Specifications

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Cisco XR 12000 Series Router SIP and SPA Software Configuration Guide, Release 3.2
Release 3.2, OL-6396-01, Rev.A1 January 9, 2006
Chapter 4 Configuring Ethernet SPAs on Cisco IOS XR Software
Configuration Tasks
IEEE 802.3z 1000 Mbps Gigabit Ethernet
Gigabit Ethernet builds on top of the Ethernet protocol, but increases speed tenfold over Fast Ethernet
to 1000 Mbps, or 1 Gbps. Gigabit Ethernet allows Ethernet to scale from 10 or 100 Mbps at the desktop
to 100 Mbps up to 1000 Mbps in the data center. Gigabit Ethernet conforms to the IEEE 802.3z protocol
standard.
By leveraging the current Ethernet standard and the installed base of Ethernet and Fast Ethernet switches
and routers, network managers do not need to retrain and relearn a new technology in order to provide
support for Gigabit Ethernet.
IEEE 802.3ae 10 Gbps Ethernet
Under the International Standards Organization’s Open Systems Interconnection (OSI) model, Ethernet
is fundamentally a Layer 2 protocol. 10-Gigabit Ethernet uses the IEEE 802.3 Ethernet MAC protocol,
the IEEE 802.3 Ethernet frame format, and the minimum and maximum IEEE 802.3 frame size. 10 Gbps
Ethernet conforms to the IEEE 802.3ae protocol standards.
Just as 1000BASE-X and 1000BASE-T (Gigabit Ethernet) remained true to the Ethernet model,
10-Gigabit Ethernet continues the natural evolution of Ethernet in speed and distance. Because it is a
full-duplex only and fiber-only technology, it does not need the carrier-sensing multiple-access with
collision detection (CSMA/CD) protocol that defines slower, half-duplex Ethernet technologies. In every
other respect, 10-Gigabit Ethernet remains true to the original Ethernet model.
MAC Accounting
The MAC address accounting feature provides accounting information for IP traffic based on the source
and destination MAC addresses on LAN interfaces. This feature calculates the total packet and byte
counts for a LAN interface that receives or sends IP packets to or from a unique MAC address. It also
records a time stamp for the last packet received or sent.
Ethernet MTU
A maximum transmission unit (MTU) is the largest size packet or frame, specified in octets (eight-bit
bytes), that can be sent in a packet- or frame-based network such as the Internet. The Internet’s TCP uses
the MTU to determine the maximum size of each packet in any transmission. Too large an MTU size
may mean retransmissions if the packet encounters a router that can’t handle the large packet. Too small
an MTU size means relatively more header overhead and more acknowledgements that have to be sent
and handled. Most computer operating systems provide a default MTU value that is suitable for most
users. The default value is 1514 for standard frames and 1518 for 802.1Q tagged frames. These numbers
exclude the 4 byte frame check sequence (FCS).
Flow Control on Ethernet Interfaces
The flow control used on Gigabit Ethernet interfaces consists of periodically sending flow control pause
frames. It is fundamentally different from the usual full- and half-duplex flow control used on standard
management interfaces. Flow control can be activated for either ingress traffic, egress traffic or
bi-directional traffic. Flow control by default is not activated on SPA Gigabit Ethernet interfaces.
Some hardware has restrictions on how flow-control can be configured. If you attempt to configure a
method of flow-control that is not supported, an error is returned at configuration verification. The
current operational flow control settings can be displayed using the show interfaces command.