advantages of distribution layer in network

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Sep 17th, 2008
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Hi all, can anyone list me some good advantages of using a distribution layer in my network, ie, more control, keeps broadcasts from core etc

help would be much appreciated.


thanks


Carl

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rohitrattan Wed, 09/17/2008 - 04:02
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Hello Carl,


I believe there are two reasons to have a distribution layer.


First:- it is used to aggregate a large number of access layer devices to the core, in case you have more access switches than you have ports on your core :-)


Second:- The core of network is meant for delivering performance and this is a highly desirable situation e.g. in Service Provider networks it's critical that the core does things at speed. So the distribution layer is where all the ACL's and policies are applied.


whereas more control and keeping broadcasts away from the core are not the things you will get out of a distribution layer. Adding another layer won't decrease the overhead related to managing network devices.


HTH


Regards

Rohit

Marwan ALshawi Wed, 09/17/2008 - 04:15
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carl

in a modren hierarchal networks the distribution layer very important because it has alot of major roles in the switched network and in medum size networks the distribution/core layers in one layer almost


so the access layers have the vlans in layer two assiegned to ports while the layer three interfaces for these vlans and the routing between these vlans done on the distribution layer

with dual distribution layer and redandunt uplink from access to Dist u can achive redundance, loadbalncing and high availabiltiy to ur network


in distribution layer most ACL filtering and QOS policing or remaring configured there


in case of core layer the distribution layer saamurize the route from the access sithes and send it to the core layer as a summary route


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carl_townshend Wed, 09/17/2008 - 04:46
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Hi there


I could do with more benefits if possible from adding a distribution layer rather than connecting my switches directly to the core.


thanks

Marwan ALshawi Wed, 09/17/2008 - 06:18
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u cant design a network like accees-to-core

but somtimes as i mentioned above the distribution layer switches do the both roles as distsribution and core at the same time which is practical for small and medume networks


with distribution layer u move ur network from flat switched network that contains alot of proplems like single point of faulor to a hirerichal switched network


the core usualy link betwenn diffrent networks block for example

lets say u have two big buldings each building has its access and distribution layers the core layer will link between those two buildings and route traffic between them on L3 then go the distribution switches in dist switches will be routed to the right L3 valn and passed to corsponding L2 vlan in the access switch


good luck


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Joseph W. Doherty Wed, 09/17/2008 - 11:21
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The purpose behind "physical" network layers, such as access/distribution/core, really concerns scalability.


If you had 30 or 300 hosts, that could be connected to one network device, would you have them connect to just one device, or multiple devices? If multiple devices, how many, what kind, and how would you structure the network device interconnections?


The prior questions answers are "it depends". You might need a distribution layer for 30 hosts and not for 300, the converse, both or neither.


I can't think of advantages of a "distribution layer" in the abstract (beyond layers in general). Actual advantages (or disadvantages) need to be examined in light of an actual network with actual requirements.

carl_townshend Thu, 10/16/2008 - 00:54
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Hi There

I have to do a presentation on the new distribution layer that we are installing, I need to tell management probably 4 or 5 benefits in simple terms , Can anyone help on this with the best things to say?

Marwan ALshawi Thu, 10/16/2008 - 02:16
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hi Carl

acording to cisco


The hierarchical network model provides a modular view of a network, making it easier to

design and build a deterministic scalable network. The hierarchical network structure is

composed of the access, distribution, and core layers. Each layer has its own functions, which

are used to develop a hierarchical network design


Access layer: Used to grant user access to network devices. In a network campus, the

access layer generally incorporates switched LAN devices with ports that provide

connectivity to workstations and servers



Distribution layer: Aggregates the wiring closets, using switches to segment workgroups

and isolate network problems in a campus environment. Similarly, the distribution layer

aggregates WAN connections at the edge of the campus and provides policy-based

connectivity

Distribution layer devices control access to resources that are available

at the core layer and must, therefore, make efficient use of bandwidth. In addition, a

distribution layer device must address the quality of service (QoS) needs for different

protocols by implementing policy-based traffic control to isolate backbone and local

environments. Policy-based traffic control enables you to prioritize traffic to ensure the best

performance for the most time-critical and time-dependent applications


The distribution layer is the place where routing and packet manipulation are performed and

can be a routing boundary between the access and core layers. The distribution layer represents

a redistribution point between routing domains or the demarcation between static and dynamic

routing protocols. The distribution layer performs tasks such as controlled routing decisions and

filtering to implement policy-based connectivity and QoS


The distribution layer uses a combination of Layer 2 and multilayer switching to segment

workgroups and isolate network problems, preventing them from impacting the core layer. The

distribution layer is commonly used to terminate VLANs from access layer switches. The

distribution layer connects network services to the access layer and implements policies

regarding QoS, security, traffic loading, and routing. The distribution layer provides default

gateway redundancy using a FHRP such as HSRP, Gateway Load Balancing Protocol (GLBP),

or Virtual Router Redundancy Protocol (VRRP) to allow for the failure or removal of one of

the distribution nodes without affecting end point connectivity to the default gateway


good luck

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