LAG indication

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶

Internet-Drafts are draft documents valid for a maximum of six months 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."¶

This Internet-Draft will expire on 9 April 2022.¶

Copyright Notice

Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶

Table of Contents

1. Introduction

An IP link may be composed a multiple layer two sub-links not visible to the IGP routing topology. When traffic crossing that IP link is load-balanced on a per flow basis, a large elephant flow will only benefit from the capacity of a single sub-link. This is an issue for the routing logic which only see the aggregated bandwidth of the IP link, and hence may incorrectly route a large flow over a link which is incapable of transporting that flow.¶

This document defines a new link flag to signal that an IP link is a Link Aggregate Group composed of multiple layer two sub-links. This flag may be automatically be set by routing nodes connected to such links, without requiring manual tagging by the network operator. A path computation logic such as a PCE or a CSPF computation on the ingress, may use that information to avoid such links for elephant flows.¶

2. Protocol extensions

3. Operational considerations

A node supporting this extension SHOULD automatically advertise the L2 LAG flag for IP links composed of multiple layer-two sub-components. Configuration knob MAY be provided to override this default.¶

In order to handle nodes not supporting this extension, network operator may need to use an admin group (color) [RFC5305] [RFC7308] in order to flag those links on legacy nodes.¶

4. IANA Considerations

   Value   Name
   ----    --------------------------------
   TBD1    L2 LAG (Link Aggregation Group)

   Bit Number   Description
   ----------   --------------------------------
   TBD2         L2 LAG (Link Aggregation Group)

5. Security Considerations

This extension advertises additional information and capabilities about a link.¶

An attacker having access to this information would gain knowledge that this link has sub components and that sending a large amount of traffic via a single flow (hence not a DOS) is more likely to overload that sub-component. On the other hand, this overloading would be limited to this specific sub-component and hence not affect other sub-component.¶

An attacker been capable of adding this information may gain ability to change the routing of some flow crossing the links, typically large elephant flows specifically configured to avoid such link.¶

An attacker been capable of removing this information may gain the ability to change the routing and direct a large elephant flow on this link, which would overload a sub component of this link and likely create packet drop for this specific flow.¶

However, in those two cases, the attacker would equally have the capability to change other routing information such as the link metric, link usability and any link characteristics. Hence this new information does not add new security considerations. Besides, as with others TLV advertisements, the use of a cryptographic authentication as defined in [RFC5304] or [RFC5310] allows the authentication of the peer and the integrity of the message and remove the ability for an attacker to modify such information.¶

.¶

6. Acknowledgments

TBD.¶

Appendix A. Changes / Author Notes

[RFC Editor: Please remove this section before publication]¶

00: Initial version.¶

01: Refresh.¶

Authors' Addresses