draft-ietf-softwire-lb-03.txt   rfc5640.txt 
Network Working Group C. Filsfils Network Working Group C. Filsfils
Internet-Draft P. Mohapatra Request for Comments: 5640 P. Mohapatra
Intended status: Standards Track C. Pignataro Category: Standards Track C. Pignataro
Expires: November 9, 2009 Cisco Systems Cisco Systems
May 8, 2009 August 2009
Load Balancing for Mesh Softwires
draft-ietf-softwire-lb-03
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Load-Balancing for Mesh Softwires
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Abstract
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at Payloads transported over a Softwire mesh service (as defined by BGP
http://www.ietf.org/ietf/1id-abstracts.txt. Encapsulation Subsequent Address Family Identifier (SAFI) information
exchange) often carry a number of identifiable, distinct flows. It
can, in some circumstances, be desirable to distribute these flows
over the equal cost multiple paths (ECMPs) that exist in the packet
switched network. Currently, the payload of a packet entering the
Softwire can only be interpreted by the ingress and egress routers.
Thus, the load-balancing decision of a core router is only based on
the encapsulating header, presenting much less entropy than available
in the payload or the encapsulated header since the Softwire
encapsulation acts in a tunneling fashion. This document describes a
method for achieving comparable load-balancing efficiency in a
network carrying Softwire mesh service over Layer Two Tunneling
Protocol - Version 3 (L2TPv3) over IP or Generic Routing
Encapsulation (GRE) encapsulation to what would be achieved without
such encapsulation.
The list of Internet-Draft Shadow Directories can be accessed at Status of This Memo
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on November 9, 2009. This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 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 in effect on the date of Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info). publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. and restrictions with respect to this document.
Abstract
Payloads carried over a Softwire mesh service as defined by BGP
Encapsulation Subsequent Address Family Identifier (SAFI) information
exchange often carry a number of identifiable, distinct flows. It
can in some circumstances be desirable to distribute these flows over
the equal cost multiple paths (ECMPs) that exist in the packet
switched network. Currently, the payload of a packet entering the
Softwire can only be interpreted by the ingress and egress routers.
Thus the load balancing decision of a core router is only based on
the encapsulating header, presenting much less entropy than available
in the payload or the encapsulated header since the Softwire
encapsulation acts in a tunneling fashion. This document describes a
method for achieving comparable load balancing efficiency in a
network carrying Softwire mesh service over Layer Two Tunneling
Protocol - Version 3 (L2TPv3) over IP or Generic Routing
Encapsulation (GRE) encapsulation to what would be achieved without
such encapsulation.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 2
2. Load Balancing Block sub-TLV . . . . . . . . . . . . . . . . . 3 2. Load-Balancing Block sub-TLV . . . . . . . . . . . . . . . . . 2
2.1. Applicability to Tunnel Types . . . . . . . . . . . . . . . 4 2.1. Applicability to Tunnel Types . . . . . . . . . . . . . . . 3
2.2. Encapsulation Considerations . . . . . . . . . . . . . . . 5 2.2. Encapsulation Considerations . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . . 6 6. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
Consider the case of a router R1 which encapsulates a packet P into a Consider the case of a router R1 that encapsulates a packet P into a
Softwire bound to router R3. R2 is a router on the shortest path Softwire bound to router R3. R2 is a router on the shortest path
from R1 to R3. R2's shortest path to R3 involves equal cost multiple from R1 to R3. R2's shortest path to R3 involves equal cost multiple
paths (ECMPs). The goal is for R2 to be able to choose which path to paths (ECMPs). The goal is for R2 to be able to choose which path to
use on the basis of the full entropy of packet P. use on the basis of the full entropy of packet P.
This is achieved by carrying in the encapsulation header a signature This is achieved by carrying in the encapsulation header a signature
of the inner header, hence enhancing the entropy of the flows as seen of the inner header, hence enhancing the entropy of the flows as seen
by the core routers. The signature is carried as part of one of the by the core routers. The signature is carried as part of one of the
fields of the encapsulation header. To aid with better description fields of the encapsulation header. To aid with better description
in the document, we define the generic term "load balancing field" to in the document, we define the generic term "load-balancing field" to
mean such a value that is specific to an encapsulation type. For mean such a value that is specific to an encapsulation type. For
example, for L2TPv3-over-IP [RFC3931] encapsulation, the load example, for L2TPv3-over-IP [RFC3931] encapsulation, the load-
balancing field is the Session Identifier (Session ID). For GRE balancing field is the Session Identifier (Session ID). For GRE
[RFC2784] encapsulation, the key field [RFC2890], if present, [RFC2784] encapsulation, the Key field [RFC2890], if present,
represents the load balancing field. This mechanism assumes that represents the load-balancing field. This mechanism assumes that
core routers base their load balancing decisions on a flow definition core routers base their load-balancing decisions on a flow definition
that includes the load balancing field. This is an obvious and that includes the load-balancing field. This is an obvious and
generic functionality as, for example, for L2TPv3-over-IP tunnels, generic functionality as, for example, for L2TPv3-over-IP tunnels,
the Session ID is at the same well-known constant offset as the TCP/ the Session ID is at the same well-known constant offset as the TCP/
UDP ports in the encapsulating header. UDP ports in the encapsulating header.
The "Encapsulation SAFI" [RFC5512] is extended such that a contiguous The Encapsulation SAFI [RFC5512] is extended such that a contiguous
block of the load balancing field is bound to the Softwire advertised block of the load-balancing field is bound to the Softwire advertised
by a BGP next-hop. On a per-inner flow basis, the ingress PE selects by a BGP next-hop. On a per-inner-flow basis, the ingress Provider
one value of the load balancing field from the block to preserve per- Edge (PE) selects one value of the load-balancing field from the
flow ordering, and at the same time to enhance the entropy across block to preserve per-flow ordering and, at the same time, to enhance
flows. the entropy across flows.
1.1. Requirements Language 1.1. Requirements Language
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 RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Load Balancing Block sub-TLV 2. Load-Balancing Block sub-TLV
This document defines a new sub-TLV for use with the Tunnel This document defines a new sub-TLV for use with the Tunnel
Encapsulation Attribute defined in [RFC5512]. The new sub-TLV is Encapsulation Attribute defined in [RFC5512]. The new sub-TLV is
referred to as the "Load Balancing Block sub-TLV" and MAY be included referred to as the "Load-Balancing Block sub-TLV" and MAY be included
in any Encapsulation SAFI UPDATE message where load balancing is in any Encapsulation SAFI UPDATE message where load-balancing is
desired. desired.
The sub-TLV type of the Load Balancing Block sub-TLV is 5. The sub- The sub-TLV type of the Load-Balancing Block sub-TLV is 5. The sub-
TLV length is 2 octets. The value represents the length of the block TLV length is 2 octets. The value represents the length of the block
in bits and it MUST NOT exceed the size of the load balancing field. in bits and MUST NOT exceed the size of the load-balancing field.
This format is very similar to the variable-length subnet masking This format is very similar to the variable-length subnet masking
(VLSM) used in IP addresses to allow arbitrary length prefixes. The (VLSM) used in IP addresses to allow arbitrary length prefixes. The
block is determined by extracting the initial sequence of 'block block is determined by extracting the initial sequence of 'block
size' bits from the load balancing field. size' bits from the load-balancing field.
If a load balancing field is not signaled (e.g., if the Encapsulation If a load-balancing field is not signaled (e.g., if the encapsulation
sub-TLV is not included in an advertisement as in the case of GRE sub-TLV is not included in an advertisement as in the case of GRE
without a Key), then the Load Balancing Block sub-TLV MUST NOT be without a Key), then the Load-Balancing Block sub-TLV MUST NOT be
included. included.
The smaller the value field of the Load Balancing Block sub-TLV, the The smaller the value field of the Load-Balancing Block sub-TLV, the
larger the space for per-flow identification, and hence the better larger the space for per-flow identification, and hence the better
entropy for potential load-balancing in the core; in addition, the entropy for potential load-balancing in the core, as well as, the
lower the polarization when mapping flows to ECMP paths. However, lower the polarization when mapping flows to ECMP paths. However,
reducing the load balancing block size consumes more L2TPv3 Session reducing the load-balancing block size consumes more L2TPv3 Session
IDs or GRE keys, resulting in potentially less number of supported IDs or GRE Keys, resulting in potentially less numbers of supported
services. A typical deployment would need to arbitrate between this services. A typical deployment would need to arbitrate between this
trade-off. trade-off.
As an example, Assume that there is a Softwire set up between R1 and As an example, assume that there is a Softwire set up between R1 and
R3 with L2TPv3-over-IP tunnel type. Assume that R3 encodes the R3 with L2TPv3-over-IP tunnel type. Assume that R3 encodes the
Session ID with value 0x1234ABCD in the encapsulation sub-TLV. It Session ID with value 0x1234ABCD in the encapsulation sub-TLV. It
also includes the load balancing block sub-TLV and encodes the value also includes the Load-Balancing Block sub-TLV and encodes the value
24. This should be interpreted as follows: 24. This should be interpreted as follows:
o If an ingress router does not understand Load Balancing Block sub- o If an ingress router does not understand the Load-Balancing Block
TLV, it continues to use the Session ID 0x1234ABCD and sub-TLV, it continues to use the Session ID 0x1234ABCD and
encapsulates all packets with that Session ID, encapsulates all packets with that Session ID.
o If an ingress router understands Load Balancing Block sub-TLV, it o If an ingress router understands the Load-Balancing Block sub-TLV,
picks the first 24 bits out of the Session ID (0x1234AB) to be it picks the first 24 bits out of the Session ID (0x1234AB) to be
used as the block and fills in the lower-order 8 bits with a per- used as the block and fills in the lower-order 8 bits with a per-
flow identifier (e.g. it can be determined based on the inner flow identifier (e.g., it can be determined based on the inner
packet's source, destination addresses and TCP/UDP ports). This packet's source, destination addresses, and TCP/UDP ports). This
selection preserves per-flow ordering of packets. selection preserves the per-flow ordering of packets.
This requirement and solution applies equally to GRE where the key This requirement and solution applies equally to GRE where the Key
plays the same role as the Session ID in L2TPv3. plays the same role as the Session ID in L2TPv3.
Needless to say, if an egress router does not support load balancing Needless to say, if an egress router does not support the Load-
block sub-TLV, the Softwire continues to operate with a single load Balancing Block sub-TLV, the Softwire continues to operate with a
balancing field that all ingress routers encapsulate with. single load-balancing field with which all ingress routers
encapsulate.
2.1. Applicability to Tunnel Types 2.1. Applicability to Tunnel Types
The load balancing block sub-TLV is applicable to Tunnel types that The Load-Balancing Block sub-TLV is applicable to tunnel types that
define a load balancing field. This document defines load balancing define a load-balancing field. This document defines load-balancing
fields for tunnel types 1 (L2TPv3 over IP) and 2 (GRE) as follows: fields for tunnel types 1 (L2TPv3 over IP) and 2 (GRE) as follows:
o L2TPv3 over IP - Session ID. Special care needs to be taken to o L2TPv3 over IP - Session ID. Special care needs to be taken to
always create a non-zero Session ID. When an egress router always create a non-zero Session ID. When an egress router
includes a load balancing sub-TLV, it MUST encode the Session ID includes a Load-Balancing Block sub-TLV, it MUST encode the
field of the Encapsulation sub-TLV in a way that ensures that the Session ID field of the encapsulation sub-TLV in a way that
most significant bits of the Session ID after extracting the block ensures that the most significant bits of the Session ID, after
are non-zero. extracting the block, are non-zero.
o GRE - GRE key o GRE - GRE Key
This document does not define a load balancing field for the IP in IP This document does not define a load-balancing field for the IP-in-IP
Tunnel Type (tunnel types 7). Future tunnel types that desire to use tunnel type (tunnel types 7). Future tunnel types that desire to use
the load balancing sub-TLV MUST define a load balancing field that is the Load-Balancing Block sub-TLV MUST define a load-balancing field
part of the encapsulating header. that is part of the encapsulating header.
2.2. Encapsulation Considerations 2.2. Encapsulation Considerations
Fields included in the encapsulation header besides the load Fields included in the encapsulation header besides the load-
balancing field are not affected by the load balancing block sub-TLV. balancing field are not affected by the Load-Balancing Block sub-TLV.
All other encapsulation fields are shared between variations of the All other encapsulation fields are shared between variations of the
load balancing field. For example, for L2TPv3-over-IP tunnel type, load-balancing field. For example, for the L2TPv3-over-IP tunnel
if the optional cookie is included in the Encapsulation sub-TLV by type, if the optional cookie is included in the encapsulation sub-TLV
the egress router during Softwire signaling, it applies to all the by the egress router during Softwire signaling, it applies to all the
"Session ID" values derived at the ingress router after applying the "Session ID" values derived at the ingress router after applying the
load balancing block as described in this document. load-balancing block as described in this document.
3. IANA Considerations 3. IANA Considerations
IANA is requested to assign the Type of 5 for the Load Balancing IANA has assigned the value 5 for the Load-Balancing Block sub-TLV,
Block sub-TLV, in the BGP Tunnel Encapsulation Attribute Sub-TLVs in the BGP Tunnel Encapsulation Attribute Sub-TLVs registry (number
registry (number space created as part of the publication of space created as part of the publication of [RFC5512]):
[RFC5512]):
Sub-TLV name Type Sub-TLV name Value
------------- ----- ------------- -----
Load Balancing Block 5 Load-Balancing Block 5
4. Security Considerations 4. Security Considerations
This document defines a new sub-TLV for the BGP Tunnel Encapsulation
Attribute. Security considerations for the BGP Encapsulation SAFI
and the BGP Tunnel Encapsulation Attribute are covered in [RFC5512].
There are no additional security risks introduced by this design. There are no additional security risks introduced by this design.
5. Acknowledgements 5. Acknowledgements
The authors would like to thank Stewart Bryant, Mark Townsley, Rajiv The authors would like to thank Stewart Bryant, Mark Townsley, Rajiv
Asati, Kireeti Kompella, and Robert Raszuk for their review and Asati, Kireeti Kompella, and Robert Raszuk for their review and
comments. comments.
6. Normative References 6. Normative References
skipping to change at page 6, line 33 skipping to change at page 6, line 12
Subsequent Address Family Identifier (SAFI) and the BGP Subsequent Address Family Identifier (SAFI) and the BGP
Tunnel Encapsulation Attribute", RFC 5512, April 2009. Tunnel Encapsulation Attribute", RFC 5512, April 2009.
Authors' Addresses Authors' Addresses
Clarence Filsfils Clarence Filsfils
Cisco Systems Cisco Systems
Brussels, Brussels,
Belgium Belgium
Email: cfilsfil@cisco.com EMail: cfilsfil@cisco.com
Pradosh Mohapatra Pradosh Mohapatra
Cisco Systems Cisco Systems
170 W. Tasman Drive 170 W. Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA USA
Email: pmohapat@cisco.com EMail: pmohapat@cisco.com
Carlos Pignataro Carlos Pignataro
Cisco Systems Cisco Systems
7200 Kit Creek Road, PO Box 14987 7200 Kit Creek Road, PO Box 14987
Research Triangle Park, NC 27709 Research Triangle Park, NC 27709
USA USA
Email: cpignata@cisco.com EMail: cpignata@cisco.com
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