Hello, dear OSPF WG. I am the main author of this draft.
First, I like to talk about the motivation of this draft. IP anycast is a vision of next generation networks. As IPv6 is not widely used yet, it is promising for OSPFv3 to provide anycast in future. In my design, I take the minimalist approach so that vendors will benefit from anycast immediately. Second, I describe my technical considerations as follows. 1) Anycast address My draft followed the definition of IPv6 anycast addresses (see RFC 4291). So there is an address aggregation here. Besides, it is better to identify anycast addresses from unicast addresses. For example, we can have new route calculation for anycast addresses. We can have additional security for anycast addresses as it is more vulnerable to attackes. This address identification is more flexible and does not disturb OSPFv3. So, Why not? 2) Anycast Route Calculation I agree that the anycast route calculation is similar to the unicast case. But there is a bug noticed in Case 1 in Sec 3.5.1 if we consider anycast the same as unicast. The last comer (anycast server) will replace the previous route entries (in the logic of unicast). As a result, there is ONLY ONE route entry for a given anycast address. This means all client requests will go to the same anycast server. And Case 2 in Sec 3.5.1 pointed out the timing problem when the best anycast server leaves. If anycast is considered the same as unicast, OSPF will simply remove the(ONLY ONE) route entry for a given anycast address and find another anycast server until the next refreshment. (Note that OSPF refreshes every 30 minutes by default.) These bugs were also observed in Zebra OSPFv3. I think OSPF WG has the responsibility to point them out in the standards. Besides, I noticed that the anycast route calculation can be done without changing SPF tree. Of course, it is only an efficient implementation. However, RFCs (e.g. OSPFv3) often provide guidelines for better implementation so that vendors can implement them easily. Right? 3) Inter-Area and Inter-Domain Anycast Route Selection This part is not important. I just give a reasonable option to select Inter-Area and Inter-domain anycast routes. We can further improve it. In sum, this draft provides one of the most efficient solutions of IP anycast routing in OSPFv3. Thanks a lot for your advice. -- Yue Wang _______________________________________________ OSPF mailing list [email protected] https://www1.ietf.org/mailman/listinfo/ospf
