Chapter 4 Fast Ethernet Switch Mobile Interface Card

Autonegotiation and Auto-MDI/MDIX

All of the Fast Ethernet interfaces support Ethernet autonegotiation for the line transmission speed. Both sides of the connection are automatically set to either 10BASE-TX or 100BASE-TX. Autonegotiation is widely used on most Ethernet interfaces, and it is the default mode.

When a 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 autonegotiation phase.

If autonegotiation 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 autonegotiation. Although it is possible to disable HP Auto-MDIX with autonegotiation enabled, the current software does not implement an explicit command-line interface (CLI) command to allow you to disable Auto-MDIX during autonegotiation.

Autonegotiation Enable

To enable autonegotiation, use the following configuration:

Router#(config) FastEthernet m/n

Router#(config-if) speed auto

where m is the slot and n is the port number.

Autonegotiation Disable

To disable autonegotiation and Auto-MDIX by forcing the line speed through a manual setting, enter the following configuration commands:

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, 37 MAC addresses are burned into Cisco 3270 Rugged Router card–equipped routers, and 33 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 are required for the bridge packet data unit (BPDU) IDs. In addition, the FESMIC needs one MAC address for VLAN routing, bringing the total of number of MAC addresses on the wired router to 34. To support future development, the MAC addresses are burned into the Mobile Access Router Card (MARC), instead of the FESMIC.

Cisco 3200 Series Router Hardware Reference

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Cisco Systems 3200 manual Autonegotiation and Auto-MDI/MDIX, MAC Address Allocation, Autonegotiation Enable

3200 specifications

Cisco Systems 3200 Series routers are designed to deliver high-performance, reliable networking solutions for enterprise and service provider environments. They are part of Cisco's extensive portfolio that addresses the challenges of modern networking, particularly in connecting remote offices and branch locations efficiently and securely.

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