Cisco WS-C2960-24TC-L Software Guide - Page 399
RSPAN Configuration Guidelines
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Chapter 26 Configuring SPAN and RSPAN Configuring RSPAN RSPAN has all the features of SPAN (see the "Understanding How SPAN Works" section on page 26-4), plus support for source ports and destination ports that are distributed across multiple switches, allowing remote monitoring of multiple switches across your network. The traffic for each RSPAN session is carried over a user-specified RSPAN VLAN that is dedicated for that RSPAN session in all participating switches. The SPAN traffic from the sources is copied onto the RSPAN VLAN through the reflector port and then forwarded over trunk ports carrying the RSPAN VLAN to RSPAN destination ports monitoring the RSPAN VLAN. Traffic sent out through the source port is also sent out on the reflector port. Because the reflector port is an access (nontrunking) port in loopback mode, the traffic is switched out with no VLAN tag and is immediately sent back to the switch. In the loopback, the traffic is encoded into the RSPAN VLAN. A switch with an RSPAN destination session receives the traffic (see Figure 26-2). The traffic type for sources (ingress, egress, or both) in an RSPAN session can be different for source switches, but must be the same for all source ports on a given switch. Do not configure any ports in an RSPAN VLAN except those selected to carry RSPAN traffic. Learning is disabled on the RSPAN VLAN. Figure 26-2 Flow of RSPAN Monitored Traffic Switch A (source) Switch B (intermediate) Switch C (destination) 58549 VLAN 609 2/2 1/1 2/1 2/3 VLAN 609 1/2 3/1 3/2 RSPAN Reflector source port port (RX) RSPAN VLAN 609 RSPAN destination port RSPAN Configuration Guidelines This section describes the guidelines for configuring RSPAN: Tip Because RSPAN VLANs have special properties, we recommend that you reserve a few VLANs across your network for use as RSPAN VLANs. Do not assign access ports to these VLANs. • All the items in the "SPAN Configuration Guidelines" section on page 26-5 apply to RSPAN. • RSPAN sessions can coexist with SPAN sessions to a maximum of five sessions. The limit on the number of sessions the Catalyst 4500 series switches can carry as an intermediate switch is the maximum number of VLANs for the switch. • For RSPAN configuration, you can distribute the source ports and the destination port across multiple switches. • A port cannot serve as an RSPAN source port or RSPAN destination port while designated as an RSPAN reflector port. 78-15486-01 Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 26-9
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