H3C H3C S3600 Series User manual

Operation Manual – DLDP
H3C S3600 Series Ethernet Switches-Release 1510 Table of Contents
i
Table of Contents
Chapter 1 DLDP Configuration ....................................................................................................1-1
1.1 DLDP Overview .................................................................................................................1-1
1.1.1 DLDP Fundamentals...............................................................................................1-2
1.1.2 Precautions during DLDP Configuration.................................................................1-6
1.2 DLDP Configuration...........................................................................................................1-7
1.2.1 DLDP Configuration Tasks......................................................................................1-7
1.2.2 Resetting DLDP State.............................................................................................1-9
1.3 DLDP Configuration Example............................................................................................1-9

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H3C S3600 Series Ethernet Switches-Release 1510 Chapter 1 DLDP Configuration
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Chapter 1 DLDP Configuration
1.1 DLDP Overview
You may have encountered unidirectional links, namely, one-way audio, 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 links can be divided into two types: one is caused by fiber
cross-connection, and the other is caused by a fiber being not connected or being
disconnected. The cross-connected fibers in Figure 1-1 refer to optical fibers which are
connected inversely. The hollow lines in Figure 1-2 refer to fibers which are not
connected or are broken.
Unidirectional links can cause many problems, such as spanning tree protocol (STP)
loop.
Device link detection protocol (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
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
Figure 1-1 Fiber cross-connection

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H3C S3600 Series Ethernet Switches-Release 1510 Chapter 1 DLDP Configuration
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SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
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.
zWhen auto-negotiation mechanism and DLDP are enabled, they work together to
detect and disable physical and logical unidirectional links, and to prevent the
failure of other protocols such as STP.
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.
1.1.1 DLDP Fundamentals
I. DLDP status
Alink can be in one of these DLDP states: initial, inactive, active, advertisement, probe,
disable, and delaydown.
Table 1-1 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

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Status Description
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 does not receive or
send DLDP 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.
II. DLDP timers
Table 1-2 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 10 seconds.
Probe sending
timer The interval is 0.5 seconds. In the probe state, DLDP sends two probe packets every second.
Echo waiting
timer
It is enabled when DLDP 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. DLDP outputs 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.

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Timer Description
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.
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.
A device in the delaydown state resumes its original DLDP state 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.
III. DLDP operating mode
DLDP can operate in two modes: normal and enhanced.

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Table 1-3 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.)
IV. DLDP implementation
1) If the DLDP-enabled link is up, DLDP sends DLDP packets to the peer device, and
analyzes and processes the DLDP packets received from the peer device. DLDP
in different states sends different types of packets.
Table 1-4 Types of packets sent by DLDP
DLDP state Packet type
Active Advertisement packets, including those with or without an RSY
tag
Advertisement Advertisement packets
Probe Probe packets
2) DLDP analyzes and processes received packets from the peer device as follows:
zIn authentication mode, DLDP authenticates the packets, and discards those
failing to pass the authentication.
zDLDP processes the received DLDP packets.

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Table 1-5 Process received DLDP packets
Packet type Processing procedure
If this neighbor entry does not exist on the
local device, DLDP creates the neighbor entry,
enables the entry aging timer, and switches to
the probe state.
Advertisement
packet
Extracts
neighbor
information If the neighbor entry alreadyexists on the local
device, DLDP updates the entry aging timer.
Flush packet Deletes the neighbor entry from the local device
Creates the neighbor entry if this neighbor
entry does not exist on the local device.
Probe packet
Sends echo
packets
containing both
neighbor and its
own information
to the peer
If the neighbor entry alreadyexists on the local
device, updates the entry aging timer.
No Discards this echo packet
No Discards this echo packet
Sets the neighbor flag bit
to bidirectional link
Echo packet
Checks
whether
the local
device is
in the
probe
state
Yes
Checks
whether
neighbor
information
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:
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 waiting timer expires.
In enhanced mode, no echo
packet is received when the
enhanced timer expires
DLDP switches to the disable state, 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. DLDP
sends an RSY message and deletes the neighbor
entry.
1.1.2 Precautions during DLDP Configuration
zDLDP works only when the link is up.

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zTo ensure unidirectional links can be detected, you must make sure that DLDP is
enabled on both sides, and that the interval between sending advertisement
packets, authentication mode, and password are consistent on both sides.
zYou can adjust the interval between sending advertisement packets in different
network circumstances so that DLDP can respond rapidly to a 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 shuts down unidirectional links. On the contrary, if too short an interval isset,
network traffic increases, and port bandwidth is reduced.
zDLDP does not process any LACP event, and treats each link in the aggregation
group as independent.
zWhen connecting two DLDP-enabled devices, make sure the software running on
them is of the same version. Otherwise, DLDP may operate improperly.
1.2 DLDP Configuration
1.2.1 DLDP Configuration Tasks
Table 1-7 DLDP configuration tasks
Operation Command Description
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.
By default,
DLDP is
disabled.
Set the authentication mode and
password
dldp authentication-mode
{none |simple
simple-password | md5
md5-password }
Optional.
By default, the
authentication
mode is none.
Set the interval of sending DLDP
packets dldp interval timer-value
Optional.
By default, the
interval is 10
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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Operation Command Description
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 DLDP operating mode dldp work-mode {enhance
|normal }
Optional.
By default,
DLDP works in
normal mode
and does not
detect
unidirectional
links.
Enter Ethernet port view interface interface-type
interface-number —
Force the duplex attribute duplex full Required
Force the speed value speed speed-value Required
Display the configuration
information about the
DLDP-enabled port
display dldp { unit-id |
interface-type
interface-number }
You can
execute this
command in
any view.
Note:
zWhen you use the dldp enable/dldp disable command in system view to
enable/disable DLDP on all optical ports of the switch, the configuration takes effect
on the existing optical ports, instead of those added subsequently.
zDLDP can operate normally only when the same authentication mode and
password are set on the local and peer ports.
zWhen the DLDP protocol works in the normal mode, the system can identify only
one type of unidirectional link caused by fiber cross-connection.
zWhen the DLDP protocol works in enhanced mode, the system can identify two
types of unidirectional links: one is caused by fiber cross-connection and the other is
caused by one fiber being not connected or being broken.
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 detected, so as to reduce the
influence of mistaken reports.

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1.2.2 Resetting DLDP State
Note:
After a port is down due to the detection of unidirectional link, you can use the dldp
reset command to restore the DLDP state to perform DLDP detection.
Table 1-8 Reset DLDP state
Operation Command Description
Enter system view system-view —
Reset the DLDP state of the
system dldp reset Optional
Enter Ethernet port view interface interface-type
interface-number —
Reset the DLDP state of a port dldp reset Optional
Caution:
The dldp reset command only applies to the ports in the DLDP down state.
1.3 DLDP Configuration 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 connected inversely.
DLDP disconnects a unidirectional link after detecting it.
zWhen the network administrator connects the fiber correctly, the port shut down by
DLDP is restored.

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II. Network diagram
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
SwitchB
SwitchA
PC
GE2/1/3
GE2/1/3 GE2/1/4
GE2/1/4
Figure 1-3 Fiber cross-connection
III. Configuration procedure
1) Configure Switch A
# Configure the ports to work in mandatory full duplex mode at a rate of 1000 Mbps.
<H3CA> system-view
[H3CA] interface gigabitethernet 2/1/3
[H3CA-GigabitEthernet2/1/3] duplex full
[H3CA-GigabitEthernet2/1/3] speed 1000
[H3CA-GigabitEthernet2/1/3] quit
[H3CA] interface gigabitethernet 2/1/4
[H3CA-GigabitEthernet2/1/4] duplex full
[H3CA-GigabitEthernet2/1/4] speed 1000
[H3CA-GigabitEthernet2/1/4] quit
# Enable DLDP globally
[H3CA] dldp enable
# Set the interval between 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 for unidirectional links to auto.
[H3CA] dldp unidirectional-shutdown auto
# Display the DLDP state
[H3CA] display dldp 1

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Note:
When two switches are connected through fibers in a crossed way, two or three ports
may be in the disable state, and the rest in the inactive state.
When a fiber is connected to a device correctly on one end with the other end
connected to no device:
zIf the device operates in the normal DLDP mode, the end that receives optical
signals is in the advertisement state; the other end is in the inactive state.
zIf the device operates in the enhance DLDP mode, the end that receives optical
signals is in the disable state; the other end is in the inactive state.
# 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.
Note:
zIn order for DLDP to detect fiber disconnection in one direction, you must configure
the port to work in mandatory full duplex mode at a mandatory rate.
zWhen the port works in non-mandatory full duplex mode at a non-mandatory rate,
even if DLDP is enabled, it does not take effect when the fiber in one direction is
disconnected. In that case, the port is down.