Design Reference

Parameter Configuration
Transmission interval 500 ms (default)
Loop Detect
Use the Loop Detect feature at the edge of a network to prevent loops. This feature detects
whether the same MAC address appears on different ports. Loop Detect can disable a VLAN
or a port. The Loop Detect 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 Detect feature detects MAC addresses that are looping
from one port to other ports. After the switch detects a loop, it disables the port on which the
MAC addresses were learned. Additionally, if Loop Detect finds a MAC address loop, it disables
the MAC address 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 that involve ARP frames on routed interfaces,
Loop-Detect does not detect the network loop condition due to how ARP frames are copied to
the CPU. Use ARP-Detect on Layer 3 interfaces. The ARP-Detect feature supports only the
vlan-block and port-down options.
VLACP
This feature provides an end-to-end failure detection mechanism that prevents potential
problems caused by misconfigurations in a switch cluster design.
Configure VLACP on an individual port basis. The system forwards traffic only across the
uplinks when VLACP is operating correctly. You must configure the ports on each end of the
link for VLACP. VLACP takes the point-to-point hello mechanism of LACP and uses it to
periodically send PDU packets to ensure end-to-end reachability and provide failure detection,
across a Layer 2 domain. If one end of the link does not receive the VLACP PDUs, it logically
disables that port and no traffic passes. This action ensures that even if no link exists on the
port at the other end, and if it is not processing VLACP PDUs correctly, no traffic is sent. This
function alleviates potential black hole situations by only sending traffic to ports that are
functioning properly.
You can reduce VLACP timers to 400 milliseconds between two Avaya Virtual Services
Platform 4000 systems. The timer provides approximately one second failure detection and
switchover. When you configure VLACP, you must configure both ends of the link with the
same multicast MAC address and timers. Most products in the Avaya Ethernet switch and
Ethernet routing switch line use the same timers, with the exception of the FastPeriodicTimer,
which is 200ms on the Ethernet Routing Switch 8800, VSP 9000, and VSP 4000; and 500ms
on all other switches.
Loop prevention and detection
Network Design Reference for Avaya VSP 4000 February 2014 45