Transcript CCNP 1: Building Scalable Cisco Internetworks

CCNP 1: Building Scalable
Cisco Internetworks
Overview Of Scalable Networks
The Hierarchical Network Design Model
Make sure that you visit the following link: Internetworking Design Basics
Core Layer
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As the center of the network,
the core layer is designed to
be fast and reliable.
Access lists should be avoided
in the core layer since they add
latency and end users should
not have access directly to the
core.
In a hierarchical network, end
user traffic should reach core
routers only after those
packets have passed through
the distribution and access
layers, where access lists may
be implemented.
Core Layer (Continued)
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The most powerful Cisco routers serve the core because they have the
fastest switching technologies and the largest capacity for physical
interfaces.
The Cisco 7000, 7200, and 7500 series routers are modular, allowing
interface modules to be added providing scalability. The large chassis of this
series can accommodate dozens of interfaces on multiple modules for
virtually any media type, which makes these routers scalable and reliable
core solutions.
Core routers achieve reliability through the use of redundant links, usually to
all other core routers.
When possible, these redundant links should be symmetrical having equal
throughput, so that equal-cost load balancing may be used.
Core routers need a relatively large number of interfaces to enable this
configuration.
Core routers achieve reliability through redundant power supplies and
usually feature two or more "hot-swappable" power supplies, which may be
removed and replaced individually without shutting down the router.
Core Layer (Continued)
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With the high-end routers and WAN links involved, the
core can become a huge expense, even in a simple
example such as this.
Some designers will choose not to use symmetrical links
in the core to reduce cost. In place of redundant lines,
packet-switched and dial-on-demand technologies, such
as Frame Relay and ISDN, may be used as backup
links.
The trade-off for saving money by using such
technologies is performance. Using ISDN BRIs as
backup links can eliminate the capability of equal-cost
load balancing.
Core Layer Continued
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The core of a network does not have to exist in the WAN. A
LAN backbone may also be considered part of the core layer.
Campus networks, or large networks that span an office
complex or adjacent buildings, might have a LAN-based core.
Switched Fast Ethernet and Gigabit Ethernet are the most
common core technologies, usually run over fiber.
Enterprise switches, such as the Catalyst 4000, 5000, and
6000 series, shoulder the load in LAN cores because they
switch frames at Layer 2 much faster than routers can switch
packets at Layer 3. In fact, as modular devices, these
switches can be equipped with route switch modules (RSMs),
adding Layer 3 routing functionality to the switch chassis.
Distribution Layer
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The following rules will protect the
core from unnecessary or
unauthorized traffic.
Distribution layer routers need fewer
interfaces and less switching speed
than their counterparts in the core
because they should handle less
traffic. Nevertheless, a lightning fast
core is useless if a bottleneck at the
distribution layer prevents user
traffic from accessing core links.
For this reason, Cisco offers robust,
powerful distribution routers, such
as the 4000, 4500, and the 3600
series router. These routers are
modular allowing interfaces to be
added and removed depending on
need. However, the smaller chassis
of these series are much more
limiting than those of the 7000,
7200, and 7500 series.
Distribution Layer Continued
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Distribution layer
routers bring policy to
the network by using a
combination of access
lists, route
summarization,
distribution lists, route
maps, and other rules
to define how a router
should deal with traffic
and routing updates
Distribution Layer Continued
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The figure shows two 3620 routers
have been added at Core A, in the
same wiring closet as the 7507. This
means that the high-speed LAN
links may be used to make the
connections between the distribution
routers and the core router.
Depending on the size of the
network, these links may be part of
the campus backbone and will most
likely be fiber running 100 or 1000
Mbps.
In this example, Dist-1 and Dist-2
are part of the Core A campus
backbone. Dist-1 serves remote
sites, while Dist-2, serves access
routers at Site A. If Site A employs
VLANs throughout the campus,
Dist-2 may be responsible for
routing between them.
Distribution Layer Continued
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Both Dist-1 and Dist-2
use access lists to
prevent unwanted
traffic from reaching the
core. In addition, these
routers summarize their
routing tables in
updates to Core A,
keeping the Core A
routing table as small
and efficient as
possible
Access Layer
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Routers at the access layer
are deployed to permit
users at Site A and remote
sites Y and Z to access the
network.
Access routers generally
offer fewer physical
interfaces than distribution
and core routers. For this
reason, Cisco access
routers, which include the
1600, 1700, 2500, and 2600
series, feature a small,
streamlined chassis that
may or may not support
modular interfaces.
Access Layer Continued
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Each remote site in the example
requires only one Ethernet interface
for the LAN side and one serial
interface for the WAN side.
The WAN interface connects by way
of Frame Relay or ISDN to the
distribution router in the wiring closet
of Site A.
For this application, the 2610 router
provides a single 10-Mbps Ethernet
port and will work well at these
locations. These remote sites, Y and
Z, are small branch offices that must
access the core through Site A.
Therefore, Dist-1 A is acting as a
WAN hub for the organization. As
the network scales, dozens of
remote sites may access the core by
connection to distribution routers at
the WAN hubs, Site A, Site B, and
Site C.
5 Characteristics of Scalable Networks
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Reliable and available – A reliable network should
be dependable and available 24 hours a day, seven
days a week. In addition, failures need to be
isolated, and recovery must be invisible to the end
user.
Responsive – A responsive network should provide
Quality of Service (QoS) for various applications and
protocols without affecting a response at the
desktop.
Adaptable – An adaptable network is capable of
accommodating different protocols, applications,
and hardware technologies.
5 Characteristics of Scalable Networks
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Efficient – Large internetworks must optimize the
use of resources, especially bandwidth. Reducing
the amount of overhead traffic, such as unnecessary
broadcasts, service location, and routing updates,
resulting in an increase in data throughput without
increasing the cost of hardware or the need for
additional WAN services.
Accessible but secure – An accessible network
allows for connections using dedicated, dialup, and
switched services while maintaining network
integrity.
Making The Network Reliable and
Available
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Scalable Routing Protocols
Routers in the core of a network should converge
rapidly and maintain reachability to all networks and
subnetworks within an Autonomous System (AS). A
scalable protocol such as Open Shortest Path First
(OSPF) or Enhanced Interior Gateway Routing
Protocol (EIGRP) should be implemented in the core
layer.
A network that consists of multiple links and
redundant routers will contain several paths to a
given destination.
Making The Network Reliable and
Available
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Load Balancing
Redundant links do not necessarily remain idle until a link fails. Routers can
distribute the traffic load across multiple links to the same destination. This
process is called load balancing. Load balancing can be implemented using
alternate paths with the same cost or metric, (equal-cost load balancing.), or
implemented over alternate paths with different metrics, (unequal-cost load
balancing). When routing IP, the Cisco IOS offers two methods of load
balancing, per packet and per destination load balancing. If process switching is
enabled, the router will alternate paths on a per packet basis. If fast switching is
enabled, only one of the alternate routes will be cached for the destination
address and all packets in the packet stream bound for a specific host will take
the same path.
Protocol Tunnels
The administrator can configure a point-to-point link through the core between
the two routers using IP. When this link is configured, IPX packets can be
encapsulated inside IP packets. IPX can then traverse the core over IP links and
the core can be spared the additional burden of routing IPX. Using tunnels, the
administrator increases the availability of network services.
Making The Network Reliable and
Available
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Dial Backup
Sometimes two redundant WAN links are not
enough or a single link needs to be fault tolerant,
however a full-time redundant link is too expensive.
In these cases a backup link can be configured over
a dialup technology, such as ISDN, or even an
ordinary analog phone line. These relatively lowbandwidth links remain idle until the primary link
fails.
Dial backup can be a cost-effective insurance policy,
but it is not a substitute for redundant links that can
effectively double throughput by using equal-cost
load balancing.
Making the network responsive
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The IOS addresses priority and responsiveness
issues through queuing. The question of priority is
most important on routers that maintain a slow WAN
connection and therefore experience frequent
congestion. Queuing refers to the process that the
router uses to schedule packets for transmission
during periods of congestion. By using the queuing
feature, a congested router may be configured to
reorder packets so that mission-critical and delay
sensitive traffic is processed first. These higher
priority packets are sent first even if other low
priority packets arrive ahead of them.
Making The Network Efficient
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An efficient network should not waste bandwidth, especially over
costly WAN links. To be efficient, routers should prevent
unnecessary traffic from traversing the WAN and should
minimize the size and frequency of routing updates. The IOS
includes several features designed to optimize a WAN
connection:
Access lists
Snapshot routing
Compression over WANs
Dial-on-demand routing (DDR)
Route summarization
Incremental updates
Making The Network Adaptable
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EIGRP is an exceptionally adaptable protocol
because it supports routing information for
three routed protocols: IP, IPX, and
AppleTalk.
The IOS also supports route redistribution.
Mixing Routable and none routable protocols
Making the Network Accessible But
Secured
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Dialup and dedicated access –
Cisco routers can be directly
connected to basic telephone
service or digital services such as
T1/E1. Dialup links can be used for
backup or remote sites that need
occasional WAN access, while
dedicated leased lines provide a
high-speed, high capacity WAN core
between key sites.
Packet switched – Cisco routers
support Frame Relay, X.25,
Switched Multi-megabit Data
Service (SMDS), and ATM. With this
variety of support, the WAN service,
or combination of WAN services, to
deploy can be determined based on
cost, location, and need.
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Web-Based Curriculum
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Labs
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Lab1.4.3: Access Control Lists basic and
extended Ping
Lab 1.4.2: Capturing HyperTerminal and
Telnet Sessions
Lab 1.4.4: Implementing Quality of Service
with Priority Queuing
Lab 1.5.2: Unequal-Coast Load Balancing
with IGRP