Cisco Ethernet switch Manuel d'utilisateur télécharger pdf (Page 52)

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l2-security-bh.ppt

Spanning Tree Attacks and Methods

¥ Standard 802.1d STP takes 30-45

seconds to deal with a failure or

Root bridge change (nice DoS)

Generally only devices affected by the

failure notice the issue

PortFast and UplinkFast can greatly

improve this

¥ Sending BPDUs from the attacker

can force these changes and create

a DoS condition on the network

¥ As a link with macof: the TCN

message will result in the CAM table

aging all entries in 15 seconds if

they do not communicate (the

default is 300 seconds)

¥ Testing using brconfig on OpenBSD

was easily able to create the DoS

condition. Depending on the

topology it could also yield more

packets available for the attacker

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