HP ProLiant BL p-Class GbE2 Interconnect Switch Compatibility with Cisco-based Networks - White Paper

The access switches and connections have been moved inside the BL p-Class server blade enclosure.

The GbE2 Interconnect Switches become the access switch layer that is in turn connected to the core

switch layer. The same network technology is used and the tiered network configuration remains

unchanged. Because the interconnect switch is an industry-standard managed layer 2 switch, it is

compatible with other industry-standard switches including Catalyst switches from Cisco.

The remainder of this paper discusses the GbE2 Interconnect Switch interoperability with Cisco

Catalyst switches in the areas of.

• VLANs and VLAN tagging (VLAN trunking)

• spanning tree

• multi-link trunking (EtherChannel)

• security

• management

• port mirroring (SPAN, RSPAN)

• multicast traffic

VLANs and VLAN tagging

Each GbE2 Interconnect Switch provides 255 port-based IEEE 802.1Q virtual local area networks

(VLANs) compatible with Catalyst switches that support this industry standard. Both the Catalyst

switches and GbE2 Interconnect Switches utilize VLAN1 as the default VLAN. This permits immediate

out-of-the-box passing of Ethernet traffic.

To create VLANs across the network, the GbE2 Interconnect Switch supports IEEE 802.3ac VLAN

Ethernet frame extensions for 801.2Q tagging

. Each switch port may be individually configured as

tagged or untagged. Therefore, GbE2 Interconnect Switch VLANs may span Cisco switches that

support the 802.1Q tagging methodology. Although Cisco typically refers to 802.1Q VLAN tagging

as VLAN trunking or dot1q trunking, the technologies are the same and, therefore, completely

interoperable. The key is to ensure that ports on both ends of the tagged link (or dot1Q trunk) are

assigned to same VLANs.

The Cisco proprietary VLAN tagging Inter Switch Link (ISL) is an alternative method that predates the

IEEE 801.1Q tagging standard. The GbE2 Interconnect Switch does not support ISL. Cisco

recommends that “…new implementations follow the IEEE 802.1q standard and older networks

gradually migrate from ISL” to allow multi-vendor interoperability, greater field exposure, greater third

party support, and, to a lesser degree, 802.1Q’s lower encapsulation overhead.

Lastly, the GbE2 Interconnect Switch cannot be used as a participating node with Cisco’s VLAN Trunk

Protocol (VTP). However, the interconnect switch may be used as a VTP transparent mode to forward

VTP information.

Spanning tree

Spanning tree is enabled by default on the GbE2 Interconnect Switch to ensure that any existing

network layer 2 loops are blocked. The GbE2 Interconnect Switch meets the IEEE 802.1D standard

and is compatible with Cisco switches that are 802.1D compliant. The bridge priorities, port costs,

and port priorities may be manually assigned on the GbE2 Interconnect Switch. This allows the core

or other Catalyst switches to be the root bridge.

The IEEE 802.3 standards have been merged into a single standard defined as IEEE 802.3-2002. IEEE 802.3-2002, section 3.5 (Elements of

the Tagged MAC Frame) now contains the specifications previously defined in IEEE 802.3ac.

Best Practices for Catalyst 4000, 5000, and 6000 Series Switch Configuration and Management, Cisco Systems, Document 13414, October

1, 2003; available at http://www.cisco.com/en/US/products/hw/switches/ps663/products_tech_note09186a0080094713.shtml