Specifications

HP Virtual Connect for Cisco Network Administrators (version 1.2x) page 48
Appendix C: Frequently Asked Questions
Q1: Why do I see lots of dropped frames (discards) on standby VC uplink ports?
A1: An external switch has no concept of which VC link is the active uplink and which is the standby uplink. As
far as the external switch is concerned, one of the uplinks is just a whole lot busier. That means that the
external switch is still going to send some types of frames down the standby link and the standby link is going to
discard them. This includes all broadcasts, multicasts, and unknown unicasts (destination lookup failure in the
CAM table on the external switch). Any of these frames that are received on the standby link will be dropped
and will be reflected in the counters.
Q2: Can I manually choose which port channel is the preferred channel for a vNet?
A2: No, VC does not currently support setting the ‘port role’ for vNets (or Shared Uplink Sets) with LACP enabled
(connect mode ‘auto’). VC determines which port channel is active and which is standby, based on the
following criteria, 1 - Number of functional uplinks per port channel, 2 – Total bandwidth provided by each port
channel, 3 – if the previous two are a tie, then the VC module with the lowest MAC address (see TOE tag) will
provide the active port channel. With the information above, the Administrator could construct the primary
port channel with one addition uplink in order to make it the preferred port channel.
Q3: Do I have to use the same load balancing algorithm on both sides of the same port channel?
A3: No, you can have different load balancing algorithms on each side of a port channel.
Q4: I see Link Layer Discovery Protocol (LLDP) frames when I connect a network trace analyzer to a VC uplink
port. What is VC doing with LLDP and can I disable it?
A4: LLDP is the IEEE equivalent to Cisco Discovery Protocol (CDP). It is a Layer 2 protocol that allows one device
to both announce itself (and some of its feature set) to a neighboring device as well as discover other
connected devices on the network. It is extremely low-bandwidth and is unobtrusive. VC uses LLDP to
determine when one of its uplinks or cross-connects is directly connected to another VC module in the same
VC domain so that it can form a stacking link. There is currently no way to disable it.
Q5: I don’t have any CX4 10Gb cables to form stacking links. Can I combine multiple 1Gb RJ-45 links instead?
A5: Yes, by adding multiple 1Gb links between modules, VC automatically aggregates them together to form a
single 802.3ad port trunk.
Q6: I am trying to get 802.3ad Port Trunking to work but can’t seem to get it to pass traffic. What am I doing
wrong?
A6: VC currently only supports LACP for 802.3ad port trunks. Cisco’s PAgP is not supported by VC. Future
versions of VC may add additional features to enhance this functionality. For LACP to work properly on a Cisco
switch, the channel mode must be set to either Active or Passive. VC can display detailed Ethernet and port
trunk statistics by clicking the desired Ethernet module under Hardware Overview in the left hand tree-view of
VCM.
Q7: How do I setup a cluster heartbeat network in Virtual Connect?
A7: Create a vNet in VC and do not assign a VC uplink port to it. Next, assign a “heartbeat” NIC from each
blade in the cluster to this vNet. All heartbeat traffic will be contained within the vNet and will not be
transmitted outside of the enclosure.
Q8: I need more than 16 VC uplinks. If I add more VC Ethernet modules to add more uplinks, am I required to
use additional NICs on my servers?
A8: No, you can add more VC Ethernet modules, stack them with the other VC Ethernet modules and just use
the uplink ports. Any VC uplink on any VC Ethernet module can be used to provide external connectivity for
any downlink on any VC Ethernet module.
Q9: I need more NICs on my blade servers. If I add more VC Ethernet modules to add more downlink ports, am
I required to use additional VC uplinks ports to provide connectivity for these new downlink ports?
A9: No, you can add more VC Ethernet modules, stack them with the other VC Ethernet modules and the new
downlink ports can be configured to use the uplinks on the existing VC-Enet modules. Any VC uplink on any VC
Ethernet module can be used to provide external connectivity for any downlink on any VC Ethernet module.
Q10: I noticed that the VC Ethernet module in interconnect bay 1 is the active Virtual Connect Manager and
that the VC module in bay 2 is the standby. Does this mean that only the VC module in bay 1 is providing
Ethernet connectivity for the blade servers?