Specifications

Chapter 2. IBM System Networking Switch 10Gb Ethernet switch features 87
Figure 2-18 shows a typical AMP topology, with two aggregators that support a number of
AMP groups.
Figure 2-18 Active Multipath Protocol topology
Each AMP group requires two links on each switch. Each AMP link consists of a single port, a
static trunk group, or an LACP trunk group. Local non-AMP ports can communicate through
local Layer 2 switching without passing traffic through the AMP links. No two switches in the
AMP loop can have another active connection between them through a non-AMP switch.
Each AMP switch has a priority value (1 - 255). The switch with the lowest priority value has
the highest precedence over the other switches. If there is a conflict between switch priorities,
the switch with lowest MAC address has the highest precedence.
When the AMP loop is broken, the STP port states are set to forwarding or blocking,
depending on the switch priority and port/trunk precedence, as follows:
򐂰 An aggregator's port/trunk has higher precedence over an access switch's port/trunk.
򐂰 Static trunks have highest precedence, followed by LACP trunks, then physical ports.
򐂰 Between two static trunks, the trunk with the lower trunk ID has higher precedence.
򐂰 Between two LACP trunks, the trunk with the lower admin key has higher precedence.
򐂰 Between two ports, the port with the lowest port number has higher precedence.
Health checks
An AMP keepalive message is passed periodically from each switch to its neighbors in the
AMP group. The keepalive message is a BPDU-like packet that passes on an AMP link even
when the link is blocked by STP. The keepalive message carries status information about
AMP ports/trunks, and is used to verify that a physical loop exists.
An AMP link is considered healthy if the switch receives an AMP keepalive message on that
link. An AMP link is considered unhealthy if a number of consecutive AMP keepalive
messages have not been received recently on that link.
AMP and access switches: For correct AMP operation, all access switches should be
configured with a higher priority value (lower precedence) than the aggregators.
Otherwise, some AMP control packets may be sent to access switches, even when their
AMP groups are disabled.