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From: Rick Jones <>
To: Helmut Grohne <>
Cc:, David Miller <>,
	Max Krasnyansky <>
Subject: Re: TUN/TAP: tap driver reports bogus interface speed in ethtool operations
Date: Tue, 23 Jul 2013 08:49:01 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 07/23/2013 06:32 AM, Helmut Grohne wrote:
> On 16.07.2013, at 23:41, Max Krasnyansky <> wrote:
>> The patch looks fine to me (must admit that I only glanced at it). Please send it to the netdev
>> mailing list, if you have't already done so.
>> CC David Miller <> and me.
> Doing that. Now summarizing the issue for the new recipients:
> Problem:
> When querying a tap device for its speed using ethtool the tun driver reports a speed
> of SPEED_10. This number is hard coded into the driver. Nowadays virtual network devices
> can go way faster than that. When doing automatic bandwidth monitoring based on the
> speed reported by ethtool, tap devices tend to come up as false positives. Arguably the
> hard coded speed is wrong.
> Proposed solution:
> To that end I propose supporting the ETHTOOL_SSET command in addition to the already
> supported ETHTOOL_GSET. It would deny setting any setting except for the bandwidth
> where it would allow arbitrary values. You can find this patch attached.
> With this patch an administrator can increase the reported speed for tap devices and
> keep using automatic detection of interface speeds.
> Workarounds:
> Using ethtool a detection utility can determine the driver for an interface. If the
> driver matches the string "tun", the reported speed should not be used.
> Helmut

I like the idea of being able to set the reported speed for a tun/tap 

rick jones

  reply	other threads:[~2013-07-23 15:49 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
     [not found] ` <>
     [not found]   ` <>
     [not found]     ` <>
     [not found]       ` <>
2013-07-23 13:32         ` TUN/TAP: tap driver reports bogus interface speed in ethtool operations Helmut Grohne
2013-07-23 15:49           ` Rick Jones [this message]
2013-07-23 15:56             ` Stephen Hemminger
2013-07-23 16:03               ` Helmut Grohne
2013-07-23 17:28           ` [RFC 1/2] tun: allow overrriding ethtool info Stephen Hemminger
2013-07-23 17:29             ` [RFC 2/2] tun: allow overriding statistics Stephen Hemminger
2013-07-23 19:04           ` TUN/TAP: tap driver reports bogus interface speed in ethtool operations Ben Hutchings
2013-07-30  6:20             ` Helmut Grohne
2013-07-30 10:51               ` Ben Hutchings

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