Re: How can I create and use a Tap device

From: Julian Elischer (julian_at_elischer.org)
Date: 11/18/04

  • Next message: Wilkinson, Alex: "Re: polling(4) rocks!" 
    Date: Thu, 18 Nov 2004 10:49:44 -0800
To: Robert Watson <rwatson@freebsd.org>

    Robert Watson wrote:

    >On Thu, 18 Nov 2004, Elton Machado wrote:
    >
    >
    >
    >>I need a virtual ethernet device, can I use tap for that?
    >>
    >>How can I create it?
    >>
    >>
    >[...]
    >
    >A couple of performance caveats:
    >
    >- Every packet delivery requires going to user space, so possibly a
    > context switch and certainly a system call.
    >- Every packet is copied to user space, and/or from user space, so you get
    > a lot of memory copying.
    >

    You can also use netgraph's eiface node.
    thid delivers teh packet to a netgraph interface which can be then used
    for further processing in the kernel..
    (e.g. a ksocket node to encapsulate it in UDP).. No extra context
    switches..

    >
    >For prototyping or light-weight stuff, tap is a great tool, but to improve
    >performance you want to run network code in the kernel, especially if
    >there are other applications running (and/or processing packets), which
    >will increase the number of context switches. The cost as it stands isn't
    >bad -- I regularly use tap-derived tunnel software for remote network
    >access without a hitch. There were recently some posts made with patches
    >to optimize the allocation of kernel memory for packets sent using a tap
    >device, which are in the mailing list archives (not sure if they were
    >merged yet).
    >
    >Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
    >robert@fledge.watson.org Principal Research Scientist, McAfee Research
    >
    >
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    >
    >

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  • Next message: Wilkinson, Alex: "Re: polling(4) rocks!"

    Relevant Pages

    • Re: How can I create and use a Tap device
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