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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 21 Configuring SPAN and RSPAN Understanding SPAN and RSPAN

Destination Port

Each local SPAN session or RSPAN destination session must have a destination port (also called a
monitoring po rt) th at rece ives a copy of traffic from the sour ce por ts and VLA Ns.
The destination port has these characteristics:
•It must re side on the sa me switch as the so urce port ( for a lo cal SPAN session).
•It can be any Ethe rnet physi cal por t.
•It can participate in only one SPAN session at a time (a destination port in one SPAN session cannot
be a destinati on port for a seco nd SPAN session).
•It canno t be a source por t or a refle ctor por t.
•It canno t be an Ether Channel grou p or a VLAN.
•It can be a physical port that is assigned to an Eth erChannel group, even if the EtherChannel group
has been specified as a SPAN source. The port is removed from the group while it is configured as
a SPAN destination port.
•When it is active, incoming traffic is disabled. The port does not transmit any traffic except that
required for the SPAN session.
•It does not participate in spanning tree while the SPAN session is active.
•When it is a destination port, it does not participate in any of the Layer 2 protocols (STP, VTP, CDP,
DTP, PagP).
•A destination port that belongs to a source VLAN of any SPAN session is excluded from the source
list and is no t monit ored.
•No add ress l ear ning occ urs on the desti nat ion por t.
•A destination port receives copies of sent and received traffic for all monitored source ports. If a
destinat ion port is oversubscribe d, it could bec ome con gested . This coul d affect traffic forwarding
on one or mo re of the sour ce ports.

Reflector Port

The reflector port is the mechanism that copies packets onto an RSPAN VLAN. The reflector port
forwards onl y the t raffic from the RSPAN source se ssion with whi ch it is a ffiliated. A ny device
connected to a port set as a reflector port loses connectivity until the RSPAN source session is disabled.
The reflector port has these characteristics:
•It is a po rt se t t o loop bac k.
•It canno t be an Ether Channel group, it d oes not trun k, and it can not do proto col filtering.
•It can be a physical port that is assigned to an Eth erChannel group, even if the EtherChannel group
is specified as a SPAN source. The port is removed from the group while it is configured as a
refle cto r p ort.
•A port u sed as a refl ect or port canno t be a SPAN sourc e or de stin at ion p ort, n or can a po rt b e a
refle ctor port for more th an one se ssion at a tim e.
•It is invisible to all VLANs.
•The nat ive VLAN for lo oped-ba ck traffic on a reflect or port is th e RSPA N VLA N.
•The re flector port loops back unta gged tr af fic to the switch . The tr af fic i s then plac ed on the R SPAN
VLAN and flooded to any trunk ports t hat carry the RSPAN VLAN.