Using Ethernet Pause Frames For Flow Control - Dell C9000 Series Networking Configuration Manual

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Table of Contents

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. The system has 10 switch cards and each card has only one port pipe and 48 ports in each.

For ports connected through the port extender, you can have a maximum of 4 sessions system.

For ports directly attached to the chassis you can have a maximum of 4 sessions per port pipe.

Port Numbering Convention

Configure MTU Size on an Interface

Maximum Transmission Unit (MTU) is defined as the entire Ethernet packet (Ethernet header + FCS +

The link MTU is the frame size of a packet, and the IP MTU size is used for IP fragmentation. If the system

determines that the IP packet must be fragmented as it leaves the interface, the system divides the packet into

fragments no bigger than the size set in the ip mtu command.

Because different networking vendors define MTU differently, check their documentation when

planning MTU sizes across a network.

The following table lists the range for each transmission media.

Transmission

MTU Range (in bytes)

The MTU range is from 594 to 12000, with a default of 1554.

The IP MTU automatically configures.

Using Ethernet Pause Frames for Flow

Ethernet Pause Frames allow for a temporary stop in data transmission. A situation may arise where a sending

device may transmit data faster than a destination device can accept it. The destination sends a PAUSE frame

back to the source, stopping the sender's transmission for a period of time.

An Ethernet interface starts to send pause frames to a sending device when the transmission rate of ingress

traffic exceeds the egress port speed. The interface stops sending pause frames when the ingress rate falls to

less than or equal to egress port speed.

The globally assigned 48-bit Multicast address 01-80-C2-00-00-01 is used to send and receive pause

frames. To allow full-duplex flow control, stations implementing the pause operation instruct the MAC to

enable reception of frames with destination address equal to this multicast address.

The PAUSE frame is defined by IEEE 802.3x and uses MAC Control frames to carry the PAUSE commands.

Ethernet pause frames are supported on full duplex only.

for the exact port location on switch line cards.

Troubleshooting