[ippm] Review on draft-ietf-ippm-ioam-data-06

Jai Kumar <jai.kumar@broadcom.com> Wed, 21 August 2019 02:22 UTC

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Date: Tue, 20 Aug 2019 19:22:16 -0700
From: Jai Kumar <jai.kumar@broadcom.com>
To: <draft-ietf-ippm-ioam-data@ietf.org>, IETF IPPM WG <ippm@ietf.org>, "Frank Brockners (fbrockne)" <fbrockne@cisco.com>
CC: Vijay Rangarajan <vijayr@arista.com>, Hugh Holbrook <holbrook@arista.com>, Anoop Ghanwani <Anoop.Ghanwani@dell.com>, "OU, Heidi" <heidi.ou@alibaba-inc.com>, Surendra Anubolu <surendra.anubolu@broadcom.com>, John Lemon <john.lemon@broadcom.com>
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Thread-Topic: [ippm] Review on draft-ietf-ippm-ioam-data-06
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Subject: [ippm] Review on draft-ietf-ippm-ioam-data-06
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Hello Frank,


This is in context of our conversation at IETF105. My goal is to provide input and improve current IOAM data draft with the learnings we had with IFA deployment.

This feedback is based on various customer interactions and concerns raised by them wrt IOAM. Each feedback is a longer topic and I am starting this thread as a summary email. This is just highlighting the issues and not yet proposing any solution. 



Feedback 1:

Section 4.2.1 Pre-allocated and Incremental Trace Options

Pre-allocated and incremental trace option is 8Bytes long. This can be easily reduced to 4Bytes.

There is a feedback that pre-allocated option is really not needed and either be removed or made optional.

Given that deployments are sensitive to the IOAM overhead (specially in 5G deployments), it’s a 50% fixed overhead savings on a per packet basis.



Feedback 2:
Section 4.1 IOAM Namespaces
Namespaces should be treated as templates (similar to IPFIX template record formats). This is more flexible way of enumerating data. 64K namespace id is a very large namespace and can be reduced to 64 IANA specified name spaces. Separate private name space can be allowed instead of interleaving of opaque data in the IANA allocated name space as suggested in the current draft “opaque state snapshot”.



Feedback 3:

Section 4.2.1 Pre-allocated and Incremental Trace Options

IOAM-Trace-Type:  A 24-bit identifier which specifies which data

      types are used in this node data list.

This is the most contentious of all. In the current proposal, as new data fields are added, there is a corresponding trace type bit need in the header. This essentially means that all possible data fields need to be enumerated. Given that we there are 64K names spaces allowed, I don’t see how we can fit all possible data fields in this 24bit vector. I know there was a suggestion of keeping last bit as an extension bit but it is still scalable and/or easy to implement in hardware. Besides this the data fields are not annotated/encoded with the data type, something like in IPFIX https://tools.ietf.org/html/rfc7011#section-6.1


Feedback 4:

There is no version field in the data header and this will make interoperability challenging. Standard will evolve and headers bit definition and/or trace type will change and without version field HW will not be able to correctly handle the IOAM data headers.


Feedback 5:

Handling of TCP/UDP traffic using GRE encap is not acceptable. Here are some of the issues I can think of
GRE encaped IOAM packets will traverse a different network path then the original packet
Not all packets can be GRE encaped to avoid the previous problem, due to wastage of network bandwidth (typically sampled traffic is used for IOAM). What about native GRE traffic, will it get further encaped in another GRE tunnel and so forth.
IP header protocol will point to GRE IP proto and IOAM ethertype (pending allocation by IEEE) need to be read from the GRE header to detect an IOAM packet. This means parsing performance penalty for all regular GRE (non IOAM) traffic.