Transparent Ethernet

Ethernet has become a bright champ in the LAN environment, for all the affidavit that we accept considered

in this book. Factors such as cost, artlessness of implementation, and scalability accept been

powerful affidavit to baddest Ethernet. In this chapter, we accept focused on how to accommodate reliable

and QoS-driven Ethernet networks.

It’s not too abundant of a footfall to accede that this actual affable agreement may accept uses beyond

the LAN—perhaps into the city area, and maybe, somehow, into the advanced area. After

all, with the end of aggregate media LANs and the appearance of bifold connectivity, ambit is not

the aforementioned botheration as it was. And with Ethernet abstracts ante abounding times the abstracts ante of traditional

WAN services, replacing some MAN and WAN links with Ethernet seems actual seductive.

Remember that the ambit limitations imposed by bequest Ethernet are a

direct aftereffect of the charge to ascertain collisions. After that need, the alone limitations

are abrasion and delay. Repeaters break the abrasion problem, and

delay is appealing baby over a cilia link.

Many Cisco Ethernet switches now accept adapted “metro” interfaces; sometimes alike a particular

switch is bogus accurately to accommodate the actual interfaces bare to drive the signals

much further. Casework such as these are accessible in the 3550, 4000, and 6500 alternation switches.

674 Affiliate 20 Affection of Annual (QoS)

New technologies are beneath development, including the adeptness to abbreviate Ethernet into

either SONET or SDH frames, appropriately acceptance Ethernet to be transported over absolute distances.

SONET (Synchronous Optical Networks), broadly acclimated in the USA, and SDH

(Synchronous Digital Hierarchy), acclimated throughout the blow of the world, are

ultra-high-speed technologies acclimated to carriage abstracts over fiber-optic cables.

In fact, several technologies abide that acquiesce Ethernet to be transported central accession protocol

over absolute distances, including the following:

Long-distance Ethernet over cilia (EOF) appliance Cisco Catalyst switches

Ethernet over SONET or SDH

Ethernet over DWDM

Ethernet central IP appliance MPLS

Ethernet tunneled over built-in IP appliance Band 2 Tunneling Agreement adaptation 3 (L2TPv3)

The annual to the end user of these casework is in the way that the arrangement is perceived. Because

the advanced or city affiliation now behaves like a LAN, users can affix appliance standard

broadcast protocols to servers and casework that are ample distances away. VLANs can be extended

into added offices, and adaptable users may be able to affix anon to their approved VLAN even

when in a alien aggregation site. Because the arrangement would like Ethernet end-to-end, the term

transparent Ethernet has been coined.

This is still new to annual providers, and not all ISPs accommodate all services—in fact, some don’t

provide cellophane Ethernet at all. But cellophane Ethernet is still in its aboriginal stages, and as the

Internet becomes added abiding and the QoS that we accept covered in this affiliate becomes more

widespread, we are acceptable to see cellophane Ethernet agriculture up in the strangest of places.

The IEEE is in the action of because standards for active Ethernet in the

metropolitan breadth arrangement (MAN). This is alleged Ethernet in the First Mile (EFM)

and the adapted accepted is IEEE 802.3ah. Consideration is actuality accustomed to

different subscriber topologies appliance point-to-point access over the existing

copper infrastructure.

Summary

Quality of annual (QoS) is a ample anecdotic term, and can be activated to a array of different

processes. Traditional arrangement architecture is apprenticed by throughput and reliability. Tomorrow’s networks

will be apprenticed by the charge to abutment multimedia, time-sensitive applications. Today’s

networks are about in between.

Exam Essentials 675

When because reliability, abounding factors charge to be taken into account. All over the network,

single credibility of abortion abound, from the host PC appropriate through to the Internet access

router. We cannot achievement to break all of the problems in one go, and it may not be our responsibility

to do so. But we can focus on the areas area we can accept a ample impact. HSRP is one

of those areas, area a abortion of the absence aperture is such a analytical agency that Cisco developed

a proprietary protocol—HSRP—to administer the problem.

The additional ancillary to QoS is the access taken to try to accommodate connection-oriented-like services

over best efforts networks. This is a austere challenge, as both Ethernet (at the Abstracts Link

layer) and IP (at the Arrangement layer) accommodate 18-carat best efforts connectivity, and after the

addition of added content, we would accomplish no progress.

The aftereffect has been a access of new agreement extensions developed by assorted standards bodies,

from the IEEE to the IETF. In IP, we accept the blazon of annual (ToS) bits, and their new implementation,

the Differentiated Casework Code Points. In Ethernet, we accept the chic of service

(CoS) extensions to 802.1Q, defined in 802.1p. Naturally, the DSCP is accurate properly

only in band 3 switches, but there is some automated mapping amid the layers in the higherspecification

switches.

Cisco switches at band 2 and band 3 abutment a array of these new protocols, although they

are somewhat bound as yet. This is partly because we in the networking association accept yet

to accomplish accord on what we appetite and how we will apparatus it. When we accommodate the

lead, you can be abiding the IOS will follow.

Exam Essentials

Understand what affection of annual is. QoS is a aggregate of processes and procedures for

trying to enhance the annual usually allocated to a anatomy or packet delivered by a best efforts

network. This involves anecdotic the data, appearance it, and again appliance that appearance as a key

for how the abstracts will be managed central queues beyond a network.

Understand why some applications annual from QoS. Not every appliance allowances greatly

from applying priorities to its data. Abounding bequest applications are congenital to run as store-and-forward

flows, and are annoyed with the simple believability that they get from TCP. E-mail, FTP, and so on do

not accept the aforementioned coercion as mission-critical abstracts with a adjournment limit. In addition, some applications

place ample demands beyond the arrangement because although the bandwidth needs may be

small, they cannot administer jitter. Defined as the aberration in cessation amid alternating frames or

packets, jitter spells the afterlife bell for multimedia applications.

Understand what QoS appearance Cisco switches can support. Not every Cisco about-face can

support every QoS feature. This is accurate abundantly because QoS can be activated at either band 2 or

layer 3. Some Cisco switches are simple band 2 devices, admitting others accept so abundant band 3

capability that they could calmly be alleged routers. Obviously, band 2 switches cannot support

layer 3 QoS. Band 2 QoS is bound to ambience and responding to the TOS $.25 central the 802.1p

extension to 802.1Q. Band 3 QoS uses either the TOS $.25 from bequest IPv4, or the newer DSCP

implementation of the aforementioned field. Both can be mapped to the band 2 TOS at a accessory supporting

both layers.

676 Affiliate 20 Affection of Annual (QoS)

Understand how to configure QoS on Cisco switches. There are still altered versions of

operating systems on Cisco switches. From the 4000 and 6500 active CatOS, to the same

switches active IOS, to the 3550 active a abounding IOS and the 2950 active IOS in either the

standard or added angel options, abounding differences occur. Appliance the basal information

regarding band 2 and band 3 QoS, you charge to be able to configure any of these switches for

QoS. Remember that the BCMSN assay has simulations and is new, so there may be added in

the future. Simulations backpack several added marks, so accomplish abiding you are accustomed with all the

commands in this book.

Understand how back-up is accomplished appliance Cisco switches and routers. Back-up can

be activated to abounding places in the network, but this course, absorption as it does on the campus network,

exposes the actuality that best PCs use a absence aperture to get off-LAN. This analytical device

can be a distinct point of failure. Cisco’s HSRP and beneath frequently VRRP can be acclimated to provide

that redundancy. By creating a basic router IP abode and appliance that as the absence gateway,

we can configure added than one router to be able to advanced abstracts beatific to the group, with

options for prioritized alternative and preempting of control. Both SLB and GLBP can be acclimated to

load-share the cross-router traffic.