Bidirectional Forwarding Detection - Avaya 8800 Planning And Engineering, Network Design

Redundant network design
LACP and Minimum Link
The Minimum Link parameter defines the minimum number of active links required for a LAG to
remain in the forwarding state. Use the Minimum-Link (MinLink) feature so that when the number of
active links in a LAG is less than the MinLink parameter, the entire LAG is declared down. Prior to
MinLink support, a LAG was always declared up if one physical link of the LAG was up.
Configure MinLink for each LAG; each LAG can have a different value, if required. The number of
minimum links configured for an end of a LAG is independent of the other end; a different value can
be configured for each end of a LAG. The default MinLink value is 1, with a range of 1 to 8.
If the number of active links in the LAG becomes less than the MinLink setting, the Avaya Ethernet
Routing Switch 8800/8600 marks the LAG as down, and informs the remote end of the LAG state by
using a Link Aggregation Protocol Data Unit (LACPDU). The switch continues to send LACPDUs to
neighbors on each available link based on the configured timers. When the number of active links in
the LAG is greater than or equal to the MinLink parameter, LACP informs the remote end, and the
LAG transitions to the forwarding (up) state.
The maximum number of active links in a LAG is 8; however, you can configure up to 16 links in a
LAG. The eight inactive links are in Standby mode. If a link goes down, Standby links take
precedence over MinLink. When an active link is disabled, the standby link with the lowest port
number immediately becomes active. MinLink operates after the Standby processes finish.
On standard MLT links, you must enable LACP to enable MinLink.
You cannot enable MinLink on Split MultiLink Trunking (SMLT) links because the minimum number
of links with SMLT can only be set to 1.
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 128 link aggregation groups are supported.
• 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
June 2016 Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
70