H3C S3100-52P Ethernet Switch Operation Manual-Release 1500(V1.02)

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10-DLDP Operation
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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.

Figure 1-1 Fiber cross-connection

Figure 1-2 Fiber broken or not connected

DLDP provides the following features:

l           As a link layer protocol, it works together with the physical layer protocols to monitor the link status of a device.

l           The auto-negotiation mechanism at the physical layer detects physical signals and faults. DLDP identifies peer devices and unidirectional links, and disables unreachable ports.

l           When 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.

l           Even if both ends of links can work normally at 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

A link 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

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

DLDP works with the following 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.

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.

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:

l           In authentication mode, DLDP authenticates the packets, and discards those failing to pass the authentication.

l           DLDP processes the received DLDP packets.

Table 1-5 Process received DLDP packets

Packet type

Processing procedure

Advertisement packet

Extracts neighbor information

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.

If the neighbor entry already exists on the local device, DLDP updates the entry aging timer.

Flush packet

Deletes 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 this neighbor entry does not exist on the local device.

If the neighbor entry already exists on the local device, updates the entry aging timer.

Echo packet

Checks whether the local device is in the probe state

No

Discards this echo packet

Yes

Checks whether neighbor information in the packet is the same as that on the local device

No

Discards this echo packet

Yes

Sets the neighbor flag bit 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.

 

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.

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.

In enhanced mode, no echo packet is received when the enhanced timer expires

 

1.1.2  Precautions during DLDP Configuration

l           DLDP works only when the link is up.

l           To 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.

l           You 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 is set, network traffic increases, and port bandwidth is reduced.

l           DLDP does not process any LACP event, and treats each link in the aggregation group as independent.

1.2  DLDP Configuration

1.2.1  DLDP Configuration Tasks

The following table describes basic DLDP configuration tasks:

Table 1-7 DLDP configuration tasks

Operation

Command

Description

Enter system view

system-view

Enable DLDP

Enable DLDP globally

dldp enable

Required.

By default, DLDP is disabled.

Enable DLDP on a port

Enter Ethernet port view

interface interface-type interface-number

Enable DLDP on a port

dldp enable

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 between sending DLDP packets

dldp interval integer

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.

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:

l      When 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.

l      DLDP can operate normally only when the same authentication mode and password are set on the local and peer ports.

l      When the DLDP protocol works in the normal mode, the system can identify only one type of unidirectional link caused by fiber cross-connection.

l      When 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.

l      When 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.

 

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,

l           Switch A and Switch B are connected through two pairs of fibers. Both of them support DLDP.

l           Suppose the fibers between Switch A and Switch B are connected inversely. DLDP disconnects a unidirectional link after detecting it.

l           When the network administrator connects the fiber correctly, the port shut down by DLDP is restored.

II. Network diagram

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.

<SwitchA> system-view

[SwitchA] interface gigabitethernet 2/1/3

[SwitchA-GigabitEthernet2/1/3] duplex full

[SwitchA-GigabitEthernet2/1/3] speed 1000

[SwitchA-GigabitEthernet2/1/3] quit

[SwitchA] interface gigabitethernet 2/1/4

[SwitchA-GigabitEthernet2/1/4] duplex full

[SwitchA-GigabitEthernet2/1/4] speed 1000

[SwitchA-GigabitEthernet2/1/4] quit

# Enable DLDP globally

[SwitchA] dldp enable

# Set the interval between sending DLDP packets to 15 seconds.

[SwitchA] dldp interval 15

 # Configure DLDP to work in enhanced mode

[SwitchA] dldp work-mode enhance

 # Set the DLDP handling mode for unidirectional links to auto.

[SwitchA] dldp unidirectional-shutdown auto

# Display the DLDP state

[SwitchA] display dldp 1

 

&  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:

l      If 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.

l      If 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

[SwitchA] dldp reset

2)          Configure Switch B

 The configuration of Switch B is the same to that of Switch A.

 

&  Note:

l      In 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.

l      When 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.