RE: [Idr] Clarification requested for RFC 4271 Section 6.8 'ConnectionCollision Detection'

Hi,

I think you just miss the significance of this:

If, among
   these connections, there is a connection to a remote BGP speaker
   whose BGP Identifier equals the one in the OPEN message, and this
   connection collides with the connection over which the OPEN message
   is received, then the local system performs the following collision
   resolution procedure:

so the first connection has already been accepted since at the
time when the first OPEN message was received there was no collision
detected yet and only upon the receival of the second OPEN message
the collision resolution procedure as specified by you below
is executed - and that procedure clearly states which of the two
connections will be closed.

Jan

The climate of Edinburgh is such that the weak
succumb young .... and the strong envy them.

                                 Dr. Johnson  

> -----Original Message-----
> From: Rohan Sen [mailto:senrohan@gmail.com] 
> Sent: 09 December 2007 18:01
> To: idr@ietf.org
> Subject: [Idr] Clarification requested for RFC 4271 Section 
> 6.8 'ConnectionCollision Detection'
> 
> Hello,
> 
> 
>  I am implementing a BGP state machine on Linux and am facing a doubt
> related to connection collision which seem to rise from a possibly
> contradicting statement in RFC 4271.
> 
>  Let me try to explain my understanding with 2 routers L (local BGP)
> and R (remote BGP).
> 
>  if (routerId(L) < routerId(R)) {
>   1. the local system closes the BGP connection that
>          already exists (the one that is already in the OpenConfirm
>          state)  <--------- What if this is the connection initiated
> by the remote peer then this connection cannot be closed and accepted
> at the same time
>   2. accepts the BGP connection initiated by the remote  system.
>  } else {
>   3. the local system closes the newly created BGP
>          connection (the one associated with the newly received OPEN
>          message) <-------- What if this is the connection initiated
> by L then we are closing the connection opened by us even if we have
> higher router id
>   4. continues to use the existing one (the one that is already in the
> OpenConfirm state)
>  }
> 
> Also elsewhere in this RFC (Page 35) it states that:
> "Based on the value of the BGP Identifier, a convention is established
>  for detecting which BGP connection is to be preserved when a
>  collision occurs. The convention is to compare the BGP Identifiers
>  of the peers involved in the collision and to retain only the
>  connection initiated by the BGP speaker with the higher-valued BGP
>  Identifier."
> 
> 
> This statement is again contradicting the other cases viz. case (1)
> and case (3).
> 
> I am really confused in this regard and would really appreciate any
> help to understand this scenario better/correctly.
> 
> -- 
> thanks,
> Rohan Sen
> 
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> 

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