The scenario that you highlight below does affect us and is one of the reasons we are actively informing the wider operator community about the caches and our implementation of them. As you quite rightly point out there are a number of asymmetric routing situations that can occur, while we are making every attempt to mitigate these situations we may miss something. That is where forums like this will be useful in helping us to resolve and maybe avoid them. If any one on the list has a fault of this nature please let us know so that we can investigate. The most likely manifestation of this will be timeouts on 'international' sites. I hope this answers your question. Regards Paul -----Original Message----- From: nznog-bounces(a)list.waikato.ac.nz [mailto:nznog-bounces(a)list.waikato.ac.nz] On Behalf Of Nathan Ward Sent: Wednesday, 12 August 2009 12:17 a.m. To: nznog Subject: Re: [nznog] Telecom International HTTP Caching On 11/08/2009, at 6:15 AM, Paul Tinson wrote:
NB. Please note that the service is only in place for Telecom Broadband Customers and "International" in this case is based on the international routing tables, as such some domestic sites may appear to Telecom as international content.
Exact implementation isn't that important, but my guess is that these caches sit inside TNZI somewhere, call it an educated guess. Depending on where exactly they sit, there is a problem that has impacted several NZ providers in the past when implementing fully transparent caching. Some conditions: 1) A destination is considered to be international by TNZI 2) The destination hands traffic back over a domestic circuit 3) Domestic inbound does not pass through the devices doing the redirection of 80/TCP traffic The effect is: 1) Outbound SYN gets sent to a cache, which regenerates it. 2) Inbound SYN+ACK comes in, and goes straight to the customer. 3) Things break in TCP There are a couple of other asymmetric routing things that can break caching as well. These sort of things are kind of unique to markets like NZ, where we differentiate between international and domestic - at least in our SP networks. Anyway, is this likely to impact the TNZ caching, or are the caches in a place so this doesn't impact them? -- Nathan Ward _______________________________________________ NZNOG mailing list NZNOG(a)list.waikato.ac.nz http://list.waikato.ac.nz/mailman/listinfo/nznog