[14161] in North American Network Operators' Group
Re: caching at windmills (i mean exchange points)
daemon@ATHENA.MIT.EDU (Ton Verschuren)
Wed Dec 3 12:26:21 1997
To: Duane Wessels <wessels@nlanr.net>
cc: nanog@merit.edu, ircache@nlanr.net
In-reply-to: Your message of "Wed, 03 Dec 1997 02:25:10 MST." <199712030925.CAA09684@ucar.edu>
Date: Wed, 03 Dec 1997 10:31:10 +0100
From: Ton Verschuren <Ton.Verschuren@surfnet.nl>
Thanks Duane,
This makes more sense. I'll discuss this further with my network
services collegues to grasp the routing issues for our case.
Ton.
==> 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
| http://squid.nlanr.net/Squid/FAQ/FAQ-7.html#ss7.6
|
| Duane W.
| --
| wessels@nlanr.net Think Globally, Cache Locally.
