Switches example

=-----+   +-------+   +-------+   +-------+   +-----+
| PC1 |---|a Sw1 b|---|a Sw2 b|---|a Sw3 b|---| PC2 |
+-----+   +-------+   +-------+   +-------+   +-----+

- If PC2 MAC address is not in Sw1 MAC table, it must flood the first frame destined to PC2 out of all connected interfaces
- If PC2 MAC address is in Sw1 MAC table, it forwards frames destined to PC2 out of port b
- When PC2 MAC address ages out, it's removed from MAC table and Sw1 must again flood the first frame
- If all switches are running LLDP or CDP, Sw1 can know something about the capabilities of Sw2
- Sw1 has no means of knowing anything about the capabilities of Sw3 or PC2
- If Sw2 isn't running LLDP or CDP, Sw1 knows nothing about its capabilities either


Examples from Sw1 (Cisco 2960) CDP and LLDP info when Sw2 is running both:

Switch#show lldp neighbors
Capability codes:
    (R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device
    (W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other
Device ID           Local Intf     Hold-time  Capability      Port ID
Switch              Fa0/1          120        B               Fa0/1

Total entries displayed: 1


Switch#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID    Local Intrfce   Holdtme    Capability   Platform    Port ID
Switch       Fas 0/1          168            S       2960        Fas 0/1