BFD Sessions
BFD must be enabled on both sides of a link in order to establish a session.
The two participating systems can assume either of two roles:
Active
The active system initiates the BFD session. Both systems can be active for the same
session.
Passive
The passive system does not initiate a session. It only responds to a request for session
initialization from the active system.
A BFD session has two modes:
Asynchronous
mode
In Asynchronous mode, both systems send periodic control messages at an agreed
upon interval to indicate that their session status is Up.’
Demand mode
If one system requests Demand mode, the other system stops sending periodic control
packets; it only sends a response to status inquiries from the Demand mode initiator.
Either system (but not both) can request Demand mode at any time.
NOTE:
Dell Networking OS supports Asynchronous mode only.
A session can have four states: Administratively Down, Down, Init, and Up.
State
Description
Administratively
Down
The local system does not participate in a particular session.
Down
The remote system is not sending control packets or at least not within the detection
time for a particular session.
Init
The local system is communicating.
Up
Both systems are exchanging control packets.
The session is declared down if:
• A control packet is not received within the detection time.
• Sufficient echo packets are lost.
• Demand mode is active and a control packet is not received in response to a poll packet.
BFD Three-Way Handshake
A three-way handshake must take place between the systems that participate in the BFD session.
The handshake shown in the following illustration assumes that there is one active and one passive system,
and that this session is the first session established on this link. The default session state on both ports is
Down.
Bidirectional Forwarding Detection (BFD)
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Summary of Contents for S4048T
Page 1: ...Dell Configuration Guide for the S4048T ON System 9 10 0 1 ...
Page 98: ... saveenv 7 Reload the system uBoot mode reset Management 98 ...
Page 113: ...Total CFM Pkts 10303 CCM Pkts 0 LBM Pkts 0 LTM Pkts 3 LBR Pkts 0 LTR Pkts 0 802 1ag 113 ...
Page 411: ...mode transit no disable Force10 Resilient Ring Protocol FRRP 411 ...
Page 590: ...Figure 67 Inspecting the LAG Configuration Link Aggregation Control Protocol LACP 590 ...
Page 646: ...Figure 87 Configuring Interfaces for MSDP Multicast Source Discovery Protocol MSDP 646 ...
Page 647: ...Figure 88 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 647 ...
Page 653: ...Figure 91 MSDP Default Peer Scenario 2 Multicast Source Discovery Protocol MSDP 653 ...
Page 654: ...Figure 92 MSDP Default Peer Scenario 3 Multicast Source Discovery Protocol MSDP 654 ...
Page 955: ...Figure 119 Single and Double Tag First byte TPID Match Service Provider Bridging 955 ...