re: [RRG] map change due to a path failure?

[Xu Xiaohu <xuxh@huawei.com>]

> On 3/25/08 5:54 PM, Brian E Carpenter allegedly wrote:
> > On 2008-03-26 03:49, Xu Xiaohu wrote:
> >> How about having the authoritative ETR to update the status of the
EID->RLOC
> >> mapping in the mapping system automatically according to the
connectivity
> >> between the ETR and the site network, while having the routing system
to
> >> determine the reachability of the ETR?
> >
> > However, we want to avoid map flapping by design (you will remember
> > that BGP4 route flapping was a big problem).

Hi Brian,

IMO, the major reason that the flap damping is a dilemma in BGP is that it's
hard to distinguish the real flap and the path hunting. On the contrary,
it's safer to enable flap damping in the mapping system since there is no
such problem.

> The current LISP trick is the "locator reachability" bits piggybacked on
> data packets.  You can separate operational changes (the kind subject to
> flaps) from configuration changes.  There is no need for mappings to
> change due to operational problems, nor timers etc.  I still don't
> understand why you think BGP would be involved.  Are you presuming that
> we are going to run BGP between nodes that are not globally routed?  Why
> would DFZ BGP even know that an ETR was dead?

Hi Scott,

To some extent, ETR plays the same role of PE in BGP/MPLS VPN. So we can use
a /32 IPv4 loopback interface address of ETR as RLOC and advertise those /32
IPv4 prefix in BGP without aggregation. In this way, the reachability of ETR
will be seen in the routing system. Of course, it will depend on the total
amount of ETR in the Internet.

If you use the "locator reachability" bits piggybacked on data packets, does
this require the intermediate router, which drops the unroutable LISP
packets, to send some ICMP unreachable like msg to the ITR? This is not the
default behavior for some routers which have switched off this function for
some reason.

The connectivity between the ETR and the site network is better to be
embodied in the mapping system. Otherwise, the cheating risk will be
introduced if ITR depends on the ETR to tell him the availability of the
EID-RLOC mapping. Authentication of ETR can be easily implemented by the
mapping system compared to the ITRs. 

Best wishes,
Xiaohu XU



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