IBM L2/3 7.1 Standards and technologies

58 Nortel Networks L2/3 Ethernet Switch Module for IBM Eserver BladeCenter

7.1 Standards and technologies

This section provides a brief overview of the networking standards which are supported on

the Nortel GbESM. Detailed examples of configurations which include these standards are

included later in this chapter.

The bulk of this chapter shows interconnection with Cisco Systems’ devices. In 7.9,

“Configuration for Extreme switches” on page 143, we include configurations for some

functions that were tested on a pair of Extreme switches. Interconnection of the GbESMs with

Nortel switches which run Alteon OS software is easily accomplished because the command

syntax is almost exactly the same as that of the GbESMs themselves.

The Nortel GbESM connects to and interoperates with products from a variety of vendors

which fully implement these standards. A limited number of other vendors’ proprietary

extensions to the standards are also supported. The Nortel GbESM configurations provided

in this chapter are not limited to use when connecting with Nortel, Cisco, or Extreme gear.

This standard defines the use of a tag field in the header of each packet which identifies the

VLAN to which the packet belongs. This feature is configured with the /cfg/port/tag

ena|dis command.

Cisco refers to this as a trunk and uses the switchport trunk command to configure it. On

the Nortel Networks L2/3 GbESM, the internal ports have tagging enabled by default to

provide support for Serial over LAN functionality. The external ports have tagging disabled.

These standards define techniques for grouping two or more parallel connections between a

pair of devices as a single logical link or trunk with the total bandwidth of its members. The

Nortel GbESM supports a prestandard implementation of static trunking which is

interoperable with similar implementations from Cisco and Extreme, among others. This is

configured with commands on the /cfg/l2/trunk menu.

The Nortel GbESM also supports Link Aggregation Control Protocol (LACP) as defined in the

standards. LACP provides dynamic negotiation of the formation of trunks and ensures that

the two devices’ configurations are consistent. This feature is configured from the

/cfg/l2/lacp menu.

Note that Cisco refers to this as a Port Channel or EtherChannel and uses the

channel-group and interface portchannel commands to configure it. Cisco also supports

a proprietary prestandard protocol known as Port Aggregation Protocol (PAgP) as well as

supporting LACP. PAgP and LACP provide almost identical functionality.

These protocols define techniques for managing Layer 2 networks whose topologies include

loops. They ensure that a broadcast packet (or any other packet) is not forwarded endlessly

around such a loop by logically blocking some ports.

Original or Classic Spanning Tree Protocol (STP) is defined by the 802.1D standard. This

standard is relatively old and many vendors, including Cisco, Nortel, and Extreme, have

implemented proprietary extensions to it. The Nortel GbESM will interoperate with Cisco’s