Re: [Lsr] Request WG adoption of TTZ

[Henk Smit <[e-mail]>]

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