Re: Congestion/latency-aware routing for MPLS?

[Dave Taht <dave.taht () gmail com>]

We have been hoping to find use cases for the babel protocol's rtt
metric, which builds on ideas from ntp, and is primarily used today in
overlay networks:
https://datatracker.ietf.org/doc/draft-ietf-babel-rtt-extension/


On Wed, Oct 18, 2023 at 7:17 AM Jason R. Rokeach via NANOG
<nanog () nanog org> wrote:
> Hi Adam,
> This sounds like a use case for MPLS-TE with TWAMP-Light. TWAMP-Light handles the latency concern and can encode your 
> measured latency in IS-IS. Juniper docs: 
> https://www.juniper.net/documentation/us/en/software/junos/is-is/topics/topic-map/enable-link-delay-advertise-in-is-is.html.
>  The configuration in steps 5 and 7 is all thats required (from a config standpoint) to get the data into IS-IS.
> You then, when building an RSVP LSP, would specify a constraint for the latency. Alternatively you can route by 
> latency on its own by setting the metric to latency, but as you've alluded to, this can be pretty dangerous in 
> environments with mixed bandwidth availability.
>
> The other option afforded for the second point on traffic balance is to use auto-bandwidth 
> (https://www.juniper.net/documentation/us/en/software/junos/mpls/topics/topic-map/basic-lsp-configurtion.html#id-configuring-automatic-bandwidth-allocation-for-lsps
>  - see also https://archive.nanog.org/sites/default/files/tues.general.steenbergen.autobandwidth.30.pdf).
>
> Other vendors support this as well.
> SR supports the use of TWAMP-Light as well if you prefer that over RSVP, but it doesn't support auto-bandwidth.
>
> _______________________
> Jason R. Rokeach
> m: 603.969.5549
> e: jason () rokea ch
> tg: jasonrokeach
>
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>
> ------- Original Message -------
> On Wednesday, October 18th, 2023 at 9:13 AM, Adam Thompson - athompson at merlin.mb.ca 
> <athompson_at_merlin_mb_ca_cbbhoxs () simplelogin co> wrote:
>
> Using a mix of Juniper hardware...
>
> Network provides VPLS to customer, over MPLS (obviously) in a dual-redundant-ring radio topology.  Each site is 
> connected to one or more neighbors, generally with two radios, in two different bands, to *each* neighbor.  So an 
> ordinary node might have 4 radios, 2 pointing in each direction.
>
> Every single radio link has different bandwidth, different latency, and different interference characteristics.
>
> These radio links do run at 100% capacity at least some of the time.
>
> It's possible to set each link's relative cost in OSPF or IS-IS, of course, but I haven't found a way to make the 
> router react to latency changes on one link or the other.  (Right now, I think costs are set equal so traffic will 
> use both links.)  This means interference in one band invisibly diminishes the Ethernet bandwidth available and 
> silently increases the latency on that link, sometimes dramatically.  This seems to do interestingly unpleasant 
> things to the client's flows.
>
> It's generally true that one band will be much more severely affected than the other, in any interference event.  
> Before anyone asks, I'm told the network is a mixture of licensed and unlicensed bands, that's not changing anytime 
> soon.
>
> In a perfect world, I'd like the routers to dynamically adjust traffic balance, but even just temporarily halting use 
> of the impaired link would be helpful (or so I believe right now, at least).
>
> Is this a pipe dream?  I'm not seeing anything in JunOS that could accomplish this...  I'm not even sure if a mesh 
> protocol could handle dual active links like this?
>
> Ideas, comments, etc. all appreciated.
>
> Also, I'm not the direct operator of use network. I'm involved, but mostly just trying to help them find better 
> solutions.  Nor am I an MPLS expert, as is obvious here.
>
> Thanks,
> -Adam
>
> Adam Thompson
>
> Consultant, Infrastructure Services
>
> MERLIN
>
> 100 - 135 Innovation Drive
>
> Winnipeg, MB R3T 6A8
>
> (204) 977-6824 or 1-800-430-6404 (MB only)
>
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>
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-- 
Oct 30: https://netdevconf.info/0x17/news/the-maestro-and-the-music-bof.html
Dave Täht CSO, LibreQos