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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.
1.
The active system sends a steady stream of control packets that indicates that its session state is Down, until the passive
system responds. These packets are sent at the desired transmit interval of the Active system. The Your Discriminator field is
set to zero.
2.
When the passive system receives any of these control packets, it changes its session state to Init and sends a response that
indicates its state change. The response includes its session ID in the My Discriminator field and the session ID of the remote
system in the Your Discriminator field.
3.
The active system receives the response from the passive system and changes its session state to Up. It then sends a control
packet indicating this state change. This is the third and final part of the handshake. Now the discriminator values have been
exchanged and the transmit intervals have been negotiated.
4.
The passive system receives the control packet and changes its state to Up. Both systems agree that a session has been
established. However, because both members must send a control packet — that requires a response — anytime there is a
state change or change in a session parameter, the passive system sends a final response indicating the state change. After
this, periodic control packets are exchanged.
Bidirectional Forwarding Detection (BFD)
145
Summary of Contents for S4048-ON
Page 1: ...Dell Configuration Guide for the S4048 ON System 9 9 0 0 ...
Page 146: ...Figure 14 BFD Three Way Handshake State Changes 146 Bidirectional Forwarding Detection BFD ...
Page 522: ...Figure 87 Configuring Interfaces for MSDP 522 Multicast Source Discovery Protocol MSDP ...
Page 523: ...Figure 88 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 523 ...
Page 528: ...Figure 91 MSDP Default Peer Scenario 1 528 Multicast Source Discovery Protocol MSDP ...
Page 529: ...Figure 92 MSDP Default Peer Scenario 2 Multicast Source Discovery Protocol MSDP 529 ...
Page 530: ...Figure 93 MSDP Default Peer Scenario 3 530 Multicast Source Discovery Protocol MSDP ...
Page 633: ...Policy based Routing PBR 633 ...
Page 777: ...Figure 119 Single and Double Tag TPID Match Service Provider Bridging 777 ...
Page 778: ...Figure 120 Single and Double Tag First byte TPID Match 778 Service Provider Bridging ...