H3C S5500-EI series User manual

Operation Manual – DLDP
H3C S5500-EI Series Ethernet Switches Table of Contents
i
Table of Contents
Chapter 1 DLDP Configuration ....................................................................................................1-1
1.1 Overview............................................................................................................................1-1
1.1.1 DLDP Introduction...................................................................................................1-2
1.1.2 DLDP Fundamentals...............................................................................................1-3
1.2 DLDP Configuration Task List .........................................................................................1-10
1.2.1 Enabling DLDP......................................................................................................1-10
1.2.2 Setting DLDP Mode ..............................................................................................1-11
1.2.3 Setting the Interval for Sending Advertisement Packets.......................................1-11
1.2.4 Setting the DelayDown Timer ...............................................................................1-12
1.2.5 Setting the Port Shutdown Mode ..........................................................................1-13
1.2.6 Configuring DLDP Authentication .........................................................................1-13
1.2.7 Resetting DLDP State...........................................................................................1-14
1.3 Displaying and Maintaining DLDP...................................................................................1-15
1.4 DLDP Configuration Example..........................................................................................1-15
1.4.1 DLDP Configuration Example...............................................................................1-15
1.5 Troubleshooting...............................................................................................................1-17

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Chapter 1 DLDP Configuration
When performing DLDP configuration, go to these sections for information you are
interested in:
zOverview
zDLDP Configuration Task List
zEnabling DLDP
zSetting DLDP Mode
zSetting the Interval for Sending Advertisement Packets
zSetting the DelayDown Timer
zSetting the Port Shutdown Mode
zConfiguring DLDP Authentication
zResetting DLDP State
zDisplaying and Maintaining DLDP
zDLDP Configuration Example
zTroubleshooting
1.1 Overview
A special kind of links, namely, unidirectional links, may occur in a network. When a
unidirectional link appears, 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 loops in a Spanning Tree Protocol (STP)
enabled network.
As for fiber links, two kinds of unidirectional links exist. One occurs when fibers are
cross-connected, as shown in Figure 1-1. The other occurs when one end of a fiber is
not connected or one fiber of a fiber pair gets disconnected, as illustrated by the hollow
arrows in Figure 1-2.

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Device A
GE1/0/50 GE1/0/51
Device B
PC
GE1/0/50 GE1/0/51
Figure 1-1 Unidirectional fiber link: cross-connected fiber
Device A
Device B
PC
GE1/0/50
GE1/0/50
GE1/0/51
GE1/0/51
Figure 1-2 Unidirectional fiber link: fiber not connected or disconnected
1.1.1 DLDP Introduction
Device Link Detection Protocol (DLDP) can detect the link status of a fiber cable or
twisted pair. On detecting a unidirectional link, DLDP can shut down the related port
automatically or prompt users to take measures as configured to avoid network
problems.
As a data link layer protocol, DLDP cooperates with physical layer protocols to monitor
the link status of a device. The auto-negotiation mechanism provided by physical layer
protocols detects physical signals and faults. DLDP, however, performs operations
such as identifying peer devices, detecting unidirectional links, and shutting down
unreachable ports. The cooperation of physical layer protocols and DLDP ensures that
physical/logical unidirectional links be detected and shut down. For a link with the
devices on the both sides of it operating properly, DLDP checks to see if the cable is

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connected correctly and if packets can be exchanged between the two devices. Note
that DLDP is not implemented through auto-negotiation.
1.1.2 DLDP Fundamentals
I. DLDP link states
A device is in one of these DLDP link states: Initial, Inactive, Active, Advertisement,
Probe, Disable, and DelayDown, as described in Table 1-1.
Table 1-1 DLDP link states
State Description
Initial This state indicates that DLDP is not enabled.
Inactive This state indicates that DLDP is enabled but the link is
down.
Active This state indicates that:
zDLDP is enabled and the link is up.
zThe neighbor entries are cleared.
Advertisement
This state indicates that a device can communicate
normally with all its neighbors in both directions or DLDP
remains in active state for more than five seconds. It is
the normal state where no unidirectional link is detected.
Probe
A device enters this state if it receives a packet from an
unknown neighbor. In this state, DLDP sends packets to
check whether the link is a unidirectional link. After a
device enters this state, the probe sending timer is
triggered, and an echo waiting timer is triggered for each
neighbor to be detected.
Disable
A device enters this state when:
zA unidirectional link is detected.
zThe contact with a neighbor in enhanced mode gets
lost.
In this state, no DLDP packet is sent or accepted.
DelayDown
A device in the Active, Advertisement, or Probe DLDPlink
state transits to this state rather than remove the
corresponding neighbor entry and transits to the Inactive
state when it detects a port-down event. When a device
transits to this state, the DelayDown timer is triggered.

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II. DLDP timers
Table 1-2 DLDP timers
DLDP timer Description
Active timer
Determines the Interval to send Advertisement packets with
RSY tag, which defaults to 1 second.
When a device transits to the active DLDP link state, it
sends Advertisement packets with RSY tag according to this
timer. The maximum number of this type of packets that can
be sent successively is 5.
Advertisement timer Determines the interval to send advertisement packets,
which defaults to 5 seconds.
Probe timer Determines the interval to send Probe packets, which
defaults to 0.5 seconds. The maximum number of this type
of packets that can be sent successively is 10.
Echo timer
This timer is set to 10 seconds and is triggered when a
device transits to the Probe state or an enhanced detect is
launched. When the Echo waiting timer expires and no Echo
packet is received from a neighbor device, the link is set as a
unidirectional link and the device transits to the Disable
state. In this case, the device sends Disable packets,
prompts the user to shut down the port or shuts down the
port automatically (depending on the DLDP down mode
configured), and removes the corresponding neighbor
entries.
Entry timer
When a new neighbor joins, a neighbor entry is created and
the corresponding entry timer is triggered. And when a
DLDP packet is received, the device updates the
corresponding neighbor entry and the entry aging timer.
In the normal mode, if no packet is received from a neighbor
when the corresponding entry aging timer expires, DLDP
sends advertisement packets with RSY tags and removes
the neighbor entry.
In the enhanced mode, if no packet is received from a
neighbor when the Entry timer expires, DLDP triggers the
enhanced timer.
The setting of an Entry timer is three times that of the
Advertisement timer.

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DLDP timer Description
Enhanced timer
In the enhanced mode, this timer is triggered if no packet is
received from a neighbor when the entry aging timer
expires. Enhanced timer is set to 10 seconds.
After the Enhanced timer is triggered, the device sends up
to eight probe packets to the neighbor at a frequency of one
packet per second. If no Echo packet is received from the
neighbor when the Echo timer expires, the link is set as a
unidirectional link and the device transits to the Disable
state. In this case, the device sends Disable packets,
prompts the user to shut down the port or shuts down the
port automatically (depending on the DLDP down mode
configured), and removes the corresponding neighbor
entries.
DelayDown timer
A device in the Active, Advertisement, or Probe DLDP link
state transits to DelayDown state rather than removes the
corresponding neighbor entry and transits to the Inactive
state when it detects a port-down event.
When a device transits to this state, the DelayDown timer is
triggered. The setting of the timer ranges from 1 to 5 (in
seconds). A device in DelayDown state only responds to
port-up events.
A device in the DelayDown state resumes its original DLDP
state if it detects a port-up event before the DelayDown
timer expires. Otherwise, it removes the corresponding
DLDP neighbor information and transits to the Inactive
state.
RecoverProbe timer Determines the interval toRecoverProbe packets, which are
used to detect whether a unidirectional link is restored. This
timer is set to 2 seconds.
III. DLDP mode
DLDP can operate in two modes: normal mode and enhanced mode, as described
below.
zIn normal DLDP mode, when an entry timer expires, the device removes the
corresponding neighbor entry and sends an Advertisement packet with RSY tag.
zIn enhanced DLDP mode, when an entry timer expires, the Enhanced timer is
triggered and the device sends up to eight Probe packets at a frequency of one
packet per second to test the neighbor. If no Echo packet is received from the
neighbor when the Echo timer expires, the device transits to the Disable state.

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Table 1-3 DLDP mode and neighbor entry aging
DLDP
mode
Detecting a
neighbor after the
corresponding
neighbor entry
ages out
Removing the
neighbor entry
immediately after the
Entry timer expires
Triggering the
Enhanced timer after
an Entry timer
expires
Normal
DLDP
mode No Yes No
Enhanced
DLDP
mode Yes No Yes
The enhanced DLDP mode is designed for addressing black holes. It prevents the
cases where one end of a link is up and the other is down. If you configure the speed
and the duplex mode by force on a device, the situation shown in Figure 1-3 may occur,
where Port B is actually down but the state of Port B cannot be detected by common
data link protocols, so PortA is still up. In enhanced DLDP mode, however, Port Atests
Port B after the Entry timer concerning Port B expires. Port A then transits to the
Disable state if it receives no Echo packet from Port Awhen the Echo timer expires. As
Port B is physically down, it is in the Inactive DLDP state.
Figure 1-3 A case for Enhanced DLDP mode
Note:
zIn normal DLDP mode, only fiber cross-connected unidirectional links (as shown in
Figure 1-1 ) can be detected.
zIn enhanced DLDP mode, two types of unidirectional links can be detected. One is
fiber cross-connected links (as shown in Figure 1-1). The other refers to fiber pairs
with one fiber not connected or disconnected (as shown in Figure 1-2). To detect
unidirectional links that are of the latter type, you need to configure the ports to
operate at specific speed and in full duplex mode. Otherwise, DLDP cannot take
effect. When a fiber of a fiber pair is not connected or gets disconnected, the port
that can receive optical signals is in Disable state; the other port is in Inactive state.

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IV. DLDP authentication mode
You can prevent network attacks and illegal detect throughDLDPauthentication. Three
DLDP authentication modes exist, as described below.
zNon-authentication. In this mode, the sending side sets the Authentication field
and the Authentication type field of DLDP packets to 0. The receiving side checks
the values of the two fields of received DLDP packets and drops the packets with
the two fields conflicting with the corresponding local configuration.
zPlain text authentication. In this mode, before sending a DLDP packet, the sending
side sets the Authentication field to the password configured in plain text and sets
the Authentication type field to 1. The receiving side checks the values of the two
fields of received DLDP packets and drops the packets with the two fields
conflicting with the corresponding local configuration.
zMD5 authentication. In this mode, before sending a packet, the sending side
encrypts the user configured password using MD5 algorithm, assigns the digest to
the Authentication field, and sets the Authentication type field to 2. The receiving
side checks the values of the two fields of received DLDP packets and drops the
packets with the two fields conflicting with the corresponding local configuration.
V. DLDP implementation
1) On a DLDP-enabled link that is in up state, DLDP sends DLDP packets to the peer
device and processes the DLDP packets received from the peer device. DLDP
packets sent vary with DLDP states. Table 1-4 lists DLDP states and the
corresponding packets.
Table 1-4 DLDP packet types and DLDP states
DLDP state Type of DLDP packets sent
Active Advertisement packet with RSY tag
Advertisement Normal Advertisement packet
Probe Probe packet
Disable Disable packet and RecoverProbe packet
Note:
When a device transits from a DLDP state other than Inactive state or Disable state to
Initial state, it sends Flush packets.
2) A received DLDP packet is processed as follows.
zIn any of the three authentication modes, the packet is dropped if it fails to pass the
authentication.

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zThe packet is dropped if the setting of the interval for sending Advertisement
packets it carries conflicts with the corresponding local setting.
zOther processes.
Table 1-5 Procedures for processing different types of DLDP packets
Packet type Processing procedure
If the corresponding neighbor entry does not
exist, creates the neighbor entry, triggers the
Entry timer, and transits to Probe state.
Advertisement
packet with
RSY tag
Retrieving the
neighbor
information. If the corresponding neighbor entry already
exists, resets the Entry timer and transits to
Probe state.
If the corresponding neighbor entry does not
exist, creates the neighbor entry, triggers the
Entry timer, and transits to Probe state.
Normal
Advertisement
packet
Retrieves the
neighbor
information. If the corresponding neighbor entry already
exists, resets the Entry timer.
If yes, no process is performed.
Flush packet
Determines
whether or not
the local port is
in Disable
state.
If not, removes the corresponding neighbor
entry (if any).
If the corresponding neighbor entry does not
exist, creates the neighbor entry, transits to
Probe state, and returns Echo packets.
Probe packet Retrieves the neighbor
information. If the corresponding neighbor entry already
exists, resets the Entry timer and returns Echo
packets.
If the corresponding neighbor entry does not
exist, creates the neighbor entry, triggers the
Entry timer, and transits to Probe state.
If the neighbor information it
carries conflicts with the
corresponding locally maintained
neighbor entry, drops the packet.
Echo packet Retrieves the neighbor
information.
The
correspon
ding
neighbor
entry
already
exists
Otherwise, sets the flag of the
neighbor as two-way connected. In
addition, if the flags of all the
neighbors are two-way connected,
the device transits from Probe
state to Advertisement state and
disables the Echo timer.
If yes, no process is performed.
Disable packet Check to see if
the local port is
in Disable
state. If not, the local port transits to Disable state.

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Packet type Processing procedure
If not, no process is performed.
RecoverProbe
packet
Check to see if
the local port is
in Disable or
Advertisement
state. If yes, returns RecoverEcho packets.
If not, no process is performed.
RecoverEcho
packet
Check to see if
the local port is
in Disable
state.
If yes, the local port transits to Active state if the
neighbor information the packet carries is
consistent with the local port information.
If not, no process is performed.
LinkDown
packet
Check to see if
the local port
operates in
Enhanced
mode. If yes and the local port is not in Disable state,
the local transits to Disable state.
3) If no echo packet is received from the neighbor, DLDP performs the following
processing.
Table 1-6 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 timer
expires.
In enhanced mode, no echo packet
is received when the enhanced
timer expires.
DLDP transits to the Disable state, outputs
log and tracking information, and sends
Disable packets. In addition, depending on
the user-defined DLDP down mode, DLDP
shuts down the local port or prompts users to
shut down the port, and removes the
corresponding neighbor entry.
VI. DLDP neighbor state
A DLDP neighbor can be in one of the three states described in Table 1-7. You can
check the state of a DLDP neighbor by using the display dldp command.
Table 1-7 Description on DLDP neighbor states
DLDP neighbor
state Description
Unknown
A neighbor is in this state when it is just detected and is being
probed. No information indicating the state of the neighbor is
received. A neighbor is in this state only when it is being probed.
It transits to Two way state or Unidirectional state after the probe
operation finishes.
Two way A neighbor is in this state after it receives response from its peer.
This state indicates the link is a two-way link.

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DLDP neighbor
state Description
Unidirectional
A neighbor is in this state when the link connecting it is detected
to be a unidirectional link. After a device transits to this state, the
corresponding neighbor entries maintained on other devices are
removed.
1.2 DLDP Configuration Task List
Complete the following tasks to configure DLDP:
Task Remarks
Enabling DLDP Required
Setting DLDP Mode Optional
Setting the Interval for Sending Advertisement Packets Optional
Setting the DelayDown Timer Optional
Setting the Port Shutdown Mode Optional
Configuring DLDP Authentication Optional
Resetting DLDP State Optional
Note that:
zDLDP works only when the link is up.
zTo ensure unidirectional links can be detected, make sure these settings are the
same on the both sides: DLDP state (enabled/disabled), the interval for sending
Advertisement packets, authentication mode, and password.
zKeep the interval for sending Advertisement packets adequate to enable
unidirectional links to be detected in time. If the interval is too long, unidirectional
links cannot be terminated in time; if the interval is too short, network traffic may
increase in vain.
zLACP (Link Aggregation Control Protocol) events have no effect on DLDP. Links
in an aggregation group are treated individually in DLDP.
z802.1X has no effect on DLDP.
zWhen connecting two DLDP-enabled devices, make sure the DLDP version ID
fields of the DLDP packets exchanged between the two devices are the same.
Otherwise, DLDP may operate improperly.
1.2.1 Enabling DLDP
Follow these steps to enable DLDP:

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To do… Use the command… Remarks
Enter system view system-view —
Enable DLDP
globally dldp enable Required
Globally disabled by default
Enter
Ethernet
port
view
interface interface-type
interface-number
Enter
Ethernet
port
view or
port
group
view
Enter
port
group
view
port-group {aggregation
agg-id |manual
port-group-name }
Either of the two is required.
The configuration performed
in Ethernet port view applies
to the current port only. The
configuration performed in
port group view applies to all
the ports in the port group.
Enable DLDP dldp enable
Required
Disabled on a port by default
You can perform this
operation on an optical port
or an electrical port.
Note:
DLDP takes effect only when it is enabled both globally and on a port.
1.2.2 Setting DLDP Mode
Follow these steps to set DLDP mode:
To do… Use the command… Remarks
Enter system view system-view —
Set DLDP mode dldp work-mode {enhance |
normal }Optional
Normal by default
1.2.3 Setting the Interval for Sending Advertisement Packets
You can set the interval for sending Advertisement packets to enable unidirectional
links to be detected in time.

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Follow these steps to set the interval for sending Advertisement packets:
To do… Use the command… Remarks
Enter system view system-view —
Set the interval for
sending
Advertisement
packets
dldp interval time
Optional
5 seconds by default
The interval for sending
Advertisement packets
applies to all the
DLDP-enabled ports.
Caution:
zSet the interval for sending Advertisement packets to a value not longer than
one-third of the STP convergence time. If the interval is too long, STP loops may
occur before unidirectional links are torn down; if the interval is too short, network
traffic may increase in vain due to excessive Advertisement packets.
zTo enable DLDP to operate properly, make sure the intervals for sending
Advertisement packets on both sides of a link are the same.
1.2.4 Setting the DelayDown Timer
On some ports, when the Tx line fails, the port goes down and then comes up again,
causing optical signal jitters on the Rx line. When a port goes down due to a Tx failure,
the device transits to the DelayDown state instead of the Inactive state to prevent the
corresponding neighbor entries from being removed. In the same time, the device
triggers the DelayDown timer. If the port goes up before the timer expires, the device
restores the original state; if the port remains down when the timer expires, the devices
transits to the Inactive state.
Follow these steps to set the DelayDown timer
To do… Use the command… Remarks
Enter system view system-view —
Set the DelayDown
timer dldp delaydown-timer time
Optional
1 second by default
DelayDown timer setting
applies to all the
DLDP-enabled ports.

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1.2.5 Setting the Port Shutdown Mode
On detecting a unidirectional link, the ports can be shut down in one of the following two
modes.
zManual mode. This mode applies to networks with low performance, where normal
links may be treated as unidirectional links. It protects service packet transmission
against false unidirectional links. In this mode, DLDP only detects unidirectional
links and generates log and traps. The operations to shut down unidirectional link
ports are accomplished by the administrator.
zAuto mode. In this mode, when a unidirectional link is detected, DLDP transits to
Disable state, generates log and traps, and set the port as DLDP Down.
Follow these steps to set port shutdown mode
To do… Use the command… Remarks
Enter system view system-view —
Set port shutdown
mode
dldp
unidirectional-shutdown
{auto | manual }
Optional
auto by default
Caution:
zOn a port with both remote OAM loopback and DLDP enabled, if the port shutdown
mode is auto mode, the port will be shut down by DLDP when it receives a packet
sent by itself, causing remote OAM loopback to operate improperly. To prevent this,
you need to set the port shutdown mode to auto mode.
zIf the device is busy, or the CPU utilization is high, normal links may be treated as
unidirectional links. In this case, you can set the port shutdown mode to manual
mode to eliminate the effects caused by false unidirectional link report.
1.2.6 Configuring DLDP Authentication
Follow these steps to configure DLDP authentication:
To do… Use the command… Remarks
Enter system view system-view —
Configure DLDP
authentication
dldp
authentication-mode
{ md5 md5-password |
none | simple
simple-password }
Required
none by default

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Caution:
To enable DLDP to operate properly, make sure the DLDP authentication modes and
the passwords of the both sides of a link are the same.
1.2.7 Resetting DLDP State
After a unidirectional link is detected, DLDP shuts down the corresponding port. To
enable the port to perform DLDP detect again, you can reset DLDP state for it. A port
can be in different state after you reset DLDP state for it. That is, it can be in Inactive
state (if the port is physically down) or in Active state (if the port is physically up) after
you reset DLDP state for it.
Caution:
zThe configuration of resetting DLDP state performed in system view applies to all
the ports shut down by DLDP.
zThe configuration of resetting DLDP state performed in port view or port group view
applies to the current port or all the ports in the port group shut down by DLDP.
I. Resetting DLDP State in System view
Follow these steps to reset DLDP in system view:
To do… Use the command… Remarks
Enter system view system-view —
Reset DLDP state dldp reset Required
II. Resetting DLDP State in Port view/Port Group View
Follow these steps to reset DLDP state in port view/port group view:

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To do… Use the command… Remarks
Enter system view system-view —
Enter
Ethernet
port view
interface interface-type
interface-number
Enter
Ethernet
port
view/port
group
view
Enter
port
group
view
port-group {aggregation
agg-id | manual
port-group-name }
Either is required.
The configuration
performed in Ethernet port
view applies to the current
port only; the configuration
performed in port group
view applies to all the ports
in the port group.
Reset DLDP state dldp reset Required
1.3 Displaying and Maintaining DLDP
To do… Use the command… Remarks
Display the DLDP
configuration of a port display dldp [ interface-type interface-number ]Available in any view
Display the statistics
on DLDP packets
passing through a port
display dldp statistics
[interface-type
interface-number ]Available in any view
Clear the statistics on
DLDP packets
passing through a port
reset dldp statistics
[interface-type
interface-number ]Available in user view
1.4 DLDP Configuration Example
1.4.1 DLDP Configuration Example
I. Network requirements
zDevice A and Device B are connected through two fiber pairs, in which two fibers
are cross-connected, as shown in Figure 1-4.
zIt is desired that the unidirectional links can be disconnected on being detected;
and the ports shut down by DLDP can be restored after the fiber connections are
corrected.

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II. Network diagram
Device A
GE1/0/50 GE1/0/51
Device B
PC
GE1/0/50 GE1/0/51
Figure 1-4 Network diagram for DLDP configuration
III. Configuration procedure
1) Configuration on Device A
# Enable DLDP on GigabitEthernet1/0/50 and GigabitEthernet 1/0/51.
<DeviceA> system-view
[DeviceA] interface gigabitethernet 1/0/50
[DeviceA-GigabitEthernet1/0/50] dldp enable
[DeviceA-GigabitEthernet1/0/50] interface gigabitethernet 1/0/51
[DeviceA-GigabitEthernet1/0/51] dldp enable
[DeviceA-GigabitEthernet1/0/51] quit
# Set the interval for sendingAdvertisement packets to 6 seconds.
[DeviceA] dldp interval 6
# Set the DelayDown timer to 2 seconds.
[DeviceA] dldp delaydown-timer 2
# Set the DLDP mode as enhanced mode.
[DeviceA] dldp work-mode enhance
# Set the port shutdown mode as auto mode.
[DeviceA] dldp unidirectional-shutdown auto
# Enable DLDP globally.
[DeviceA] dldp enable
# Check the information about DLDP.
[DeviceA] display dldp
DLDP global status : enable

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DLDP interval : 6s
DLDP work-mode : enhance
DLDP authentication-mode : none
DLDP unidirectional-shutdown : auto
DLDP delaydown-timer : 2s
The number of enabled ports is 2.
Interface GigabitEthernet1/0/50
DLDP port state : disable
DLDP link state : down
The neighbor number of the port is 0.
Interface GigabitEthernet1/0/51
DLDP port state : disable
DLDP link state : down
The neighbor number of the port is 0.
The output information indicates that both GigabitEthernet1/0/50 and
GigabitEthernet1/0/51 are in Disable state and the links are down, which means
unidirectional links are detected and the two ports are thus shut down.
# Reset DLDP state for the ports shut down by DLDP.
[DeviceA] dldp reset
2) Configuration on Device B
The configuration on Device B is the same as that on Device A and is thus omitted.
Note:
If two fibers are cross-connected, all the four ports involved will be shut down by DLDP.
1.5 Troubleshooting
Symptom:
Two DLDP-enabled devices, Device A and Device B, are connected through two fiber
pairs, in which two fibers are cross-connected. The unidirectional links cannot be
detected; all the four ports involved are in Advertisement state.
Analysis:
The problem can be caused by the following.
zThe intervals for sending Advertisement packets on Device A and Device B are
not the same.

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H3C S5500-EI Series Ethernet Switches Chapter 1 DLDP Configuration
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zDLDP authentication modes/passwords on Device A and Device B are not the
same.
Solution:
Make sure the interval for sending Advertisement packets, the authentication mode,
and the password on Device Aand Device B are the same.