Re: [Lsr] Request WG adoption of TTZ

[Tianran Zhou <[e-mail]>]

Hi Henk,

Thanks very much for your long email.
I fully agree with what you said on the criterion. This is generally always correct. 
But still you cannot score a draft with it.
That means I can probably say most of the IETF RFCs has  no use. 
I can also list one hundred RFCs that is not implemented. Are you going to obsolete them all?
Who knows if they are useful in the future?
If you find it no use, just not to implement it. How could it make your system complex?

Best,
Tianran

-----Original Message-----
From: Henk Smit [mailto:[e-mail]] 
Sent: Thursday, July 16, 2020 4:46 PM
To: Tianran Zhou <[e-mail]>
Cc: Huaimo Chen <[e-mail]>; [e-mail]
Subject: Re: [Lsr] Request WG adoption of TTZ


Hello Tianran,

Warning, long email again.

> What's the criterion to evaluate the benefit?

As people have asked before, did any provider or enterprise ever use rfc8099 in their network ?

As I wrote, one of my criteria is rfc1925. I like technology to be understandable. I like protocols to be (relatively) easy to implement. The more unused cruft there is, the further we get away from that goal.


I'll give you an example. Did you, or your company ever implement rfc2973 ? That's mesh-groups in IS-IS.
I'm sure some customers put it on their wishlist.
Did any provider or customer ever use it ?
I asked this question at my last job, and nobody knew the answer. I suspect nobody in the world ever used mesh-groups.

Around the time I got in touch with IS-IS, in spring 1996, there was a problem that was seen 2 of the 3 largest ISPs in the US (UUnet and iMCI). Both networks melted because of IS-IS. All routers in their networks were 100% cpu time running IS-IS, busy exchanging LSPs. While no progress was made. The only solution was to reboot all routers in the backbone at the same time (several hundred routers).
This happened more than once in both networks.

To relieve the burden of flooding, mesh-groups were implemented, and rfc2973 was written. However, a short while later I became the sole IS-IS programmer for that router vendor. I was able to reproduce the problem in the lab.
I then realized what the issue was. A fix of 10 lines of extra code fixed the problem. No customer ever reported those meltdowns again. That fix was the real solution.
Not writing another RFC.

In the mean-time, we have an extra RFC, about mesh-groups.
Every book and manual on IS-IS has to spent time explaining what mesh-groups are. Every vendor has to implement it.
Even when nobody in the world is using it. Mesh-groups were a superfluous idea. What I (and many others) are saying is that we don't want to specify and implement unnecessary things.
Even when nobody is using such a thing, it will live on forever.

> What I see the TTZ does have benefit.

Yes, TTZ and proxy-areas have benefit. Nobody is disagreeing.

But what people don't like is the new concept of a zone.
If you can abstract exactly one area into exactly one proxy-LSP, that is good enough for 99.9 % of cases. In OSPF it is harder to split or merge an area. In IS-IS it is a lot easier. So a network operator can design and change his areas first. And then implement proxy-areas as she/he wishes. Without much downtime.

If we introduce the concept of a "zone", someone is going to have to explain that to everybody in the world who uses IS-IS.
Have you ever taught a class on IS-IS to people who don't know routing protocols very well ?

> I am also wandering how it hurts the protocol in the long run ?

Adding stuff that nobody uses makes everything more complex.
I know it seems as if the goal over the last 15 years was to make every thing more complex. So what's the problem with adding yet another RFC ?

But I like simple things.

henk.


Tianran Zhou wrote on 2020-07-16 02:41:

> > "Adding a new concept, with very little benefit, hurts the protocol 
> > in the long run. The ability to abstract an area, and not also a 
> > zone, is strong enough to be worthwhile, imho."
> 
> Your conclusion here seems very subjective.
> What's the criterion the evaluate the benefit? What I see the TTZ does 
> have benefit.
> I am also wandering how it hurts the protocol in the long run?
> ....
> 
> Tianran