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Re: STP mitm attack idea

Portfast modifies STP, it does not disable it. 

This does make a good argument for pvst and similar technologies running at the vlan level for enterprise networking. 

But it is probably best to assume someone with access to a segment can see everything on that segment, pretend to be anyone else on that subnet, and inject anything onto that subnet. In other words, it is nearly impossible to protect reliability and somewhat privacy on a shared link. 

On Apr 29, 2010, at 12:19 AM, news <news@xxxxxxxxxxx> wrote:

> Le mercredi 28 avril 2010 Ã 18:20 +0200, Jann Horn a Ãcrit :
>> Am Dienstag, den 27.04.2010, 19:55 +0200 schrieb Przemyslaw Borkowski:
>>> Second scenario:
>>> 1. Station C and station D starts to send frames to break link beetween switch 1 and switch 2, and announce non existing connection and switch from C port on switch 1 to D port on switch 2
>>> A ---- switch 1 --X-- switch 2 ----- B
>>>          |              |
>>>          |              |
>>>          C  --no conn-- D
>>> 2. Station A sends frame to B
>>> 3. Frame is forwarded to C station
>>> 4. Station C stores frame in memory
>>> 5. After equal timing station C and station D repair link beetween switch 1 and 2
>>> 6. station C resends stored packet to station D (ie in tunnel or encapsulated in ip packet)
>>> 7. stations C and D break link beetween switches 1 and 2
>>> 8. station D sends transmitted packet to station B
>> If you had a WLAN-link, you could simplify that a lot - as far as I
>> understand, you are able to make the switches redirect the traffic to
>> your machines.
>> Anyway, this attack sounds like something a good switch can easily
>> prevent by having a list of "STP trusted ports" or something like that.
>> Doesn't that exist?
> I think I have heard about this attack before.
> Yes, a good admin should set all the port used by machine as portfast
> (no STP), keeping only the STP on the port attached to network devices.
> Then the attack would be really too noisy to be successful.
> It is also highly recommended to lock down the ports at L2 (port
> security). Well I hope every one here is doing it, as it can make such
> attacks really hard.