Brian J. Murrell wrote: >What I don't understand is why I have to specify an upstream bandwidth in the >tcinterfaces. I guess I had always thought that Shorewall's Simple TC was >simply prioritization, not bandwidth allocation. I would have >thought TC didn't need to know the upstream bandwidth to simply >prioritize the de-queuing of packets in the higher bands.
That could be the case if the only constraint was your local link - but it isn't in all cases. Case 1) At work we get an internet connection via fibre, nice 20Mbps uncontended, unmetered, unfiltered connection - at an eye watering price ! The bandwidth management is handled by a Cisco router somewhere upstream of us - there is at least one switch between us and the router. If we send at more than our permitted rate then initially we get to burst above it, but then it drops back. Latency rockets because the router has it's own buffers that we're filling up. So even though we prioritise our traffic, if we don't keep the overall rate below the level at which queues build up in the ISP router then it won't work. Case 2) Assume you have a PPP0E connection to the ISP - so there is no intervening router between you and the DSL line that restricts upstream bandwidth. Even though we may prioritise packets in the packet routing layer, I wouldn't be surprised to find a queue in the PPP layer and then in the hardware/driver layer. So even though everything is notionally under your control, there are still elements that will trip you up. -- Simon Hobson Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed author Gladys Hobson. Novels - poetry - short stories - ideal as Christmas stocking fillers. Some available as e-books. ------------------------------------------------------------------------------ RSA(R) Conference 2012 Save $700 by Nov 18 Register now http://p.sf.net/sfu/rsa-sfdev2dev1 _______________________________________________ Shorewall-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/shorewall-users
