Enabling Pause FramesEnable Ethernet pause frames flow control on all ports on a chassis or a line card. If not, the system may exhibit unpredictablebehavior.NOTE: Changes in the flow-control values may not be reflected automatically in the show interface output. As aworkaround, apply the new settings, execute shut then no shut on the interface, and then check the running-configof the port.NOTE: If you disable rx flow control, Dell Networking recommends rebooting the system.The flow control sender and receiver must be on the same port-pipe. Flow control is not supported across different port-pipes.To enable pause frames, use the following command.• Control how the system responds to and generates 802.3x pause frames on 1 and 10 Gig ports.INTERFACE modeflowcontrol rx [off | on] tx [off | on]– rx on: enter the keywords rx on to process the received flow control frames on this port.– rx off: enter the keywords rx off to ignore the received flow control frames on this port.– tx on: enter the keywords tx on to send control frames from this port to the connected device when a higher rate oftraffic is received.– tx off: enter the keywords tx off so that flow control frames are not sent from this port to the connected device whena higher rate of traffic is received.– negotiate: enable pause-negotiation with the egress port of the peer device. If the negotiate command is not used,pause-negotiation is disabled. 40 gigabit Ethernet interfaces do not support pause-negotiation.Configure the MTU Size on an InterfaceIf a packet includes a Layer 2 header, the difference in bytes between the link MTU and IP MTU must be enough to include the Layer2 header.For example, for VLAN packets, if the IP MTU is 1400, the Link MTU must be no less than 1422:1400-byte IP MTU + 22-byte VLAN Tag = 1422-byte link MTUThe MTU range is from 592 to 12000, with a default of 1500. IP MTU automatically configures.The following table lists the various Layer 2 overheads found in Dell Networking OS and the number of bytes.Table 16. Layer 2 OverheadLayer 2 Overhead Difference Between Link MTU and IP MTUEthernet (untagged) 18 bytesVLAN Tag 22 bytesUntagged Packet with VLAN-Stack Header 22 bytesTagged Packet with VLAN-Stack Header 26 bytesLink 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.306 Interfaces
