What is the SPAN reflector?
A. This is a fairly complex problem that arose due to one ASIC missing on the FWSM compared to other regular CEF256 6500 linecards. That ASIC is called “TITAN” and is a “central rewrite engine” responsible for multicast replication and other traffic such as GRE. When there is no switch fabric in the system (system in bus mode), the FWSM uses the supervisor’s TITAN ASIC and all works well. When a fabric is installed (Sup720 has a fabric onboard), multicast/GRE traffic can no longer reach the central TITAN. A software workaround was developed to circumvent the problem: a SPAN session is used to send mcast/GRE to the central ASIC. Certain network topologies require the SPAN reflector, you can find an example in this paper. However, the SPAN reflector is known for having a few serious side effects such as CSCee10005 and CSCef55314. Whenever possible, try running the FWSM in bus-mode by using the “fabric switching-mode force bus” 6500 config mode command – be aware that this will reboot the
