Internet DRAFT - draft-raunak-pim-gir-support
draft-raunak-pim-gir-support
Network Working Group R. Chokkanathapuram
Internet-Draft R. Banthia
Intended status: Standards Track Cisco Systems, Inc.
Expires: December 30, 2018 June 28, 2018
PIM Router Graceful Insertion and Removal
draft-raunak-pim-gir-support-00
Abstract
Graceful Insertion and Removal (GIR) of routers is often adopted by
many network administrators as an alternative to ISSU. This document
discusses various scenarios, requirements and possible solutions to
make PIM gracefully shut down and isolate the multicast router with
minimal network disruption when a router goes through maintenance
procedures.
Status of This Memo
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This Internet-Draft will expire on December 30, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Graceful RPF change . . . . . . . . . . . . . . . . . . . . . 2
5. GIR removal procedure for a PIM router . . . . . . . . . . . 3
6. GIR insertion procedure for a PIM router . . . . . . . . . . 4
7. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 5
8. PIM GIR TLV . . . . . . . . . . . . . . . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
10. Security Considerations . . . . . . . . . . . . . . . . . . . 5
11. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
When a network administrator wishes to perform maintenance activity
on a router, a system maintenance mode command need to be configured.
This isolates the router from the network by gracefully shutting down
various protocols running on the router. Multicast protocols will
also require graceful migration in order to achieve minimal traffic
disruption when a maintenance activity is performed on a router.
This document proposes a possible solution to perform GIR with PIM
routers gracefully.
2. Terminology
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 [RFC2119] .
With respect to PIM, this document follows the terminology that has
been defined in [RFC7761]
3. Applicability
The proposed change described in this specification applies to PIM
routers only.
4. Graceful RPF change
Multicast routing protocol uses Unicast reachability information to
find unique Reverse Path Forwarding Neighbor (RPF). Any change in
unicast routing triggers multicast RPF changes. Multicast flows need
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to change the RPF in a graceful manner to have minimal or no
disruption in traffic flow. To achieve graceful RPF change, PIM
should not change RPF immediately following unicast routing change.
PIM should join the new path and wait for the traffic to arrive on
the new path before pruning the old path. Until the packets arrive
on the new path, the packets are accepted and forwarded on the old
path. Since we have not changed the RPF to new one, we would see RPF
failures. The RPF failures on the new path will indicate that the
flow is available on the new path, upon which the RPF for the flows
will be changed from old to new. Using this method, we will be able
to achieve non-stop forwarding of multicast traffic thereby
minimizing traffic disruption. The graceful RPF change, however, is
not advisable in a normal RPF change scenario. This is because old
path could be down due to link failures and the RPF change may take
more time which could increase convergence time. Multicast flows can
do a graceful RPF change in a GIR scenario since the flow will be
available via the old path.
5. GIR removal procedure for a PIM router
A multicast router undergoing a graceful insertion/removal must
indicate the same to all the routers in PIM domain. This will ensure
that all routers will gracefully change RPF for the multicast flows
within the GIR window. This information needs to be propagated
before the unicast metrics are altered by the GIR router. To achieve
this, a PIM Flooding Mechanism message (PFM) [RFC8364] TLV is
originated from the router undergoing GIR. The GIR details will be
carried in the PFM TLV. This message is flooded periodically in the
PIM domain and the RECOMMENDED interval to send this message is 60
secs. The propagation of this message will ensure that all the
routers (in the PIM domain) knows the router undergoing GIR and can
gracefully migrate flows from old path to new path when the unicast
infinite metrics are advertised from the router undergoing GIR in the
GIR window.
Procedure for PIM routers (GIR mode)-
1. The router undergoing GIR (GIR router) will send a PFM message
with a new TLV option (GIR TLV) to all its PIM neighbors
indicating that the router wishes to go to maintenance mode. The
router could send more than one PFM message so that the loss of
the PFM messages are minimized. The value fields in the TLV will
be populated with the following hold-time values -
1. graceful-rpf-start - This value indicates the seconds until
the PIM router will start doing graceful RPF change
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2. graceful-rpf-stop - This value indicates the seconds after
which the PIM router will stop doing graceful RPF change.
The time period between the graceful-rpf-start and graceful-
rpf-stop indicates the duration during which the routers in
the network will do graceful RPF changes for multicast flow.
2. Upon receipt of the PFM message with GIR TLV option from GIR
router, PIM neighbors will compute the RPF towards the originator
ip address in the incoming PFM message. If the RPF matches with
the interface where this message is received, the router will
perform the following, else pim will just drop the message.
1. Start a timer for graceful-rpf-start, if not already started.
Once the graceful-rpf-start timer expires, the routers will
be in graceful RPF change mode until the hold-time period
stop. During this time period, router will do Graceful RPF
change (as described in section above) as soon as it receives
unicast metric change. The unicast infinite metric change
from the router undergoing GIR has to be sequenced between
the advertised graceful-rpf-start and graceful-rpf-stop.
2. Forward PFM message with the GIR TLV to its immediate PIM
neighbors. This is to propagate PFM message with the GIR TLV
to all the routers in the PIM domain.
The above method could be further optimized if PFM messages could
carry the source prefixes of the multicast states present on the GIR
router. The routers receiving the PFM GIR message can examine the
source prefixes and move to Graceful RPF change mode only if the
routers have the multicast state for the source prefixes. With this,
not all routers needs to do Graceful RPF change. This will ensure
Graceful RPF change occurs only on the routers that are impacted by
the router undergoing GIR.
6. GIR insertion procedure for a PIM router
The same method as described above will be used to gracefully insert
a router with no traffic disruption after system maintenance mode.
When a router is inserted into network, it will send the PFM GIR
message with the graceful-rpf-start timer value set to 0, and
graceful-rpf-stop timer set to seconds until Graceful RPF stop.
During this window, the inserted router will start bringing up the
unicast protocols. Every router in the PIM domain will examine the
PFM message and do a Graceful RPF change for the window specified in
the message. Once the GIR router is inserted and fully operational,
it should send at least one message with both timers (graceful-rpf-
start and graceful-rpf-stop) set to 0
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7. Compatibility
The router undergoing GIR must set the Transitive bit to 1 in the PFM
message so that when a router that doesn't support GIR, receives a
PFM GIR TLV, it will forward the message to the PIM neighbors.
8. PIM GIR 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Type = TBD | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Graceful RPF Start |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Graceful RPF Stop |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PIM GIR TLV
where
Type : TBD
Length : The length of the value in octets
Graceful RPF Start : Timer value in seconds until PIM router start
doing graceful RPF change
Graceful RPF Stop : Timer value in seconds after which the PIM
router will stop doing graceful RPF change
9. IANA Considerations
A new PIM PFM option is TBD for GIR.
10. Security Considerations
Security of the new PFM TLV is only guaranteed by the security of PFM
message, so the security considerations for PFM message as described
in [RFC8364] apply here.
11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8364] Wijnands, IJ., Venaas, S., Brig, M., and A. Jonasson, "PIM
Flooding Mechanism (PFM) and Source Discovery (SD)",
RFC 8364, DOI 10.17487/RFC8364, March 2018,
<https://www.rfc-editor.org/info/rfc8364>.
Authors' Addresses
Ramakrishnan Chokkanathapuram
Cisco Systems, Inc.
Tasman Drive
San Jose CA 95134
United States of America
Email: ramaksun@cisco.com
Raunak Banthia
Cisco Systems, Inc.
Tasman Drives
San Jose CA 95134
United States of America
Email: rbanthia@cisco.com
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