Re: [Idr] WG adoption call for draft-abraitis-bgp-version-capability-08, to end September 25

[Jeffrey Haas <[e-mail]>]

Linda,

On Mon, Jan 16, 2023 at 06:54:29PM +0000, Linda Dunbar wrote:
> RFC4271 states that if the version number is not supported, an error message should be sent. But RFC4271 didn't say if the BGP Open session should be failed.
> I am just curious if BGP session can be started even if the  version number is not supported?

RFC 4271, §6.2:
: 6.2.  OPEN Message Error Handling
: 
:    All errors detected while processing the OPEN message MUST be
:    indicated by sending the NOTIFICATION message with the Error Code
:    OPEN Message Error.  The Error Subcode elaborates on the specific
:    nature of the error.
: 
:    If the version number in the Version field of the received OPEN
:    message is not supported, then the Error Subcode MUST be set to
:    Unsupported Version Number.  The Data field is a 2-octet unsigned
:    integer, which indicates the largest, locally-supported version
:    number less than the version the remote BGP peer bid (as indicated in
:    the received OPEN message), or if the smallest, locally-supported
:    version number is greater than the version the remote BGP peer bid,
:    then the smallest, locally-supported version number.

Tersely, if you don't support the right version number, you hang up the
session with a NOTIFICATION and leave enough of a breadcrumb that the next
OPEN could arrive at a possibly mutually supported version.

-- Jeff