CCNP SWITCH 642-813 英文学习指南：权威认证详解

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《CCNP SWITCH (642-813) - 学习指南 - 英文版》是一本由Richard Froom、CCIENo.5102，Balaji Sivasubramanian以及Erum Frahim、CCIENo.7549共同编写的权威教材，旨在帮助读者准备并通过Cisco的Implementing Cisco IP Switched Networks (SWITCH)课程的642-813考试。该书版权属于Cisco Systems, Inc., 出版社是Cisco Press，地址位于美国印第安纳州印第安纳波利斯。该学习指南强调了阅读英文原版的重要性，因为这样能够确保获取最直接、最新和最准确的信息。书中内容涵盖了IP交换网络的基础知识和实施技术，包括但不限于VLAN设计与配置、STP和RSTP协议、QoS策略、路由策略在交换网络中的应用、VXLAN和Overlay网络、以及数据中心网络架构等核心知识点。作者们努力确保信息的全面性和准确性，但必须指出，所有内容仅提供参考，不包含任何形式的保修或适合性声明，读者应基于自己的判断使用，并遵循版权规定，除非获得出版商书面许可，否则不得进行复制或传播，即使是简短引用也需符合相关版权法要求。本书于2010年6月首次印刷，且已提交至美国国会图书馆进行目录编目，具有ISBN-13编号978-1-58705-884-4。同时，书中还包含了警告和免责声明，明确表示读者自行承担学习风险，书中提供的信息仅适用于教育目的，可能不适用于所有实际环境。《CCNP SWITCH (642-813) - 学习指南 - 英文版》是备考者寻求深入了解和掌握Cisco IP交换网络技术的宝贵资源，对于想要提升专业技能并准备通过专业认证的网络工程师来说，它是一份不可或缺的学习资料。在阅读过程中，考生需要密切关注章节内容，结合实践操作，以便在理论和实践之间建立扎实的桥梁。

load balancing, a Layer 4 to Layer 7 switching feature, can use TCP information such as TCP SYN, FIN,

and RST to make forwarding decisions. (Refer to RFC 793 for explanations of TCP SYN, FIN, and RST.) As

a result, Layer 4 switches can distinguish different types of IP traffic flows, such as differentiating the FTP,

Network Time Protocol (NTP), HTTP, Secure HTTP (S-HTTP), and Secure Shell (SSH) traffic.

Layer 7 switching is switching based on application information. Layer 7 switching capability implies

content-intelligence. Content-intelligence with respect to web browsing implies features such as

inspection of URLs, cookies, host headers, and so on. Content-intelligence with respect to VoIP can

include distinguishing call destinations such as local or long distance.

Table 1-1 summarizes the layers of the OSI model with their respective protocol data units (PDU), which

represent the data exchanged at each layer. Note the difference between frames and packets and their

associated OSI level. The table also contains a column illustrating sample device types operating at the

specified layer.

Table 1-1. PDU and Sample Device Relationship to the OSI Model

OSI Level OSI Layer PDU Type Device Example Address

1 Physical Electrical signals Repeater, transceiver None

2 Data link Frames Switches MAC address

3 Network Packet Router, multilayer switches IP address

4 Transport TCP or UDP data

segments

Multilayer switch load

balancing based on TCP port

number

TCP or UDP port

numbering

7 Application Embedded

application

information in

data payload

Multilayer switch using

Network-Based Application

Recognition (NBAR) to

permit or deny traffic based

on data passed by an

application

Embedded

information in

data payload

Layer 2 Switching In-Depth

Layer 2 switching is also referred to as hardware-based bridging. In a Layer 2-only switch, ASICs handle

frame forwarding. Moreover, Layer 2 switches deliver the ability to increase bandwidth to the wiring closet

without adding unnecessary complexity to the network. At Layer 2, no modification is required to the

frame content when going between Layer 1 interfaces, such as Fast Ethernet to 10 Gigabit Ethernet.

In review, the network design properties of current-generation Layer 2 switches include the following:

• Designed for near wire-speed performance

• Built using high-speed, specialized ASICs

• Switches at low latency

• Scalable to a several switch topology without a router or Layer 3 switch

• Supports Layer 3 functionality such as Internet Group Management Protocol (IGMP) snooping and

QoS marking

• Offers limited scalability in large networks without Layer 3 boundaries

Layer 3 Switching In-Depth

Layer 3 switching is hardware-based routing. Layer 3 switches overcome the inadequacies of Layer 2

scalability by providing routing domains. The packet forwarding in Layer 3 switches is handled by ASICs

and other specialized circuitry. A Layer 3 switch performs everything on a packet that a traditional router

does, including the following:

• Determines the forwarding path based on Layer 3 information

• Validates the integrity of the Layer 3 packet header via the Layer 3 checksum

• Verifies and decrements packet Time-To-Live (TTL) expiration

• Rewrites the source and destination MAC address during IP rewrites

• Updates Layer 2 CRC during Layer 3 rewrite

• Processes and responds to any option information in the packet such as the Internet Control

Message Protocol (ICMP) record

• Updates forwarding statistics for network management applications

• Applies security controls and classification of service if required

Layer 3 routing requires the ability of packet rewriting. Packet rewriting occurs on any routed

boundary. Figure 1-6 illustrates the basic packet rewriting requirements of Layer 3 routing in an example

in which two workstations are communicating using ICMP.

Figure 1-6. Layer 3 Packet Rewriting

[View full size image]

Address Resolution Protocol (ARP) plays an important role in Layer 3 packet rewriting. When Workstation

A in Figure 1-6 sends five ICMP echo requests to Workstation B, the following events occur (assuming all

the devices in this example have yet to communicate, use static addressing versus DHCP, and there is no

event to trigger a gratuitous ARP):

1. Workstation A sends an ARP request for its default gateway. Workstation A sends this ARP to

obtain the MAC address of the default gateway. Without knowing the MAC address of the default

gateway, Workstation A cannot send any traffic outside the local subnet. Note that, in this

example, Workstation A’s default gateway is the Cisco 2900 router with two Ethernet interfaces.

2. The default gateway, the Cisco 2900, responds to the ARP request with an ARP reply, sent to the

unicast MAC address and IP address of Workstation A, indicating the default gateway’s MAC

address. The default gateway also adds an ARP entry for Workstation A in its ARP table upon

receiving the ARP request.

3. Workstation A sends the first ICMP echo request to the destination IP address of Workstation B

with a destination MAC address of the default gateway.

4. The router receives the ICMP echo request and determines the shortest path to the destination IP

address.

5. Because the default gateway does not have an ARP entry for the destination IP address,

Workstation B, the default gateway drops the first ICMP echo request from Workstation A. The

default gateway drops packets in the absence of ARP entries to avoid storing packets that are

destined for devices without ARP entries as defined by the original RFCs governing ARP.

6. The default gateway sends an ARP request to Workstation B to get Workstation B’s MAC address.

7. Upon receiving the ARP request, Workstation B sends an ARP response with its MAC address.

8. By this time, Workstation A is sending a second ICMP echo request to the destination IP of

Workstation B via its default gateway.

9. Upon receipt of the second ICMP echo request, the default gateway now has an ARP entry for

Workstation B. The default gateway in turn rewrites the source MAC address to itself and the

destination MAC to Workstation B’s MAC address, and then forwards the frame to Workstation B.

10. Workstation B receives the ICMP echo request and sends an ICMP echo reply to the IP address of

Workstation A with the destination MAC address of the default gateway.

Figure 1-6 illustrates the Layer 2 and Layer 3 rewriting at different places along the path between

Workstation A and B. This figure and example illustrate the fundamental operation of Layer 3 routing and

switching.

The primary difference between the packet-forwarding operation of a router and Layer 3 switching is the

physical implementation. Layer 3 switches use different hardware components and have greater port

density than traditional routers.

These concepts of Layer 2 switching, Layer 3 forwarding, and Layer 3 switching are applied in a single

platform: the multilayer switch. Because it is designed to handle high-performance LAN traffic, a Layer 3

switch is locatable when there is a need for a router and a switch within the network, cost effectively

replacing the traditional router and router-on-a-stick designs of the past.

Understanding Multilayer Switching

Multilayer switching combines Layer 2 switching and Layer 3 routing functionality. Generally, the

networking field uses the terms Layer 3 switch and multilayer switch interchangeably to describe a switch

that is capable of Layer 2 and Layer 3 switching. In specific terms, multilayer switches move campus

traffic at wire speed while satisfying Layer 3 connectivity requirements. This combination not only solves

throughput problems but also helps to remove the conditions under which Layer 3 bottlenecks form.

Moreover, multilayer switches support many other Layer 2 and Layer 3 features besides routing and

switching. For example, many multilayer switches support QoS marking. Combining both Layer 2 and

Layer 3 functionality and features allows for ease of deployment and simplified network topologies.

Moreover, Layer 3 switches limit the scale of spanning tree by segmenting Layer 2, which eases network

complexity. In addition, Layer 3 routing protocols enable load-balancing, fast convergence, scalability,

and control compared to traditional Layer 2 features.

In review, multilayer switching is a marketing term used to refer to any Cisco switch capable of Layer 2

switching and Layer 3 routing. From a design perspective, all enterprise campus designs include

multilayer switches in some aspect, most likely in the core or distribution layers. Moreover, some campus

designs are evolving to include an option for designing Layer 3 switching all the way to the access layer

with a future option of supporting Layer 3 network ports on each individual access port. Over the next

few years, the trend in the campus is to move to a pure Layer 3 environment consisting of inexpensive

Layer 3 switches.

Note

The remainder of this text uses the term multilayer switch and Layer 3 switch interchangeably.

Introduction to Cisco Switches

Cisco has a plethora of Layer 2 and Layer 3 switch models. For brevity, this section highlights a few

popular models used in the campus, core backbone, and data center. For a complete list of Cisco

switches, consult product documentation at Cisco.com.

Cisco Catalyst 6500 Family of Switches

The Cisco Catalyst 6500 family of switches are the most popular switches Cisco ever produced. They are

found in a wide variety of installs not only including campus, data center, and backbone, but also found in

deployment of services, WAN, branch, and so on in both enterprise and service provider networks. For

the purpose of CCNP SWITCH and the scope of this book, the Cisco Catalyst 6500 family of switches are

summarized as follows:

• Scalable modular switch up to 13 slots

• Supports up to 16 10-Gigabit Ethernet interfaces per slot in an over-subscription model

• Up to 80 Gbps of bandwidth per slot in current generation hardware

• Supports Cisco IOS with a plethora of Layer 2 and Layer 3 switching features

• Optionally supports up to Layer 7 features with specialized modules

• Integrated redundant and high-available power supplies, fans, and supervisor engineers

• Supports Layer 3 Non-Stop Forwarding (NSF) whereby routing peers are maintained during a

supervisor switchover.

• Backward capability and investment protection have lead to a long life cycle

Cisco Catalyst 4500 Family of Switches

The Cisco Catalyst 4500 family of switches is a vastly popular modular switch found in many campus

networks at the distribution layer or in collapsed core networks of small to medium-sized networks.

Collapsed core designs combine the core and distribution layers into a single area. The Catalyst 4500 is

one step down from the Catalyst 6500 but does support a wide array of Layer 2 and Layer 3 features. In

summary, the Cisco Catalyst 4500 family of switches are summarized as follows:

• Scalable module switch with up to 10 slots

• Supports multiple 10 Gigabit Ethernet interfaces per slot

• Supports Cisco IOS

• Supports both Layer 2 switching and Layer 3 switching

• Optionally supports integrated redundant and high-available power supplies and supervisor

engines

Cisco Catalyst 4948G, 3750, and 3560 Family of Switches

The Cisco Catalyst 4948G, 3750, and 3560 family of switches are popular switches used in campus

networks for fixed-port scenarios, most often the access layer. These switches are summarized as

follows:

• Available in a variety of fixed port configurations with up to 48 1-Gbps access layer ports and 4

10-Gigabit Ethernet interfaces for uplinks to distribution layer

• Supports Cisco IOS

• Supports both Layer 2 and Layer 3 switching

• Not architected with redundant hardware

Cisco Catalyst 2000 Family of Switches

The Cisco Catalyst 2000 family of switches are Layer 2-only switches capable of few Layer 3 features

aside from Layer 3 routing. These features are often found in the access layer in campus networks. These

switches are summarized as follows:

• Available in a variety of fixed port configurations with up to 48 1-Gbps access layer ports and

multiple 10-Gigabit Ethernet uplinks

• Supports Cisco IOS

• Supports only Layer 2 switching

• Not architected with redundant hardware

Nexus 7000 Family of Switches

The Nexus 7000 family of switches are the Cisco premier data center switches. The product launch in

2008; and thus, the Nexus 7000 software does not support all the features of Cisco IOS yet. Nonetheless,

the Nexus 7000 is summarized as follows:

• Modular switch with up to 18 slots

• Supports up to 230 Gbps per slot

• Supports Nexus OS (NX-OS)

• 10-slot chassis is built on front-to-back airflow

• Supports redundant supervisor engines, fans, and power supplies

Nexus 5000 and 2000 Family of Switches

The Nexus 5000 and 2000 family of switches are low-latency switches designed for deployment in the

access layer of the data center. These switches are Layer 2-only switches today but support cut-through

switching for low latency. The Nexus 5000 switches are designed for 10-Gigabit Ethernet applications and

also support Fibre Channel over Ethernet (FCOE).

Hardware and Software-Switching Terminology

This book refers to the terms hardware-switching and software-switching regularly throughout the text.

The industry term hardware-switching refers to the act of processing packets at any Layers 2 through 7,

via specialized hardware components referred to as application-specific integrated circuits (ASIC). ASICs

can generally reach throughput at wire speed without performance degradation for advanced features

such as QoS marking, ACL processing, or IP rewriting.

Note

Other terms used to describe hardware-switching are in-hardware, using ASICs, and hardware-based.

These terms are used interchangeably throughout the text. Multilayer switching (MLS) is another term

commonly used to describe hardware-switching. The term MLS can be confusing; for example, with the

Catalyst 5500, the term MLS described a legacy hardware-switching method and feature. With today’s

terminology, MLS describes the capability to route and switch frames at line-rate (the speed of all ports

sending traffic at the same time, full-duplex, at the maximum speed of the interface) with advanced

features such as Network Address Translation (NAT), QoS, access controls, and so on using ASICs.

Switching and routing traffic via hardware-switching is considerably faster than the traditional software-

switching of frames via a CPU. Many ASICs, especially ASICs for Layer 3 routing, use specialized memory

referred to as ternary content addressable memory (TCAM) along with packet-matching algorithms to

achieve high performance, whereas CPUs simply use higher processing rates to achieve greater degrees

of performance. Generally, ASICs can achieve higher performance and availability than CPUs. In addition,

ASICs scale easily in switching architecture, whereas CPUs do not. ASICs integrate not only on Supervisor

Engines, but also on individual line modules of Catalyst switches to hardware-switch packets in a

distributed manner.

ASICs do have memory limitations. For example, the Catalyst 6500 family of switches can accommodate

ACLs with a larger number of entries compared to the Catalyst 3560E family of switches due to the larger

ASIC memory on the Catalyst 6500 family of switches. Generally, the size of the ASIC memory is relative

to the cost and application of the switch. Furthermore, ASICs do not support all the features of the

traditional Cisco IOS. For instance, the Catalyst 6500 family of switches with a Supervisor Engine 720 and

an MSFC3 (Multilayer Switch Feature Card) must software-switch all packets requiring Network Address

Translation (NAT) without the use of specialized line modules. As products continue to evolve and

memory becomes cheaper, ASICs gain additional memory and feature support.

For the purpose of CCNP SWITCH and campus network design, the concepts in this section are overly

simplified. Use the content in this section as information for sections that refer to the terminology. The

next section changes scope from switching hardware and technology to campus network types.

Campus Network Traffic Types

Campus designs are significantly tied to network size. However, traffic patterns and traffic types through

each layer hold significant importance on how to shape a campus design. Each type of traffic represents

specific needs in terms of bandwidth and flow patterns. Table 1-2 lists several different types of traffic

that might exist on a campus network. As such, indentifying traffic flows, types, and patterns is a

prerequisite to designing a campus network.

Table 1-2. Common Traffic Types

Traffic Type Description Traffic Flow BW

Network

Management

Many different types of network

management traffic may be present on

the network. Examples include bridge

protocol data units (BPDU), Cisco

Discovery Protocol (CDP) updates,

Simple Network Management Protocol

(SNMP), Secure Shell (SSH), and

Remote Monitoring (RMON) traffic. Some

designers assign a separate VLAN to the

task of carrying certain types of network

management traffic to make network

troubleshooting easier.

Traffic is found flowing

in all layers.

Low

Voice (IP

Telephony)

There are two types of voice traffic:

signaling information between the end

devices (for example, IP phones and soft

switches, such as Cisco CallManager)

and the data packets of the voice

conversation itself. Often, the data to

and from IP phones is configured on a

separate VLAN for voice traffic because

the designer wants to apply QoS

measures to give high priority to voice

traffic.

Traffic generally moves

from access layer to

servers in core layer or

data center.

Low

IP Multicast IP multicast traffic is sent from a

particular source address to group MAC

addresses. Examples of applications that

generate this type of traffic are video

such as IP/TV broadcasts and market

data applications used to configure

analysis trading market activities.

Multicast traffic can produce a large

amount of data streaming across the

network. Switches need to be configured

to keep this traffic from flooding to

devices that have not requested it, and

routers need to ensure that multicast

traffic is forwarded to the network areas

where it is requested.

Market data applications

are usually contained

within the data center.

Other traffic such as

IP/TV and user data

flows from access layer

to core layers and to the

data center.

Very

High

Normal Data This is typical application traffic related

to file and print services, email, Internet

browsing, database access, and other

shared network applications. You may

need to treat this data the same or in

different ways in different parts of the

network, based on the volume of each

type. Examples of this type of traffic are

Server Message Block, Netware Core

Protocol (NCP), Simple Mail Transfer

Protocol (SMTP), Structured Query

Language (SQL), and HTTP.

Traffic usually flows

from the access layer to

core layer and to the

data center.

Low to

Mid

Scavenger class Scavenger class includes all traffic with

protocols or patterns that exceed their

normal data flows. It is used to protect

the network from exceptional traffic

flows that might be the result of

malicious programs executing on end-

Traffic patterns vary. Mid to

High

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CCNP SWITCH 642-813 英文学习指南：权威认证详解

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CCNP SWITCH 642-813 Official Certification Guide

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CCNP_SWITCH_642-813_Official_Certification_Guide.pdf

Cisco SWITCH 642-813 学习宝典：IP交换网络实现

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