On Friday 13 October 2006 18:32, Jon Hart wrote:
hi jon,
i had a similar situation in a switched environment. certain frames to a
particular server where to be seen at every port on all switches within the
same vlan. the reason was that the server was attached with several cards for
loadbalancing. arp request for the virtual address where answered by each
server card but when the client send ip packets using the learned virtual mac
the server cards replied using their physical address which is stupid since
the vmac was never used as a source and so it could not be learned by the
switches. as a result frames that had the vmac as a destination where always
flooded...also a nice example on how to turn expensive network equipment into
a hub :)
regards
jan
Greetings,
I've got a situation here that I can't quite figure out. It is well
known that it is possible to cause a switched network to act like an
unswitched network by flooding the CAM table. There are countless tools
and documents out there that cover the offensive and defensive measures
related to this issue.
While this isn't Cisco's official documentation on this issue,
http://xrl.us/r8k7 says:
"Content-addressable memory (CAM) overflow: A CAM table is used to
determine where to direct incoming frames depending on which port the
incoming MAC address came from. When the CAM receives a frame with an
unknown destination, the proper procedure is to flood frames within
the acceptable Layer 2 domain (the proper VLAN). Hardware and
software tools are available (some for free), that can flood a switch
with MAC addresses. Once the CAM table limit is exceeded, switches
behave differently depending on the brand of the switch."
My question is, has anyone seen a situation where the same broadcast
behavior occurs, but the CAM table itself is not overloaded and there is
no good reason for entries to be expiring? Furthermore, even if the
entries were expired, has anyone encountered situations (malicious or
otherwise), where a given port will receive traffic outside of its own
L2?
Thanks,
-jon
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