Avaya 8800 Planning And Engineering, Network Design page 60

Redundant network design
Figure 15: VLACP sub-100 millisecond convergence
VLACP recommendations and considerations
Avaya recommends the following:
• When connecting to a stackable switch, Avaya recommends settings VLACP to use a time-out
scale of 5, short timers, and a timeout value of 500 milliseconds. Both faster timers and lower
time-out scales are supported, but if any VLACP flapping occurs, increase the time-out scale
and the short timer to their recommended values. Both the 8895 SF/CPU and 8692 SF/CPU
with SuperMezz can support a fast periodic timer value as low as 30 milliseconds (ms).
• Do not use VLACP on configured LACP MLTs because LACP provides the same functionality
as VLACP for link failure. VLACP and LACP running on the same link is not recommended.
• Although the software configuration supports VLACP short timers of less than 30 ms, using
values less than 30 ms is not supported in practice. The shortest (fastest) supported VLACP
timer is 30 ms with a timeout of 3, which is used to achieve sub-100 millisecond failover
(seeVLACP sub-100 ms convergence
Availability (HA) mode, and may not be stable in scaled networks.
• For interswitch trunk (IST) links, Avaya recommends using a time-out scale of 5, long timers,
and slow-periodic-time of 10000. For IST MLTs, Avaya recommends that you do not set the
VLACP long periodic timer to less than 30 seconds.
• If you plan to use a Layer 3 core with Equal Cost Multipath Protocol (ECMP), do not configure
VLACP timers to less than 100 ms. This recommendation assumes a combination of basic
Layer 2 and Layer 3 with OSPF. Some more complex configurations require higher timer
values.
• When a VLACP-enabled port does not receive a VLACPDU, it normally enters 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.
• VLACP is configured by port. The port can be either an individual port or a MLT member.
VLACPDUs are 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 is taken down after the expiry timeout occurs (timeout scale x periodic
June 2016
on page 59 ). 30 ms timers are not supported in High
Planning and Engineering — Network Design
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