Configuring the Link Characteristics on Ethernet Interfaces

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Full-duplex communication means that both ends of the communication can send and receive signals at the same time. Half-duplex is also bidirectional communication, but signals can flow in only one direction at a time.

By default, the routing platform’s management Ethernet interface, fxp0, autonegotiates whether to operate in full-duplex or half-duplex mode. J-series Gigabit Ethernet interfaces and Fast Ethernet interfaces, except the J-series ePIM Fast Ethernet interfaces, can operate in either full-duplex or half-duplex mode, and all other interfaces can operate only in full-duplex mode. For Gigabit Ethernet and 10-Gigabit Ethernet, the link partner must also be set to full duplex.

Note: When you configure the Tri-Rate Ethernet copper interface to operate at 1 Gbps, autonegotiation must be enabled.

Note: On a J-series ePIM Fast Ethernet interface, if you specify half-duplex (or if full-duplex mode is not autonegotiated), the following message is written to the system log: "Half-duplex mode not supported on this PIC, forcing full-duplex mode."

Note: When you manually configure Fast Ethernet interfaces on the M-series and T-series routers, link mode and speed must both be configured. If both these values are not configured, the router uses autonegotiation for the link and ignores the user-configured settings.

To explicitly configure an Ethernet interface to operate in either full-duplex or half-duplex mode, include the link-mode statement at the [edit interfaces interface-name] hierarchy level:



[edit interfaces interface-name]

link-mode (full-duplex
| half-duplex);

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