Bidirectional Forwarding Detection - Avaya 8800 Planning And Engineering

Redundant network design
Link aggregation group rules
Link aggregation is compatible with the Spanning Tree Protocol (STP/RSTP/MSTP). Link
aggregation groups operate under the following rules:
• All ports in a link aggregation group must operate in full-duplex mode.
• All ports in a link aggregation group must use the same data rate.
• All ports in a link aggregation group must be in the same VLANs.
• Link aggregation groups must be in the same STP groups.
• If the ntstg parameter is false, STP BPDU transmit on only one link.
• Ports in a link aggregation group can exist on different modules.
• Link aggregation groups are formed using LACP.
• A maximum of 32 link aggregation groups are supported in non-R mode (both Classic
and R series modules).
• A maximum of 128 link aggregation groups are supported in R mode (R or RS series
modules only).
• A maximum of eight active links are supported per LAG.
For LACP fundamentals and configuration information, see Avaya Ethernet Routing Switch
8800/8600 Configuration — Link Aggregation, MLT, and SMLT, NN46205-518.

Bidirectional Forwarding Detection

The Avaya Ethernet Routing Switch 8800/8600 supports Bidirectional Forwarding Detection
(BFD). BFD is a simple Hello protocol used between two peers. In BFD, each peer system
periodically 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
72 Planning and Engineering — Network Design November 2010