caching at windmills (i mean exchange points)

Ton Verschuren Ton.Verschuren at
Wed Dec 3 09:31:10 UTC 1997

Thanks Duane,

This makes more sense. I'll discuss this further with my network 
services collegues to grasp the routing issues for our case.


==> From: Duane Wessels

| Ton Verschuren writes:
| >I know. Still, for a cache to fill it has to fetch docs and thus act as 
| >a parent. If the NLANR cache acts as a parent for all MW connected 
| >ISP's than *all* misses from those ISP's get routed through the NLANR 
| >cache and for the transatlantic traffic the lines of NLANR's ISP will 
| >fill up. No?
| In order for the cache to fill, yes some MW customers will need to call
| the cache a parent.  Some could call the cache a sibling.
| However, it isn't so black-and-white as that.  Squid can be configured
| to measure RTTs to origin servers.  Squid's ICP replies will include
| the RTT estimations, and the child cache can compare these values to
| its own measurements, or those made by other (parent) caches.
| Additionally, for the MW cache, we have modified Squid to return an
| ICP_MISS_NOFETCH reply for requests origin servers which appear to be
| unreachable (presumably due to incomplete routing info).  Upon
| receiving this reply, the child cache will not forward the request to
| us.
| Thus, a child cache can use our MW cache as a parent only for origin
| servers which are reachable by us, and which our cache is "closer" to.
| If the child cache is closer, then it will forward the request
| directly.
| A potential problem is that the RTT measurement feature is not compiled
| in by default.  It requires building Squid with a macro defined, and
| installing the ICMP sending/receiving program with root privs.
| A few more details can be found at
| Duane W.
| --
| wessels at                           Think Globally, Cache Locally.

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