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how to plan for backbone Switch

Posted on 2013-01-02
Medium Priority
Last Modified: 2013-01-10
If I understand L3 switches can be configured with Vlans and Vlan interfaces and IP routing.
Now if I trunk one switch to another and allow vlans from one switch to access the other switch, then connect the last switch in the chain to a Router, why would I need the backbone switch.
I know that most of companies use a backbone switch, that usually has fastest ports than the switches used to plug in workstations. but would like to know when should I use the backbone switch .

Thank you
Question by:jskfan
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LVL 20

Assisted Solution

wolfcamel earned 664 total points
ID: 38735814

if you have three switches and assume gigabit
a has 16 ports and one port is connected to switch B
B has 16 ports - 1 port goes to A and one port goes to C
C has 16 ports - 1 port goes to B and one goes to a router, and others go to servers

if switch A has 15 users all doing a lot of data transfer, then you have to realize that switch A can only transfer via one gigabit link to switch B - so the performance may be as low as 1/15th of gigabit. If switch B is similarly saturated performance will drop even further.

irrespective of Vlans - the backbone switch provides a higher capacity between switches, and just represents another part of your planning. You need to know your network and know where the traffic bottlenecks will be.

Assisted Solution

thpipfh earned 664 total points
ID: 38735914
Also known as a core switch and a tandem switch, a backbone switch is a high-capacity switch positioned in the physical core, or backbone, of a network. In the context of a public wide area network (WAN), a backbone switch serves to interconnect edge switches, which are positioned at the network edge, and does not connect to desktop machines or other end user terminals. In the context of a local area 0 +3V -3V 0 +3V -3V 1 0 0 0 0 0 0 0 0 1 1 0 0 0 + - 0 - + 1 Eight Zeros Substitution with Bipolar Violation network (LAN), a backbone switch serves to interconnect relatively low capacity workgroup switches that serve the needs of groups of workers who are geographically clustered.

Assisted Solution

thpipfh earned 664 total points
ID: 38735916
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Author Comment

ID: 38739261
CORE SWITCHLet me see if I understand how the connection is set up:

** I am assuming the Switches (where the workstations connect to) nowadays are all layer3 switches, with Vlans and interface Vlans are configured as well as IP Routing.

**You trunk each Switch to the Core Switch port ( you might etherchannel the trunk for fault talerance and more bandwidth)

***you connect the Core Switch to a Router for external connection OR to another Core Switch if you have a larger Network.

Correct ?
LVL 20

Assisted Solution

wolfcamel earned 664 total points
ID: 38740173
looks good and makes sense

Author Comment

ID: 38742836
By the way, is there any other configuration to do on the Core Switch to make all VLANs from other switches talk to each other.
I mean other than the Trunk ports that will be configured on the Core Switch, what else needs to be done or configured ?
LVL 18

Assisted Solution

by:Garry Glendown
Garry Glendown earned 336 total points
ID: 38761886
Make sure you have all VLANS configured on the core switches, otherwise they may not be forwarded if unknown to a switch (might be depending on the brand/model of the switch), other than that, a trunk port should forward anything thrown at it ;) Also make sure you don't have any VLAN overlap, with same number VLAN meaning different things in the then-connected areas ... that might lead to some undesirable consequences, especially once you get into DHCP etc ...
LVL 17

Accepted Solution

pergr earned 336 total points
ID: 38762253
To make all vlans 'talk' to each other on the core switch, you need to not only create the vlans there - you also need to create a "vlan interface" with an IP address for each vlan.

That IP address will be the default gateway for all PC on the vlan.

The reason you do routing between vlan on the core switch, is that it can do that routing of traffic at full wire-speed, which may be 1G or even 10G. A router can typically not handle the same bandwidth.

While a router may be slower than L3 switch, the router can handle larger routing tables, and also do more buffering and QoS.

Author Closing Comment

ID: 38764248

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