Switching

Unanswered Question
May 28th, 2010

     I am designing a new network(LAN network) in an ar

ea and i want to connect different buildings . My main node (Switch L3) is

at the center of the area. For decrease the cost i tried not to put any fiber optics so

i designed the LAN with CAT 6 (underground cable). The problem that i face is

that in order to succeed(because distance between Switch and Switch must not be more than 100m)

i connect in series 5 switches(all cisco 2960 model) including the

central L3 switch(4507 Series). 4507->2960->2960->2960->2960.

Does anyone tell me if i will face a problem with bandwidth, delay, loss packets of this design?

If yes shall i use Fiber Optics for the solution?

How many Switches is the max in serial connection for good quality traffic?

All Switches are 10/100/1000 Mbps ports.

Thanks for your time

Moses

I have this problem too.
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Calin Chiorean Fri, 05/28/2010 - 03:10

Each node (switch) will add some latency due to the switching process that's taking care on each device, but depending on the configuration, this added latency may not influence your communication at all. If you are planning to use Voice over IP services, you might want to do some tests before, but still I don't think this will be a problem. I have links with 220ms over WAN and VoIP is working fine. To reduce even more the problems that can occur, use quality cable, be sure if it's possible not to pass over any electrical cable in the path, use cabling structure that support 1Gbps speed, and some port-security like BPDU Guard to avoid problems on access-ports and so on...the regular advices.

While I would recommend the typical connection with core switch, distribution and so on, we all know that sometimes this is not possible due the cost reasons which we have to fight every day.

The problem that I see mainly in this "cascade" is reachability. If one of the swiches crash, or a link connection is broken on the secondary switch, than all you other switches will be affected. If it possible and you can afford, I would suggest at leas one fiber optic from the last switch (2960) to the first one (4507). In this case, with the help of STP, you can achive some redundancy. In the other case, like it's designed now, you can have a single point of failure, and when it's possible this should be avoided.

Let me know if this helps!

Hitesh Vinzoda Fri, 05/28/2010 - 03:37

Hi,

I dont see any problem with this design what you are planning

4507->2960->2960->2960->2960.

As per Cisco I believe you can have 7 switches in a ring for better performance of STP, so i would prefer not to have 7 switches connected in a Spur. As in your case it seems that pulling cable from the last switch back to 4507 will be not be possible. If those switches are 2960G (all ports 1000 mbps) you may think of configuring etherchannel between them to give more bandwidth and some redundancy across the switches upto 4507.

Regards

HTH

Hitesh Vinzoda

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Jon Marshall Fri, 05/28/2010 - 05:06

moses12315 wrote:

     I am designing a new network(LAN network) in an ar

ea and i want to connect different buildings . My main node (Switch L3) is

at the center of the area. For decrease the cost i tried not to put any fiber optics so

i designed the LAN with CAT 6 (underground cable). The problem that i face is

that in order to succeed(because distance between Switch and Switch must not be more than 100m)

i connect in series 5 switches(all cisco 2960 model) including the

central L3 switch(4507 Series). 4507->2960->2960->2960->2960.

Does anyone tell me if i will face a problem with bandwidth, delay, loss packets of this design?

If yes shall i use Fiber Optics for the solution?

How many Switches is the max in serial connection for good quality traffic?

All Switches are 10/100/1000 Mbps ports.

Thanks for your time

Moses

Moses

As Calin said obviously you are trying to keep costs down but this is not a good solution for a new network. You have a chain of single points of failure all the way from the 4500 to the end 2960 switch. If any one of the 2960 switches fails then every other switch behind it is cut off and loses connectivity to the 4500.

If you have explained that to the business ie. a single failure can take out multiple switches or in their terms can cut off a lot of users and they are happy with this then document it. Otherwise i would be pushing for fiber connectivity from each 2960 back to the 4500. It does cost more but it is a more resilient and scalable network.

Bear in mind also that each 2960 closer to the 4500 has to handle it's traffic and all the traffic from the switches behind it. There is a potential for bottlenecks in addition to which you are not really utilising the 4500 to it's full extent.

I appreciate money is tight these days and you can't always design and deliver the "perfect" network solution but you need to balance the cost of fiber runs versus the lost business time if one of the switches fails.

Jon

Leo Laohoo Fri, 05/28/2010 - 18:49

If a switch fails, it's a pain, but you can send a replacment.  But if your cable gets pulled by a cable-hunting-backhoe then it's "Goodnight Seattle"! 

In the network world, if you need to get things done, get it done right ... once!  Otherwise, don't even bother because you'll spend more to fix the problem.

glen.grant Fri, 05/28/2010 - 19:25

     There can be issues with a difference in electrical potential

between buildings when using copper .   I would do a search on this topic and decide on what you would want to do . Fiber is a much better idea when running between different buildings.

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