User guide

HP Virtual Connect for Cisco Network Administrators (version 4.x)
Document Number: C01386629 Date: January 2014
page 40
• A server reverts to the factory-default MAC address when removed from the enclosure or
when no VC Server Profile is applied to
it.
• VC generates 2 MAC addresses per NIC port in order to support multi-function adapters
that may require more than one MAC address per port.
• Customers requiring a centralized database for managing the VC managed MAC
address pools should consider implementing Virtual Connect Enterprise Manager. See
www.hp.com/go/vcem for more details.
Spanning Tree
Since Virtual Connect does not present itself to the external Cisco network as another “Ethernet
switch”, the subject of “spanning tree interoperability” is not an applicable topic when discussing
the two products. In other words, in the same way that a server (with multiple NICs) does not need
to be configured for spanning tree, Virtual Connect (with multiple uplinks that look like NICs to
the external Cisco network) does not need to be configured for spanning tree either. This means
that the network administrator does not have to worry about STP interoperability issues between VC
and Cisco since VC uplink ports do not transmit or receive STP BPDUs (Spanning Tree
configuration frames) and cannot interfere with the external switched infrastructure’s
implementation of STP any more than a multihomed server can. This also means that all questions
about PVST+ support, Rapid Spanning Tree, MST, etc. are not applicable for Virtual Connect
deployment discussions.
Since VC uplink ports simply look to the network like “regular old server ports” with multiple
MAC addresses, HP recommends that Cisco downlink ports connected to the VC uplink ports be
configured as if they are connected directly to server NIC ports. In other words, configure the Cisco
downlink ports as “access” or “trunk” ports with PortFast enabled. Enabling BPDUGuard is also
an acceptable option for customers that regularly enable it for other Cisco switch ports
connected directly to server ports. In summary, since Virtual Connect allows the c-Class enclosure
to connect to the external network in much the same way as a VMware ESX server connects to
the external network, it is easy to understand why Virtual Connect, just like a VMware ESX
server, does not participate in the external network’s spanning tree domain.
Unidirectional Link Detection (UDLD)
UDLD is a Cisco proprietary feature that only operates between two directly connected Cisco
devices. The purpose of UDLD is to detect unidirectional links (UniDirectional Link Detection)
in situations where spanning tree is being used to detect and prevent loops. If a unidirectional
link goes undetected, spanning tree won’t properly detect the loop and won’t block the port to
prevent a loop on the network. Since spanning tree is not used between VC uplinks and external
Cisco switches, a spanning tree loop caused by a unidirectional link is not possible. Therefore,
UDLD is not required nor supported on Virtual Connect uplinks.
Quality of Service
In the current version of firmware, Virtual Connect does support user-configurable settings for
traffic classification, marking, or prioritization. VC does utilize layer 2 quality of service
markings (802.1p Class of Service) and layer 3 quality of service markings (TOS, DSCP) for
frame prioritization. There are three modes of operation, 1. No QOS – First in First out. 2. Honoring
mode, VC will honor the markings already made