Loop Detect; Vlacp - Avaya 8800 Planning And Engineering

Port congestion time
Primary (P) – primary target for convergence Secondary (S) – secondary target for
convergence Tertiary (T) – third target for convergence Quarternary (Q) – fourth target for
convergence Avaya does not recommend the Ext CP-Limit HardDown option for software
Release 4.1 or later. Only use this option if SLPP is not available.

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.
Planning and Engineering — Network Design
Setting
SLPP, Loop Detect, and Extended CP-Limit
Value
P = 4 seconds S = 70 seconds T = 140
seconds Q = 210 seconds
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