Allied Telesis SwitchBlade x3100 Series Manual page 860

Introduction
SBx3112
SBx3100
RSTP
SBx3112
SBx3100
RSTP
DS3_Miswire_3112
To address this problem, BFD uses a unique discriminator value in the protocol messages that ensures that BFD
frames are being exchanged between the same peer. When there is such a mis-wiring BFD will declare an
interface failure.
It is also possible that a system cannot by itself conclude that it is mis-wired. If a system A receives packets with
a discriminator 0, it cannot determine from only the packet whether the peer on the other end is not receiving
packets from system A or not receiving packets from some other intended peer. In the figure, System A only
knows that the remote end is not receiving its packets. It is actually system B that detects the mis-wiring.
Another example of mis-wiring is possible in which system reports cannot tell from where it is sending or
receiving that there is a mis-wiring configuration.
7.7.4.4 BFD with XE4 Interfaces
The BFD concept includes all XE4 interfaces, and is called Universal Forwarding Detection (UFD). This would
occur when a topology includes a transport facility; a topology feature (such as RSTP) could report its links
were still up, while a fault within the facility could stop the packet flow. Refer to the following figure.
7-122
Software Reference for SwitchBlade x3100 Series Switches (Network Management)
DS3 Module
1.0
GE
2.0
DS3 Module
DS3 Module
1.0
GE
2.0
DS3 Module
FIGURE 7-18
DS3 Module
DS3 Module
DS3
DS3 Module
Network
X
DS3 Module
Mis-wired DS3s Configuration
Possible Fault Scenarios
SBx3112
SBx3100
1.0
GE
RSTP
2.0
SBx3112
SBx3100
1.0
GE
RSTP
2.0