Subject: [lisp] advertising shorter EID prefix

From: Yakov Rekhter <[email-masked]>
Date: Fri, 20 May 2011 11:28:55 -0700

Folks,

Assume that a PTR advertises mapping for 10.128/16.  It means that
for any site that is not LISP-capable, but whose addresses are
subsidiaries of 10.128/16, traffic to that site must flow through
that PTR. That is probably ok for sites connected to the ISP that
hosts that PTR. But what happen if some of these sites are connected
to other ISPs ? Is it correct that in this case traffic to these
sites could take a suboptimal route, as it would need to traverse
through the ISP that hosts the PTR that advertises mapping for
10.128/16 ?

Yakov.

---

From: Dino Farinacci <[email-masked]>
Date: Fri, 20 May 2011 12:00:22 -0700

> Assume that a PTR advertises mapping for 10.128/16.  It means that

PTRs do not advertise mappings. I think you mean what if an PITR  
advertises an EID-prefix into the DFZ. Is that right?

> that PTR. That is probably ok for sites connected to the ISP that

PITRs will advertise coarse EID-prefixes. So if there are any non-LISP  
sites that use address covered by the coarse prefix, they will have  
more-specifics directly to the non-LISP site.

This overlap will be unlikely for IPv6 since the EID-space and the  
RLOC-space (existing allocations) will not overlap. For IPv4, where we  
do not want sites to renumber when they withdraw their routes from BGP  
and put them into the mapping database (when they move from being a  
non-LISP site to a LISP site), there will be overlap.

And we do anticipate there will not be increased stretch if the PITRs  
are deployed close to the edges of the the ISPs and are in path to  
most of not all destinations.

> to other ISPs ? Is it correct that in this case traffic to these

There will be more specifics that are used so path through another ISP  
will be taken.

> through the ISP that hosts the PTR that advertises mapping for

No, not at all.

Dino

>
> Yakov.
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