establishing a new
LSP through a new next hop. It has triggered a LSP control block to
send an LDP-REQUEST towards the new next hop and is waiting for the
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LDP-MAPPING message.
3.1.6.3 Events
-- Internal New NH
The LSR detects there is a new next hop for a FEC.
-- Internal Retry Timeout
The LSP retry timer expires.
-- Internal LSP UP
The LSP to the new Next Hop is UP
-- Internal LSP NAK
The LSP through the new next hop could not get set up
-- Internal Destroy
This event is triggered when the LSR lost the LDP session with its
upstream neighbor.
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3.1.6.4 State Transition for next hop change
|
|
|
| Internal New NH
|
v
+---------------------+
| | Internal destroy
| NEW_NH_RETRY |--------------
| | |
+---------------------+ |
| |
| |
| (Internal retry timeout) |
| |
v |
+---------------------+ |
| | Internal |
| NEW_NH_RESPONSE | Destroy |
| _AWAITED |-------------|
| | |
+---------------------+ |
| |
| (Internal LSP UP) |
| (Internal LSP NAK) |
v v
the control block is deleted
3.01.3 State Machine
3.01.3.1 State -- "IDLE"
State: IDLE
Event: Internal New NH
New States: NEW_NH_RETRY
Actions:
Start the LSP retry timer and go to the 'NEW_NH_RETRY' state.
State: IDLE
Event: Internal retry timeout
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New States: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal LSP UP
New States: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal LSP NAK
New States: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal destroy
New States: IDLE
Actions:
Ignore. It is an internal implementation error.
3.01.3.2 State -- "NEW_NH_RETRY"
State: NEW_NH_RETRY
Event: Internal New NH
New States: NEW_NH_RETRY
Actions:
Restart the LSP retry timer.
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State: NEW_NH_RETRY
Event: Internal retry timeout
New States: NEW_NH_RESPONSE_AWAITED
Actions:
If the new next hop is the same one as the old next hop, delete the
control block.
Otherwise, create an LSP control block which will try to establish a
new LSP through the new next hop. And send event "Internal Setup" to
its state machine.
State: NEW_NH_RETRY
Event: Internal LSP UP
New States: NEW_NH_RETRY
Actions:
Ignore. It is an internal implementation error.
State: NEW_NH_RETRY
Event: Internal LSP NAK
New States: NEW_NH_RETRY
Actions:
Ignore. It is an internal implementation error.
State: NEW_NH_RETRY
Event: Internal destroy
New States: IDLE
Actions:
Stop the timer and delete the control block.
3.01.3.3 State -- "NEW_NH_RESPONSE_AWAITED"
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State: NEW_NH_RESPONSE_AWAITED
Event: Internal New NH
New States: NEW_NH_RETRY
Actions:
Restart the LSP retry timer, send "Internal destroy" to the control
block of the LSP for the new next hop and go to the 'NEW_NH_RETRY'
state.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal retry timeout
New States: NEW_NH_RESPONSE_AWAITED
Actions:
Ignore. It is an internal implementation error.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal LSP UP
New States: IDLE
Actions:
Send event "Internal cross-connect" event to the LSP control block of
the new next hop.
Send event "Internal destroy" event to the original LSP control
block.
Then delete the control block.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal LSP NAK
New States: IDLE
Actions:
Delete the control block.
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State: NEW_NH_RESPONSE_AWAITED
Event: Internal destroy
New States: IDLE
Actions:
Send event "Internal destroy" the control block for the new LSP
through the new next hop.
3.1.7 LDP Related Message Handling
- If an LSR receives an LDP-REQUEST from an upstream LSR:
a) If this is a duplicate request, discard the msg. A duplicate
request means that there is a LSP_Control_Block which has same FEC,
same Upstream Label Request ID and same Upstream LDP Session
Identifier.
b) Otherwise, create a new LSP_Control_Block, store the relevant
information from the message into the control block, then pass the
event `LDP Request' to its state machine.
- If an LSR receives an LDP-MAPPING from a downstream LSR:
a) Extract the 'Label Request Message ID' field and from the LDP-
MAPPING message.
b) Find an LSP_Control_Block which has the same Downstream Label
Request ID and the same Downstream LDP Session Identifier.
c) If an LSP_Control_Block is found, pass the event `LDP Mapping' to
its state machine.
d) If there is no matching LSP_Control_Block found, then try to find
an LSP_Control_Block which has the same Downstream Lable and the same
Downstream LDP Session Identifier.
e) If an LSP_Control_Block is found, pass the event 'LDP Mapping' to
its state machine.
f) Otherwise, ignore the LDP-MAPPING message.
- If an LSR receives an LDP-RELEASE from an upstream LSR:
a) Find an LSP_Control_Block which has the same Upstream Label and
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the same Upstream LDP Session Identifier.
b) If an LSP_Control_Block is found, pass the event 'LDP Release' to
its state machine.
c) Otherwise, ignore the message.
- If an LSR receives an LDP-WITHDRAW from a downstream LSR:
a) Find an LSP_Control_Block which has the same Downstream Label and
the same Downstream LDP Session Identifier.
b) If an LSP_Control_Block is found, pass the event 'LDP Withdraw' to
its state machine.
c) Otherwise, ignore the LDP-WITHDRAW message.
- If an upstream LDP peer is lost:
a) Find all the LSP_Control_Blocks whose upstream LDP peer is that
LSR.
b) Then pass the event 'Upstream Lost' to their state machines.
- If a downstream LDP peer is lost:
a) Find all the LSP_Control_Blocks whose downstream LDP peer is that
LSR.
b) Then pass the event 'Downstream Lost' to their state machines.
- If the LSR detects a new next hop for an FEC:
For each LSP which needs "local repair", or it needs "global repair"
and it is the ingress of the LSP, pass event "Internal New NH" to its
state machine.
- If an LSR receives an LDP-NAK from an upstream LSR:
a) Extract the LDP Request ID value from the LDP-NAK message.
b) Find an LSP_Control_Block which has the same Upstream Label
Request ID and the same Upstream LDP Session Identifier.
c) If an LSP_Control_Block is found, pass the event 'LDP Upstream
Nak' to its state machine.
d) Otherwise, ignore the message.
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- If the LSR receives an LDP-NAK from a downstream LSR:
a) Extract the LDP Request ID value from the LDP-NAK.
b) Find an LSP_Control_Block which has the same Downstream Label
Request ID and the same Downstream LDP Session Identifier.
c) If an LSP_Control_Block is found, pass the event
d) Otherwise, ignore the message.
3.2. ATM Switch LSR with VC-merge
3.2.1 VC-merge
A VC-merge capable LSR can map multiple incoming labels(VPI/VCI) into
one outgoing label. It is possible that this LSR can only merge a
limited number of incoming labels into a single outgoing label. As
described in [Ref2], suppose, for example, that due to some hardware
limitation a node is capable of merging four incoming labels into a
single outgoing label. Suppose however, that this particular node has
six incoming labels arriving at it for a particular FEC. In this
case, this node may merge these into two outgoing labels.
When an upstream LSR has a limited merging capability, it is
difficult for a downstream LSR to know how many labels should be
assigned to each FEC. In this case, downstream-on-demand is
recommended.
3.2.2 Control Block
There are 3 types of control blocks involved:
Upstream_LSP_Control_Block, Downstream_LSP_Control_Block, and Next
Hop Trigger Control Block.
There is one Upstream_LSP_Control_Block for each LDP-REQUEST
received.
There is one Downstream_LSP_Control_Block for each unique LDP-
REQUEST sent to a downstream LSR. There can be multiple
Downstream_LSP_Control_Blocks per FEC in an LSR. This can be the
result of an upstream LSR asking for a label of an FEC. This LSR must
assign a unique upstream label and it can not merge this upstream
label into an existing downstream label of this FEC.
There is one Next Hop Trigger Control Block for each FEC which was
detected with a better next hop and the LSR decides to switch over to
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this better next hop. It could be the result of "local repair" or
"global repair" if the LSR is the ingress LSR of the LSP.
A Downstream_LSP_Control_Block contains a list of pointers to
Upstream_LSP_Control_Blocks or the Next Hop Trigger Control Block.
This means that this LSR has decided to map the multiple labels
listed in the Upstream_LSP_Control_Blocks and the Next Hop Trigger
Control Block into a single label listed in the
Downstream_LSP_Control_Block.
An Upstream_LSP_Control_Block may contain the following information:
- Upstream LDP Session Identifier
- State
- Upstream Label(assigned by this LSR)
- Downstream_LSP_Control_Block pointer
- Upstream LDP Request ID (assigned by the Upstream LSR in
downstream-on-demand mode)
- Next_Hop_Trigger_Block pointer
Upstream Label and Upstream LDP Session Identifier can be used to
locate a unique Upstream_LSP_Control_Block.
If an LSR is using downstream-on-demand mode, it can use the Upstream
LDP Request ID and the Upstream LDP Session Identifier to locate a
unique Upstream_LSP_Control_Block.
An Next_Hop_Trigger_LSP_Control_Block may contain the following
information:
- Upstream_LSP_Control_Block pointer, which points to the one
which is needed to switch over to the better next hop
- State
- Downstream_LSP_Control_Block pointer
A Downstream_LSP_Control_Block may contain the following information:
- FEC
- State
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- Downstream LDP Session Identifier
- list of pointers to the Upstream_LSP_Control_Blocks or the
Trigger_Control_Blocks which are merged at this LSR for this
FEC
- Downstream Label(assigned by the downstream LSR)
- Downstream Label Request ID (assigned by the LSR itself if
it is using downstream-on-demand mode)
Downstream Label, Downstream LDP Session Identifier can be used to
locate a unique Downstream_LSP_Control_Block.
If an LSR is using downstream-on-demand mode, it can also use the
Downstream Label Request ID and the Downstream LDP Session Identifier
to locate a unique Downstream_LSP_Control_Block.
The following diagram details the relationship between these 2 types
of control blocks:
For example, the LSR has decided to merge 3 LDP-REQUESTs of a FEC
from upstream LSR1,LSR2,LSR3 into one LDP-REQUEST and sent it to a
downstream LSR4.
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+---------------------+
| |
| Upstream_LSP_Control|
| _Block for Upstream|-------+
| LSR1 | |
+---------------------+ |
|
|
|
|
|
+---------------------+ |
| | |
| Upstream_LSP_Control| | (merged into)
| _Block for Upstream |-------+
| LSR2 | |
+---------------------+ |
|
|
|
| +------------------------------+
| | |
+-->| Downstream_LSP_Control_Block |
| | for Downstream LSR4 |
| | |
| +------------------------------+
|
+---------------------+ |
| Next_Hop_Trigger_ | |
| LSP_Control_Block | |
| |-------+
| |
+---------------------+
3.2.3 State Machines for Downstream-on-demand Mode
The following sections describe the state machines used in
downstream-on-demand mode.
3.2.3.1 State of the Upstream_LSP_Control_Block's State Machine
for Downstream-on-demand Mode
-- IDLE
This is the initial LSP state.
-- RESPONSE_AWAITED
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This state means that the LSR has received and processed an LDP-
REQUEST from an upstream LSR, and has sent a new LDP-REQUEST towards
a downstream LSR. The LSR is waiting for the LDP-MAPPING message from
the downstream LSR.
-- ESTABLISHED
This state means that the LSR has received the LDP-MAPPING message
from the downstream LSR and the LSP is up and operational.
-- RELEASE_AWAITED
This state means that the LSR has sent a LDP-WITHDRAW message
upstream and is waiting for the LDP-RELEASE before freeing up the
label resource.
3.2.3.2 Events of the Upstream_LSP_Control_Block's State Machine
for Downstream-on-demand Mode
-- LDP Request
The LSR receives an LDP-REQUEST from an upstream LSR.
-- Internal Downstream Mapping
This event is sent by one Downstream_LSP_Control_Block's state
machine. This Downstream_LSP_Control_Block is the merged
Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
event is the result of receiving an LDP-MAPPING message by the
Downstream_LSP_Control_Block's state machine.
-- LDP Release
The LSR receives an LDP-RELEASE from an upstream LSR.
-- Internal Downstream Withdraw
This event is sent by one Downstream_LSP_Control_Block's state
machine. This Downstream_LSP_Control_Block is the merged
Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
event is the result of receiving an LDP-WITHDRAW message by the
Downstream_LSP_Control_Block's state machine.
-- LDP Upstream Nak
The LSR receives an LDP-NAK from an upstream LSR.
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-- Internal Downstream Nak
This event is sent by one Downstream_LSP_Control_Block's state
machine. This Downstream_LSP_Control_Block is the merged
Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
event is the result of receiving an LDP-NAK message by the
Downstream_LSP_Control_Block's state machine, or it detects an error.
-- Upstream Lost
The LSR loses the LDP session with its upstream LDP peer.
-- Internal New NH
The LSR detects there is better next hop and decides to establish the
lsp through this better next hop
-- Internal Re-Cross-Connect
This event is used to trigger splicing into a different downstream
LSP. This can happens when it is switched over to a better LSP
through the new next hop.
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3.2.3.3 State Transitions of the Upstream_LSP_Control_Block's State
Machine for Downstream-on-demand Mode
+-------------------+
| |
+-------->| IDLE |<------------+
| | | |
| +-------------------+ |
|(LDP Upstream Nak)| |
|(Internal |(LDP Request) |
| Downstream Nak) | |
|(Upstream Lost) | |
| v |
| +-------------------+ |
| | | |
+---------| RESPONSE_AWAITED | |
| | |(Upstream Lost)
+-------------------+ |
| |
|(Internal Downstream |
| mapping) |(LDP Release)
| |
v |
+-------------------+ |
| | |(LDP Upstream Nak)
| ESTABLISHED |------->-----+
| | |
+-------------------+ |
| |
| |
|(Internal Downstream Withdraw)
|(Internal Downstream Nak)
v
+-------------------+ |
| | |
|RELEASE_AWAITED |------->-----+
| |
+-------------------+
3.2.3.4 Upstream_LSP_Control_Block's State Machine
for Downstream-on-demand Mode
3.2.3.4.1 State -- "IDLE"
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State: IDLE
Event: LDP Request
New State: Depends upon the action routine.
Actions:
If this LSR is the LSP Egress or Proxy Egress [Ref2],
Then:
choose an upstream label, allocate the resources, connect this
upstream label to the local IP forwarding module, send an LDP-
MAPPING upstream with the upstream label and go to the state
'ESTABLISHED'.
else
Obtain a next hop(or interface). Find a
Downstream_LSP_Control_Block which has the same FEC and the same
next hop and also is able to merge more input labels. If not found,
create a new Downstream_LSP_Control_Block with the state 'IDLE'.
If the state of the Downstream_LSP_Control_Block is `ESTABLISHED',
choose an upstream label, connect the upstream label with the
downstream label and send an LDP-MAPPING message upstream with the
upstream label, and go to the state `ESTABLISHED'.
If the state of Downstream_LSP_Control_Block is not `ESTABLISHED',
set the state of the Upstream_LSP_Control_Block to
'RESPONSE_AWAITED'. If the LSR use the independent control
mode[Ref2], choose an upstream label, and send an LDP-MAPPING
message upstream.
Pass the event `Internal AddUpstream' to the
Downstream_LSP_Control_Block's state machine.
If unable to process the request for any reason, issue an LDP-NAK
message to the sender with the appropriate error code and delete the
control block.
State: IDLE
Event: Internal Downstream Mapping
New State: IDLE
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Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Release
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Internal Downstream Withdraw
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Upstream Nak
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Internal Downstream Nak
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Upstream Lost
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New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Internal Re-Cross-Connect
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Internal New NH
New State: IDLE
Actions:
Ignore the event. It is an internal implementation error.
3.2.3.4.2 State -- "RESPONSE_AWAITED"
State: RESPONSE_AWAITED
Event: LDP Request
New State: RESPONSE_AWAITED
Actions:
Ignore the event. It is an internal implementation error.
State: RESPONSE_AWAITED
Event: Internal Downstream Mapping
New State: Depends on the action routine
Actions:
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If the LSR uses the ordered control mode, assign an upstream label.
Connect the upstream label to the downstream label and allocate the
resources.
Send an LDP-MAPPING message upstream with the upstream label.
Then go to the state 'ESTABLISHED'.
If unable to process the message for any reason, issue an LDP-NAK
message upstream and an LDP-RELEASE message downstream and delete the
control block.
State: RESPONSE_AWAITED
Event: LDP Release
New State: RESPONSE_AWAITED
Actions
Ignore the event. It is an protocol error from the upstream peer.
State: RESPONSE_AWAITED
Event: Internal Downstream Withdraw
New State: RESPONSE_AWAITED
Actions
Ignore the event. It is an internal implementation error.
State: RESPONSE_AWAITED
Event: LDP Upstream Nak
New State: IDLE
Actions
If the LSR uses the independent control mode, free the upstream label
and the resources.
Send the event 'Internal DeleteUpstream' to its
Downstream_LSP_Control_Block's state machine.
Delete the control block.
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State: RESPONSE_AWAITED
Event: Internal Downstream Nak
New State: IDLE
Actions:
If the LSR uses the independent control mode, free the upstream label
and the resources. Then, send an LDP-WITHDRAW message upstream.
If the LSR uses the ordered control mode, propagate the LDP-NAK
message upstream.
Delete the control block.
State: RESPONSE_AWAITED
Event: Upstream Lost
New State: IDLE
Actions
If the LSR uses the independent control mode, free the upstream label
and the resources.
Send the event 'Internal DeleteUpstream' to its
Downstream_LSP_Control_Block's state machine.
Delete the control block.
State: RESPONSE_AWAITED
Event: Internal Re-Cross-Connect
New State: RESPONSE_AWAITED
Actions:
Ignore the event. It is an internal implementation error.
State: RESPONSE_AWAITED
Event: Internal New NH
New State: depends on the actions
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Actions:
Send event "Internal DeleteUpstream" to its old downstream control
block.
Find a Downstream_LSP_Control_Block which has the same FEC and the
same next hop and also is able to merge more input labels. If not
found, create a new Downstream_LSP_Control_Block with the state
'IDLE'.
If the state of the Downstream_LSP_Control_Block is `ESTABLISHED',
choose an upstream label, connect the upstream label with the
downstream label and send an LDP-MAPPING message upstream with the
upstream label, and go to the state `ESTABLISHED'.
If the state of Downstream_LSP_Control_Block is not `ESTABLISHED',
set the state of the Upstream_LSP_Control_Block to
'RESPONSE_AWAITED'.
Pass the event `Internal AddUpstream' to the new
Downstream_LSP_Control_Block's state machine.
3.2.3.4.3 State -- "ESTABLISHED"
State: ESTABLISHED
Event: LDP Request
New State: ESTABLISHED
Actions
Ignore the event. It is an internal implementation error.
State: ESTABLISHED
Event: Internal Downstream Mapping
New State: ESTABLISHED
Actions
Process the new attributes of the mapping and then propagate the
LDP-MAPPING message upstream.
State: ESTABLISHED
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Event: LDP Release
New State: IDLE
Actions
Disconnect the upstream label from the downstream label, free the
upstream label and resources.
Send the event 'Internal DeleteUpstream' to its
Downstream_LSP_Control_Block's state machine.
Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
state machine if the LSR was in the middle of switching over to the
better next hop.
Delete the control block.
State: ESTABLISHED
Event: Internal Downstream Withdraw
New State: Depends on the action routine
Actions
If it uses independent mode,set its state to 'IDLE' and create a
internal 'LDP Request' and send to its own state machine.
Else
Disconnect the upstream label from the downstream label.
Propagate the LDP-WITHDRAW upstream and go to state
'RELEASE_AWAITED'.
Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
state machine if the LSR was in the middle of switching over to the
better next hop.
State: ESTABLISHED
Event: LDP Upstream Nak
New State: IDLE
Actions
Disconnect the upstream label from the downstream label, free the
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upstream label and the resources.
Send the event 'Internal DeleteUpstream' to its
Downstream_LSP_Control_Block's state machine.
Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
state machine if the LSR was in the middle of switching over to the
better next hop.
Delete the control block.
State: ESTABLISHED
Event: Internal Downstream Nak
New State: Depends on the actions
Actions:
If it uses independent mode,set its state to 'IDLE' and create a
internal 'LDP Request' and send to its own state machine.
Else
Disconnect the upstream label from the downstream label
Send an LDP-WITHDRAW upstream and go to state 'RELEASE_AWAITED'.
Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
state machine if the LSR was in the middle of switching over to the
better next hop.
State: ESTABLISHED
Event: Upstream Lost
New State: IDLE
Actions:
Disconnect the upstream label from the downstream label, free the
upstream label and the resources.
Send the event 'Internal DeleteUpstream' to its
Downstream_LSP_Control_Block's state machine.
Send the event "Internal Destroy' to the Next_Hop_Trigger_Block's
state machine if the LSR was in the middle of switching over to the
better next hop.
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Delete the control block.
State: ESTABLISH
Event: Internal Re-Cross-Connect
New State: ESTABLISH
Actions:
Reconnect the upstream lable to the new downstream lable.
Send the event 'Internal DeleteUpstream' to its old
Downstream_LSP_Control_Block's state machine.
State: ESTABLISH
Event: Internal New NH
New State: ESTABLISH
Actions:
Create a new Next_Hop_Trigger_Control_Block and pass event
3.2.3.4.4 State -- "RELEASE_AWAITED"
State: RELEASE_AWAITED
Event: LDP Request
New State: RELEASE_AWAITED
Actions:
Ignore the event. It is a protocol error from the upstream LSR.
State: RELEASE_AWAITED
Event: Internal Downstream Mapping
New State: RELEASE_AWAITED
Actions:
Ignore the event. It is an internal implementatin error.
State: RELEASE_AWAITED
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Event: LDP Release
New State: IDLE
Actions:
Free the upstream lable resource. and delete the control block.
State: RELEASE_AWAITED
Event: Internal Downstream Withdraw
New State: RELEASE_AWAITED
Actions:
Ignore the event. It is a protocol error from the downstream LSR.
State: RELEASE_AWAITED
Event: LDP Upstream Nak
New State: IDLE
Actions:
Free the upstream lable resource. and delete the control block.
State: RELEASE_AWAITED
Event: Internal Downstream Nak
New State: RELEASE_AWAITED
Actions:
Ignore the event. And continue waiting for the LDP-RELEASE msg.
State: RELEASE_AWAITED
Event: Upstream Lost
New State: IDLE
Actions:
Free the upstream lable resource. and delete the control block.
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State: RELEASE_AWAITED
Event: Internal New NH
New State: RELEASE_AWAITED
Actions:
Ignore the event. And continue waiting for the LDP-RELEASE msg.
State: RELEASE_AWAITED
Event: Internal Re-Cross-Connect
New State: RELEASE_AWAITED
Actions:
Ignore the event. It is an internal implementation error.
3.2.3.5 State of the Downstream_LSP_Control_Block's State Machine
for Downstream-on-demand Mode
-- IDLE
This is the initial LSP state.
-- RESPONSE_AWAITED
This state means that the LSR has received an LDP-REQUEST from an
upstream LSR, has processed the LDP-REQUEST, and has sent a new LDP-
REQUEST towards a downstream LSR. The LSR is waiting for the LDP-
MAPPING message from the downstream LSR.
-- ESTABLISHED
This state means that the LSR has received the LDP-MAPPING message
from the downstream LSR and the LSP is up and operational.
3.2.3.6 Events of the Downstream_LSP_Control_Block's State Machine
for Downstream-on-demand Mode
-- Internal AddUpstream
This event is sent by an Upstream_LSP_Control_Block's state machine
when it is created.
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-- Internal DeleteUpstream
This event is sent by an Upstream_LSP_Control_Block's state machine
when it is deleted.
-- LDP Mapping
The LSR receives an LDP-MAPPING message from a downstream LSR.
-- LDP Withdraw
The LSR receives an LDP-WITHDRAW message from a downstream LSR.
-- LDP Downstream Nak
The LSR receives an LDP-NAK from a downstream LSR.
-- Downstream Lost
The LSR loses the LDP session with its downstream LSR.
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3.2.3.7 State Transitions of the Downstream_LSP_Control_Block'S
State Machine for Downstream-on-demand mode
+-------------------+
| |
| IDLE |<--------------+
| | |(last Internal
+-------------------+ | DeleteUpstream)
| |(LDP Withdraw)
|(1st Internal AddUpstream)|
| |(LDP Downstream
v | Nak)
+-------------------+ |(Downstream
| | | Lost)
| RESPONSE_AWAITED |---------->----^
| | |
+-------------------+ |
| |
|(LDP Mapping) |
| |
v |
+-------------------+ |
| | |
| ESTABLISHED |-------->------^
| |
+-------------------+
3.2.3.8 Downstream_LSP_Control_Block'S State Machine for
Downstream-on-demand Mode.
3.2.3.8.1 State -- "IDLE"
State: IDLE
Event: Internal AddUpstream
New State: RESPONSE_AWAITED
Actions
Initialize the list of pointers in the Upstream_LSP_Control_Block to
contain the newly added upstream pointer.
Send a new LDP-REQUEST downstream and go to the state
'RESPONSE_AWAITED'.
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State: IDLE
Event: Internal DeleteUpstream
New State: IDLE
Actions
Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Mapping
New State: IDLE
Actions
Ignore the event. It is an internal implementation error.
State: IDLE
Event: LDP Withdraw
New State: IDLE
Actions
Ignore the event.It is an internal implementation error.
State: IDLE
Event: LDP Downstream Nak
New State: IDLE
Actions
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Downstream Lost
New State: IDLE
Actions
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Ignore the event. It is an internal implementation error.
3.2.3.8.2 State -- "RESPONSE_AWAITED"
State: RESPONSE_AWAITED
Event: Internal AddUpstream
New State: RESPONSE_AWAITED
Actions
Add the pointer to new Upstream_LSP_Control_Block to the
Upstream_LSP_Control_Blocks pointer list.
State: RESPONSE_AWAITED
Event: Internal DeleteUpstream
New State: Depend on the action routine
Actions
Delete the Upstream_LSP_Control_Block pointer from the
Upstream_LSP_Control_Block pointers list.
If the list becomes empty, release the resources, send an LDP-NAK
downstream, and then delete the control block.
State: RESPONSE_AWAITED
Event: LDP Mapping
New State: ESTABLISHED
Actions
For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
pointers list, pass the event 'Internal Downstream Mapping' to its
state machine.
State: RESPONSE_AWAITED
Event: LDP Withdraw
New State: RESPONSE_AWAITED
Actions
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Ignore the event. It is a protocol error from the downstream LDP
peer.
State: RESPONSE_AWAITED
Event: LDP Downstream Nak
New State: IDLE
Actions
For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
pointers list, pass the event 'Internal Downstream Nak' to its state
machine.
Release the resources, and delete the control block.
State: RESPONSE_AWAITED
Event: Downstream Lost
New State: IDLE
Actions
For each Upstream_LSP_Control_Block in the
Upstream_LSP_Control_Block pointers list, pass the event 'Internal
Downstream Nak' to its state machine.
Release the resources, and delete the control block.
3.2.3.8.3 State -- "ESTABLISHED"
State: ESTABLISHED
Event: Internal AddUpstream
New State: ESTABLISHED
Actions
Add the pointer to new Upstream_LSP_Control_Block to the
Upstream_LSP_Control_Block pointers list.
State: ESTABLISHED
Event: Internal DeleteUpstream
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New State: Depends on the action routine
Actions
Delete the pointer of Upstream_LSP_Control_Block from its
Upstream_LSP_Control_Block pointers list.
If the list becomes empty, release the resources, send an LDP-RELEASE
downstream, and then delete the control block.
State: ESTABLISHED
Event: LDP Mapping
New State: ESTABLISHED
Actions
For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
pointers list, pass the event 'Internal Downstream mapping' to its
state machine.
State: ESTABLISHED
Event: LDP Withdraw
New State: IDLE
Actions
For each Upstream_LSP_Control_Block in the Upstream_LSP_Control_Block
pointers list, pass the event 'Internal Downstream withdraw' to its
state machine.
Release the resources, and delete the control block.
State: ESTABLISHED
Event: LDP Downstream Nak
New State: ESTABLISHED
Actions
It is a protocol error from the downstream LDP peer.
3.2.3.9 State of the Next_Hop_Trigger_Control_Block's State Machine
for Downstream-on-demand Mode
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-- IDLE
This is the initial LSP state.
-- NEW_NH_RETRY
This is the state where an LSR waits for a retry timer to expire and
then tries to establish an LSP through a new next hop.
-- NEW_NH_RESPONSE_AWAITED
This state means that the LSR has sent a new LDP-REQUEST towards a
downstream LSR. The LSR is waiting for the LDP-MAPPING message from
the downstream LSR.
3.2.3.10 Events of the Next_Hop_Trigger_Control_Block's State Machine
for Downstream-on-demand Mode
-- Internal New NH
Trigger to setup an LSP through a better next hop.
-- Internal Downstream Mapping
This event is sent by one Downstream_LSP_Control_Block's state
machine. This Downstream_LSP_Control_Block is the merged
Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
event is the result of receiving an LDP-MAPPING message by the
Downstream_LSP_Control_Block's state machine.
-- Internal Downstream Nak
This event is sent by one Downstream_LSP_Control_Block's state
machine. This Downstream_LSP_Control_Block is the merged
Downstream_LSP_Control_Block of this Upstream_LSP_Control_Block. The
event is the result of receiving an LDP-NAK message by the
Downstream_LSP_Control_Block's state machine, or it detects an error.
-- Internal Destroy This event is used to stop the procedure of
switching over to the better next hop.
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3.2.3.11 State Transitions of the Next_Hop_Trigger_Control_Block's State
Machine for Downstream-on-demand Mode
|
|
|
| Internal New NH
|
v
+---------------------+
| | Internal destroy
| NEW_NH_RETRY |--------------
| | |
+---------------------+ |
| |
| |
| (Internal retry timeout) |
| |
v |
+---------------------+ |
| | Internal |
| NEW_NH_RESPONSE | Destroy |
| _AWAITED |-------------|
| | |
+---------------------+ |
| |
| (Internal Downstream |
| Mapping |
| (Internal Downstream |
| Nak) |
v v
the control block is deleted
3.2.3.12 State Machine
3.2.3.12.1 State -- "IDLE"
State: IDLE
Event: Internal New NH
New States: NEW_NH_RETRY
Actions:
Start the LSP retry timer and go to the 'NEW_NH_RETRY' state.
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State: IDLE
Event: Internal retry timeout
New States: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal Downstream Mapping
New States: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal Downstream Nak
New States: IDLE
Actions:
Ignore. It is an internal implementation error.
State: IDLE
Event: Internal destroy
New States: IDLE
Actions:
Ignore. It is an internal implementation error.
3.2.3.12.2 State -- "NEW_NH_RETRY"
State: NEW_NH_RETRY
Event: Internal New NH
New States: NEW_NH_RETRY
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Actions:
Restart the LSP retry timer.
State: NEW_NH_RETRY
Event: Internal retry timeout
New States: NEW_NH_RESPONSE_AWAITED
Actions:
If the new next hop is the same one as the old next hop, delete the
control block.
Otherwise, find an downstream LSP control block which go through the
same next hop for the same FEC, if there is no one, create one, and
pass "Internal AddUpstream'event to its state machine.
State: NEW_NH_RETRY
Event: Internal Downstream Mapping
New States: NEW_NH_RETRY
Actions:
Ignore. It is an internal implementation error.
State: NEW_NH_RETRY
Event: Internal Downstream NAK
New States: NEW_NH_RETRY
Actions:
Ignore. It is an internal implementation error.
State: NEW_NH_RETRY
Event: Internal destroy
New States: IDLE
Actions:
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Stop the timer and delete the control block.
3.2.3.12.3 State -- "NEW_NH_RESPONSE_AWAITED"
State: NEW_NH_RESPONSE_AWAITED
Event: Internal New NH
New States: NEW_NH_RETRY
Actions:
Restart the LSP retry timer, send "Internal destroy" to the control
block of the LSP for the new next hop and go to the 'NEW_NH_RETRY'
state.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal retry timeout
New States: NEW_NH_RESPONSE_AWAITED
Actions:
Ignore. It is an internal implementation error.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal Downstream Mapping
New States: IDLE
Actions:
Send event "Internal Re-cross-connect" event to the Upstream LSP
control block of the new next hop.
Send event "DeleteUpstream" event to the downstream LSP control block
of the the new next hop, since the upstream has spliced into the new
next hop.
Then delete the control block.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal Downstream NAK
New States: IDLE
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Actions:
Delete the control block.
State: NEW_NH_RESPONSE_AWAITED
Event: Internal destroy
New States: IDLE
Actions:
Send event "Internal DeleteUpstream" the control block for the new
LSP through the new next hop.
3.2.4 LDP Related Message Processing
- If an LSR receives an LDP-REQUEST message:
a) If this is a duplicate request, discard the msg. A duplicate
request means that there is a LSP_Control_Block which has same FEC,
same Upstream Label Request ID and same Upstream LDP Session
Identifier.
b) Otherwise, create a new Upstream_LSP_Control_Block. Then pass the
event `LDP Request' to this Upstream_LSP_Control_Block's state
machine.
- If an LSR receives an LDP-MAPPING message:
Locate a Downstream_LSP_Control_Block which has the same FEC, the
same Downstream LDP Session Identifier and the same Downstream Label.
If a Downstream_LSP_Control_Block is found, pass the event `LDP
Mapping' to its state table. This could mean that the attributes of
label binding have changed.
Otherwise, use the Downstream LDP request ID(the 'Lable Request
Message ID' field in the LDP-MAPPING MSG) and Downstream LDP Session
Identifier to locate the Downstream_LSP_Control_Block and pass the
event `LDP Mapping' to its state machine. If no
Downstream_LSP_Control_Block is found, ignore the message.
- If an LSR receives an LDP-RELEASE message:
Locate an Upstream_LSP_Control_Block which has the same FEC, the same
Upstream Label, the same Upstream LDP Session Identifier. If no
Upstream_LSP_Control_Block is found, ignore the message. If an
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Upstream_LSP_Control_Block is found, send the event `LDP Release' to
its state machine.
- If an LSR receives an LDP-WITHDRAW message:
Find a Downstream_LSP_Control_Block which has the same FEC, the same
Downstream LDP Session Identifier and the same Downstream Label. Pass
the event `LDP Withdraw' to its state machines.
- If an Upstream LDP peer is lost:
Pass the event `Upstream Lost' to the state machines of all the
Upstream_LSP_Control_Blocks whose upstream LDP peer is that LSR.
- If a Downstream LDP peer is lost:
Pass the event `Downstream Lost' to the state machines of all the
Downstream_LSP_Control_Blocks whose the downstream LDP peer is that
LSR.
- If a next hop of an FEC is changed:
For all the Upstream_LSP_Control_Blocks which are infected by this
change, pass the event 'Internal New NH' to their state machines.
- If an LSR receives an LDP-NAK from an Upstream LSR:
Use the Upstream LDP Request ID and Upstream LDP Session Identifier
to locate the Upstream_LSP_Control_Block and pass the event `LDP
Upstream Nak' to its state machine.
- If an LSR receives an LDP-NAK from a downstream LSR:
Use the Downstream LDP Request ID and Downstream Session Identifier
to locate a Downstream_LSP_control_block and pass the event `LDP
Downstream Nak' to its state machine.
3.2.4 Downstream Unsolicited
The following sections describe the state machines for the ATM-LSR
which uses downstream unsolicited mode.
While both independent LSP control and ordered LSP control modes are
possible, only the ordered mode is taken into account, because the
independant LSP control mode uses the liberal label retention mode
and so is considered burning too many ATM resources.
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In downstream unsolicited mode, multiple path is not allowed in this
version and will be For Further Study(FFS). We suspect with multiple
next hops and Downstream mode, it is easy to get into loop condition.
3.2.4.0 Control Block
There are 2 types of control blocks involved:
Upstream_LSP_Control_Block, Downstream_LSP_Control_Block.
There is a list of Upstream_LSP_Control_Blocks for each FEC in the
routing table, with each one correspondng to a LDP peer. A
Upstream_LSP_Control_Block is created for each FEC when there is a
label ready to be distributed to that upstream. It is deleted when
the FEC is deleted from the FEC table, or the LDP peer disappears, or
the downstream label is withdrawed.
There is one Downstream_LSP_Control_Blocks for each FEC in the
routing table. It is created when the FEC is inserted into the
forwarding table and deleted when the FEC is removed from the
forwarding table.
An Upstream_LSP_Control_Block may contain the following information:
- Upstream LDP Session Identifier
- State
- Upstream Label(assigned by this LSR)
- FEC
Upstream Label and Upstream LDP Session Identifier, or FEC and
Upstream LDP Session Identifier can be used to locate a unique
Upstream_LSP_Control_Block.
A Downstream_LSP_Control_Block may contain the following information:
- FEC
- State
- Downstream LDP Session Identifier
- Downstream Label(assigned by the downstream LSR)
- Downstream Label Request ID (assigned by the LSR itself)
Downstream Label and Downstream LDP Session Identifier, or FEC and
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Downsteam LDP Session Identifier can be used to locate a unique
Downstream_LSP_Control_Block.
3.2.4.1 States of the Upstream_LSP_Control_Block's State Machine
for Downstream Mode
-- IDLE
This is the initial LSP state.
-- ESTABLISHED
This state means that the LSR has received the LDP-MAPPING message
from the downstream LSR and the LSP is up and operational.
-- RELEASE_AWAITED
This state means that the LSR is waiting for the LDP-RELEASE msg in
respond to the LDP-WITHDRAW sent by this LSR.
-- RESOUCES_AWAITED
This state means that the LSR is waiting for the label resources.
3.2.4.2 Events of the Upstream_LSP_Control_Block's State Machine
for Downstream Mode
-- Internal Downstream Mapping
This event is sent by one Downstream_LSP_Control_Block's state
machine. The event is the result of receiving an LDP-MAPPING message
by the Downstream_LSP_Control_Block's state machine. Or when the LDP
peer is discovered and there is a downstream Label available for this
FEC.
-- LDP Release
The LSR receives an LDP-RELEASE from an upstream LSR.
-- Internal Withdraw
This event is sent by Downstream_LSP_Control_Block's state machine.
The event is the result of receiving an LDP-WITHDRAW message by the
Downstream_LSP_Control_Block's state machine.
-- Resource Available
This event means the local resource(such as label) becomes available.
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-- Delete FEC
This event means that either the FEC is removed from the forwarding
table.
-- Upstream Lost
This event means that the upstream LDP peer is lost.
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3.2.4.3 State Transitions of Upstream_LSP_Control_Block's State
Machine for Downstream Mode
|
|(created when
|a label is to be distributed
| to the LDP peer)
v
+-------------------+
| |
| IDLE |<--------------+
| | |
+-------------------+ |
| |(LDP Release)
| |
| |
| |
|(Internal Downstream |
+-------------------| Mapping) |
| | |
|(no label resource)v |
| +-------------------+ |
| | | |
| +-----| ESTABLISHED |---------------+
| | | | ^
| | +-------------------+ |
| |(delete FEC) ^ |
| |(Internal |(Resource Available) | (LDP Release)
| | Withdraw) | | (Internal
| | | | Downstraem
| | | | Withdraw)
| | +-------------------+ |
+--------->| | |
| |RESOURCES_AWAITED |---------------+
| | | |
| +-------------------+ |
| |
| (Internal Downstream Withdraw) |(LDP Release)
| +-------------------+ |
| | | |
+---->| RELEASE_AWAITED |---------------+
| |
+-------------------+
3.2.4.4 Upstream_LSP_Control_Block's State Machine for
Downstream Mode
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3.2.4.4.1 : State -- "IDLE"
State: IDLE
Event: Internal Downstream mapping
New State: Depends on the action.
Actions
Choose an upstream label, connect the upstream label with the
downstream label. And go to state 'ESTABLISHED'
Propagate the LDP-MAPPING upstream.
If there is no resource for the upstream label, go to state
'RESOURCE_AWAITED'.
State: IDLE
Event: LDP Release
New State: IDLE
Actions
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Internal Downstream Withdraw
New State: IDLE
Actions
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Resource Available
New State: IDLE
Actions
Ignore the event. It is an internal implementation error.
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State: IDLE
Event: Delete FEC
New State: IDLE
Actions
Delete the control block.
State: IDLE
Event: Upstream Lost
New State: IDLE
Actions
Delete the control block.
3.2.4.4.2 : State -- "ESTABLISHED"
State: ESTABLISHED
Event: Internal Downstream Mapping
New State: ESTABLISHED
Actions
Process the new attributes of the new mapping msg.
Propagate the LDP-MAPPING upstream.
State: ESTABLISHED
Event: LDP Release
New State: IDLE
Actions
Disconnect upstream label from downstream label.
Release the upstream label resource
Delete the control block.
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State: ESTABLISHED
Event: Internal Downstream Withdraw
New State: RELEASE_AWAITED
Actions
Disconnect upstream label from downstream label.
Propagate the LDP-WITHDRAW upstream.
State: ESTABLISHED
Event: Resource Available
New State: ESTABLISHED
Actions
Ignore the event. It is an internal implementation error.
State: ESTABLISHED
Event: Delete FEC
New State: RELEASE_AWAITED
Actions
Send a LDP-WITHDRAW upstream.
State: ESTABLISHED
Event: Upstream Lost
New State: IDLE
Actions
Release the upstream label and delete the control block.
3.2.4.4.2 : State -- "RELEASE_AWAITED"
State: RELEASE_AWAITED
Event: Internal Downstream Mapping
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New State: RELEASE_AWAITED
Actions
Ignore the msg.
State: RELEASE_AWAITED
Event: LDP Release
New State: IDLE
Actions
Release the upstream label and delete the control block.
State: RELEASE_AWAITED
Event: Internal Downstream Withdraw
New State: RELEASE_AWAITED
Actions
Ignore the event.
State: RELEASE_AWAITED
Event: Resource Available
New State: RELEASE_AWAITED
Actions
Ignore the event. It is an internal implementation error.
State: RELEASE_AWAITED
Event: Delete FEC
New State: RELEASE_AWAITED
Actions
Do nothing.
State: RELEASE_AWAITED
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Event: Upstream Lost
New State: IDLE
Actions
Release the upstream label and delete the control block.
3.2.4.4.2 : State -- "RESOURCE_AWAITED"
State: RESOURCE_AWAITED
Event: Internal Downstream Mapping
New State: RESOURCE_AWAITED
Actions
Ignore the msg.
State: RESOURCE_AWAITED
Event: LDP Release
New State: RESOURCE_AWAITED
Actions
Ignore the msg. It is an internal implementation error.
State: RESOURCE_AWAITED
Event: Internal Downstream Withdraw
New State: IDLE
Actions
Delete the control block.
State: RESOURCE_AWAITED
Event: Resource Available
New State: ESTABLISHED
Actions
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Allocate an upstream label, connect the upstream label with the
downstream label, and send LDP-MAPPING upstream.
State: RESOURCE_AWAITED
Event: Delete FEC
New State: IDLE
Actions
Delete the control block.
State: RESOURCE_AWAITED
Event: Upstream Lost
New State: IDLE
Actions
Delete the control block.
3.2.4.5 State of the Downstream_LSP_Control_Block's State Machine
for Downstream Mode
-- IDLE
This is the initial LSP state.
-- ESTABLISHED
This state means that the LSR has received the LDP-MAPPING msg from
the downstream LSR.
3.2.4.6 Events of the Downstream_LSP_Control_Block's State Machine
for Downstream Mode
-- LDP Mapping
The LSR receives an LDP-MAPPING msg from a downstream LSR.
-- LDP Withdraw
The LSR receives an LDP-WITHDRAW msg from a downstream LSR.
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-- Delete FEC
The FEC is deleted from the forwarding table.
-- Next Hop Change
The next hop for this FEC is change to different LSR.
-- Downstream Lost
The downstream peer is gone.
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3.2.4.7 State Transitions of Downstream_LSP_Control_Block's State
Machine for Downstream Mode
|
|(FEC is being added into the forwarding
table)
v
+-------------------+
| |
| IDLE |<--------------+
| | |
+-------------------+ |
| |
| |(LDP Withdraw)
| |(Internal New NH)
| |(Downstream Lost)
| (LDP Mapping) |
| |
v |
+-------------------+ |
| | |
| ESTABLISHED |---------------+
| |
+-------------------+
|
|(FEC is deleted from the forwarding table)
v
3.2.4.8 Downstream_LSP_Control_Block's State Machine
for Downstream Mode
3.2.4.8.1 : State -- "IDLE"
State: IDLE
Event: LDP mapping
New State: ESTABLISHED
Actions
For all the LDP peers except the downstream LSR which assigned the
label, create an Upstream_LSP_Control_Block, and pass the event
`Internal Downstream Mapping' to each of the
Upstream_LSP_Control_Block's state machines.
State: IDLE
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Event: LDP withdraw
New State: IDLE
Actions
Ignore the event. It is an internal implementation error.
State: IDLE
Event: Delete FEC
New State: IDLE
Actions
Delete the control block.
State: IDLE
Event: Next Hop Change
New State: IDLE
Actions
Ignore the event.
State: IDLE
Event: Downstream Lost
New State: IDLE
Actions
Ignore the event.
3.2.4.8.1 : State -- "ESTABLISHED"
State: ESTABLISHED
Event: LDP mapping
New State: ESTABLISHED
Actions
For each Upstream_LSP_control_block of this FEC, pass event `Internal
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downstream mapping' to its state machine.
State: ESTABLISHED
Event: LDP withdraw
New State: IDLE
Actions
For each Upstream_LSP_control_block for this FEC, pass event
`Internal downstream Withdraw' to its state machine.
Send a LDP Withdraw downstream.
State: ESTABLISHED
Event: Delete FEC
New State: IDLE
Actions
Send LDP-RELEASE downstream and delete the control block.
State: ESTABLISHED
Event: Next Hop Change
New State: IDLE
Actions
For each Upstream_LSP_control_block for this FEC, pass event
`Internal downstream Withdraw' to its state machine.
Send LDP-REQUEST to the new next hop.
State: ESTABLISHED
Event: Downstream Lost
New State: IDLE
Actions
Send LDP-WITHDRAW to all Upstream_Control_Block's state machine of
this FEC.
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3.2.4.5 LDP Related Message Processing for downstream mode.
- If an LSR receives an LDP-REQUEST message:
If there is a next hop for this FEC and there is a
Downstream_Control_Block for this FEC whose state is 'ESTABLISHED',
create a new Upstream_Control_Block and pass 'internal Mapping' event
to its state machine.
- If an LSR receives an LDP-MAPPING message:
Locate a Downstream_LSP_Control_Block which has the same FEC, the
same Downstream LDP Session Identifier and the same Downstream Label.
If a Downstream_LSP_Control_Block is found, pass the event `LDP
Mapping' to its state table. This could mean that the attributes of
label binding have changed.
Otherwise, if there is no matching Downstream_LSP_Control_Block
found, find a Downstream_LSP_Control_Block of this FEC and its next
hop is the this downstream peer, pass the event `LDP Mapping' to its
state machine.
- If an LSR receives an LDP-RELEASE message:
Locate an Upstream_LSP_Control_Block which has the same FEC, the same
Upstream Label, the same Upstream LDP Session Identifier. If no
Upstream_LSP_Control_Block is found, ignore the message. If an
Upstream_LSP_Control_Block is found, send the event `LDP Release' to
its state machine.
- If an LSR receives an LDP-WITHDRAW message:
Find a Downstream_LSP_Control_Block which has the same FEC, the same
Downstream LDP Session Identifier and the same Downstream Label. Pass
the event `LDP Withdraw' to its state machines.
- If an Upstream LDP peer is lost:
Pass the event `Upstream Lost' to the state machines of all the
Upstream_LSP_Control_Blocks whose upstream LDP peer is that LSR.
- If a Downstream LDP peer is lost:
Pass the event `Label Withdraw' to the state machines of all the
Downstream_LSP_Control_Blocks whose the downstream LDP peer is that
LSR.
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- If a next hop of an FEC is changed:
Find all the Downstream_LSP_Control_Blocks which has the same FEC and
the same next hop and pass the event `Next Hop Change' to their state
machine
- If there is a FEC being added to the forwarding table
Create a new Downstream_LSP_Control_Block with state 'IDLE'
- If the FEC is deleted from the forwarding table
Send the 'Delete FEC' event to the its control block.
- If an LSR receives an LDP-NAK from an Upstream LSR:
Ignore the msg. An LDP-NAK should never appear in the downstream-mode
LSR
- If an LSR receives an LDP-NAK from a downstream LSR:
Ignore the msg. It is an protocol error from the downstream LSR.
4. The Possible Future Works
The following is a list of items that might need to be worked on in
the future:
1) Support senario such that: in a downstream-on-demand mode, a Label
request contains multiple FEC items, whereas the corresponding Label
Withdraw only withdraw one FEC item.
2) The impact of loop detection, loop recovery and loop prevention
3)Once the LSP is operational, whether the LSR can receive an LDP-NAK
message is also debatable.
4)In this draft, for the VC-merge case, the LDP-REQUEST message only
goes up to the merge point. Whether the LDP-REQUEST need to go all
the way to the egress and back in order for the path to be setup
(brute force way) is debatable.
5) Define all the necessary information for the control block. For
example, the ER-HOP list information used to re-build a Label Request
in case of "local repair".
5. Security Considerations
Wu, et al. [Page 76]
INTERNET DRAFT LDP State Machines Feb 1999
Security considerations will be addressed in a future revision of
this document.
6. Acknowledgements
The authors would like to acknowledge the helpful comments and
suggestions of the following people:
7. Authors's Address
Liwen Wu
Alcatel
44983 Knoll Square
Ashburn, VA. 20147
U.S.A
Phone: 703-724-2619
Email:liwen.wu@adn.alcatel.com
Pierrick Cheval
Alcatel
44983 Knoll Square
Ashburn, VA. 20147
U.S.A
Phone: 703-724-2080
Email: pierrick.cheval@adn.alcatel.com
Christophe Boscher
Alcatel CIT
Le Mail
44700 Nantes-Orvault
France
Phone: (33) 251781828
Email: christophe.boscher@or.cit.alcatel.fr
Eric Gray
Lucent Technologies, Inc.
1600 Osgood Street
North Andover, MA 01845
Email: ewgray@lucent.com
8. References
1."Use of Label Switching With ATM", Bruce Davie, Jeremy Lawrence,
Wu, et al. [Page 77]
INTERNET DRAFT LDP State Machines Feb 1999
Keith McCloghrie, Yakov Rekhter, Eric Rosen, George Swallow, Paul
Doolan, work in progress, Internet Draft, <draft-ietf-mpls-atm-01.txt>
2."Multiprotocol Label Switching Architecture", Eric C Rosen, Arun
Viswanathan, Ross Callon, work in progress, Internet Draft, <draft-
ietf-mpls-arch-02.txt>
3."Definition of Managed Objects for the Multiprotocol Label Switching,
Label Distribution Protocol (LDP)", Joan Cucchiara, Hans Sjostrand,
James V. Luciani, work in progress, Internet Draft, <draft-ietf-mpls-
ldp-mib-00.txt>
4."Requirements for Traffic Engineering Over MPLS", Daniel O.Awduche,
Joe Malcolm, Johnson Agogbua, Mike O'Dell, Jim McMaus, work in
progress,Internet Draft, <draft-ietf-mpls-traffic-eng-00.txt>
5. "LDP Specification", Loa Andersson, Paul Doolan,Nancy Feldman, Andre
Fredette, Bob Thomas, work in progress, Internet Draft, <draft-ietf-
mpls-ldp-03.txt>
6. "MPLS Loop Prevention Mechanism", Yoshihiro Ohba, Yasuhiro Katsube,
Eric Rosen, Paul Doolan, work in progress, Internet Draft, <draft-
ohba-mpls-loop-prevention-02.txt>
Wu, et al. [Page 78]
