Jari, On Jun 20, 2011, at 9:09 AM, Jari Arkko wrote:
> I have reviewed this draft. > > I think it is in good shape and can move forward once we resolve one issue. > Here's the issue: > >> A node that forwards a flow whose flow label value in arriving >> packets is zero MAY change the flow label value. In that case, it is >> RECOMMENDED that the forwarding node sets the flow label field for a >> flow to a uniformly distributed value as just described for source >> nodes. >> o The same considerations apply as to source hosts setting the flow >> label; in particular, the normal case is that a flow is defined by >> the 5-tuple. >> o This option, if implemented, would presumably be used by first-hop >> or ingress routers. It might place a considerable per-packet >> processing load on them, even if they adopted a stateless method >> of flow identification and label assignment. This is why the >> principal recommendation is that the source host should set the >> label. >> > I think this recommendation is problematic. I agree that the first hop router > should insert the flow label, but requiring it to do fragment reassembly in > order to find the 5-tuple is a big burden, and I'm not sure its even called > for. I agree that requiring a router to reassembly isn't worthwhile. Better to just leave the flow label as zero. > > The RFC 2119 language above is fine. But I'd like to change the part about > normal case being the 5-tuple. I think the normal case should be the 2-tuple > under these circumstances. The source has access to the 5-tuple; a router is > not guaranteed to have access to it. > > In addition, I'm not sure I understand how a router knows that it is a first > hop router. Are there cases where a device might mistakenly believe it is a > first hop router at a point where the traffic has already been load-balanced > to multiple routers? Are there situations where the multiple first hop > routers are used from the same host? The document should provide some > guidance about operational conditions where the recommendations for the first > hop router can be applied. The document should state how such functionality > is turned on (per configuration? automatically?) and provide assurances that > problematic conditions can be avoided. I suppose the simple test is if the source address is from a prefix on the incoming interface. RFC 4311 "IPv6 Host-to-Router Load Sharing" requires (SHOULD) that hosts send packets for a particular destination to the same router (when it has multiple routers to choose from). I think the flow label draft behavior for setting zero flow labels is compatible with this. Does this help answer your questions? Bob > > Jari > > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > ipv6@ietf.org > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
