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Alteon OS Application Guide
Appendix A: Troubleshooting
24942C4911, January 2007
Layer 3 Port Mirroring (Both Ports in Different GEAs)
In this scenario, you observe Layer 3 port mirroring on an egress port, but the egress port and
the monitoring port reside on different Gigabit Ethernet Aggregator (GEA) units. To find out
which GEA unit each port resides on, use the /info/geaport command.
NOTE – In general, the GbESM mirrors all Layer 3 ingress packets after the packets are routed,
that is, all Layer 3 packets observed at the monitoring port have source MAC address, destina-
tion MAC address, VLAN, TTL, IP checksum changed as if they have gone through the rout-
ing process to the egress port.
Same VLAN as Mirrored Port
Both ports tagged: Tagged packet with VID of the VLAN to which the ports belong
Mirrored port tagged, Monitoring port untagged: Untagged packet
Mirrored port untagged, Monitoring port tagged: Tagged packet with VID of the
VLAN to which the ports belong
Both ports untagged: Untagged packet
Different VLAN from Mirrored Port
Both ports tagged: Tagged packet with VID of the VLAN to which the ports belong
Mirrored port tagged, Monitoring port untagged: Tagged packet with VID of the
VLAN to which the ports belong
Mirrored port untagged, Monitoring port tagged: Tagged packet with VID of the
VLAN to which the ports belong
Both ports untagged: Tagged packet with VID of the VLAN to which the ports belong
NOTE – When the monitoring port belongs to a different VLAN, all mirrored packets have
an 802.1q tag field with the VID of the VLAN to which the mirrored port belongs. The VID
included in the tag field depends on which port is monitored.
For example, assume a packet traverses from port EXT1 (VLAN 1) to EXT2 (VLAN 2), and is
monitored on port EXT3. When you monitor EXT1, the packet’s tag includes the VID of
VLAN 1. When you monitor EXT2, the packet’s tag includes the VID of VLAN 2.