Vlacp Flap Detect And Damping - Avaya 8600 Configuration Manual

configuration as simple as possible with routed VLANs, but without ECMP. For fast
convergence, Avaya recommends that you use RSMLT rather than ECMP.
• If the value of VLACP timer is not set to a multiple of 10, VLACP may not function properly
because the VLACP port may not be able to send out any VLACP PDUs. VLACP timers
must always be set to some multiple of 10.
• When VLACP is configured, the log message LACP WARNING Received MAC-
mismatched PDUs on port <port_number>, MAC <mac_address>, Please
check your VLACP configuration. is sometimes observed. In the event of a
VLACP misconfiguration, this message will be logged continuously in the log file, and the
configuration should be corrected. If VLACP is not misconfigured and the message is
observed sporadically, it should be disregarded as there is no impact to traffic.
• When a VLACP-enabled port does not receive a VLACPDU, it should enter the disabled
state. There are occasions when a VLACP-enabled port does not receive a VLACPDU
but remains in the forwarding state. To avoid this situation, ensure that the VLACP
configuration at the port level is consistent – both sides of the point-to-point connection
should be either enabled or disabled.
• Traffic loss has been observed for 1-2 seconds after a port link up occurs. This is caused
by the edge switch transmitting traffic immediately upon connecting to the aggregation
(IST core) switch. As soon as the link is enabled, it takes a while before VLACP engages
and stops the traffic from flowing on that link.
VLACP is configured on a per port basis. The port can be either an individual port or a MLT
member. VLACPDUs are be sent periodically on each port where VLACP is enabled. This
allows the exchange of VLACPDUs from an end-to-end perspective. If VLACPDUs are not
received on a particular link, that link will be taken down after the expiry timeout occurs (timeout
scale x periodic time). This implies that unless VLACP is enabled on the IST peer, the ports
will stay in a disabled state. When VLACP is enabled at the IST peer, the VLACPDU is received
and the ports will be re-enabled. This behavior can be replicated despite the IST connectivity
between the end-to-end peers. When you enable VLACP on the IST ports at one end of the
IST, the ports are taken down along with the IST. However, the IST at the other end will stay
active until the expiry timeout occurs on the other end. As soon you enable VLACP at the other
end, the VLACPDU is received by the peer and the ports are brought up at the software
level.

VLACP flap detect and damping

Link instability or packet loss can cause the Virtual Link Aggregation Control Protocol (VLACP)
state of a link to toggle (flap) rapidly, bringing services (such as IP multicast) up and down in
rapid succession. This behavior can cause system-wide instability, including high CPU
utilization. VLACP flap detect and damping is used to automatically shut down selected VLACP
links until a network administrator is able to resolve the root cause of the VLACP flapping.
VLACP flap detect and damping does not support auto-recovery, therefore a network
administrator must re-enable the interface manually.
When enabled, VLACP flap detect and damping shuts off a selected VLACP link if the interface
flaps a specified number of times within a user-defined time frame. For example, VLACP flap
Configuration — Link Aggregation, MLT, and SMLT
Virtual Link Aggregation Control Protocol
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