Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute

[Gyan Mishra <[e-mail]>]

Robert

Responses in-line



On Thu, Jan 13, 2022 at 5:55 AM Robert Raszuk <[e-mail]> wrote:

> Gyan,
>
> I see what the draft is trying to do now. /* I did not even consider this
> for the reason described below. */
>
> But what you wrote requires little correction:
>
> "So now the server you are on gets overloaded and a site cost gets
> advertised in the IGP at which point the connection receives a TCP reset"
>
> if you *s/connection/all connections/* then you quickly realize that what
> is proposed here is a disaster.
>

   Gyan>  Remember this is Anycast proximity based routing along with ECMP
/ UCMP flow based load balancing and most vendors modern routers support
some sort of  x-tuple ECMP/UCMP hash so the flows would be evenly
distributed, so if you have 10s of 100s of paths, the flows would be evenly
distributed across all the paths.  Since it’s Anycast proximity each path
leads to a different Application LB VIP and backend server.  So all the TCP
connections would be uniformly distributed across all the paths.

Only the connections hashed to the path with overloaded server would get
reset and it would be no different then if the server went down as the
connections would get reset anyway in that case.

 In this case instead of being pinned to a bad connection you are now reset
to a good connection resulting in better QOE for the end user and a Happy
customer.

To me thats a positive not a negative.

 A good analogy would be let’s say you are on WIFI and on the same channel
that your neighbors are on and have horrible bandwidth.  Do you stay on
that bad channel and limp along all day or to you flip to an unused channel.

Another example is if you have a server that has run out of resources.  Do
you fail production traffic off the server taking it out of rotation or let
it stay as is and pray things get better.  This draft is a good example of
how IGP can save the day with site metric.

>
> Breaking all existing flows going to one LB to suddenly timeout and all go
> to the other LB(s) is never a technique any one would seriously deploy in a
> production network.
>

Gyan> Application load balancing can be done with DNS based GEO load
balancing based on client and server IP database where you have more
discrete control however the failover is much slower.

>
> Leave alone that doing that has potential to immediately overload the
> other LB(s)/server(s) too.
>

Gyan> The idea with Anycast load balancing is that you may have 10 or even
100s of paths, so if one server fails the load can be evenly distributed
based on statistical multiplexing algorithm calculated by the server teams
engineering the sizing of the server clusters to ensure what you described
won’t happen.

>
> For me the conclusion is that IGP transport level is not the proper layer
> to address the requirement.
>
> Cheers,
> Robert.
>
>
> On Thu, Jan 13, 2022 at 7:05 AM Gyan Mishra <[e-mail]> wrote:
>
>>
>> Hi Les
>>
>> Agreed.
>>
>> My thoughts are that the context of the draft is based on an Anycast VIP
>> address of a server which is proximity based load balancing and not
>> necessarily ECMP/UCMP and only if the proximity is the same for multiple
>> paths to the Anycast VIP would there be a ECMP/UCMP possibility.
>>
>> Let’s say if it’s proximity based and one path is preferred, the flow
>> will take that path.  So now the server you are on gets overloaded and a
>> site cost gets advertised in the IGP at which point the connection receives
>> a TCP reset and flow re-establishes on the alternate path based on the site
>> cost and remains there until the server goes down or  gets overloaded or a
>> better path comes along.
>>
>> For ECMP case, ECMP has flow affinity so the flow will stay on the same
>> path long lived until the connection terminates.
>>
>> So now in ECMP case the flow hashed to a path and maintains its affinity
>> to that path.  Now all of sudden the server gets overloaded and we get a
>> better site cost advertised.  So now the session terminates on current path
>> and establishes again on the Anycast VIP new path based on the site cost
>> advertised.
>>
>> The failover I believe results in the user refreshing their browser which
>> is better than hanging.
>>
>> As the VIP prefix is the only one that experiences reconvergence on new
>> path based on site cost if there is any instability with the servers that
>> will be reflected to the IGP Anycast prefix as well.
>>
>> Is that a good or bad thing.  I think if you had to pick your poison as
>> here the issue Linda is trying to solve is a server issue but leveraging
>> the IGP to force re-convergence when the server is in a half baked state
>> meaning it’s busy and connections are being dropped or very slow QOE for
>> end user.  If you did nothing and let it ride the the user would be stuck
>> on a bad connection.
>>
>> So this solution dynamically fixed the issue.
>>
>> As far as oscillation that is not a big deal as you are in a much worse
>> off state connected to a dying server on its last leg as far as memory and
>> CPU.
>>
>> This solution I can see can apply to any client / server connection and
>> not just 5G and can be used by enterprises as well as SP for their
>> customers to have an drastically improved QOE.
>>
>> I saw some feedback on the TLV and I think once that is all worked out I
>> am in favor of advancing this draft.
>>
>> Kind Regards
>>
>> Gyan
>>
>>
>> On Wed, Jan 12, 2022 at 10:16 PM Les Ginsberg (ginsberg) <
>> [e-mail]> wrote:
>>
>>> Gyan –
>>>
>>>
>>>
>>> The difference between ECMP and UCMP is not significant in this
>>> discussion.
>>>
>>> I don’t want to speak for Robert, but for me his point was that IGPs can
>>> do “multipath” well – but this does not translate into managing flows.
>>>
>>> Please see my other responses on this thread.
>>>
>>>
>>>
>>> Thanx.
>>>
>>>
>>>
>>>     Les
>>>
>>>
>>>
>>>
>>>
>>> *From:* Gyan Mishra <[e-mail]>
>>> *Sent:* Wednesday, January 12, 2022 5:26 PM
>>> *To:* Robert Raszuk <[e-mail]>
>>> *Cc:* Les Ginsberg (ginsberg) <[e-mail]>; Linda Dunbar <
>>> [e-mail]>; [e-mail]
>>> *Subject:* Re: [Lsr] Seeking feedback to the revised
>>> draft-dunbar-lsr-5g-edge-compute
>>>
>>>
>>>
>>>
>>>
>>> Robert
>>>
>>>
>>>
>>> Here are a few examples of UCMP drafts below used in core and data
>>> center use cases.
>>>
>>>
>>>
>>> https://datatracker.ietf.org/doc/html/draft-ietf-bess-evpn-unequal-lb-15
>>>
>>>
>>>
>>> https://datatracker.ietf.org/doc/html/draft-mohanty-bess-weighted-hrw-02
>>>
>>>
>>>
>>> https://datatracker.ietf.org/doc/html/draft-ietf-idr-link-bandwidth
>>>
>>>
>>>
>>> https://datatracker.ietf.org/doc/html/draft-mohanty-bess-ebgp-dmz
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> There are many use cases in routing for unequal cost load balancing
>>> capabilities.
>>>
>>>
>>>
>>> Kind Regards
>>>
>>>
>>>
>>> Gyan
>>>
>>>
>>>
>>> On Wed, Jan 12, 2022 at 2:23 PM Robert Raszuk <[e-mail]> wrote:
>>>
>>> Linda,
>>>
>>>
>>>
>>> > IGP has been used for the Multi-path computation for a long time
>>>
>>>
>>>
>>> IGP can and does ECMP well. Moreover, injecting metric of anycast server
>>> destination plays no role in it as all paths would inherit that external to
>>> the IGP cost.
>>>
>>>
>>>
>>> Unequal cost load balancing or intelligent traffic spread has always
>>> been done at the application layer *for example MPLS*
>>>
>>>
>>>
>>> Thx a lot,
>>>
>>> R.
>>>
>>>
>>>
>>> On Wed, Jan 12, 2022 at 8:18 PM Linda Dunbar <[e-mail]>
>>> wrote:
>>>
>>> Robert,
>>>
>>>
>>>
>>> Please see inline in green:
>>>
>>>
>>>
>>> *From:* Robert Raszuk <[e-mail]>
>>> *Sent:* Wednesday, January 12, 2022 1:00 PM
>>> *To:* Linda Dunbar <[e-mail]>
>>> *Cc:* Les Ginsberg (ginsberg) <[e-mail]>; [e-mail]
>>> *Subject:* Re: [Lsr] Seeking feedback to the revised
>>> draft-dunbar-lsr-5g-edge-compute
>>>
>>>
>>>
>>> Hi Linda,
>>>
>>>
>>>
>>> *[LES:] It is my opinion that what you propose will not achieve your
>>> goals – in part because IGPs only influence forwarding on a per packet
>>> basis – not a per flow/connection basis.*
>>>
>>> *[Linda] Most vendors do support flow based ECMP, with Shortest Path
>>> computed by attributes advertised by IGP.*
>>>
>>>
>>>
>>> I am with Les here. ECMP has nothing to do with his point.
>>>
>>>
>>>
>>> [Linda] Les said that “IGP only influence forwarding on a per packet
>>> basis”.  I am saying that vendors supporting “forwarding per flow” with
>>> equal cost computed by IGP implies  that forwarding on modern routers are
>>> no longer purely per packet basis.
>>>
>>>
>>>
>>>
>>>
>>> Draft says:
>>>
>>>
>>>
>>> *When those multiple server instances share one IP address (ANYCAST),
>>> the transient network and load conditions can be incorporated in selecting
>>> an optimal path among server instances for UEs.*
>>>
>>>
>>>
>>> So if we apply any new metric to indicate load of a single anycast
>>> address how is this going to help anything ?
>>>
>>>
>>>
>>> [Linda] The “Load” or “Aggregated Site Cost” is to differentiate
>>> multiple paths with the same routing distance.
>>>
>>>
>>>
>>>
>>>
>>> You would need a mechanism where the network is smart and say per
>>> src-dst tuple or more spreads the traffic. IGP does not play that game
>>> today I am afraid.
>>>
>>> [Linda] There is one SRC and multiple paths to one DST. IGP has been
>>> used for the Multi-path computation for a long time.
>>>
>>>
>>>
>>> Thank you, Linda
>>>
>>>
>>>
>>> Thx a lot,
>>> R.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Lsr mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/lsr
>>>
>>> --
>>>
>>> [image: Image removed by sender.] <http://www.verizon.com/>
>>>
>>> *Gyan Mishra*
>>>
>>> *Network Solutions Architect *
>>>
>>> *Email [e-mail] <[e-mail]>*
>>>
>>> *M 301 502-1347*
>>>
>>>
>>>
>> --
>>
>> <http://www.verizon.com/>
>>
>> *Gyan Mishra*
>>
>> *Network Solutions A**rchitect *
>>
>> *Email [e-mail] <[e-mail]>*
>>
>>
>>
>> *M 301 502-1347*
>>
>> --

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *

*Email [e-mail] <[e-mail]>*



*M 301 502-1347*