3Com Switch 7750 Configuration Guide

214 CHAPTER 27: DLDP CONFIGURATION
1 If the DLDP-enabled link is up, DLDP sends DLDP packets to the peer device, and
analyzes/processes the DLDP packets received from the peer device. DLDP packets
sent in different DLDP states are of different types.
2 A DLDP packet received is processed as follows:
■ In authentication mode, the DLDP packet is authenticated and is then dropped
if it fails the authentication.
■ The packet is further processed, as described in Table 144.
3 If no echo packet is received from the neighbor, DLDP performs the following
processing:
Recover Echo Recover echo packets are response to recover probe packets in the
port auto-recovery mechanism. A link is considered to restore to the
bidirectional state if a port on one end sends a recover probe packet,
receives a recover echo packet, and the neighbor information
contained in the recover echo packet is consistent with that of the
local port.
Table 142 DLDP packet types
DLDP packet type Function
Table 143 DLDP state and DLDP packet type
DLDP state Type of the DLDP packets sent
Active Advertisement packets, with the RSY
flag set or not set.
Advertisement Advertisement packets
Probe Probe packets
Table 144 The procedure to process a received DLDP packet
Packet type Processing procedure
Advertisement
packet
Extracts neighbor
information
If the corresponding neighbor entry does not exist on
the local device, DLDP creates the neighbor entry,
triggers the entry aging timer, and switches to the
probe state.
If the corresponding neighbor entry already exists on
the local device, DLDP resets the aging timer of the
entry.
Flush packet Removes the neighbor entry from the local device
Probe packet Sends echo packets
containing both
neighbor and its
own information to
the peer
Creates the neighbor entry if it does not exist on the
local device.
Resets the aging timer of the entry if the neighbor
entry already exists on the local device.
Echo packet Checks to
see if the
local device
is in the
probe state
No Drops the echo packet
Yes Checks to see
if the
neighbor
information
contained in
the packet is
the same as
that on the
local device
No Drops the echo packet
Yes Sets the flag bit of the
neighbor to bidirectional link
If all neighbors are in the
bidirectional link state, DLDP
switches from the probe state
to the advertisement state,
and sets the echo waiting
timer to 0.