关于思科UDLD与H3CDLDP协议的比较及分析

1星需积分: 48 69 浏览量 2015-07-05 14:11:17 上传评论收藏 1012KB PDF 举报

Table of contents Overview ..................................................................................................................................... 2 Introduction to UDLD.................................................................................................................. 2 UDLD protocol architecture ......................................................................................................... 2 UDLD detection modes ............................................................................................................... 3 UDLD packet format .................................................................................................................. 3 Introduction to DLDP ...................................................................................................................... 5 Device Link Detection Protocol (DLDP) overview ............................................................................ 5 DLDPDU format ......................................................................................................................... 6 Unidirectional link detection procedure ........................................................................................ 7 DLDP operating modes .............................................................................................................. 8 Port shutdown modes ................................................................................................................. 8 UDLD configuration and verification procedures ............................................................................... 9 Network diagram ..................................................................................................................... 9 Default settings ......................................................................................................................... 9 Configuring UDLD ..................................................................................................................... 9 Verifying the UDLD configuration .............................................................................................. 10 DLDP configuration and verification procedures .............................................................................. 10 Network diagram ................................................................................................................... 10 Default settings ....................................................................................................................... 11 Configuring DLDP ................................................................................................................... 11 Verifying the DLDP configuration ............................................................................................... 11 Migrating from Cisco UDLD to H3C DLDP ...................................................................................... 12

资源详情

资源评论

Migration from Cisco UDLD to industry standard DLDP

Technical white paper

Table of contents

Overview ..................................................................................................................................... 2

Introduction to UDLD.................................................................................................................. 2

UDLD protocol architecture ......................................................................................................... 2

UDLD detection modes ............................................................................................................... 3

UDLD packet format .................................................................................................................. 3

Introduction to DLDP ...................................................................................................................... 5

Device Link Detection Protocol (DLDP) overview ............................................................................ 5

DLDPDU format ......................................................................................................................... 6

Unidirectional link detection procedure ........................................................................................ 7

DLDP operating modes .............................................................................................................. 8

Port shutdown modes ................................................................................................................. 8

UDLD configuration and verification procedures ............................................................................... 9

Network diagram ..................................................................................................................... 9

Default settings ......................................................................................................................... 9

Configuring UDLD ..................................................................................................................... 9

Verifying the UDLD configuration .............................................................................................. 10

DLDP configuration and verification procedures .............................................................................. 10

Network diagram ................................................................................................................... 10

Default settings ....................................................................................................................... 11

Configuring DLDP ................................................................................................................... 11

Verifying the DLDP configuration ............................................................................................... 11

Migrating from Cisco UDLD to H3C DLDP ...................................................................................... 12

Overview

Introduction to UDLD

Unidirectional Link Detection (UDLD) is a Cisco-proprietary protocol that detects unidirectional links.

UDLD is a light-weight protocol that can be used to detect and disable one-way connections before they create

dangerous situations such as “spanning tree” loops or other protocol malfunctions.

In a network that has an extensive fiber cabling plant, problems may arise when incorrect patching leads to a switch

port having its RX fiber strand connected to one switch port and its TX fiber strand connected to another. In these

cases, a port may be deemed active if it is receiving an optical signal on its RX strand. However, the problem is that

this link does not provide a valid communication path at Layer 2 (and above).

If this scenario of wrongly connected fiber strands is applied to multiple ports to create a fiber loop, each device in

the loop could directly send packets to a neighbor but would not be able to receive from the same device to which it

is sending to. Albeit the above scenario is rather extreme, it exemplifies how the lack of mutual identification of the

neighbors can bring protocols to the wrong assumption that during a transmission the sender and the receiver at the

other end of the link match.

Another equally dangerous incorrect assumption is that the lack of reception of protocol messages on a port

unmistakably indicates the absence of transmitting protocol entities at the other end of the link.

The UDLD protocol was implemented to help correct certain assumptions made by other protocols and in particular to

help the spanning tree protocol to function properly so as to avoid the creation of dangerous Layer 2 loops.

UDLD protocol architecture

UDLD uses two basic mechanisms:

• It advertises a port’s identity and learns about its neighbors on a specific LAN segment; it keeps the acquired

information on the neighbors in a cache table.

• It sends a train of echo messages in certain circumstances that require fast notifications or fast resynchronization of

the cached information.

Due to this, the algorithm run by UDLD requires that all the devices connected to the same LAN segment run the

protocol, so that potential misconfiguration is detected and prompt corrective action is taken.

UDLD periodically sends “hello” packets (also called “advertisements” or “probes”) on every active interface to keep

each device informed of its neighbors. When a hello message is received, it is cached and kept in memory for a defined

time interval, called “hold time” or “time-to-live”, after which the cache entry is considered stale and is aged out.

If a new hello message is received when a correspondent old cache entry has not been aged out yet, then the old

entry is dropped and is replaced by the new one with a reset time-to-live timer.

The echoing mechanism is the base of UDLD’s detection algorithm: whenever a UDLD device learns about a new

neighbor or receives a resynchronization request from an out-of-synch neighbor, it (re)starts the detection process on

its side of the connection and sends N-echo messages in reply. (This mechanism implicitly assumes that N-packets are

sufficient to get through a link and reach the other end, even though some of them might get dropped during the

transmission.) Since this behavior must be the similar among all the neighbors, the sender of the echoes expects to

receive after some time an echo in reply. If the detection process ends without the proper echo information being

received, under specific conditions the link is considered to be unidirectional.

UDLD detection modes

UDLD can function in two modes: normal mode and aggressive mode.

In normal mode, a protocol determination at the end of the detection process is always based on information

received in UDLD messages: whether it’s the information about the exchange of proper neighbor identifications or the

information about the absence of such proper identifications. Hence, albeit bound by a timer, normal mode

determinations are always based on gleaned information, and as such are “event-based”. If no such information can

be obtained (for example, because of a bidirectional loss of connectivity), UDLD follows a conservative approach

based on the considerations in and deems a port to be in “undetermined” state. In other words, normal mode shuts

down a port only if it can explicitly determine that the associated link is faulty for an extended period of time.

Instead, in the aggressive mode, UDLD shuts down a port if it loses bidirectional connectivity with the neighbor for the

same extended period of time mentioned above. Subsequently, repeated last-resort attempts fail to re-establish

communication with the other end of the link. This mode of operation assumes that loss of communication with the

neighbor is a meaningful network event in itself and is a symptom of a serious connectivity problem. Because this type

of detection can be event-less, and lack of information cannot always be associated to an actual malfunction of the

link, this mode is optional and is recommended only in certain scenarios (typically only on point-to-point links, where

no communication failure between two neighbors is admissible).

UDLD packet format

Figure 1. UDLD PDU format

The protocol header fields are defined as follows:

Ver (3 bits):

0x01: UDLD PDU version number

Opcode (5 bits):

0x00: Reserved

0x01: Probe message

0x02: Echo message

0x03: Flush message

0x04-0x1F: Reserved for future use

Flags (8 bits):

bit 0: Recommended timeout flag (RT)

bit 1: ReSynch flag (RSY)

bit 2...7: Reserved for future use

PDU Checksum (16 bits):

IP-like checksum.

剩余11页未读，继续阅读

评论收藏

内容反馈

silencew

2019-09-26

太垃圾了了，标题不对本，浪费我的积分

关于思科 UDLD 与 H3C DLDP协议的比较及分析

评论1

最新资源

关于思科 UDLD 与 H3C DLDP协议的比较及分析

评论1

最新资源

相关推荐

H3C与Cisco的区别

了解和配置单向链路检测协议UDLD

H3C与cisco互联技术交流问题

cisco与h3c交换机生成树兼容对接

抓包源文件（573个） 主流协议你想要的都包括.zip

思科、华为、H3C常用命令对照表

Aruba竞争分析_与思科moto/H3C/3COM/RUCKUS/HP的比较分析

思科华为华三交换机常用命令的对比

導入UDLD技術

协议分析系列_抓包源文件（573个） 主流协议你想要的都包括.zip

解决IP地址冲突的完美方法--DHCP SNOOPING

UDLD.rar

思科华为命令对照表

奥普泰配置的手册打包下载

奥普泰交换机命令的手册

Catalyst_2_Meraki_Config_Checker:针对Meraki MS检查Catalyst配置的功能

Switching (已精编).

通信与网络中的交换机err-disable故障解决方法

华为eNSP防火墙USG6000v安装包

华为新版ENSP-PRO虚拟机

华为ENSP CE12800导入设备包

【基于Multisim的超外差中波调幅接收机设计】

win11-PL23XX_Prolific_DriverInstaller_v206

解决：电脑前面板耳机没声，后插孔有声，找不到Realtek高清晰音频管理器，安装realtek hd audio dIver失败

Ensp模拟器CE12800设备包

基于eNSP的校园网络规划（三层核心mstp、vrrp、ospf、nat、AC/AP、防火墙、链路聚合等等）

爱快Q1800固件分享

华为ensp模拟器安装包

抓包源文件（573个）主流协议你想要的都包括.zip

协议分析系列_抓包源文件（573个）主流协议你想要的都包括.zip