User guide

HP Virtual Connect for Cisco Network Administrators (version 4.x)
Document Number: C01386629 Date: January 2014
page 23
(see Appendix A for a description of the elements in the above diagram)
An administrator can choose to manually configure a vNet (or Shared Uplink Set) for only fault
tolerance by setting the vNet’s connection mode to ‘failover’. When a vNet’s connection mode is set
to ‘failover’, the LACP protocol is disabled for the vNet and the administrator can change the VC
uplink “Port Role” to “Primary” or “Secondary”. This port role setting allows the administrator to
manually choose which VC uplink should be the preferred active uplink.
Note:
For a sample configuration showing VC uplinks connected to a Cisco switch, see the section below
entitled “Sample Virtual Connect Ethernet and Cisco Configurations”
A vNet (or Shared Uplink Set) will failover from one uplink to another whenever the active uplink
loses link. As soon as VC detects link loss on the active uplink, VC will choose a new active uplink
from the group of available standby uplinks also assigned to the same vNet. This process of choosing
a new active uplink typically occurs in under five seconds. If the upstream Cisco switch has been
properly configured on all the uplinks associated with the vNet, the server connectivity should be
restored in under five seconds. If the previous active uplink has it’s link restored, VC will
automatically failback to it. As long as the external Cisco switch port has been properly configured
by enabling PortFast, connectivity to servers should be restored in under five seconds.
Virtual Connect uses a mechanism called “Fast MAC Cache Failover” to proactively update the
CAM tables on the upstream Cisco switch ports. Whenever a vNet fails over or fails back from one
uplink to another, this mechanism will transmit a single frame on the new active uplink for every
server MAC address that is active within the VC domain. Fast MAC Cache Failover enables VC to
immediately update the external Cisco infrastructure with the new location of the active VC uplink
for a particular vNet. Fast MAC Cache Failover is very similar to the CAM table update process used
by Link-State Tracking on Cisco switches.
VC Uplink Load Balancing
Virtual Connect provides load balancing (and fault tolerance) across multiple VC uplinks on the
same physical VC-Enet module by means of IEEE 802.3ad port trunking or port channeling
(EtherChannel) using the Link Aggregation Control Protocol (LACP). The vNet (or Shared Uplink
Set) must have its “connection mode” set to “auto” (default) and not in mode “failover”.
If the external switch is a Cisco switch, the ports in the EtherChannel must be set to either “mode
active” or “mode passive”. Both of these modes on the Cisco switch enable the use of 802.3ad
LACP (the only port channeling protocol VC supports). VC does not support port channeling with
Cisco switch ports when set to “mode on”, “mode desirable” or “mode auto”.
Note:
An EtherChannel can only be formed between VC and a Cisco switch if the VC vNet is set to
connection mode “Auto” and the Cisco switch’s channel-group is set to either “mode active” or