Subject: Re: [OSPF] OSPF Topology Transparant Zone

From: "Alvaro Retana (aretana)" <[email-masked]>
Date: Thu, 2 Jan 2014 18:27:32 +0000

On 12/28/13 6:42 PM, "Acee Lindem" <[email-masked]> wrote:

Acee:

Hi!  Happy New Year!

>We've discussed this proposal at several IETF meetings now and at IETF 88
>we committed to more discussion on the list due to the variance in
>opinions. I feel that while the TTZ mechanism has some admirable goals.
>However, I don't believe it satisfies its claims and believe this would
>be apparent if it were to implemented and deployed.

I'm not going to argue with that.  It is very easy to discuss either side
on paper. ;-)

But I do want to clarify one point that you mention several times:
connectivity inside the TTZ.  You mention it when talking about policy and
management.

There is no topology information advertised outside the TTZ, but
reachability *is* advertised.  Specifically Section 6 says:

   In addition, the LSA may contain a third group of links, which are
   stub links for other destinations inside the TTZ. They may be the
   loopback addresses to be accessed by a node outside of the TTZ.

I know you made a point about scalability advertising the reachability
this way.  My point here is just to clarify that (1) there is no
additional policy needed because the reachability is in fact advertised
(unless you have a use case not to), and  (2) there is no change to
management because all the internal nodes should be reachable (besides
being aware of the TTZ, of course).

Alvaro.

> 
>
>The main goal of TTZ is scalability. However, all the comparisons have no
>IP visibility into the TTZ. This begs the question of why the TTZ
>internal routers exist in the first place if there is nothing to be
>advertised outside the TTZ.

>Also, even without any connectivity, there is full mesh of P2P
>connections between TTZ border routers. The LSAs for the border routers
>will change every time any P2P cost across the TTZ changes. Thus one is
>trading more small LSAs for fewer LSAs that are larger and change more
>frequently. This is not necessarily a win.
> 
>
>A secondary claim is that the TTZ requires less policy. However, I don't
>believe it is realistic to have no connectivity inside the TTZ. Hence, we
>will need some type of policy to control what is and isn't leaked. So, we
>are trading a TBD TTZ policy for the area policies that have been
>deployed for decades.

> 
>Given there are no summary LSAs, one will need to advertise these leaked
>routes as stub networks in the TTZ border router-LSAs. This will further
>add to the scaling problems with large frequently changing router-LSAs.
>IMO, this is a very bad tradeoff.
>
>There is also a claim of simpler Traffic Engineering. This assumes that
>the TTZ border routers perform so unspecified magic to make it all
>transparent. It would seem the RSVP signaling would have to somehow be
>made transparent as well as OSPF.
>
>Finally, if the core of the TTZ is opaque - how are providers going to
>manage it? 
>
>Thanks,
>Acee

---

From: Acee Lindem <[email-masked]>
Date: Thu, 2 Jan 2014 18:51:14 +0000

Hi Alvaro, 

>   loopback addresses to be accessed by a node outside of the TTZ.

If you don't have any policy, how do you know WHICH stub networks to advertise outside the TTZ? 

> being aware of the TTZ, of course).

So, I guess you are statically configuring the routers hidden by the TTZ in order to manage them? I don't see this as advancing the art. 

Thanks,
Acee

---

From: "Alvaro Retana (aretana)" <[email-masked]>
Date: Thu, 2 Jan 2014 20:03:27 +0000

On 1/2/14 1:51 PM, "Acee Lindem" <[email-masked]> wrote:

>>. . .

Just like an area border: everything.

To your point before about connectivity inside, why wouldn't you advertise
everything?

>So, I guess you are statically configuring the routers hidden by the TTZ
>in order to manage them? I don't see this as advancing the art.

I don't understand what you mean by 'statically configuring'.

The internal nodes are routers just like any other..yes, they would know
(as written in the draft) that they are internal to the TTZ..just like a
router knows that it is internal to an area.

Alvaro.