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Troubleshooting common issues
Chapter 16: Troubleshooting 357
For a 6500/6000 Series Switch running Native IOS 12.1 or later you must configure
the destination port as a trunk port prior to configuring the SPAN, which have
the following syntax:
C6500(config)#Interface Type slot/port
C6500(config-if)#Switchport
C6500(config-if)#Switchport trunk encapsulation { ISL | dot1q }
C6500(config-if)#Switchport mode trunk
C6500(config-if)#Switchport nonnegotiate
To monitor 802.1Q VLAN traffic passing through Fast Ethernet 02 via a SPAN port
set up on Fast Ethernet 0/6, you would enter the following commands:
C6500 (config) # interface fastethernet 0/6
C6500 (config-if) #switchport
C6500 (config-if) #switchport trunk encapsulation dot1q
C6500 (config-if) #switchport mode trunk
C6500 (config-if) #switchport nonnegotiate
C6500 (config-if) #exit
C6500 (config) # monitor session 1 source interface fastethernet 0/2
C6500 (config) # monitor session 1 destination interface fastethernet 0/6
Using Discover Network Names on a Layer 3 switch that uses
VLANS
Symptoms : While running Discover Network Names against a Layer 3 Switch
that uses VLANs, you see only a limited number of MAC addresses, which
typically have multiple IP Addresses associated with them.
Causes : Layer 3 Switches that have been configured to perform routing replace
the originating station's MAC Address with the MAC Address of the switch port.
For example, suppose CADStation1 has a MAC Address of 00:00:03:AB:CD:00 and
an IP Address of 10.0.0.1. It is connected to switch port 1 through a hub. Port 1 of
this switch has a MAC Address of 00:11:22:33:44:55.
When a probe is connected to a SPAN or mirror port of that switch, it shows
CADStation1 with an IP of 10.0.0.1 and MAC address of 00:11:22:33:44:55 rather
than 00:00:03:AB:CD:00 because of this substitution.
Now, suppose there is another station (CADStation2) with MAC address of
00:00:03:AB:EF:01 and has an IP address of 10.0.0.2 that is also connected to
port 1 of the switch through a hub. Because Discover Network Names stores
station information by MAC address (i.e., the MAC address is the unique station
identifier), it changes the IP address of switch port 1's MAC address.
Because a switch configured as such hides originating station MAC addresses
from Observer, MAC-based station statistics (such as Top Talkers-MAC, Pair
Statistics matrix, etc.) can only be calculated by port. To make the Observer
displays more useful, follow this solution.
Solutions : By examining the switch configuration you can obtain a list of
MAC addresses that are associated with each port of your switch. Then, use
Discover Network Names to edit the alias entry for 00:11:22:33:44:55, labeling it
“SwitchPort1.“
The IP based statistical modes (Internet Observer, Top Talkers – IP (by IP Address)
still show you statistics calculated from individual stations by their IP address.
But MAC-based statistical modes (Pairs Statistics Matrix, Protocol Distribution,