Re: hop-count header

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> Hi
>
> > I've thought about this as well. I think it would be very useful.
> > I'm thinking of something like
> >
> > X-Max-Cache-Hops: 3
> >
> > And each cache would decrement the counter before forwarding. When
> > the count reaches zero, the request could only be forwarded to the
> > origin server.
>
> A question though:
>
> We have 3 caches - currently they all talk to one another with the 'proxy-only'
> flag. If someone chose not to use this flag, though, couldn't you end
> up with a forwarding loop? (especially without this flag)

  You can, and you will. But thats totally different story.
 
> cache1 has the object. cache2 wants the object. cache2 has a policy that won't
> allow it to accept objects that have hopped more than 3 times. It sends
> ICP queries and finds out that cache1 has the object, but doesn't know how
> many times it's hopped - so it starts the download form cache1, only to find
> the object has hopped too many times. It then has to abort the download
> and try the other siblings which responded... not nice.

 Wait a minute. You'll not mark ondisk object with any hopcounts. You'll only
 ask your immediate neighbors with a special request header that it shouldn't
 forward your request further if it has a miss. This solves cases when neighbor
 has responded with a hit, but upon fetch via other request headers gets a miss,
 neighbor may issue itself a icp query to its neighbors, have a hit, go there,
 there again have a miss, etc... with hop-countdown you can limit the number
 of caches your _request_ can go to, before resorting to direct fetch. This is
 exactly to limit radius of your "trusted" neighbors. If you don't trust
 neighbor of your neighbor, you set max-hops 1 for this neighbor. For parents,
 you can set this hop-limit to other values or don;t set at all.
 
> Other way of doing it, you don't respond to ICP queries if you have an object
> that's had more than X hops.... another flag to keep in ram though, and
> you have to trust your siblings not to feed you ancient objects, and they
> have to run software which supports X-Max-Cache-Hops

 ----------------------------------------------------------------------
  Andres Kroonmaa mail: andre@online.ee
  Network Manager
  Organization: MicroLink Online Tel: 6308 909
  Tallinn, Sakala 19 Pho: +372 6308 909
  Estonia, EE0001 http://www.online.ee Fax: +372 6308 901
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Received on Tue Jul 29 2003 - 13:15:44 MDT