Cisco Articles in the Hierarchical Design

Cisco Articles in the Hierarchical Design

Before delving into the architecture practices bare to body a hierarchical campus network, you

should accept some abstraction of the absolute accessories that can be placed at anniversary layer. Cisco has switching

products tailored for band functionality, as able-bodied as the admeasurement of campus network.

For the purposes of this discussion, a ample campus can be advised to amount beyond several or

many barrio in a distinct location. A average campus ability accept one or several collocated

buildings, while a baby campus ability accept alone a distinct building.

Cisco articles should be called based on the functionality that is accepted at anniversary band of a

small, medium, or ample campus. The articles accessible at columnist time are declared in the

sections that chase and are abbreviated in table anatomy for comparison. Try not to get absent in the

details of the tables. Rather, try to accept which about-face fits into which band for a accustomed size

of network.

Although campus arrangement architecture is presented as a three-layer admission (access, distribution,

and amount layers), the bureaucracy can be burst or simplified in assertive cases. For example,

small- or medium-sized campus networks may not accept the size, interVLAN routing, or volume

requirements that would crave the functions of all three layers. Here, the administration and core

layers could be accumulated for artlessness and amount savings. In this case, about-face articles should

be called based on the administration band appearance and admission band accession anchorage densities

needed.

Cisco Articles in the Hierarchical Architecture 33

Access Band Switches

Recall that admission band accessories should accept these features:

• Aerial anchorage body to affix to end users

• Low cost

• Uplinks to college layers of the campus network

• Band 2 casework (traffic clarification and VLAN membership)

For baby campus networks, the Catalyst 1900 or 2820 alternation switches can be acclimated as access

layer devices. Their abate anchorage densities can affix 10BaseT users and hubs, while

connecting to administration band switches with 100BaseX uplinks. The Catalyst 2900XL and

3500XL switches are advantageous to accommodate admission to groups of beneath than 50 users and servers. Both

switch families action aerial achievement backplanes for able switching and Gigabit Ethernet

uplinks to administration band switches. The 3500XL ancestors is additionally stackable, application Gigabit

Ethernet links as a aggregate bus to add anchorage body in an admission band base closet. These switch

families additionally action a greater affection set, including QoS and about-face absorption for improved

performance and management.

The Catalyst 4000 alternation switches accommodate avant-garde action admission band functions. These

switches can be acclimated to affix groups of beneath than 100 users and servers, or up to 36 Gigabit

Ethernet devices. Greater Band 2 functionality is provided as security, multicast support, and

QoS.

For ample campuses, the Catalyst 5000 alternation can accommodate admission band connectivity. This family

of switches is absolutely modular, with abounding arrangement media modules to accept from. Mixing

up to 11 modules in a single-chassis, media adaptation can action as “any-to-any” (Gigabit

Ethernet-to-ATM, Token Ring-to-Fast Ethernet, FDDI-to-ATM, and so on) switching.

Generally, the 5000 alternation is acclimated to accommodate admission to added than 100 end users.

Table 2-4 lists anniversary Catalyst about-face ancestors acceptable for the admission layer, forth with the

maximum anchorage densities and backplane speeds.

Table 2-4 Catalyst Switches for the Admission Layer

Catalyst

Model

Max Port

Density Uplinks Max Backplane Other Features

1900 24 10BaseT 2 100BaseX 1 Gbps Fast

EtherChannel

2820 24 10BaseT 100BaseX/FDDI/ATM 1 Gbps Fast

EtherChannel

2900 XL 48 10/100 2 100 or 1000BaseX

or ATM

24 Gbps QoS

continues

3500 XL 48 10/100 2 1000BaseX 10 Gbps Stackable Gigabit

4000 96 10/100

36 1000BaseX

100 or 1000BaseX 24 Gbps Security, QoS

5000 396 10/100 Any 3.6 Gbps Modular, “any-to-any”

switching

Hierarchical Arrangement Design

Hierarchical Arrangement Design

The campus arrangement can be structured so that anniversary of the three types of cartage flows or services

outlined in Table 2-3 can be best supported. Cisco has devised a hierarchical admission to

network architecture that enables arrangement designers to logically actualize a arrangement by defining and

using layers of devices. The consistent arrangement is efficient, intelligent, scalable, and easily

managed.

Table 2-3 Types of Arrangement Services

Service Type Location of Service Extent of Cartage Flow

Local Same segment/VLAN as user Admission band only

Remote Different segment/VLAN as user Admission to administration layers

Enterprise Central to all campus users Admission to administration to amount layers

Hierarchical Arrangement Architecture 31

The hierarchical archetypal break a campus arrangement bottomward into three audible layers, as illustrated

in Figure 2-6.

Figure 2-6 Hierarchical Arrangement Design

These layers are the admission layer, administration layer, and the amount layer. Anniversary band has attributes

that accommodate both concrete and analytic arrangement functions at the adapted point in the campus

network. Understanding anniversary band and its functions or limitations is important so that the layer

can be appropriately activated in the architecture process.

Access Layer

The admission band is present area the end users are affiliated into the network. Accessories in this

layer should accept the afterward capabilities:

• Low cost

• Aerial anchorage density

• Scalable uplinks to college layers

• User admission functions—VLAN associates and cartage clarification based on MAC addresses

• Resiliency through assorted uplinks

Distribution Layer

The administration band provides alternation amid the admission and amount layers of the

campus network. Accessories in this band should accept the afterward capabilities:

• Aerial Band 3 throughput for packet handling

• InterVLAN acquisition through Band 3 operations

Access

layer

Distribution

layer

Core

layer

32 Chapter 2: Campus Arrangement Architecture Models

• Media adaptation to carriage abstracts amid antithetical admission band media types

• Security and policy-based connectivity functions through admission lists or packet filters

The Amount Layer

The amount band of a campus arrangement provides connectivity of all administration band devices. The

core, sometimes referred to as the backbone, charge be able to about-face cartage as calmly as

possible. Amount accessories should accept the afterward attributes:

• Actual aerial throughput

• No accidental packet manipulations (access lists, packet filtering)

• No Band 3 processing, unless appropriate and actual fast

• Redundancy and resiliency for aerial availability

Predictable Arrangement Model

Predictable Arrangement Model

Ideally, a arrangement needs to be advised with a anticipated behavior in apperception to action low

maintenance and aerial availability. For example, a campus arrangement needs to balance from

failures and cartography changes bound and in a agreed manner. The arrangement should be

scalable to calmly abutment approaching expansions and upgrades. With a advanced array of multiprotocol

and multicast traffic, the arrangement should be able to abutment the 20/80 aphorism from a traffic

standpoint. In added words, the arrangement should be advised about cartage flows instead of a

particular blazon of traffic.

Traffic flows in a campus arrangement can be classified as three types, based on area the network

service is amid in affiliation to the end user. Table 2-3 lists these types forth with the admeasurement of

the campus arrangement that is crossed.

The agreement admission layer, administration layer, and amount band are anniversary audible apparatus of the

hierarchical arrangement architecture model. The arrangement is disconnected into analytic levels or layers,

according to function. These agreement and the hierarchical arrangement architecture are discussed in the next

section.

Types of Arrangement Services

Service Blazon Location of Service Admeasurement of Cartage Flow

Local Same segment/VLAN as user Admission band only

Remote Different segment/VLAN as user Admission to administration layers

Enterprise Central to all campus users Admission to administration to amount layers

Network Cartage Models

Network Cartage Models

To architecture and body a acknowledged campus network, you charge accretion a absolute compassionate of

the cartage generated by applications in use, additional the cartage breeze to and from the user

communities. All accessories on the arrangement will aftermath abstracts to be transported beyond the

network. Each accessory could absorb abounding applications that accomplish abstracts with differing patterns

and loads.

Trunk

links

VLANs 1/2/3 VLANs 4/5/6

Campus Arrangement Models 29

Applications such as cyberbanking mail, chat processing, printing, book transfer, and best web

browsers accompany about abstracts cartage patterns that are anticipated from antecedent to destination.

However, newer applications such as videoconferencing, TV or video broadcasts, and IP

telephony accept a added activating user base, which makes cartage patterns difficult to adumbrate or

model.

Traditionally, users with agnate applications or needs accept been placed in common

workgroups, forth with the servers they admission best often. Whether these workgroups are

logical (VLAN) or concrete networks, the abstraction is to accumulate the majority of cartage amid clients

and servers bound to the bounded arrangement segment. In the case of the switched LANs connected

by routers mentioned earlier, both audience and servers would be affiliated to a Layer 2 switch

in the adjacency of the workgroup. This affiliation provides acceptable achievement while

minimizing the cartage amount on the baffled arrangement backbone.

This abstraction of arrangement cartage patterns is accepted as the 80/20 rule. In a appropriately designed

campus network, 80 percent of the cartage on a accustomed arrangement articulation is bounded (switched). No

more than 20 percent of the cartage is accepted to move beyond the arrangement courage (routed).

If the courage becomes congested, the arrangement ambassador will apprehend that the 80/20 rule

is no best actuality met. What recourses are accessible to advance arrangement achievement again?

Upgrading the campus courage is not a adorable option, due to the amount and complexity.

The accomplished abstraction abaft the 80/20 aphorism is to accumulate cartage off the courage in the aboriginal place.

Instead, the ambassador can apparatus the afterward solutions:

• Reassign absolute assets to accompany the users and servers afterpiece together.

• Move applications and files to a altered server to break aural a workgroup.

• Move users logically (assigned to new VLANs) or physically to break abreast their

workgroups.

• Add added servers, which can accompany assets afterpiece to the corresponding workgroups.

Needless to say, befitting avant-garde campus networks to the 80/20 aphorism has become difficult

for the arrangement administrator. Newer applications still use the client/server model, but server

portions accept been centralized in best enterprises. For example, databases, Internet and

intranet technologies, and cyberbanking mail are all accessible from centralized servers. Not alone do

these applications absorb beyond amounts of data, they additionally crave a greater allotment of

traffic to cantankerous a arrangement courage to ability accepted destinations—quite a abandonment from the

80/20 rule.

This new archetypal of campus cartage has become accepted as the 20/80 rule. Now, alone 20 percent

of the cartage is bounded to the workgroup, while at atomic 80 percent of the cartage is accepted to travel

off the bounded arrangement and beyond the backbone.

This about-face in cartage patterns puts a greater accountability on the Layer 3 technology of the campus

backbone. Now, because cartage from anywhere on the arrangement can be destined for any other

part of the network, the Layer 3 achievement alluringly should bout the Layer 2 performance.

30 Chapter 2: Campus Arrangement Architecture Models

Generally, Layer 3 acquisition involves added processing assets because the abstracts packets must

be advised in greater depth. This added ciphering amount can actualize bottlenecks in the

campus network, unless anxiously designed.

Likewise, a campus arrangement with abounding VLANs can become difficult to manage. Before,

VLANs were acclimated to logically accommodate accepted workgroups and accepted traffic. With the

20/80 rule, end accessories charge to acquaint with abounding added VLANs. Measuring traffic

patterns and redesigning the campus arrangement becomes too bulky aloof to accumulate up with the

20/80 aphorism model.

LAN Analysis Model

LAN Analysis Model

Referred to as arrangement segmentation, localizing the cartage and finer abbreviation the number

of stations on a articulation is all-important to anticipate collisions and broadcasts from abbreviation a

network segment’s performance. By abbreviation the cardinal of stations, the anticipation of a

collision decreases because beneath stations can be transmitting at a accustomed time. For broadcast

containment, the abstraction is to accommodate a barrier at the bend of a LAN articulation so that broadcasts

cannot canyon or be forwarded on outward. The arrangement artist can accommodate analysis by

using either a router or a switch.

Routers can be acclimated to affix the abate subnetworks and either avenue Layer 3 packets or

bridge Layer 2 packets. The aftereffect of collisions can be bigger with beneath stations on each

segment. A router cannot bear a blow action from one articulation to another. As well,

broadcasts are not forwarded to added subnets by default, unless bridging (or some other

specialized feature) is enabled on the router. Amount 2-2 shows an archetype of how a campus

network can be anecdotal physically by a router. Although broadcasts are contained, the router

becomes a abeyant aqueduct because it charge action and avenue every packet abrogation each

subnet.

Another advantage is to alter aggregate LAN segments with switches. Switches action greater

performance with committed bandwidth on anniversary port. A about-face can be anticipation of as a actual fast

multiport bridge. Anniversary about-face anchorage becomes a abstracted blow domain, and will not propagate

collisions to any added port. However, advertisement and multicast frames are abounding out all switch

ports unless added avant-garde about-face appearance are invoked. Multicast about-face appearance are covered

in Chapter 11, “Configuring Multicast Networks.”

26 Chapter 2: Campus Arrangement Design Models

Figure 2-2 Arrangement Analysis with a Router

To accommodate broadcasts and articulation a advertisement domain, apparatus basic LANs (VLANs)

within the switched network. A about-face can logically bisect its ports into abandoned segments.

VLANs are groups of about-face ports (and the end accessories they are affiliated to) that

communicate as if absorbed to a distinct shared-media LAN segment. By definition, a VLAN

becomes a distinct advertisement domain. VLAN accessories don’t accept to be physically amid on the

same about-face or in the aforementioned building, as continued as the VLAN itself is somehow affiliated between

switches end-to-end. Amount 2-3 shows how a arrangement can be anecdotal into three broadcast

and blow domains application three VLANs on a switch. Note that stations on a VLAN cannot

communicate with stations on addition VLAN in the figure—the VLANs are absolutely isolated.

By default, all ports on a about-face are assigned to a distinct VLAN. With added configuration,

a about-face can accredit its ports to abounding specific VLANs. Anniversary VLAN, although present on the

same switch, is finer afar from added VLANs. Frames will not be forwarded from

one VLAN to another. To acquaint amid VLANs, a router (or Layer 3 device) is

required as illustrated by Amount 2-4.

192.168.1.0

192.168.1.0 192.168.2.0

Campus Arrangement Models 27

Figure 2-3 Analysis Application VLANs

Figure 2-4 Routing Cartage with VLANs

VLAN 3: 192.168.3.0 VLAN 2: 192.168.2.0

VLAN 1: 192.168.1.0

VLAN 3: 192.168.3.0 VLAN 4: 192.168.4.0

VLANs 1,3 VLANs 2,4

VLAN 1: 192.168.1.0 VLAN 2: 192.168.2.0

28 Chapter 2: Campus Arrangement Design Models

Ports on the about-face accept been aggregate and assigned to three VLANs. A anchorage from anniversary VLAN

also connects to the router. The router again assiduously packets amid VLANs through these

ports. Note that anniversary about-face articulation in the amount supports two VLANs. Because a about-face articulation can

be configured alone for one VLAN, it has been configured for trunking, or accustomed multiple

VLANs. (Trunking is discussed in Chapter 4, “VLANs and Trunking.”)

To accretion the best account from baffled approaches and VLAN approaches, best campus

networks are now congenital with both LAN switches and routers. Again, the Layer 2 switches are

generally placed area the baby advertisement domains are located, affiliated by routers that provide

Layer 3 functionality. In this manner, advertisement cartage can be controlled or limited. Users also

can be organized and accustomed admission to accepted workgroups, while cartage amid workgroups

can be commutual and secured. Amount 2-5 illustrates the anatomy of a archetypal baffled and

switched campus network.

Figure 2-5 Archetypal Campus Arrangement Structure

VLANs 1/2/3 VLANs 4/5/6

Trunk

links