R2511-HP MSR Router Series Layer 2 - LAN Switching Configuration Guide(V5)

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aggregation group, see "Choosing a reference port" in the section "Aggregating links in static mode."
For information about how a reference port is selected in a dynamic link aggregation group, see
"Choosing a reference port" in the sec
tion "Aggregating links in dynamic mode."
Link aggregation modes
Link aggregation can be done in dynamic mode or static mode. Dynamic link aggregation uses the IEEE
802.3ad LACP, but static link aggregation does not. Table 12 c
ompares the two aggregation modes.
Table 12 A comparison between static and dynamic aggregation modes
Aggregation
mode
LACP status on
member
p
orts
Pros Cons
Static Disabled
Aggregation is stable. Peers do
not affect the aggregation state of
member ports.
Member ports do not
automatically align their
aggregation state with their peer
ports. The administrator must
manually maintain link
aggregations.
Dynamic Enabled
The peer systems maintain the
aggregation state of member
ports automatically.
Aggregation is unstable. The
aggregation state of member
ports is susceptible to network
changes.
In a dynamic link aggregation group, a Selected port can receive and send LACPDUs. An Unselected
port can receive and send LACPDUs only if it is up and has the same class-two configurations as the
aggregate interface.
LACP
IEEE 802.3ad LACP enables dynamic aggregation of physical links. It uses LACPDUs for exchanging
aggregation information between LACP-enabled devices.
1. LACP functions:
Basic LACP functions can be implemented through the basic LACPDU fields, including the system
LACP priority, system MAC address, port aggregation priority, port number, and operational key.
Each member port in a LACP-enabled aggregation group exchanges the preceding information
with its peer. When a member port receives an LACPDU, it compares the received information
with the information received on other member ports. In this way, the two systems reach an
agreement on which ports should be placed in Selected state.
2. LACP priorities:
LACP priorities have the following types: system LACP priority and port aggregation priority. The
smaller the priority value, the higher the priority.
Table 13 LACP priorities
T
yp
e Descri
p
tion
System LACP
priority
Used by two peer devices (or systems) to determine which one is superior in link
aggregation.
In dynamic link aggregation, the system with higher system LACP priority sets the
Selected state of member ports on its side first, and then the system with lower
priority sets the port state accordingly.