Reference Guide

Table 39. Layer 2 Overhead
Layer 2 Overhead Difference Between Link MTU and IP MTU
Ethernet (untagged) 18 bytes
VLAN Tag 22 bytes
Untagged Packet with VLAN-Stack Header 22 bytes
Tagged Packet with VLAN-Stack Header 26 bytes
Link MTU and IP MTU considerations for port channels and VLANs are as follows.
Port Channels:
• All members must have the same link MTU value and the same IP MTU value.
• The port channel link MTU and IP MTU must be less than or equal to the link MTU and IP MTU values
configured on the channel members.
For example, if the members have a link MTU of 2100 and an IP MTU 2000, the port channel’s MTU
values cannot be higher than 2100 for link MTU or 2000 bytes for IP MTU.
VLANs:
• All members of a VLAN must have the same IP MTU value.
• Members can have different Link MTU values. Tagged members must have a link MTU 4–bytes higher
than untagged members to account for the packet tag.
• The VLAN link MTU and IP MTU must be less than or equal to the link MTU and IP MTU values
configured on the VLAN members.
For example, the VLAN contains tagged members with Link MTU of 1522 and IP MTU of 1500 and
untagged members with Link MTU of 1518 and IP MTU of 1500. The VLAN’s Link MTU cannot be higher
than 1518 bytes and its IP MTU cannot be higher than 1500 bytes.
Port-Pipes
A port pipe is a Dell Networking-specific term for the hardware packet-processing elements that handle
network traffic to and from a set of front-end I/O ports. The physical, front-end I/O ports are referred to
as a port-set. In the command-line interface, a port pipe is entered as port-set port-pipe-
number.
CR4 Auto-Negotiation
You can configure interface type as CR4 with auto-negotiation enabled. Many DAC cable link issues are
resolved by setting the interface type as CR4. If the CR4 optic fails to come up, use the autoneg option.
To configure interface type as CR4 with auto-negotiation enabled, use the following commands.
• Set the interface type as CR4 with auto-negotiation enabled.
INTERFACE mode
intf-type cr4 autoneg
To disable CR4 auto-negotiation, use the no intf-type cr4 autoneg command.
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Interfaces