Avaya 8800 Planning And Engineering, Network Design page 71

transmits BFD packets to each other. If one of the systems does not receive a BFD packet after a
certain period of time, the system assumes that the link or other system is down.
BFD provides low-overhead, short-duration failure detection between two systems. BFD also
provides a single mechanism for connectivity detection over any media, at any protocol layer.
Because BFD sends rapid failure detection notifications to the routing protocols that run on the local
system, which initiates routing table recalculations, BFD helps reduce network convergence time.
BFD supports IPv4 single-hop detection for static routes, OSPF, and BGP. The Ethernet Routing
Switch 8800/8600 BFD implementation complies with IETF drafts draft-ietf-bfd-base-06 and draft-
ietf-bfd-v4v6-1hop-06.
Operation
The Avaya Ethernet Routing Switch 8800/8600 uses one BFD session for all protocols with the
same destination. For example, if a network runs OSPF and BGP across the same link with the
same peer, only one BFD session is established, and BFD shares session information with both
routing protocols.
You can enable BFD over data paths with specified OSPF neighbors, BGP neighbors, and static
routing next-hop addresses.
The Ethernet Routing Switch 8800/8600 supports BFD asynchronous mode, which sends BFD
control packets between two systems to activate and maintain BFD neighbor sessions. To reach an
agreement with its neighbor about how rapidly failure detection occurs, each system estimates how
quickly it can send and receive BFD packets.
A session begins with the periodic, slow transmission of BFD Control packets. When bidirectional
communication is achieved, the BFD session comes up. The switch only declares a path as
operational when two-way communication is established between systems.
After the session is up, the transmission rate of Control packets can increase to achieve detection
time requirements. If Control packets are not received within the calculated detection time, the
session is declared down. After a session is down, Control packet transmission returns to the slow
rate.
If a session is declared down, it cannot come back up until the remote end signals that it is down
(three-way handshake). A session can be kept administratively down by configuring the state of
AdminDown.
BFD restrictions
The Avaya Ethernet Routing Switch 8800/8600 supports up to 256 BFD sessions, however, the
number of BFD sessions plus the number of VLACP sessions cannot exceed 256.
The Ethernet Routing Switch 8800/8600 does not support the following IETF BFD options:
• Echo packets
• BFD over IPv6
• Demand mode
• authentication
The Ethernet Routing Switch 8800/8600 does not support:
• BFD on a VRRP virtual interface
June 2016 Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
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