Re: LMP Messages

["Bradford, Richard" <rbradfor@cisco.com>]

Comments inline.
At 06:06 PM 10/2/2001 -0400, Balasubramania N. Pillai wrote:
>Hi
>
>I have a basic doubt regarding LMP Messages based on the latest LMP draft.
>
>Section 3, paragraph 5 of the draft says
>
> > There are four LMP messages that are used to manage individual
> > control channels.  They are the Config, ConfigAck, ConfigNack, and
> > Hello messages. These messages MUST be transmitted on the channel to
> > which they refer.  All other LMP messages may be transmitted over
> > any of the active control channels between a pair of LMP adjacent
> > nodes.
>
>Why is it that these messages MUST be transmitted on the channel to which
>they refer. I can understand why LMP Hello messages need to be sent over the
>control channel, which it refers to. But is it necessary to force the other
>messages.
>
>
>
>          ----------                      ----------
>         |          |         C1         |          |
>         |          |--------------------|          |
>         | Switch 1 |                    | Switch 1 |
>         |          |--------------------|          |
>         |          |         C2         |          |
>          ----------                      ----------
>
>
>Based on the above picture assume that there are 2 control channels between
>Switches 1 & 2. LMP messages are sent over IP. If I have to force messages
>over individual channels then I need to get down to Layer 2. If I don't have
>to force it, I can let IP routing pick any one of the available channels to
>carry the message.
Here's my take. You COULD do what you want by defining a single control 
channel, where that IPCC is routed (Note following argument applies to a 
single IPCC where underlying links are load shared/bundled).
What you would lose is an indication that either C1 or C2 was no longer 
passing data. Let's say routing prefers C1 and somewhere along C2 there's a 
disruption. At this point the switches have no backups but have no 
indication that there are no backups.  If LMP is configured with multiple 
IPCCs and IFF hello's are going over those IPCCs, then you will know if 
there's a problem with one of the IPCCs.
Another reason is that the CONFIG for inband IPCC can be used in lieu of 
LinkVerify for determining  the mapping of links between the switches, but 
only if the CONFIG message goes over the correct link.
-- rich




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Rich Bradford          Email: rbradfor@cisco.com
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