Specifications

HP Virtual Connect for Cisco Network Administrators (version 1.2x) page 15
between the VC Ethernet module and the external switch. A vNet may form more than one port
channel with an external switch or switches. Each port channel behaves as a single logical path.
Like in the previous section describing simple fault tolerance, a vNet can only have one active
logical path at any given time. As such, a vNet with multiple port channels will only use one port
channel as the active logical path and all other port channels in the same vNet will be in standby
mode. See the figure below as an example.
Figure 5. A vNet Utilizing Port Channeling for Load Balancing and Fault Tolerance
(see Appendix A for a description of the elements in the above diagram)
Note:
Port channels can only form when VC uplink ports on the same physical VC Ethernet module are
connected to the same external switch. VC does not support port channels that span across
different VC Ethernet modules.
Port Channeling (802.3ad) Load Balancing Algorithm
VC-Enet’s implementation of port channeling, or EtherChannel, uses a load balancing algorithm for
the purpose of distributing frames across the physical ports that make up the port channel. The
biggest concern in distributing frames across multiple physical ports is “frame ordering”. For any
particular conversation between two network devices (e.g. FTP transfer, telnet session, etc.), it is
optimal that the network infrastructure deliver the frames in the order in which the transmitter
transmitted them. This minimizes frame reordering on the receivers end. Also, while TCP provides
header information for putting frames back into the correct order, other protocols, such as UDP, do
not. Therefore, frame ordering is critical. This means that any load balancing algorithm used by port
channeling must load balance frames but also maintain frame ordering. This is accomplished by
using an algorithm that makes the same load balancing decision for frames from the same
conversation.
Typical EtherChannel Load Balancing Algorithms (from worst to best):
• Source MAC address