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Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
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Chapter 38 Configuring SPAN and RSPAN
SPAN and RSPAN Session Limits
Trunk VLAN Filtering
Trunk VLAN filtering is analysis of network traffic on a selected set of VLANs on trunk source ports.
You can combine trunk VLAN filtering with other source ports that belong to any of the selected
VLANs, and you can also use trunk VLAN filtering for RSPAN. Based on the traffic type (ingress,
egress, or both), SPAN sends a copy of the network traffic in the selected VLANs to the destination port.
Use trunk VLAN filtering only with trunk source ports. If you combine trunk VLAN filtering with other
source ports that belong to VLANs not included in the selected list of filter VLANs, SPAN includes only
the ports that belong to one or more of the selected VLANs in the operational sources.
When a VLAN is cleared, it is removed from the VLAN filter list. A SPAN session is disabled if the
VLAN filter list becomes empty.
Trunk VLAN filtering is not applicable to VSPAN sessions.
SPAN Traffic
All network traffic, including the multicast and bridge protocol data unit (BPDU) packets, can be monitored
using SPAN (RSPAN does not support monitoring of BPDU packets or Layer 2 protocol packets such as
CDP, DTP, and VTP). Multicast packet monitoring is enabled by default.
In some SPAN configurations, multiple copies of the same source packet are sent to the SPAN
destination port. For example, a bidirectional (both ingress and egress) SPAN session is configured for
sources a1 and a2 to a destination port d1. If a packet enters the switch through a1 and gets switched to
a2, both incoming and outgoing packets are sent to destination port d1; both packets would be the same
(if a Layer-3 rewrite occurs, the packets are different). Similarly, for RSPAN sessions with sources
distributed in multiple switches, the destination ports might forward multiple copies of the same packet.
SPAN and RSPAN Session Limits
You can configure (and store in NVRAM) a maximum of 30 SPAN sessions in a Catalyst 6000 family
switch. See
Table 38-1
for the supported combinations of SPAN/RSPAN sessions. You can configure
multiple ports or VLANs as sources for each session.
Table 38-1 SPAN and RSPAN Session Limits
SPAN/RSPAN Sessions
Catalyst 6000 Family Switches
1
1.
When an RSPAN source session is configured, it will reduce the limit for
rx
or
both
SPAN sessions by one.
rx
or
both
SPAN sessions
2
tx
SPAN sessions
4
tx
,
rx
, or
both
RSPAN source sessions
1
RSPAN destinations
24
Total SPAN sessions
30
2
2.
2
rx
or
both
SPAN se 4
tx
SPAN se 24 RSPAN destination sessions = 30 total SPAN sessions.