Re: [ippm] [spring] Monitoring metric to detect and locate congestion

[Robert Raszuk <[e-mail]>]

Hi,

Two clarifications:

[RG1] the measurements pass the routers on forwarding plane.

Well if I have 20K CEs and would like to measure this end to end that means
it better run on a router ... I can not envision installing 20K new PCs
just for this. At min such end point it should run on a well designed CPE
as an LXC.

[RG1] Up to now, the conditions in Deutsche Telekom’s backbone network
require a careful design of router probing interval and counters to be
read.

Sure. I actually had in mind telemetry push model where you only get
notified to yr monitoring station when applied queue threshold is crossed.
Very little mgmt traffic in the network limited to only information which
is important.

I know some vendors resist to locally (at LC or local RE) apply filtering
to telemetry streaming but this is IMHO just sick approach.

Thx,
R.





On Wed, Feb 26, 2020 at 12:01 PM <[e-mail]> wrote:

> Hi Robert,
>
>
>
> Thanks, my replies in line marked [RG1]
>
>
>
> I have read your draft and presentation with interest as I am a
> big supporter and in some lab trials  of end to end network path probing.
>
>
>
> Few comments, observations, questions:
>
>
>
> You are essentially measuring and comparing delay across N paths
> traversing known network topology (I love "network tomography" name !)
>
>
>
> [RG1] it’s telemetry with a constrained set up, but the term doesn’t
> appear in the draft yet…that can be changed.
>
>
>
> ------
>
> * First question - this will likely run on RE/RP and in some platforms
> path between LC and RE/RP is completely deterministic and can take 10s or
> 100s of ms locally in the router. So right here the proposal to compare
> anything may not really work - unless the spec mandates that actually
> timestamping is done in hardware on the receiving LC. Then CPU can process
> it when it has cycles.
>
>
>
> [RG1] the measurements pass the routers on forwarding plane. High-end
> routers add variable processing latencies. It’s on a level of double or
> lower triple digit [us] on Deutsche Telekom backbone routers. If a
> dedicated sender receiver system is used, timestamping may be optimized for
> the purpose.
>
> ------
>
>
>
> * Second question is that congestion usually has a very transient
> character ... You would need to be super lucky to find any congestion in
> normal network using test probes of any sort. If you have interfaces always
> congested then just the queue depth time delta may not be visible in end to
> end measurements.
>
>
>
> [RG1] The probing frequency depends on the characteristics of congestion
> the operator wants to be aware of. Unplanned events may cause changes in
> measurement delays lasting for minutes or longer (congestion or hardware
> issues). The duration of a reliably detectable “event” correspond to the
> measurement packet distance (I don’t intend to replace hello-exchanges or
> BFD by the metric).
>
> ------
>
>
>
> * Third - why not simply look at the queue counters at each node ? Queue
> depth, queue history, min, avg, max on a per interface basis offer tons of
> information readily available. Why would anyone need to inject loops of
> probe packets in known network to detect this ? And in black box unknown
> networks this is not going to work as you would not know the network
> topology in the first place. Likewise link down/up is already reflected in
> your syslog via BFD and IGP alarms. I really do not think you need end to
> end protocol to tell you that.
>
>
>
> [RG1] Up to now, the conditions in Deutsche Telekom’s backbone network
> require a careful design of router probing interval and counters to be
> read. The proposed metric allows to capture persistent issues impacting
> forwarding. It points out, where these likely occur. An operator may then
> have a closer look at an interface/router to analyse what’s going on, using
> the full arsenal of accessible information and tools. As unusual events
> happen rarely, it may still be a fair question for which purpose linecard-
> and central processing cycles of routers are consumed.
>
> -------
>
> + Thanks for catching the nit below..
>
>
>
> Regards, Ruediger
>
>
>
> s/nodes L100 and L200 one one/nodes L100 and L200 on one/
>
>
>
> :)
>
>
>
> Many thx,
>
> R.
>
>
>
> On Wed, Feb 26, 2020 at 8:55 AM <[e-mail]> wrote:
>
> Dear IPPM (and SPRING) participants,
>
>
>
> I’m solliciting interest in a new network monitoring metric which allows
> to detect and locate congested interfaces. Important properties are
>
>    - Same scalability as ICMP ping in the sense one measurement relation
>    required per monitored connection
>    - Adds detection and location of congested interfaces as compared to
>    ICMP ping (otherwise measured metrics are compatible with ICMP ping)
>    - Requires Segment Routing (which means, measurement on forwarding
>    layer, no other interaction with passed routers – in opposite to ICMP ping)
>    - Active measurement (may be deployed using a single sender&receiver
>    or separate sender and receiver, Segment Routing allows for both options)
>
>
>
> I’d be happy to present the draft in Vancouver.. If there’s community
> interest. Please read and comment.
>
>
>
> You’ll find slides at
>
>
>
>
> https://datatracker.ietf.org/meeting/105/materials/slides-105-ippm-14-draft-geib-ippm-connectivity-monitoring-00
>
>
>
> Draft url:
>
>
>
> https://datatracker.ietf.org/doc/draft-geib-ippm-connectivity-monitoring/
>
>
>
> Regards,
>
>
>
> Ruediger
>
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