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Posted by Jeff Lundstrom on January 22, 2008, 10:04 am
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> > > =A0Wondering if anyone can tell me what methods they use to find a
> > >Ethernet loop in a large network. =A0Recently the company that I work
> > >for is having issues with users plugging both ends of the Ethernet
> > >cables in the same switch creating a loop. =A0Is there an easy and quic=
k
> > >way to isolate and find this loop given a large corporate network?
>
> > Enable STP so all ports send STP BPDUs, and on all except the
> interconnection
> > ports, enable the feature to immediately block the port when such a BPDU=
> is
> > received. =A0When that happens, syslog messages should be generated givi=
ng
> you
> > the relevant port number. =A0When you see one of those, get out your
> approved
> > baseball bat equivalent, and visit that switch/port.
>
> other posters mention spanning tree - i dont like network designs that
> depend on spanning tree since it doesnt "fail soft", but using it to
> minimise the effect of errors makes things much more stable in the long ru=
n.
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> You may need "port fast" turned on, so that the port start up delay doesnt=
> cause other issues, and running spanning tree on links between switches an=
d
> routers may degrade the convergence time in your network - you need to che=
ck
> it doesnt break something important.
>
> or turn on "port security" or equivalent on all end user device ports, and=
> limit the port to "x" MAC addresses.
> (x =3D 1 for simple ports, 2 or 3 if you daisy chain IP phones). Dont both=
er
> making the port lock to the 1st MAC.
>
> Also limits the effect of rogue wireless access points, but not someone
> adding a SOHO router.
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> this assumes users can only get at the cabling to desks and so on - if the=
y
> can plug into unused ports and alter cabling, then you have another issue.=
>
> it helps to actually lock wiring closets, use a ID carded access, and / or=
> set up a motion detect camera - it is amazing how the number of "no one
> moved the cable" problems goes down when people think you might be able to=
> tell who did it.......
>
> > best regards
> > =A0 Patrick
>
> --
> Regards
>
> stephen_h...@xyzworld.com - replace xyz with ntl- Hide quoted text -
>
> - Show quoted text -
Thanks everyone for this information!
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