Loop Detect; Vlacp; Loop Prevention Recommendations - Avaya 8800 Planning And Engineering, Network Design

Loop Detect

The Loop Detection feature is used at the edge of a network to prevent loops. It detects whether the
same MAC address appears on different ports. This feature can disable a VLAN or a port. The Loop
Detection feature can also disable a group of ports if it detects the same MAC address on two
different ports five times in a configurable amount of time.
On a individual port basis, the Loop Detection feature detects MAC addresses that are looping from
one port to other ports. After a loop is detected, the port on which the MAC addresses were learned
is disabled. Additionally, if a MAC address is found to loop, the MAC address is disabled for that
VLAN.
ARP Detect
The ARP-Detect feature is an enhancement over Loop Detect to account for ARP packets on IP
configured interfaces. For network loops involving ARP frames on routed interfaces, Loop-Detect
does not detect the network loop condition due to how ARP frames are copied to the SF/CPU . Use
ARP-Detect on Layer 3 interfaces. The ARP-Detect feature supports only the vlan-block and port-
down options.

VLACP

Although VLACP has already been discussed previously in this document, it is important to discuss
this feature in the context of Loop Prevention and CPU protection of Switch Cluster networks. This
feature provides an end-to-end failure detection mechanism which will help to prevent potential
problems caused by misconfigurations in a Switch Cluster design.
VLACP is configured on a per port basis and traffic can only be forwarded across the uplinks when
VLACP is up and running correctly. The ports on each end of the link must be configured for
VLACP. If one end of the link does not receive the VLACP PDUs, it logically disables that port and
no traffic can pass. This insures that even if there is a link on the port at the other end, if it is not
processing VLACP PDUs correctly, no traffic is sent. This alleviates potential black hole situations
by only sending traffic to ports that are functioning properly.

Loop prevention recommendations

The following table describes the loop prevention features available for release 4.1.x and later. For
best loop prevention, Avaya recommends that you use SLPP.
Table 23: Loop prevention by release
Software release
4.1.x and on
June 2016
CP-Limit Loop detect
Yes (see Note 1) No
Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
SLPP, Loop Detect, and Extended CP-Limit
Ext-CP-Limit SLPP
Yes (soft down) Yes (see Note 3)
(see Notes 1 and 2)
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