Hi Brian, see my responses below. Brian E Carpenter wrote:
On 2007-10-12 22:24, Michael R Meisel wrote:If you have more than one user-space destination address, such as from DNS A records, which you could address a (end-to-end) packet to, that will work the same way with APT as it would today.Logically, yes, but...APT failover handles the case where the tunnel exit point (that is, the ETR) for a given user-space *prefix* fails. Note that this is in the middle of the network, not at an endpoint. In the existing network, the failure would have caused a BGP route change. With APT, there is no announcement or timeout involved, the first packet is simply re-routed to a working ETR if possible, and the ITR is notified so that subsequent packets are tunneled directly to the working ETR.Yes, if there *is* a working path. But if there isn't, it will be a long timebefore the upper layer tries the next address that it knows about, I think. Or do you think the upper layer will just time out anyway? In any case, the upper layer code will be trying to get around apt instead of working with it.
The upper layer will certainly just time out anyway. This would work exactly the same as if there were no BGP path to your destination prefix in the network today. If none of the ETRs for a destination user-space prefix are reachable, APT isn't doing anything to make the destination address /appear/ reachable. That address is simply unreachable currently, and packets can't get to it. This isn't "getting around" APT any more than timing out and trying a different address is "getting around" BGP today.
And the standard question: how will this work with SCTP?APT will be invisible to end users. This means that it should not have any effect on any transport-layer protocol.But SCTP doesn't *want* that invisibility, because it explicitly chooses to change to an alternative address in order to use an alternative path. How do you allow SCTP to do its job?
The same way BGP allows SCTP to do its job today. If you try a different address, you are just as likely to get a different path through the network with APT in place are you are without it. When I say that APT is invisible, I mean that end hosts shouldn't be able to tell whether it's being used or not -- everything should work the same as it does today from their perspective.
-Michael -- to unsubscribe send a message to rrg-request@psg.com with the word 'unsubscribe' in a single line as the message text body. archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg