[ippm] IOAM Direct Exporting Open Issue
Tal Mizrahi <tal.mizrahi.phd@gmail.com> Sun, 30 August 2020 05:53 UTC
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From: Tal Mizrahi <tal.mizrahi.phd@gmail.com>
Date: Sun, 30 Aug 2020 08:52:31 +0300
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Subject: [ippm] IOAM Direct Exporting Open Issue
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Hi, There is an open issue in the DEX draft about whether to include an explicit Hop Count field in the DEX header, or to rely on the existing Hop_Lim/Node_ID data field. Section 7 of the draft presents the pros and cons of each of these alternatives. This issue has also been discussed on the mailing list a couple of times, and on the last few IPPM meetings. We would like to encourage non-authors to express their opinion about which approach should be taken: (1) use an explicit Hop Count field, or (2) rely on the existing Hop_Lim/Node_ID data field. Cheers, Tal. Here is a link to the draft: https://datatracker.ietf.org/doc/draft-ietf-ippm-ioam-direct-export/ Section 7 of the draft, which presents the two alternatives is quoted here for convenience. Hop Limit / Hop Count: in order to help correlate and order the exported packets, it is possible to include a 1-octet Hop Count field in the DEX header (presumably by claiming some space from the Flags field). Its value starts from 0 at the encapsulating node and is incremented by each IOAM transit node that supports the DEX option. The Hop Count field value is also included in the exported packet. An alternative approach is to use the Hop_Lim/ Node_ID data field; if the IOAM-Trace-Type [I-D.ietf-ippm-ioam-data] has the Hop_Lim/Node_ID bit set, then exported packets include the Hop_Lim/Node_ID data field, which contains the TTL/Hop Limit value from a lower layer protocol. The main advantage of the Hop_Lim/Node_ID approach is that it provides information about the current hop count without requiring each transit node to modify the DEX option, thus simplifying the data plane functionality of Direct Exporting. The main advantage of the Hop Count approach is that it counts the number of IOAM- capable nodes without relying on the lower layer TTL, especially when the lower layer cannot prvide the accurate TTL information, e.g., Layer 2 Ethernet or hierarchical VPN. It also explicitly allows to detect a case where an IOAM-capable node fails to export packets. In order to facilitate the Hop Count approach it is possible to use a flag to indicate an optional Hop Count field, which enables to control the tradeoff. On one hand it addresses the use cases that the Hop_Lim/Node_ID cannot cover, and on the other hand it does not require transit switches to update the option if it is not supported or disabled. Further discussion is required about the tradeoff between the two alternatives.
- [ippm] IOAM Direct Exporting Open Issue Tal Mizrahi
- Re: [ippm] IOAM Direct Exporting Open Issue Frank Brockners (fbrockne)
- Re: [ippm] IOAM Direct Exporting Open Issue Barak Gafni
- Re: [ippm] IOAM Direct Exporting Open Issue MORTON, ALFRED C (AL)
- Re: [ippm] IOAM Direct Exporting Open Issue Haoyu Song
- Re: [ippm] IOAM Direct Exporting Open Issue Haoyu Song
- Re: [ippm] IOAM Direct Exporting Open Issue Tommy Pauly
- Re: [ippm] IOAM Direct Exporting Open Issue Barak Gafni
- Re: [ippm] IOAM Direct Exporting Open Issue Barak Gafni
- Re: [ippm] IOAM Direct Exporting Open Issue Tal Mizrahi
- Re: [ippm] IOAM Direct Exporting Open Issue Tommy Pauly
- Re: [ippm] IOAM Direct Exporting Open Issue Haoyu Song
- Re: [ippm] IOAM Direct Exporting Open Issue Tal Mizrahi
- Re: [ippm] IOAM Direct Exporting Open Issue Frank Brockners (fbrockne)
- Re: [ippm] IOAM Direct Exporting Open Issue Haoyu Song