Re: [Lsr] I-D Action: draft-ietf-lsr-isis-area-proxy-03.txt

[[e-mail]]

Hi Bruno,


> At this point, area proxy spec is clear with regards to nominal behavior. So indeed we are discussing error handling / transitions. (and thank you for considering those cases, much appreciated).
>  
> From memory, my understanding is the area proxy nominal behaviour requires:
> -          All routers in the area are L1 & L2
> -          All inside routers advertise the area proxy TLV
> -          An area leader advertises the Area Proxy System Identifier Sub-TLV


Something that we’re not allowed to talk about in the spec is that we’re assuming that ALL routers in the Inside Area are configured to enable Area Proxy.  Partial configuration is a misconfiguration or transitional to full configuration.

 
> If the above is not fulfilled, what is the expected behaviour? There is a priori 2 options:
> -          A) Return to regular IS-IS behaviour. i.e. all L2 LSPs from inside routers are flooded to L2 outside routers
> o   Pro: no new behaviour/code as this is regular IS-IS. Correct transit forwarding across the area.
> o   Con: suddenly increase size of L2 LSDB
> -          B) Keep filtering L2 LSP from inside routers
> o   Pro: no sudden increase of L2 LSDB size
> o   Con: transit traffic is partially dropped (if area LSP advertised while some routers are L1 only), no transit is possible (if area LSP is not advertised), or partial transit (some inside edge node do not advertise the area proxy TLV).
> §  Lack of transit is not an issue if there is a backup proxy area (e.g. a proxy area a replace a big single chassis).  It’s likely an issue is there is no backup proxy area (e.g. the area has built-in redundancy (e.g. spife/leaf) hence there is no need for another/backup proxy area. Network operator needs to be well aware in order to choose the correct design (rather than experience a bad surprise)
>  
> That’s an open question.
> As this point I do not have a preference, although naively I had “A” in mind. From your below answer, I think that you have “B” in mind. 


Yes. Given the above assumption, we want to assume transition.


> A priori the choice may be dependent on the missing condition.
> Possibly this could be clarified in a “operational consideration” or “error handling” section for network operator to be aware of the behaviour under failure/transition condition.


I’m open to suggestions and/or contributions.


> FYI, I’m considering such failure to be plausible over the years as all it need is one L1 router to boot and not advertise the area proxy TLV or be configured as L1 only.


30 years of doing this says that any crazy thing is possible and WILL happen somewhere, someplace in the fullness of time. Yes, ok, withdrawing the Proxy LSP in these cases is probably not optimal.  What should we say instead? Some failures are clearly fatal, some are not. What’s the right thing to do without a dissertation worth of analysis and special cases?

Tony