3Com WX2200 3CRWX220095A Switch User Manual

Remotely Monitoring Traffic 639
Best Practices for
Remote Traffic
Do not specify an observer that is associated with the MAP where the
snoop filter is running. This configuration causes an endless cycle of
snoop traffic.
If the snoop filter is running on a Distributed MAP, and the MAP used
a DHCP server in its local subnet to configure its IP information, and
the MAP did not receive a default router (gateway) address as a result,
the observer must also be in the same subnet. Without a default
router (gateway), the MAP cannot find the observer.
The MAP that is running a snoop filter forwards snooped packets
directly to the observer. This is a one-way communication, from the
MAP to the observer. If the observer is not present, the MAP still sends
the snoop packets, which use bandwidth. If the observer is present
but is not listening to TZSP traffic, the observer continuously sends
ICMP error indications back to the MAP. These ICMP messages can
affect network and MAP performance.
To inform you of this condition, MSS generates a log message such as the
following the first time an ICMP error message is received following the
start of a snoop filter:
MAP Mar 25 13:15:21.681369 ERROR DAP 3 ap_network: Observer is not accepting TZSP packets
To prevent ICMP error messages from the observer, 3Com recommends
using the Netcat application on the observer to listen to UDP packets on
the TZSP port.
Configuring a Snoop
To configure a snoop filter, use the following command:
set snoop filter-name [condition-list] [observer ip-addr]
[snap-length num]
The filter-name can be up to 15 alphanumeric characters.
The condition-list specifies the match criteria for packets. Conditions in
the list are ANDed. Therefore, to be copied and sent to an observer, a
packet must match all criteria in the condition-list. You can specify up to
eight of the following conditions in a filter, in any order or combination:
frame-type {eq | neq} {beacon | control | data | management |
channel {eq | neq} channel
bssid {eq | neq} bssid