draft-ietf-pim-ecmp-01.txt   draft-ietf-pim-ecmp-02.txt 
Network Working Group Yiqun Cai Network Working Group Yiqun Cai
Internet-Draft Liming Wei Internet-Draft Liming Wei
Intended status: Standards Track Heidi Ou Intended status: Standards Track Heidi Ou
Expires: May 1, 2012 Cisco Systems, Inc. Expires: August 6, 2012 Cisco Systems, Inc.
Vishal Arya Vishal Arya
Sunil Jethwani Sunil Jethwani
DIRECTV Inc. DIRECTV Inc.
October 29, 2011 February 3, 2012
Protocol Independent Multicast ECMP Redirect Protocol Independent Multicast ECMP Redirect
draft-ietf-pim-ecmp-01.txt draft-ietf-pim-ecmp-02.txt
Abstract Abstract
A PIM router uses RPF procedure to select an upstream interface and A PIM router uses the RPF procedure to select an upstream interface
router to build forwarding state. When there are equal cost multiple and router to build forwarding state. When there are equal cost
paths (ECMP), existing implementations often use hash algorithms to multiple paths (ECMP), existing implementations often use hash
select a path. Such algorithms do not allow the spread of traffic algorithms to select a path. Such algorithms do not allow the spread
among the ECMPs according to administrative metrics. This usually of traffic among the ECMPs according to administrative metrics. This
leads to inefficient or ineffective use of network resources. This usually leads to inefficient or ineffective use of network resources.
document introduces the ECMP Redirect, a mechanism to improve the RPF This document introduces the ECMP Redirect, a mechanism to improve
procedure over ECMPs. It allows ECMP path selection to be based on the RPF procedure over ECMPs. It allows ECMP path selection to be
administratively selected metrics, such as data transmission delays, based on administratively selected metrics, such as data transmission
path preferences and routing metrics. delays, path preferences and routing metrics.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 1, 2012. This Internet-Draft will expire on August 6, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Requirements Notation 1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Introduction 2. Introduction
A PIM [RFC4601] router uses RPF procedure to select an upstream A PIM [RFC4601] router uses the RPF procedure to select an upstream
interface and a PIM neighbor on that interface to build forwarding interface and a PIM neighbor on that interface to build forwarding
state. When there are equal cost multiple paths (ECMP) upstream, state. When there are equal cost multiple paths (ECMP) upstream,
existing implementations often use hash algorithms to select a path. existing implementations often use hash algorithms to select a path.
Such algorithms do not allow the spread of traffic among the ECMP Such algorithms do not allow the spread of traffic among the ECMP
according to administrative metrics. This usually leads to according to administrative metrics. This usually leads to
inefficient or ineffective use of network resources. This document inefficient or ineffective use of network resources. This document
introduces the ECMP Redirect, a mechanism to improve the RPF introduces the ECMP Redirect, a mechanism to improve the RPF
procedure over ECMP. It allows ECMP path selection to be based on procedure over ECMP. It allows ECMP path selection to be based on
administratively selected metrics, such as data transmission delays, administratively selected metrics, such as data transmission delays,
path preferences and routing metrics, or a combination of metrics. path preferences and routing metrics, or a combination of metrics.
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hash value over the destination and source addresses. hash value over the destination and source addresses.
While implementations supporting ECMP have been deployed widely, the While implementations supporting ECMP have been deployed widely, the
existing RPF selection methods have weaknesses. The lack of existing RPF selection methods have weaknesses. The lack of
administratively effective ways to allocate traffic over alternative administratively effective ways to allocate traffic over alternative
paths is a major issue. For example, there is no straightforward way paths is a major issue. For example, there is no straightforward way
to tell two downstream routers to select either the same or different to tell two downstream routers to select either the same or different
RPF neighbor routers for the same traffic flows. RPF neighbor routers for the same traffic flows.
With the ECMP Redirect mechanism introduced here, the upstream With the ECMP Redirect mechanism introduced here, the upstream
routers use a new PIM ECMP Redirect message to instruct the routers use a PIM ECMP Redirect message to instruct the downstream
downstream routers on how to tie-break among the upstream neighbors. routers on how to tie-break among the upstream neighbors. The PIM
The PIM ECMP Redirect message conveys the tie-break information based ECMP Redirect message conveys the tie-break information based on
on metrics selected administratively. metrics selected administratively.
2.1. Overview 2.1. Overview
The existing PIM Assert mechanism allows the upstream router to The existing PIM Assert mechanism allows the upstream router to
detect the existence of multiple forwarders for the same multicast detect the existence of multiple forwarders for the same multicast
flow onto the same downstream interface. The upstream router sends a flow onto the same downstream interface. The upstream router sends a
PIM Assert message containing a routing metric for the downstream PIM Assert message containing a routing metric for the downstream
routers to use for tie-breaking among the multiple upstream routers to use for tie-breaking among the multiple upstream
forwarders on the same RPF interface. forwarders on the same RPF interface.
With ECMP interfaces between the downstream and upstream routers, the With ECMP interfaces between the downstream and upstream routers, the
PIM ECMP Redirect mechanism works in a similar way, but extends the PIM ECMP Redirect mechanism works in a similar way, but extends the
ability to resolve the selection of forwarders among different ability to resolve the selection of forwarders among different
interfaces in the ECMP. interfaces in the ECMP.
When a PIM router downstream of the ECMP interfaces creates a new When a PIM router downstream of the ECMP interfaces creates a new
(*,G) or (S,G) entry, it will populate the RPF interface and RPF (*,G) or (S,G) entry, it will populate the RPF interface and RPF
neighbor information according to the rules specified by [RFC4601]. neighbor information according to the rules specified by [RFC4601].
This router will send its initial joins to that RPF neighbor. This router will send its initial PIM Joins to that RPF neighbor.
When the RPF neighbor router receives the join message and finds that When the RPF neighbor router receives the Join message and finds that
the receiving interface is one of the ECMP interfaces, it will check the receiving interface is one of the ECMP interfaces, it will check
if the same flow is already being forwarded out of another ECMP if the same flow is already being forwarded out of another ECMP
interface. If so, this RPF neighbor router will send a PIM ECMP interface. If so, this RPF neighbor router will send a PIM ECMP
Redirect message onto the interface the join was received on. The Redirect message onto the interface the Join was received on. The
PIM ECMP Redirect message contains the address of the desired RPF PIM ECMP Redirect message contains the address of the desired RPF
neighbor, an interface ID [RFC6395], along with other parameters used neighbor, an interface ID [RFC6395], along with other parameters used
as tie breakers. In essence, a PIM ECMP Redirect message is sent by as tie breakers. In essence, a PIM ECMP Redirect message is sent by
an upstream router to notify downstream routers to redirect PIM Joins an upstream router to notify downstream routers to redirect PIM Joins
to the new RPF neighbor via a different interface. When the to the new RPF neighbor via a different interface. When the
downstream routers receive this message, they should trigger PIM downstream routers receive this message, they should trigger PIM
Joins toward the new RPF neighbor specified in the packet. Joins toward the new RPF neighbor specified in the packet.
This new PIM ECMP Redirect message has similar functions as existing This PIM ECMP Redirect message has similar functions as the existing
PIM Assert message, PIM Assert message,
1. It is sent by an upstream router; 1. It is sent by an upstream router;
2. It is used to influence the RPF selection by downstream routers; 2. It is used to influence the RPF selection by downstream routers;
And And
3. A tie breaker metric is used. 3. A tie breaker metric is used.
However, the existing Assert message is used to select an upstream However, the existing Assert message is used to select an upstream
router within the same multi-access network (such as a LAN) while the router within the same multi-access network (such as a LAN) while the
new Redirect message is used to select both a network and an upstream Redirect message is used to select both a network and an upstream
router. router.
One advantage of this design is that the control messages are only One advantage of this design is that the control messages are only
sent when there is need to "re-balance" the traffic. This reduces sent when there is need to "re-balance" the traffic. This reduces
the amount of control traffic. the amount of control traffic.
2.2. Applicability 2.2. Applicability
The use of ECMP Redirect applies to shared trees or source trees The use of ECMP Redirect applies to shared trees or source trees
built with procedures described in [RFC4601]. The use of ECMP built with procedures described in [RFC4601]. The use of ECMP
Redirect in "Protocol Independent Multicast - Dense Mode" [RFC3973] Redirect in "Protocol Independent Multicast - Dense Mode" [RFC3973]
or in "Bidirectional Protocol Independent Multicast" [RFC5015] is not or in "Bidirectional Protocol Independent Multicast" [RFC5015] is not
considered. considered in this document.
The enhancement described in this document can be applicable to a The enhancement described in this document can be applicable to a
number of scenarios. For example, it allows a network operator to number of scenarios. For example, it allows a network operator to
use ECMP paths and have the ability to perform load splitting based use ECMP paths and have the ability to perform load splitting based
on bandwidth. To do this, the downstream routers perform RPF on bandwidth. To do this, the downstream routers perform RPF
selection with bandwidth instead of IP addresses as a tie breaker. selection with bandwidth instead of IP addresses as a tie breaker.
The ECMP Redirect mechanism assures that all downstream routers The ECMP Redirect mechanism assures that all downstream routers
select the desired network link and upstream router whenever select the desired network link and upstream router whenever
possible. Another example is for a network operator to impose a possible. Another example is for a network operator to impose a
transmission delay limit on certain links. The ECMP Redirect transmission delay limit on certain links. The ECMP Redirect
mechanism provides a mean for an upstream router to instruct a mechanism provides a means for an upstream router to instruct a
downstream router to choose a different RPF path. downstream router to choose a different RPF path.
This specification does not dictate the scope of applications of this This specification does not dictate the scope of applications of this
mechanism. mechanism.
3. Protocol Specification 3. Protocol Specification
3.1. ECMP Bundle 3.1. ECMP Bundle
An ECMP bundle is a set of PIM enabled interfaces on a router, where An ECMP bundle is a set of PIM enabled interfaces on a router, where
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An outgoing interface is considered "non-desired" when, An outgoing interface is considered "non-desired" when,
o The upstream router is already forwarding the same flow out of o The upstream router is already forwarding the same flow out of
another interface belonging to the same ECMP bundle; another interface belonging to the same ECMP bundle;
o The upstream router is not forwarding the flow yet out any o The upstream router is not forwarding the flow yet out any
interfaces of the ECMP bundle, but there is another interface with interfaces of the ECMP bundle, but there is another interface with
more desired attributes. more desired attributes.
An upstream router may choose not to send ECMP Redirects if it An upstream router may choose not to send ECMP Redirects if it
becomes aware that some of the downstream routers do not support the becomes aware that some of the downstream routers do not support the
new message, or unreachable via some links in ECMP bundle. message, or are unreachable via some links in ECMP bundle.
3.3. Receiving ECMP Redirect 3.3. Receiving ECMP Redirect
When a downstream router receives an ECMP Redirect, and detects the When a downstream router receives an ECMP Redirect, and detects that
desired RPF path from its upstream router's point of view is the desired RPF path from its upstream router's point of view is
different from its current one, it should choose to prune from the different from its current one, it should choose to prune from the
current path and join to the new path. The exact order of such current path and join the new path. The exact order of such actions
actions is implementation specific. is implementation specific.
If a downstream router receives multiple ECMP Redirects sent by If a downstream router receives multiple ECMP Redirects sent by
different upstream routers, it SHOULD use the Preference, Metric, or different upstream routers, it SHOULD use the Preference, Metric, or
other fields as specified below, as the tie breakers to choose the other fields as specified below, as the tie breakers to choose the
most preferred RPF interface and neighbor. most preferred RPF interface and neighbor.
If an upstream router receives an ECMP Redirect from another upstream If an upstream router receives an ECMP Redirect from another upstream
router, it SHOULD NOT change its forwarding behavior even if the ECMP router, it SHOULD NOT change its forwarding behavior even if the ECMP
Redirect makes it a less preferred RPF neighbor on the receiving Redirect makes it a less preferred RPF neighbor on the receiving
interface. interface.
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bundle, a downstream router may lose connection to its RPF neighbor bundle, a downstream router may lose connection to its RPF neighbor
and the normal ECMP Redirect operation may be interrupted and the normal ECMP Redirect operation may be interrupted
temporarily. In such an event, the following actions are temporarily. In such an event, the following actions are
recommended. recommended.
The down stream router may re-select a new RPF neighbor. Among all The down stream router may re-select a new RPF neighbor. Among all
ECMP upstream routers, the one on the same LAN as the previous RPF ECMP upstream routers, the one on the same LAN as the previous RPF
neighbor is preferred. neighbor is preferred.
If there is no upstream router reachable on the same LAN, the down If there is no upstream router reachable on the same LAN, the down
stream router will select a RPF neighbor on a different LAN. Among stream router will select an RPF neighbor on a different LAN. Among
all ECMP upstream routers, the one served as RPF neighbor before the all ECMP upstream routers, the one that served as RPF neighbor before
link failure is preferred. Such a router can be identified by the the link failure is preferred. Such a router can be identified by
Router ID which is part of the Interface ID in the PIM ECMP Redirect the Router ID, which is part of the Interface ID in the PIM ECMP
Hello option. Redirect Hello option.
During normal ECMP Redirect operations, when PIM Joins for the same During normal ECMP Redirect operations, when PIM Joins for the same
(*,G) or (S,G) are received on a different LAN, an upstream router (*,G) or (S,G) are received on a different LAN, an upstream router
will send ECMP Redirect to prune the non-preferred LAN. Such ECMP will send ECMP Redirect to prune the non-preferred LAN. Such ECMP
Redirects during partial network outage can be suppressed if the Redirects during partial network outage can be suppressed if the
upstream router decides that the non-preferred PIM Join is from a upstream router decides that the non-preferred PIM Join is from a
router that is not reachable via the preferred LAN. This check can router that is not reachable via the preferred LAN. This check can
be performed by retrieving the downstream's Router ID, using the be performed by retrieving the downstream's Router ID, using the
source address in the PIM join, and searching neighbors on the source address in the PIM Join, and searching neighbors on the
preferred LAN for one with the same router ID. preferred LAN for one with the same router ID.
3.5. Interoperability 3.5. Interoperability
If a PIM router supports this draft, it MUST send the new Hello If a PIM router supports this specification, it MUST send the Hello
option ECMP-Redirect-Supported TLV in its PIM Hello messages. A PIM option ECMP-Redirect-Supported TLV in its PIM Hello messages. A PIM
router sends ECMP Redirects on an interface only when it detects that router sends ECMP Redirects on an interface only when it detects that
all neighbors have sent this Hello option. If a PIM router detects all neighbors have sent this Hello option. If a PIM router detects
that any of its neighbor does not support this Hello option, it MUST that any of its neighbor does not support this Hello option, it MUST
not send ECMP Redirects, however, it SHOULD still process any ECMP not send ECMP Redirects, however, it SHOULD still process any ECMP
Redirects received. Redirects received.
3.6. Packet Format 3.6. Packet Format
3.6.1. PIM ECMP Redirect Hello Option 3.6.1. PIM ECMP Redirect Hello Option
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-- ... Metric ... -+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-- ... Metric ... -+-+-+-+-+-+-+-+-+
| | | |
+- .. Metric .. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +- .. Metric .. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 2: ECMP Redirect Message Format Figure 2: ECMP Redirect Message Format
Type: TBD Type: TBD
Neighbor Address (32/128 bits): Address of desired upstream Neighbor Address (32/128 bits): Address of desired upstream
neighbor where the downstream receiver should redirect PIM Joins neighbor where the downstream receiver should redirect PIM Joins.
to. This address MUST be associated with an interface in the same This address MUST be associated with an interface in the same ECMP
ECMP bundle as the ECMP Redirect message's outgoing interface. If bundle as the ECMP Redirect message's outgoing interface. If the
the "Interface ID" field (see below) is ignored, this "Neighbor "Interface ID" field (see below) is ignored, this "Neighbor
Address" field uniquely identifies a LAN and an upstream router to Address" field uniquely identifies a LAN and an upstream router to
which a downstream router should redirect its Join messages to, which a downstream router should redirect its Join messages, and
and an ECMP Redirect message MUST be discarded if the "Neighbor an ECMP Redirect message MUST be discarded if the "Neighbor
Address" field in the message does not match cached neighbor Address" field in the message does not match cached neighbor
address. address.
Interface ID (64 bits): This field is used in IPv4 when one or more Interface ID (64 bits): This field is used in IPv4 when one or more
RPF neighbors in the ECMP bundle are unnumbered, or in IPv6 where RPF neighbors in the ECMP bundle are unnumbered, or in IPv6 where
link local addresses are in use. For other IPv4 usage, this field link local addresses are in use. For other IPv4 usage, this field
is zero'ed when sent, and ignored when received. If the "Router is zero'ed when sent, and ignored when received. If the "Router
ID" part of the "Interface ID" is zero, the field must be ignored. ID" part of the "Interface ID" is zero, the field must be ignored.
See [RFC6395] for details of its assignment and usage in PIM See [RFC6395] for details of its assignment and usage in PIM
Hellos. If the "Interface ID" is not ignored, the receiving Hellos. If the "Interface ID" is not ignored, the receiving
router of this message MUST use the "Interface ID", instead of router of this message MUST use the "Interface ID", instead of
"Neighbor Address", to identify the new RPF neighbor, and an ECMP "Neighbor Address", to identify the new RPF neighbor, and an ECMP
Redirect message MUST be discarded if the "Interface ID" field in Redirect message MUST be discarded if the "Interface ID" field in
the message does not match cached interface ID. the message does not match the cached interface ID.
Preference (8 bits): The first tie breaker when ECMP Redirects from Preference (8 bits): The first tie breaker when ECMP Redirects from
multiple upstream routers are compared against each other. multiple upstream routers are compared against each other.
Numerically smaller value is preferred. A reserved value (15) is Numerically smaller value is preferred. A reserved value (15) is
used to indicate the metric value following the "Preference" field used to indicate the metric value following the "Preference" field
is a timestamp, taken at the moment the sending router started to is a timestamp, taken at the moment the sending router started to
forward out of this interface. forward out of this interface.
Metric (64 bits): The second tie breaker if the the "Preference" Metric (64 bits): The second tie breaker if the "Preference" values
values are the same. Numerically smaller metric is preferred. are the same. Numerically smaller metric is preferred. This
This "Metric" can contain path parameters defined by users. When "Metric" can contain path parameters defined by users. When both
both "Preference" and "Metric" values are the same, "Neighbor "Preference" and "Metric" values are the same, "Neighbor Address"
Address" or "Interface ID" field is used as the third tie-breaker, or "Interface ID" field is used as the third tie-breaker,
depends on which field is used to identify the RPF neighbor, and depending on which field is used to identify the RPF neighbor, and
the bigger value wins. the bigger value wins.
4. IANA Considerations 4. IANA Considerations
A new PIM Hello Option type is requested to assign to the PIM ECMP A PIM Hello Option Type is requested to be assigned to the PIM ECMP
Redirect Hello Option. According to [HELLO-OPT], this document Redirect Hello Option. According to [HELLO-OPT], this document
recommends 32 (0x20) as the new "PIM ECMP Redirect Hello Option recommends 32 (0x20) as the "PIM ECMP Redirect Hello Option Type".
Type".
A new PIM Type is requested to assign to the ECMP Redirect messages. A PIM Message Type is requested to be assigned to the ECMP Redirect
According to [RFC6166], this document recommends 11 (0xB) as the new message. According to [RFC6166], the next available Type value is 11
"PIM ECMP Redirect Type". (0xB).
5. Security Considerations 5. Security Considerations
Security of the ECMP Redirect is only guaranteed by the security of Security of the ECMP Redirect is only guaranteed by the security of
the PIM packet, the security considerations for PIM Assert packets as the PIM packet, the security considerations for PIM Assert packets as
described in [RFC4601] apply here. Spoofed ECMP Redirect packets may described in [RFC4601] apply here. Spoofed ECMP Redirect packets may
cause the downstream routers to send PIM Joins to an undesired cause the downstream routers to send PIM Joins to an undesired
upstream router, and trigger more ECMP Redirect messages. upstream router, and trigger more ECMP Redirect messages.
6. Acknowledgement 6. Acknowledgement
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