Encapsulation Configuration; Ingress Packets - Cisco 4500M Software Manual

Encapsulation Configuration

Encapsulation Configuration
When configuring a SPAN destination port, you can explicitly specify the encapsulation type used by
the port. Packets sent out the port are tagged in accordance with the specified mode. (The encapsulation
mode also controls how tagged packets are handled when the ingress packet option is enabled.) The
Catalyst 4500 series switch supervisor engines support ISL encapsulation and 802.1q encapsulation, as
well as untagged packets. The "replicate" encapsulation type (in which packets are transmitted from the
destination port using whatever encapsulation applied to the original packet) is not supported. If no
encapsulation mode is specified, the port default is untagged. To view the task of configuring
encapsulation, see the command table below.

Ingress Packets

When ingress is enabled, the SPAN destination port accepts incoming packets (potentially tagged
depending on the specified encapsulation mode) and switches them normally. When configuring a SPAN
destination port, you can specify whether or not the ingress feature is enabled and what VLAN to use to
switch untagged ingress packets. (Specifying an ingress VLAN is not required when ISL encapsulation
is configured, as all ISL encapsulated packets have VLAN tags.) Although the port is STP forwarding,
it does not participate in the STP, so use caution when configuring this feature lest a spanning-tree loop
be introduced in the network. When both ingress and a trunk encapsulation are specified on a SPAN
destination port, the port will go forwarding in all active VLANs. Configuring a non-existent VLAN as
an ingress VLAN is not allowed.
By default, host learning is disabled on SPAN destination ports with ingress enabled. The port is also
removed from VLAN floodsets, so regular traffic will not be switched out of the destination port. If
learning is enabled, however, then traffic for hosts learned on the destination port will be switched out
the destination port. It is also possible to configure static host entries (including a static ARP entry and
a static entry in the MAC-address table) on SPAN destination ports.
Note This configuration will not work if the SPAN session does not have a source configured; the session is
half configured with only the SPAN destination port.
To configure ingress packets and encapsulation, perform this task:
Command
Switch(config)# [no] monitor session
< session_number > destination interface
<interface> [encapsulation {isl | dot1q}]
[ingress [vlan vlan_IDs ] [learning]]
Software Configuration Guide—Release 12.2(25)EW
39-12
Chapter 39 Configuring SPAN and RSPAN
Purpose
Specifies the configuration of the ingress
packet and the encapsulation type of the
destination port.
For session_number, specifies the session
number identified with this SPAN session (1
through 6).
For interface, specifies the destination
interface.
For vlan_IDs, specifies the destination VLAN.
Use the no keyword to restore the defaults.
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