82 Nortel Networks L2/3 Ethernet Switch Module for IBM Eserver BladeCenter
The Advanced Layer 2 topology offers a good compromise between performance and high
availability. It is made up of dual GbESMs, each with two, 2-port aggregated links, going to a
pair of Core switches, each Core switch joined to each other via a single link (simulating a
Layer 2 network beyond the switches). The 2-port aggregation itself provides for higher
performance and the second 2-port aggregation link provides for full redundancy on a
connection-loss or a switch-failure situation.
In the examples presented in this chapter, the Core switches are always forced to be the
Spanning Tree Root Bridges. Having the Root Bridge directly attached to the GbESM is not
necessarily recommended in redundant configurations, as flow patterns can become less
than obvious. But it is highly recommended to have the Root Bridge outside the BladeCenter.
Summary of disconnect procedure, to be performed for each example
When performing initial configurations or making changes to existing configurations that
might have an impact on Spanning Tree (such as changing link aggregation), it is
recommended that you leave connections un-cabled, or shut down, prior to making the
configuration changes. This will reduce the likelihood of any temporary Spanning Tree loops
and possible network-down conditions that might result in the process of adding or changing
configurations.
Shut down the ports on GbESM_1 and GbESM_2
/oper/port EXT1/dis
/oper/port EXT2/dis
/oper/port EXT5/dis
/oper/port EXT6/dis
Shut down the ports on Core1 and Core2
conf t
int range g0/1-2, g0/11-12
shut
7.7.1 Dynamic link aggregation IEEE 802.3ad (LACP)In contrast to the static trunks configured in 7.6, “Basic Layer 2 entry topology” on page69,
dynamic Link Aggregation Control Protocol (LACP) is used now for the connections
GbESM_1 to Core1 and GbESM_2 to Core2. The additional cross connections, GbESM_1
ports EXT5-6 to ports G0/11-12 on Core2 and similar GbESM_2 ports EXT5-6 to ports
G0/11-12 on Core1 are configured as LACP trunks as well, including IEEE 802.1Q tagging
(VLAN 5 untagged/native). Remember to shut down the ports before starting the
configuration changes as mentioned before.
Important: There is a high probability that any existing network will already have a desired
switch configured as the root. It is very important that you understand the proper selection
of the root bridge and that the GbESM not be allowed to become the root bridge. Allowing
the GbESM to become the root bridge can result in sub-optimal data flow within the Layer
2 network.