Date: Mon, 10 Nov 2008 01:31:41 -0800 From: Jeremy Chadwick <koitsu@FreeBSD.org> To: Peter Maxwell <peter@allicient.co.uk> Cc: freebsd-pf@freebsd.org Subject: Re: Blocking udp flood trafiic using pf, hints welcome Message-ID: <20081110093141.GA63259@icarus.home.lan> In-Reply-To: <7731938b0811090947j4796680cj7344ca3333c05779@mail.gmail.com> References: <1814bfe70811090137v39cd6434l49b545eb3b6eb88c@mail.gmail.com> <20081109112125.GA36707@icarus.home.lan> <1814bfe70811090544o28c29c5u185e3c0f2b8e85b4@mail.gmail.com> <7731938b0811090947j4796680cj7344ca3333c05779@mail.gmail.com>
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On Sun, Nov 09, 2008 at 05:47:54PM +0000, Peter Maxwell wrote: > ii) Ensure you're using a good NIC, the CPU offload abilities in Intel > (and I think Broadcom) cards can reduce the impact on CPU generally. I think (hope) what you're referring to are TSO, LRO, and TX/RX checksum offloading. Assuming you are, you should be aware of the following: * These features do not greatly reduce CPU usage; the impact is minimal. * Both TSO and TX/RX checksums are known to be buggy on many NICs, including some developed within the past year. I can refer you to many threads on -hardware, -current, and -stable discussing this fact, specifically from the driver authors themselves. Sometimes it's just rxcsum which is buggy, or just txcsum. I do not believe Broadcom or Intel NICs are affected by such issues, but regardless it's important users understand these features *can* lead to packet corruption on some NICs. * TX/RX checksum offloading often confuse users who use tcpdump or Wireshark -- "why are all of my packets showing checksum errors??!" being a common question even today. It often leads users on a wild goose chase, thinking those messages indicate the source of their problems If you weren't referring to these features, what were you referring to? I'm curious to know. -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB |
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