Administrator Guide

Table Of Contents
Port Characteristics 593
Auto-Negotiation
Dell Networking N-Series switches implement IEEE 802.3 auto-negotiation
for 1000BASE-T, 1000BASE-X, and 10GBASE-T based copper interfaces.
1000BASE-X fiber interfaces also implement auto-negotiation. Auto-
negotiation is required to be present and enabled for 1000BASE-T and
10GBASE-T copper interfaces in order for a clock master to be selected.
The administrator can configure the advertised capabilities, including the
acceptable link speeds, or may disable auto-negotiation altogether. Auto-
negotiation must be disabled and full-duplex must be enabled on certain
fiber interfaces. Disabling auto-negotiation on copper interfaces is not
recommended as it can lead to a duplex mismatch, where one or both
interfaces may appear to come up but, in fact, they have not agreed on the
speed, duplex, or clock master. This may occur when the devices are
connected as follows:
One end is set manually to half-duplex and the other is manually set to
full-duplex
One end is set to auto-negotiation and the other is manually set to full-
duplex
Both sides are manually set to full-duplex, with one side set to auto-
negotiate with the link partner and the other side configured with auto-
negotiation disabled.
Maximum Transmission Unit
Dell Networking N-Series switches allow the operator to configure the
maximum transmission unit for the switch to a value larger than the IEEE
802.3 standard allows. This jumbo frames technology is employed in certain
situations to reduce the task load on a server CPU and to transmit large
amounts of data efficiently. The need for jumbo frames predominantly
appears where certain applications would benefit from using a larger frame
size (for example, Network File System (NFS). The larger frame size
eliminates some of the need for fragmentation, leading to greater throughput.
The increase in throughput is particularly valuable on data center servers,
where the larger frame size increases the efficiency of the system and allows
processing of more requests. The Dell Networking jumbo frames feature
extends the standard Ethernet MTU (Max Frame Size) from 1518 bytes