B-73
Monitoring and Analyzing Switch Operation
Traffic Mirroring
Figure B-39. Example of Configuring a Remote Mirroring Session for Traffic Inbound on a Port
Maximum Supported Frame Size
The IPv4 encapsulation of mirrored traffic adds a 54-byte header to each
mirrored frame. If a resulting frame exceeds the MTU (Maximum Transmis-
sion Unit) allowed in the network, the frame is dropped.
N o t e
Mirroring does not truncate frames, and oversized mirroring frames will be
dropped. Also, remote mirroring does not allow downstream devices in a
mirroring path to fragment mirrored frames.
If jumbo frames are enabled on the mirroring source switch, then the mirroring
destination switch and all downstream devices connecting the source switch
to the mirroring destination must be configured to support jumbo frames.
Enabling Jumbo Frames To Increase the Mirroring Path MTU
On 1 Gbps and 10 Gbps ports in the mirroring path, you can reduce the number
of dropped frames by enabling jumbo frames on all intermediate switches and
routers. (The maximum transmission unit—MTU—on the switches covered
by this manual is 9220 bytes for frames having an 802.1Q VLAN tag, and 9216
bytes for untagged frames.) For information on configuring the switch for
jumbo frames, refer to “Configuring Jumbo Frame Operation” on page 13-29.
Switch-A(config)# mirror 2 remote ip 10.10.10.119 9400 10.10.40.1
Caution: Please configure destination switch first.
Do you want to continue [y/n]? y
Switch-A(config)# interface c12 monitor all in mirror 2
Configures port C12 as the source of traffic to mirror (inbound).
Uses the source IP address and random UDP port number to identify session 2 mirrored
traffic from VLAN 10, and specifies the destination IP address for this traffic. (The mirror
exit port for this traffic is a member of the VLAN identified by the destination IP address.)
1
2
1
2
Interface to
Monitor
Directional Criteria for
Selecting Traffic To Mirror
Mirror
Session
Mirror Session
2 Identity
Mirror Session
Destination
3500-5400-6200-8200-MCG-Jan08-K_13_01.book Page 73 Monday, January 28, 2008 10:04 AM