RE: Questions on GMPLS ASON OSPF-TE ID

["Bardalai, Snigdho" <Snigdho.Bardalai@us.fujitsu.com>]

Title: Re: Questions on GMPLS ASON OSPF-TE ID

Hi Dimitri,

 

Thanks for your responses. Please see in-line for [SCB]

 

Snigdho

 

 

---

From: dimitri papadimitriou [mailto:dpapadimitriou@psg.com]
Sent: Mon 11/6/2006 6:12 PM
To: Bardalai, Snigdho
Cc: ccamp; rabbat@alum.mit.edu
Subject: Re: Questions on GMPLS ASON OSPF-TE ID

hi - see inline

Bardalai, Snigdho wrote:

> Hi Dimitri,
> 
> As mentioned in today's meeting I have the following questions on this
> ID:
> 
> 1. The Addressing Draft requires that the TERouterID to be an addressable IP
>     address i.e. one can ping this address.
> 
>     The ID needs to clearly state what is the requirement for ASON.

isn't section 5.1 clear enough concerning this TE Router ID usage ?

[SCB] I am a bit confused because as per RFC3630 each router can only

           advertise one router address top level TLV. In case a router

           represents "N" TE nodes then there can be multiple TE Router IDs.

           My question is - which TE Router ID can be set in the router address

           TLV ?

note that ASON does not list requirements on TE Router ID itself (since
implementation independent)

[SCB] OK.

> 2. Upward / downward LSA transformation
> 
>     When LSAs are exported from one level to another then these LSAs need to be
>     transformed. The ID does not clearly specify how the transformation takes place.
> 
>     The specific scenarios are:
>     + Upward LSA transformation - what values are used for the adv Router ID, Router Address
>        and LINK ID ?

see below

>     + Downward LSA transformation - what values are used (for above mentioned fields) ?

only case where there is any information processing is in case of
reachability such as to aggregate information

for the rest everything there is no processing of the opaque LSA
information -

[SCB] What about downward dissemination of higher level topology elements ?

concerning the adv.router_id i will add a statement in next revision
(without any surprise here)

[SCB] OK, and what about the associated TE Router ID for the reachability information ?

> 3. TE Links LSAs
> 
>     From reading the ID I can infer that every TE link advertised at a particular level
>     needs to be a link between 2 routers i.e. Router ID, because the LINK ID MUST
>     be set to the neighboring router's Router ID as per RFC 3630.

yes - there is no need to change anything from that perspective

>     In that case when there is only one router for a set of TE nodes then how will
>     the TE link LSAs look like when they get advertised by that single router. Or is it
>     expected that these TE link LSAs never get advertised by that single router
>     (i.e. all TE nodes must get represented as an abstract node) ?

ok i see ... there is no advertizement of internal structure of abstract
nodes otherwise make use of the logical link case - see RFC 4652

 

[SCB] So are we saying logical links are limited to cases 1 & 2 ?

> 4. Upward / downward discovery and selection
> 
>    The ID describes a procedure by which routers can automatically discover and select
>    the upward and downward speaker router.
> 
>    It is quite clear that when the current speaker sees a router with a router ID larger than
>    its own and the U or D bit set it will stop importing or exporting LSAs.
> 
>    What is not clear is that how does the router with the highest router ID know when to
>    start importing or exporting LSAs, because it has no knowledge which is the current
>    speaker and there is no clear way to figure out when it has stopped importing or exporting
>    LSAs.
> 
>    Could you please explain how this works ?

hysteresis mechanisms is expained in section 6.2.1 prevents from
disturbing the routing information dissemination process once selection
has been performed - so the condition you are describing does not occur
if import/export is already in place.

 

[SCB] There are 2 types of information that is being discussed here -

            1. regular routing information being flooded in the area

            2. upward / downward routing information

 

           The rule is that the router with the highest router ID will disseminate

           the upward / downward information. The router with the highest router ID

           is identified using the regular routing information being flooded in the area.

 

           Now a new router is added which is the highest router ID. This router

           must NOT disseminate upward/downward routing information even though it

           has the highest router ID because another router is already selected. How does

           it figure out that it must NOT disseminate the upward / downward routing information

           i.e. another router is already selected for the job ?

hope this clarifies
- d.



> Thanks,
> Snigdho
>