Design Reference

Chapter 7: Link redundancy
You can build link redundancy into your network to:
• Help eliminate a single point of failure in your network (provide physical and link layer
redundancy)
• Prevent a service interruption caused by a faulty link (provide link layer redundancy)
This chapter explains the following design options that you can use to achieve link redundancy
(provide alternate data paths) :
• Physical layer redundancy
• MultiLink Trunking
• 802.1ad-based link aggregation
Physical layer redundancy
To ensure that a faulty link does not cause a service interruption, you can provide physical layer
redundancy in your network.
You can also configure the platform to detect link failures with, for example:
• Remote fault indication
• Virtual Link Aggregation Control Part (VLACP)
Gigabit Ethernet and remote fault indication
The 802.3z gigabit Ethernet standard defines remote fault indication (RFI) as part of the Auto-
Negotiation function.
Because RFI is part of the Auto-Negotiation function, if you disable Auto-Negotiation, you
automatically disable RFI.
The stations on both ends of a fiber pair use RFI to inform one another after a problem occurs on
one of the fibers.
Avaya recommends that you enable Auto-Negotiation on gigabit Ethernet links when the devices on
both ends of a fiber link support Auto-Negotiation because, without RFI support, if one of two
unidirectional fibers that form the connection between the two platforms fails, the transmitting side
cannot determine that the link is broken in one direction (see the following figure).
36 Network Design Reference for Avaya VSP 4000 Series June 2015
Comments on this document? [e-mail]