Re: [Idr] draft-walton-bgp-add-paths-06.txt as IDR WG document

[Uli Bornhauser <[e-mail]>]

Hi Robert,

I think I did not get your point yet. Why do you think that a
misconfiguration is needed for the example?
Client C-ID.5 keeps two eBGP sessions (to R-ID.6 and R-ID.3) and thus
receives q1 and p1. Client C-ID.8 also holds two external sessions (to
R-ID.9 and R-ID.2) and receives p2 and q2. The Route Reflector of
clients C-ID.5 and C-ID.8 receives all paths, and re-advertises its
first and second best (which are q1 and q2).
Thus, client C-ID.5 is provided with q1, q2, and p1. Knowing q2 has no
effect on its routing decision. Path p2 is not visible at C-ID.5 at all.

Can you please explain I detail from where client C-ID.5 should learn
path p2?

Thank you and Regards

Uli

Robert Raszuk schrieb:
> Hi Uli,
>
> > Client C-ID.5 receives the paths q1 and p1.
>
> This is already not the correct observation. In the correct
> architecture of this network (no misconfiguration) C-ID.5 would
> receive all 4 paths. Therefor p2 will win.
>
> Cheers,
> R.
>
>> Hi Robert,
>>
>> here should be a simple example for the problem regarding Add-path, Best
>> / Second Best, and Border Router Attr Set I mentioned:
>>
>> -------------------------------------
>>
>> ---------+        RR        +--------
>>       ASx|   d1 .    . d1   |ASy
>>          |     .      .     |
>>  R-ID.6.....C-ID.5  C-ID.8.....R-ID.2
>>      q1->|    .        .    |<-q2
>>          |    .        .    |
>> ---------+    .        .    +--------
>>               .        .
>>          MED2 .        . MED1
>>        +------.--------.----+
>>        |ASz p1.        .p2  |
>>        |      .        .    |
>>        |   R-ID.3    R-ID.9 |
>>
>> -------------------------------------
>> q1, q2, p1, p2: Paths advertised from neighboring systems.
>>      R: Routers in neighboring systems, Route Reflector or Clients
>>      C: Client in own System
>>     RR: Route Reflector in own System
>> *-ID.x: Router has BGP ID .x
>>     d1: Links with a distance of 1
>>    ASa: AS with ID a
>>
>> Client C-ID.5 receives the paths q1 and p1. Path p1 is the best (lower
>> BGP ID, .3) and path q1 is the second best.
>> Client C-ID.8 receives the paths q2 and p2. Path q2 is the best (lower
>> BGP ID, .2) and path p2 is the second best.
>>
>> Both clients advertise both path to the reflector RR of the system.
>>
>> Comparison of p1, p2, q1, q2 at RR:
>> p1 is discarded due to the higher MED (2, path p2 has a MED of 1)
>> p2 and q2 are discarded due to the higher BGP ID (.8)
>> --> Path q1 is the "first" best on RR.
>> --> Path p1 is also removed (due to the same BGP ID .5 (or even
>> Nexthop), cf. Draft)
>>
>> Comparison of p2, q2 at RR:
>> p2 is discarded due to the higher BGP ID in the Border Router
>> Attribute Set
>> --> Path q2 is the second best.
-- 
______________________________________________________________
ULI BORNHAUSER                University of Bonn
                              Institute of Computer Science IV
Web:   www.cs.bonn.edu/IV/ub  Roemerstr. 164
Email: [e-mail]      D - 53117 Bonn
Phone: [phone] - 4550    Germany
Fax:   [phone] - 4571

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