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 an 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 Address Resolution Protocol (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 because of 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 sending traffic only to ports that are functioning properly.
You can reduce VLACP timers to 400 milliseconds between two VSP 4000 systems. The timer
provides approximately 1-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 200 milliseconds on the Ethernet Routing Switch
8800, VSP 9000, and VSP 4000; and 500 milliseconds on all other switches.
SLPP example scenarios
The following examples illustrate some situations where Layer 2 loops can occur and how SLPP
prevents loops in those cases.
SLPP example scenarios
December 2014 Network Design Reference for Avaya VSP 4000 Series 47
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