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How to use switch to boost signal on multiple long cat-5 runs

I felt like this would be some easy scenario, but I'm second guessing myself, and want to ask for advice.

Note that I am a Systems Administrator, NOT a Network Engineer, and while I know my way around networks to a point, when it comes to the more complex stuff with switches and routing, I don't know what the hell I am doing :-)

The scenario:

We have a downstairs office that is more than 100 meters away, so we have four cat-5 lines going to a telco closet that is approximately at the half way point, then another four cat-5 lines going from the closet to the downstairs office.  Both sets of runs end up being under 100 meters.  There is a cheapo SMC non-managed smart switch in that telco closet that joins the runs. All eight ends of the cat-5 runs in the telco closet are plugged into the 8-port switch.  (My predecessor set all this stuff up, so I don't know how right or wrong it is).

we've labelled the 4 cat-5 runs BB1 thu BB4 on either end (BB = backbone).

Currently, we are using only one of these backbones. The other three backbones don't have anything plugged into them on either end, but they are all plugged in to the SMC switch.

Both Voice and Data traffic are on the same subnet, and both go over the same backbone.  The issue we recently ran into is that the downstairs folks are complaining of muddy voice quality.  The first step in troubleshooting this was to buy a Cisco SG300-10 switch to replace the cheapo SMC in that telco closet. This switch is managed... nothing crazy fancy, but enough to help troubleshoot the network traffic.

OK, so here it is:  It seems to me like each BB should have its own VLAN on the switch, instead of them all being joined together on the same default VLAN, am I right?  I mean, it doesn't matter now, since we're only using one of them, but if we start using the other BB's for other traffic, or if I want to implement LACP over two of the backbones for increased bandwidth or failover, there's going to be potential for collisions and cross talk between the different BB's at the switch, right?

I basically just want to divvy up the ports in pairs, so that in essence, there are 4 separate switches, one for each BB. 

What's the simplest way of doing that so that I can manage the switch from any one of those VLANs? (I've created 4 separate VLAN's, but I can only manage the switch from one of them. I'd like to manage it from any of the VLANs. I know this isn't best practice, but I don't care).

I'm using the web-based gui on the switch, but I could hook it up to a COM port for cli if need be.

Also, I'm a little confused by all the VLAN terminolgy: General, Customer, Forbidden, etc. I know what tagged and untagged are, but again, I'm not a network engineer so some of these concepts are currently beyond me. 

Any quick suggestions on how you would approach this?  Sorry if I made this post more verbose than necessary. There's probably a lot of detail above that I didn't need to write about....

Thanks ahead of time.



Accepted Solutions
Rick Morris
Frequent Contributor

The short answer, yes using a switch in the middle will provide you the ability to extend network connections to where you need them.

Second, no to the separate vlans per cable.  The best way to set this up is via trunks and etherchannels.  This will provide you with increased bandwidth as well as fault tolerance and redunancy.  In the trunk config you will specify all or some of the vlans to allow across the trunk link.

This link may help

View solution in original post

Alessio Andreoli

Hi Scott,

it would be very helpful if you could draw some diagrams for us... by the way, if in your new solution you are using all the 4 ethernet cables you don't really need for different vlan. From a data transfer point of view the first floor switch will see the ground floor switch like the end of a point to point connection. I would actually leave that old switch in place acting like an active hub (transparent signal refreshing) and i would configure an etherchannel (LACP or PAgP)on the switches working on the ends (first floor and ground floor if i am not wrong).  An therchannel is one way to group up to 8 cables providing to the switch the perception having a single logical cable connecting two ends with a theoretical nx100Mbps (n=number of cable, 100Mbps is an assumption of the port speed that in your case could be 1000 or 10 Mbps too) bandwidth capability.

By the way, there is no use in setting 4 different vlan on this , physically speaking, point to point connection. If you want, you could set one vlan for out of band management and one vlan where to transfer the voice and the data over the trunk.



sw#vlan data

sw(vlan)# vlan 10 name data

sw(vlan)# vlan 20 name voice

sw(vlan)# vlan 30 name management




sw#conf t

sw(config)#int vlan 10

sw(config-if)# description vlan data

sw(config-if)# int vlan 20

sw(config-if)# description vlan voice

sw(config-if)# int vlan 30

sw(config-if)# description vlan management




sw#conf t


sw(config)# int fa0/1

sw(config-if)# description trunk dot1q to the other floor switch over BB1

sw(config-if)# switchport encapsulation dot1q

sw(config-if)# switchport mode trunk

sw(config-if)# end


This would be the configuration on the cisco switches on the first or ground floor working with only one cable (the one connected to Fasthethernet0/1 and would be using a vlan for management, one for voice and one for data. this would reduce your broadcast domains that very likely are the problems of the voice quality.

Pay attention to this: IF you use (as you should) different vlan for the different communication you should extend to the access ports (where your users are connected) the vlans (assuming you are working in a layer 2 environment (read no routed)) like it follows:

access_sw#conf t

access_sw(config)# int fa0/7

access_sw(config-if)# switchport mode access

access_sw(config-if)# switchport access vlan 10

access_sw(config-if)# switchport voice vlan 20

access_sw(config-if)# description User Switch Port


access_sw#write memory


and this should be done for each switch along creating the vlan 10,20,30 as above shown.

Take a look to this link too. It'll help for etherchannel configuration.

All what i have suggested must be check from a syntax point of view because each platform is varying a little bit in IOS and hardware specs but FIRST OF ALL, you need to have clear in mind the design of your network.

If you want more help post switch model and IOS and a design of your infrastructure. Nearly forgetting !!! the voice issues are very very likely due to the amount of broadcas traffic you have in your infrastructure. To verify that just capture some traffic with wireshark or similar and analyse the amount of broadcast packet with a filter.

Hope this helps


Alessio, first, thanks so much for the response.  I have made note of your configuration suggestions above, and will try them out when I get to that point.  Also, I will get a traffic capture via wireshark as suggested.

Next, see this link for a diagram of my network:

I would welcome any critisism or suggestions! Much of this network was set up by my predesessor when our company was much smaller, so it may be time for a redisign :-)

BB7 - BB9 are the backbones that go downstairs, and are the runs that need the signal boost. 

BB4 and BB5 are the backbones that go to our West Wing on the same floor (short run, so no signal boost needed). BB4 is used for the voice switch, and BB5 for the data switch. Remember, at this point on the network, both voice and data are on the same VLAN (VLAN 20), even though I am utilizing separate backbones runs for the data and voice switches.

Question: Should I do this same thing on the downstairs run by utilizing BB8 for, say, data only, and BB7 for voice only? Or would this not really help (in other words, I need to take that a step further and do a fully separate VLAN for voice across my entire network)? 

I just purchased a Cisco SG300 managed switch to replace the cheap auto-sening switch in the 4th Floor Telco Closet, but it sounds like you don't think that will be necessary?  I was planning on utilizing its monitoring features to help troubleshoot traffic flow, but I guess I could accomplish the same thing if I have managed switches on either end.

Speaking of which, we have a Cisco Catalyst 2960 on the downstairs end of the backbone link, but the switch on the upstairs end is a non-managed Cisco SG100, so I'll need to replace that with something a bit more robust. 

Note that there are several Adtran 1224 switches on my network (voice switches), but they are managed by our Telco. I may be able to request access to them, but haven't needed to do so yet.

Thanks again!


Hi Scott,

please give me some time to analyse your infrastructure and i'll definitely come back to you..but you should make me a favour.. Would you please specify where in your network there is only layer 2 (switched or not routed) technology and where routing takes place? Can you confirm that your only Layer 3 point is the Cisco router 37x5 connecting the HN408(i assume a Telco device) and the Adtran TA904 connected on the right hand side of the cisco router?

Other question:

VLAN 90 is just a vlan or a private vlan as it should be?

Hear you soon


PS: Email me more details if you believe

PS2: i assume the diagram you sent is the most updated

Alessio, thanks again.

As to your question, yes, currently, the only L3 device in the diagram is the Cisco 3700 series, which is owned and managed by the telco (though they could probably configure it on request).

I do, however, have a Cisco SG300 (10 port) L3 managed switch at my disposal (which is not mentioned in the diagram), and while I can't spend a fortune on upgrading our network gear, I can certainly justify purchase of an additional L3 device or two if its the right thing to do.

Also, VLAN 90 is a private vlan, indeed. Guest wifi, which pfSense routes privately for external access only.

I made that network diagram yesterday, and it is complete, accurate, and up to date!

I'll keep you posted if I think of any other details, but I can't think of any more at the moment.



Rick Morris
Frequent Contributor

The short answer, yes using a switch in the middle will provide you the ability to extend network connections to where you need them.

Second, no to the separate vlans per cable.  The best way to set this up is via trunks and etherchannels.  This will provide you with increased bandwidth as well as fault tolerance and redunancy.  In the trunk config you will specify all or some of the vlans to allow across the trunk link.

This link may help

View solution in original post

(Editing my previous response here)           

I'm marking your response as the correct answer, Rick, since it was so concise and to the point.

Alessio, you gave me a lot of great useful info (much appreciated) but because of lack of knowledge of advanced network engineering priciples, I had a hard time sorting it all out.  I think Rick's response leads me to the solution as quickly and efficiently as possible.

Thanks to both of you.