User's Manual

2-2
Cisco 3200 Series Mobile Access Router Hardware Guide
OL-5816-04
Chapter 2 Fast Ethernet Switch Mobile Interface Card (FESMIC)
Auto-Negotiation and Auto-MDI/MDIX
Auto-Negotiation and Auto-MDI/MDIX
All of the 10/100 Fast Ethernet interfaces support Ethernet auto-negotiation for the line transmission
speed. Both sides of the connection are automatically set to either 10BASE-TX or 100BASE-TX.
Auto-negotiation is widely used on most Ethernet interfaces, and it is the default mode.
When a 10/100 Fast Ethernet interface is enabled, one end of the link must perform media dependent
interface (MDI) crossover (MDIX), so that the transmitter on one end of the data link is connected to the
receiver on the other end of the data link (a crossover cable is typically used). The Auto-MDIX feature
eliminates the need for crossover cabling by performing an internal crossover when a straight cable is
detected during the auto-negotiation phase.
If auto-negotiation is disabled, Auto-MDI/MDIX cannot work because there is no signal transmission at
initialization to sample the cabling with. Therefore, as in all systems not supporting the HP Auto-MDIX
feature, cabling must be correct for the devices being connected. The Auto-MDIX feature is disabled if
you explicitly set the line speed rather than leaving the default mode of auto-negotiation. Although it is
possible to disable HP Auto-MDIX with auto-negotiation enabled, the current software does not
implement an explicit CLI command to allow you to disable Auto-MDIX during auto-negotiation.
Auto-negotiation Enable
To enable auto-negotiation, do the following:
Router#(config) FastEthernet m/n
Router#(config-if) speed auto
where m is the slot and n is the port number.
Auto-negotiation Disable
To disable auto-negotiation and auto-MDIX by forcing the line speed through a manual setting, do the
following:
Router#(config) FastEthernet m/n
Router#(config-if) speed 10
or
Router#(config) FastEthernet m/n
Router#(config-if) speed 100
MAC Address Allocation
The 4-port FESMIC stores 4 unique MAC addresses for the 10/100 Ethernet interfaces. The
2-port FESMIC stores 2 unique MAC addresses for the 10/100 Ethernet interfaces. In addition, 33
unique MAC addresses are burned into the Mobile Access Router Card (MARC) to support the FESMIC
per-VLAN spanning tree (PVST) and inter-VLAN routing features.
To provide support for up to 32 VLANs, and the 32 Spanning Tree Protocol (STP) sessions that might
be running, 32 unique MAC addresses required for the bridge packet data unit (BPDU) IDs. In addition,
one MAC address is needed by the FESMIC for VLAN routing., bringing the total of number of MAC
addresses on the wired router to 34. The MAC addresses are burned in the MARC, instead of the
FESMIC to support future development.