Erik Romijn wrote:
Hi,
sorry for the late input.
Larry Blunk wrote:
Would you be in favor of changing the draft language
to use From/To or Source/Destination instead of the current
Peer/Local distinction and explicitly permit the logging of
locally generated messages? In the case of locally generated
messages, the AS numbers and IP's would be swapped.
I think it is sensible to change the language.
Off line you suggested only doing this for AS numbers. I'm fine with
that, or changing it for AS numbers and IP addresses.
I rethought things a bit and decided that it what
would probably be best to simply add 2 new subtypes
to make it perfectly clear that the messages were locally
generated. It wasn't as bad as I thought since it only
affected the BGP4MP_MESSAGE and BGP4MP_MESSAGE_AS4
types. I think this will avoid potential confusion (although
it will require implementations to make a modest update to
support).
- The most important question is whether difference in BGP4MP_MESSAGE
and BGP4MP_MESSAGE_AS4 is just in MRT message header format, or if it
is also semantic information whether these BGP messages were received
in 'AS4-style' session or 'old' session (and therefore whether
AS_PATH attribute in UPDATE messages contains 2B or 4B AS numbers).
For the current implementation in Quagga there is semantic information.
The code checks whether the AS4 capability is present on the session
and, if so, uses BGP4MP_MESSAGE_AS4. If the AS4 capability is absent, it
will use BGP4MP_MESSAGE and write the AS_PATH and AS4_PATH attributes as
received from the peer.
However, I am not entirely sure whether it should be an explicit
requirement to store this semantic information in this way.
Could you and Ondrej come up with some text on what you
would like to see in the draft?
Basically, the issue is that if you do not have semantic information,
you do not know how to read the AS_PATH attribute.
So, we can either embed this information elsewhere, or require a MESSAGE
to have 2-byte numbers in the AS_PATH, and a MESSAGE_AS4 to have 4-byte
AS numbers in the AS_PATH.
Based on that choice, I think we should do the second, and say something
like: In case of a BGP4MP_MESSAGE, the AS_PATH must only consist of
2-byte AS numbers. In case of a BGP4MP_MESSAGE_AS4, the AS_PATH must
only consist of 4-byte AS numbers.
Note that this is a subtle intentional difference from "whether or not
the peer it was received from had AS4 capabilities".
Okay, I've added this text.
-Larry
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