Load Balancing for voice and data

Posted on 2011-09-10
Last Modified: 2012-06-27
Hi all

I was asked to design a scenario where a head office will provide voice and data services for remote workers. All remote users will be about 15-20 and all will be using cisco client vpn and cisco ip softphones. I have some considerations regarding the bandwidth because the head office is limited to work only under ADSL connections with 8mbps Down/512kbps Up

I am thinking of having 2 ADSL connections connected on a load balancer in order to increase the upload speed and from the load balancer to connect 2 routers, one cisco UC500 router for voice and one cisco 871 for data.

However i am not quite sure how i will connect both routers to communicate with each other since the users who will use the vpn to access the head office will need to access the data network and the voice network simultaneously.

However i am not sure if what i m thinking is right or wrong. I really appreciate to have some guidance on this scenario please

Question by:giorgosy78
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Expert Comment

ID: 36516514
The first ting to do is to make sure the routers can talk to each other. this means they should have in IP address on the same subnet and static routes to each other.  if you're using a VPN concentrator (or if i'ts part of the router features) just make sure you have both subnets defined as an object group and permit the users access to that.  In truth, users do not need to have a VPN active to use softphone software, if you have a public IP address open for it.

Author Comment

ID: 36516626
Ok just to understand the whole concept here.

1. You are not mentioning the load balancer. Is the load balancer still in the game?
2. Are you talking about WAN IP Address that should be on the same subnet?
3. When you say to make sure the routers can talk to each other , this is actually my big question.How? I mean physically how first and then the configuration. I suppose it goes like this:
 a) Load balancer first, b) then a switch  c) both routers connecting their WAN ports on the switch d) setup static routes? No i m not using a VPN concetrator...
3. I have seen on cisco doumentation that i will need to open lots of ports for the softphone to communicate with the CME over the internet. However Isn't this a huge security issue i should consider?


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Expert Comment

ID: 36516735
1.  sorry, forgot about eh load balancer.   It's still in the game.  I usually use stacked switches to load balance
2.  No not the WAN IP address.  
3.  Example:
     Router A-Int 1:WAN
                    Int2: Data Subnet   (
                    Int 3: Connector subnet (

     RouterB  Int 1: connecter subnet (
                    Int 2:  voice subnet (192168.200.0/24)

My understanding is you basically want to aggregate 2 ASDL lines.  it' possible and you don't need a load balancer to do it.  You can use an router that allows for port aggregation. this will give you 16 Mbps down and 1 Mbps up.   Load balancing might not give you all the bandwidth you want

        Physically, what kinds of interface do you have, you usually need a cross over cable to connect router to router, so Router A Int2 connects to Router B int 1 with a cross-over cable.  

4.  there's always a security issue opening any port, but you can communicate without opening ports right?  Port 25 is a risk to have open, but everyone uses it.  The key is not only open ports you need.  if you don't open those ports and allow the services, your phones wont' work.
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Author Comment

ID: 36518057
Well that was very interesting and i sure learned some new things here.

Last questions please.

1. So i connect the 2 ADSL lines on a a router that supports port aggregation to load balance, connect the 2 routers on that router and from there do the configuration as you told me right?

2.  You said "The key is not only open ports you need.  if you don't open those ports and allow the services, your phones wont' work" . Are we talking here in case of a non VPN scenario? Because if i do VPN there is no need to open any ports right?

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Accepted Solution

SuperTaco earned 500 total points
ID: 36518881
Feel free to ask as many questions as you like, that's what we're all here for :)

1.  not exactly.  the point it to use one of the routers as the ""load balancer" if you will.  I pull the extra hardware out of hte game.  most firewalls and routers are capable of doing this  The second router will attach to that first router.

2.  that should be "the key is to only open the ports you need"   that as an "oppps" typo.  Yes I was talking about a non VPN scenario.

Author Comment

ID: 36519083
That was a very helpful discussion. I shall start working on this from tomorrow.

Thanks for everything , appreciate it


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