Design Reference

Figure 8: Problem description (2 of 2)
However, if you use VLACP to detect far-end failures and allow MLT to failover when end-to-
end connectivity is not guaranteed for links in an aggregation group, then VLACP prevents the
failure scenario in the preceding figure.
Avaya recommends that you use the following guidelines for VLACP implementation:
• Do not use VLACP on configured LACP MLTs because LACP provides the same
functionality as VLACP for link failure. Virtual Services Platform 4000 does not support
VLACP and LACP on the same link.
• Use the following best practice standard settings for VLACP :
- a short timer—no less than 500 milliseconds (ms)
- a time-out scale of 5
Tip:
The Avaya Virtual Services Platform 4000 supports both faster timers and lower time-
out scales, but if VLACP flapping occurs, increase the short timer and the time-out scale
to their recommended values: 500 and 5, respectively. Although the software
configuration supports VLACP short timers of less than 30 ms, the platform does not
support using values less than 30 ms in practice. The shortest (fastest) supported
VLACP timer is 30 ms with a timeout of 3, which achieves sub-100 ms failover.
• Do not configure VLACP timers to less than 100 ms if you plan to use a Layer 3 core with
Equal Cost Multipath (ECMP).
Note:
This recommendation assumes a combination of basic Layer 2 and Layer 3 with Open
Shortest Path First (OSPF). If you have more complex configurations, you can require
higher timer values.
• Ensure that the VLACP configuration at the port level is consistent, that both sides of the
point-to-point connection are either enabled or disabled. If a VLACP-enabled port does
not receive a VLACP protocol data unit (PDU), it enters the disabled state. However,
occasions exist when a VLACP-enabled port does not receive a VLACP PDU but remains
Link redundancy
38 Network Design Reference for Avaya VSP 4000 February 2014
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