H3C S7500 Series User manual

Operation Manual – DLDP
H3C S7500 Series Ethernet Switches Table of Contents
i
Table of Contents
Chapter 1 DLDP Configuration ....................................................................................................1-1
1.1 Overview............................................................................................................................1-1
1.1.1 Introduction..............................................................................................................1-1
1.2 DLDP Fundamentals .........................................................................................................1-2
1.2.1 DLDP Implementation.............................................................................................1-2
1.2.2 DLDP Status............................................................................................................1-6
1.2.3 DLDP Timers...........................................................................................................1-7
1.2.4 DLDP Operating Mode............................................................................................1-8
1.2.5 DLDP Neighbor State.............................................................................................. 1-8
1.2.6 Link Auto-recovery Mechanism...............................................................................1-9
1.3 DLDP Configuration.........................................................................................................1-10
1.3.1 Configuring DLDP.................................................................................................1-10
1.3.2 Resetting DLDP Status.........................................................................................1-12
1.3.3 Precautions During DLDP Configuration ..............................................................1-13
1.4 DLDP Network Example..................................................................................................1-14

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Chapter 1 DLDP Configuration
When configuring Device Link Detection Protocol (DLDP), go to these sections for
information you are interested in:
zOverview
zDLDP Fundamentals
zDLDP Configuration
zDLDP Network Example
1.1 Overview
1.1.1 Introduction
You may have encountered unidirectional links in networking. When a unidirectional
link occurs, the local device can receive packets from the peer device through the link
layer, but the peer device cannot receive packets from the local device. Unidirectional
link can cause problems such as Spanning Tree Protocol (STP) loops.
Unidirectional links can be caused by
zFiber cross-connection, as shown in Figure 1-1
zFibers that are not connected or disconnected, as shown in Figure 1-2, the hollow
lines in which refer to fibers that are not connected or disconnected.
DLDP can detect the link status of an optical fiber cable or copper twisted pair (such as
super category 5 twisted pair). If DLDP finds a unidirectional link, it disables the related
port automatically or prompts you to disable it manually according to the configurations,
to avoid network problems.
SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3 GE2/0/4
GE2/0/4
SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3 GE2/0/4
GE2/0/4
Figure 1-1 Fiber cross-connection

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SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3 GE2/0/4
GE2/0/4
SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3 GE2/0/4
GE2/0/4
d Figure 1-2 Fiber broken or not connecte
DLDP provides the following features:
zAs a link layer protocol, it works together with the physical layer protocols to
monitor the link status of a device.
zThe auto-negotiation mechanism at the physical layer detects physical signals and
faults. DLDP identifies peer devices and unidirectional links, and disables
unreachable ports.
zEven if both ends of links can work normallyat the physical layer, DLDP can detect
whether these links are connected correctly and whether packets can be
exchanged normally at both ends. However, the auto-negotiation mechanism
cannot implement this detection.
Note:
zIn order for DLDP to detect fiber disconnection in one direction, you need to
configure the port to work in mandatory full duplex mode at a mandatory rate.
zWhen the port determines the duplex mode and speed through auto-negotiation,
even if DLDP is enabled, it does not take effect when the fiber in one direction is
disconnected. In this case, the port is considered down.
1.2 DLDP Fundamentals
1.2.1 DLDP Implementation
DLDP detects link status by exchanging the following types of packets.

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Table 1-1 DLDP packet types
DLDP packet type Function
Advertisement
Notifies the neighbor devices of the existence of the local
device. An advertisement packet carries only the local port
information, and it does not require response from the peer
end.
RSY-Advertisement
packets (referred to
as RSY packets
hereafter)
Advertisement packet with the RSY flag set to 1. RSY
advertisement packets are sent to request synchronizing the
neighbor information when neighbor information is not
locally available or a neighbor information entry ages out.
Flush-Advertisement
packets (referred to
as flush packets
hereafter)
Advertisement packet with the flush flag set to 1. A flush
packet carries only the local port information (instead of the
neighbor information) and is used to trigger neighbors to
remove the information about the local device.
Probe
Probe packets are used to probe theexistence of a neighbor.
Echo packets are required from the corresponding neighbor.
Probe packets carry the local port information. Neighbor
information is optional for probe packets. A probe packet
carrying neighbor information probes the specified
neighbors;A probe packet carrying no neighbor information
probes all the neighbors.
Echo
Response to probe packets. An echo packet carries the
information about the response port and the neighbor
information it maintains. Upon receiving an echo packet, a
port checks whether the neighbor information carried in the
echo packet is consistent with that of itself. If yes, the link
between the local port and the neighbor is regarded as
bidirectional.
Disable
Disable packets are used to notify the peer end that the local
end is in the disable state. Disable packets carry only the
local port information instead of the neighbor information.
When a port detects a unidirectional link and enters the
disable state, the port sends disable packets to the neighbor.
A port enters the disable state upon receiving a disable
packet.

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DLDP packet type Function
LinkDown
Linkdown packets are used to notify unidirectional link
emergencies (a unidirectional link emergency occurs when
the local port is down and the peer port is up). Linkdown
packets carry only the local port information instead of the
neighbor information. In some conditions, a port is
considered to be physically down if the link connecting to the
port is physically abnormal (for example, the Rx line of the
fiber on the port is disconnected, while the Tx line operates
properly). But for the peer end, as Rx signals can still be
received on the physical layer, the port is still considered to
be normal. Such a situation is known as unidirectional link
emergency.
When a unidirectional link emergency occurs, DLDP sends
linkdown packets immediately to inform the peer of the link
abnormality. Without linkdown packets, the peer can detect
the link abnormality only after a period when the
corresponding neighbor information maintained on the
neighbor device ages out, which is three times the
advertisement interval. Upon receiving a linkdown packet, if
the peer end operates in the enhanced mode, it enters the
disable state, and sets the receiving port to the DLDP down
state (auto shutdown mode) or gives an alarm to the user
(manual shutdown mode).
Recover Probe
Recover probe packets are used to detect whether a link
recovers to implement the port auto-recovery mechanism.
Recover probe packets carry only the local port information
instead of the neighbor information. They request for recover
echo packets as the response.A port in the DLDP down
state sends a recover probe packet every two seconds.
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.
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.
Table 1-2 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

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2) A DLDP packet received is processed as follows:
zIn authentication mode, the DLDP packet is authenticated and is then dropped if it
fails the authentication.
zThe packet is further processed, as described in Table 1-3.
Table 1-3 The procedure to process a received DLDP packet
Packet type Processing procedure
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.
Advertisement
packet
Extracts
neighbor
information 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
Creates the neighbor entry if it does not exist
on the local device.
Probe packet
Sends echo
packets
containing both
neighbor and its
own information
to the peer
Resets the aging timer of the entry if the
neighbor entry already exists on the local
device.
No Drops the echo packet
No Drops the echo packet
Sets the flag bit of the
neighbor to bidirectional
link
Echo packet
Checks
to see if
the local
device is
in the
probe
state
Yes
Checks to
see if the
neighbor
information
contained
in the
packet is
the same
as that on
the local
device
Yes 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.
3) If no echo packet is received from the neighbor, DLDP performs the following
processing:

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Table 1-4 Processing procedure when no echo packet is received from the neighbor
No echo packet received from the
neighbor Processing procedure
In normal mode, no echo packet is
received when the echo waiting timer
expires.
In enhanced mode, no echo packet is
received when the enhanced timer
expires
DLDP switches to the disable state,
outputs logand tracking information, and
sends flush packets. Depending on the
user-defined DLDP down mode, DLDP
disables the local port automatically or
prompts you to disable the port
manually. DLDP sends RSY messages
and removes the corresponding
neighbor entries.
1.2.2 DLDP Status
Alink can be in one of these DLDPstates: initial, inactive, active, advertisement, probe,
disable, and delaydown.
Table 1-5 DLDP status
Status Description
Initial Initial status before DLDP is enabled.
Inactive DLDP is enabled but the corresponding link is down
Active DLDP is enabled, and the link is up or an neighbor entry is
cleared
Advertisement
All neighbors communicate normally in both directions, or
DLDP remains in active state for more than five seconds and
enters this status. It is a stable state where no unidirectional link
is found
Probe DHCP sends packets to check whether the link is a
unidirectional. It enables the probe sending timer and an echo
waiting timer for each target neighbor.
Disable DLDP detects a unidirectional link, or finds (in enhanced mode)
that a neighbor disappears. In this case, DLDP sends and
receives only recover probe packets and recover echo packets.
DelayDown
When a device in the active, advertisement, or probe DLDP
state receives a port down message, it does not removes the
corresponding neighbor immediately, neither does it changes
to the inactive state. Instead, it changes to the delaydown state
first.
When a device changes to the delaydown state, the related
DLDP neighbor information remains, and the DelayDown timer
is triggered.After the DelayDown timer expires, the DLDP
neighbor information is removed.

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1.2.3 DLDP Timers
Table 1-6 DLDP timers
Timer Description
Advertisement
sending timer
Interval between sending advertisement packets, which can be
configured on a command line interface.
By default, the timer length is 5 seconds.
Probe sending
timer The interval is 0.5 seconds. In the probe state, DLDP sends two probe packets in a second.
Echo waiting
timer
It is enabled whenDLDP enters the probe state. The echo waiting
timer length is 10 seconds.
If no echo packet is received from the neighbor when the Echo
waiting timer expires, the state of the local end is set to
unidirectional link (one-way audio) and the state machine turns
into the disable state. DLDPoutputs log and tracking information,
sends flush packets. Depending on the user-defined DLDP down
mode, DLDP disables the local port automatically or prompts you
to disable the port manually. At the same time, DLDP deletes the
neighbor entry.
Entry aging
timer
When a new neighbor joins, a neighbor entry is created and the
corresponding entry aging timer is enabled
When an advertisement packet is received from a neighbor, the
neighbor entry is updated and the corresponding entry aging
timer is updated
In the normal mode, if no packet is received from the neighbor
when the entry aging timer expires, DLDP sends an
advertisement packet with an RSY tag, and deletes the neighbor
entry.
In the enhanced mode, if no packet is received from the neighbor
when the entry aging timer expires, DLDP enables the enhanced
timer
The entry aging timer length is three times the advertisement
timer length.
Enhanced timer
In the enhanced mode, if no packet is received from the neighbor
when the entry aging timer expires, DLDP enables the enhanced
timer for the neighbor. The enhanced timer length is 10 seconds
The enhanced timer then sends one probe packet every second
and eight packets successively to the neighbor.
If no echo packet is received from the neighbor when the
enhanced timer expires, the state of the local end is set to
unidirectional communication state and the state machine turns
into the disable state. DLDP outputs log and tracking information
and sends flush packets. Depending on the user-defined DLDP
down mode, DLDP disables the local port automatically or
prompts you to disable the port manually. Meanwhile, DLDP
deletes the neighbor entry.

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Timer Description
DelayDown
timer
When a device in the active, advertisement, or probe DLDP state
receives a port down message, it does not removes the
corresponding neighbor immediately, neither does it changes to
the inactive state. Instead, it changes to the delaydown state first.
When a device changes to the delaydown state, the related DLDP
neighbor information remains, and the DelayDown timer is
triggered. The DelayDown timer is configurable and ranges from
1 to 5 seconds.
A device in the delaydown state only responds to port up
messages.
Adevice in the delaydown state resumes its original DLDPstate if
it receives a port up message before the delaydown timer expires.
Otherwise, it removes the DLDP neighbor information and
changes to the inactive state.
1.2.4 DLDP Operating Mode
DLDP can operate in two modes: normal and enhanced.
Table 1-7 DLDP operating mode and neighbor entry aging
DLDP
operating
mode
DLDP detects whether
neighbors exist or not
when neighbor tables
are aging
The entry aging
timer is enabled or
not during neighbor
entry aging
The enhanced
timer is enabled
or not when the
entry aging timer
expires
Normal
mode No
Yes (The neighbor
entry ages out after
the entry aging timer
expires)
No
Enhanced
mode Yes
Yes (The enhanced
timer is enabled after
the entry aging timer
expires)
Yes (When the
enhanced timer
expires, the state
of the local end is
set to
unidirectional link,
and the neighbor
entry is aged out.)
1.2.5 DLDP Neighbor State
A DLDP neighbor can be in one of these two states: two way and unknown. You can
check the state of a DLDP neighbor by using the display dldp command.

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Table 1-8 Description on the two DLDP neighbor states
DLDP neighbor state Description
two way The link to the neighbor operates properly.
unknown The device is detecting the neighbor and the neighbor
state is unknown.
1.2.6 Link Auto-recovery Mechanism
If the shutdown modeof a port is set to auto shutdown, the port is set to the DLDP down
state when DLDP detects the link connecting to the port is a unidirectional link. Aport in
DLDP down state does not forward service packets or receive/send protocol packets
except DLDPDUs.
Aport in the DLDP down state recovers when the corresponding link recovers. Aport in
the DLDP down state sends recover probe packets periodically. On receiving a correct
recover echo packet (which means that the unidirectional link is restored to a
bidirectional link), it is brought up by DLDP. The detailed process is as follows.
1) A port in the DLDP down state sends a recover probe packet every 2 seconds.
Recover probe packets carry only the local port information.
2) Upon receiving a recover probe packet, the peer end responds with a recover
echo packet.
3) Upon receiving a recover echo packet, the local end checks to see if the neighbor
information carried in the recover echo packet is consistent with that of the local
port. If yes, the link between the local port and the neighbor is considered to be
recovered to bidirectional, the port changes from the disable state to the active
state, and neighboring relationship is reestablished between the local port and the
neighbor.
Note:
Only ports in the DLDP down state can send and process recover probe packets and
recover echo packets. The auto-recovery mechanism does apply to ports that are shut
down manually.

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1.3 DLDP Configuration
1.3.1 Configuring DLDP
Note:
For a port with DLDP enabled, you are not recommended to execute the port monitor
last command on the port. If it is necessary, the value argument in this command must
be less than 10.
Follow these steps to configure DLDP:
To do… Use the command… Remarks
Enter system view system-view —
Enable DLDP
globally dldp enable
Enter
Ethernet
port view
interface interface-type
interface-number
Enable
DLDP Enable
DLDP
on a
port Enable
DLDP on
a port dldp enable
Required.
Enable DLDP
globally and
then enable
DLDP on the
specified port.
Set the authentication mode and
password
dldp authentication-mode
{none |simple
simple-password | md5
md5-password }
Optional
By default, the
authentication
mode is none,
that is,
authentication
is not
performed.
Set the interval of sending DLDP
packets dldp interval value
Optional. By
default, the
interval of
sending DLDP
packets is 5
seconds.
Set the delaydown timer dldp delaydown-timer
delaydown-time
Optional
By default, the
delaydown
timer expires
after 1 second
it is triggered.

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To do… Use the command… Remarks
Set the DLDP handling mode
when an unidirectional link is
detected
dldp
unidirectional-shutdown
{auto |manual }
Optional
By default, the
handling mode
is auto
Set the operating mode of DLDP dldp work-mode {enhance
|normal }
Optional
By default,
DLDP works in
normal mode.
Enter Ethernet port view interface interface-type
interface-number —
Force the duplex attribute duplex full
Required
If you want to
use DLDP to
detect which
fiber of the two
fibers is not
connected or
fails, you must
configure the
ports to work in
the mandatory
full duplex
mode.
Force the speed value speed speed-value Required
Display the configuration
information about the
DLDP-enabled ports
display dldp [ interface-type
interface-number ] —

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Note:
zWhen you use the dldp enable/dldp disable command in system view to
enable/disable DLDP globally on all optical ports of the switch, this command is only
valid for existing optical ports on the device, however, it is not valid for those added
subsequently.
zDLDP can operate normally only when the same authentication mode and
password are set for local and peer ports.
zWhen the DLDP protocol works in normal mode, the system can identify only one
type of unidirectional links: cross-connected fibers.
zWhen the DLDP protocol works in enhanced mode, the system can identify two
types of unidirectional links: the first type is the cross-connected fiber, and the
second type is one of the two fibers is not connected or fails.
zWhen the device is busy with services and the CPU utilization is high, DLDP may
issue mistaken reports. You are recommended to configure the operating mode of
DLDP as manual after unidirectional links are discovered.
zFor the dldp interval integer command, make sure that the same interval for
transmitting advertisement packets is set on the ports used to connected both
devices; otherwise DLDP will not operate properly.
1.3.2 Resetting DLDP Status
Note:
Only after the ports are DLDP down due to the detection of unidirectional links can you
use the dldp reset command to reset the DLDP status of these ports to retrieve DLDP
probes.
Follow these steps to reset DLDP status:
To do… Use the command… Remarks
Enter system view system-view —
Reset the status of DLDP globally dldp reset Optional

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To do… Use the command… Remarks
Enter Ethernet port
view interface interface-type
interface-number —
Reset the status of
DLDP on 100 M
Ethernet ports dldp reset
Reset the
status of
DLDP on a
port Reset the status of
DLDP on Gigabit
Ethernet ports dldp reset
Optional
Caution:
zThis command only applies to the ports in DLDP down status.
zIf a port is DLDP down, it can return to the up state automatically. You donot need to
reset DLDP on the port.
1.3.3 Precautions During DLDP Configuration
zDLDP does not work on a port where you configure duplex and rate forcibly, such
as 10 GE port.
zDLDP works only when the link is up.
zTo insure that DLDP neighbors can be established properly and unidirectional
links can be detected, you must make sure: DLDP is enabled on both ends, and
the interval of sending DLDP advertisement packets, authentication mode and
password are consistent on both ends.
zYou can adjust the interval of sending DLDP advertisement packets (which is 5
seconds by default and in the range of 1 seconds to 100 seconds) in different
network circumstances, so that DLDP can respond rapidly to link failure. The
interval must be shorter than one-third of the STP convergence time, which is
generally 30 seconds. If too long an interval is set, an STP loop may occur before
DLDP shut down unidirectional links. On the contrary, if too short an interval is set,
network traffic increases, and port bandwidth is reduced.
zDLDP is also applicable to STP Discarding ports. Ports discarded by STP can set
up normal DLDP neighbors and detect unidirectional links.
zDLDP does not process any LACP event, and treats each link in the aggregation
group as independent.
zThe mandatory duplex mode must be enabled on both ends of the DLDP link. In
this way, unidirectional links will be reported and the ports can be shut down as
required; if the auto-negotiation duplex mode is configured on both ends,

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unidirectional links will not be reported and ports will not be shut down, while only
the state of DLDP neighbors changes.
zIf DLDP is enabled after unidirectional links appear, DLDP cannot detect
unidirectional links.
zDLDP cannot be used together with similar protocols of other companies, that is,
you cannot enable DLDP on one end and enable one of the similar protocols of
other companies.
For XGbus products, pay attention to the following points:
zWhen interface boards are hot swapped, if the plugged interface board is of the
same type as the pulled interface board, DLDP restores automatically.
zWhen active/standby switchover is performed on an SRPU, the standby SRPU
detects unidirectional links instead of the SRPU. DLDP parameters remain the
same and unidirectional links are detected again on each port.
1.4 DLDP Network Example
I. Network requirements
As shown in Figure 1-3:
zSwitch A and Switch B are connected through two pairs of fibers. Both of them
support DLDP;
zSuppose the fibers between Switch A and Switch B are cross-connected. DLDP
disconnects the unidirectional links after detecting them;
zWhen the network administrator connects the fiber correctly, the ports taken down
by DLDP are restored.
II. Network diagram
Switch
Switc
B
hA
PC
GE2/0/3
GE2/0/3 GE2/0/4
GE2/0/4
Switch
Switc
B
hA
PC
GE2/0/3
GE2/0/3 GE2/0/4
GE2/0/4
Figure 1-3 Fiber cross-connection
III. Configuration procedure
1) Configure Switch A
# Configure the ports to work in mandatory full duplex mode at the speed of 1000 Mbps.

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<H3CA> system-view
[H3CA] interface gigabitethernet 2/0/3
[H3CA-GigabitEthernet2/0/3] duplex full
[H3CA-GigabitEthernet2/0/3] speed 1000
[H3CA-GigabitEthernet2/0/3] quit
[H3CA] interface gigabitethernet 2/0/4
[H3CA-GigabitEthernet2/0/4] duplex full
[H3CA-GigabitEthernet2/0/4] speed 1000
[H3CA-GigabitEthernet2/0/4] quit
# Enable DLDP globally
[H3CA] dldp enable
# Set the interval of sending DLDP packets to 15 seconds
[H3CA] dldp interval 15
# Configure DLDP to work in enhanced mode
[H3CA] dldp work-mode enhance
# Set the DLDP handling mode to auto after unidirectional links are detected
[H3CA] dldp unidirectional-shutdown auto
# Display the DLDP status
[H3CA] display dldp
Note:
If the fibers are correctly connected between the two switches, the system displays the
connections with the neighbor as bidirectional links.
When the fibers are not correctly connected:
zWhen the fibers are cross-connected, both ends are unidirectional links and the two
ends are displayed as in Disable status;
zWhen one end is correctly connected and the other end is not connected, one end is
in Advertisement status and the other is in Inactive status.
# Restore the ports taken down by DLDP
[H3CA] dldp reset
2) Configure Switch B
The configuration of Switch B is the same to that of SwitchA.

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Note:
Suppose the port works in the mandatory full duplex mode and the connection at both
ends of the link is normal. After DLDP is enabled, if the optical fiber in one end is not
connected, DLDP will report that the link is a unidirectional link.