DHCP Over dedicated T1 circuit for IP phones

Posted on 2011-09-02
Last Modified: 2012-06-27
Hey all,

  Hoping to get a little advice. I am about to roll out a new project at a remote site. The remote site will consist of a dedicated T1 circuit back to HQ This will actually be 2 bonded T1's. The remote site has no server what so ever, no direct connection to the internet, no dns, dhcp etc. The remote site will consist of cisco IP phones and some PC's. It should look something like the below diagram.

              HQ                                                               Remote
                | --------------------------------------------|
         Cisco 2851                                 Cisco 2811 (Networks will be learned via EIGRP)
                |                                                                       |
   Cisco 6509 switch                Cisco 3560G   Vlan's 2,3,4,5 (4&5 are Voice) VLAN 100(MGMNT)
                |                                                    /        \----Fiber
   Call Manager/Unity            2 2960's Stacked     single 2960
                                                                 |                          |
                                                      VLAN's 3&5          VLAN's 2&4

I'm a little confused as to where I would configure DHCP for the IP phones and PC's at the remote office to reach the Call manager/Unity servers and also for the PC's to get internet?

Here's what I have so far for IP's on the 3560 at the remote site
vlan 2 = - Data
vlan 3 = - Data
vlan 4 = - Voice
vlan 5 = - Voice
vlan 100 = - MGMNT

2811 fa0/0 connection to the remote local lan = - port in Vlan 100
2811 multilink T1 interface =
2851 multilink T1 interface =
2851 fa0/1 port is configured for vlan 61
6509 mgmnt vlan =

Can this setup work with what I have? Any help is appreciated.
Question by:jwil320
LVL 26

Assisted Solution

Soulja earned 250 total points
ID: 36476141
It looks like your 3560g is doing the routing for the vlans correct? All routing is functional between sites?  If so, just put an ip helper pointing to your dhcp server on each vlan interface. Done!
LVL 26

Expert Comment

ID: 36476448
For internet, you can just create a default route pointing to your internet gateway.

Author Comment

ID: 36476739
Thanks for the reply.

Will I need an ip helper-address on the fa0/1 interface of the router also?

Correct the 3560 will be doing all the routing for the remote site but it will not have eigrp configured on it only the router. Should I also configure the 3560 for eigrp or will a default route suffice?

Author Comment

ID: 36476743
I meant to say does the 2811 need an ip helper-address on the fa0/0 interface the one connecting to the local LAN.
LVL 36

Expert Comment

ID: 36477415
I would put an a DHCP server at the remote site
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LVL 15

Expert Comment

by:Robert Sutton Jr
ID: 36477707
You shouldn't need another DHCP server at the remote site. I do agree with what Souja said above in placing the Ip-helper address(the actual Ip of your DHCP server) on each vlan interface on the remote end requiring a DHCP address for your phones. You shouldn't need to put it on your 2811. I'm assuming your tft server(containing your phone configs) is also at the HQ site?
LVL 26

Expert Comment

ID: 36478002
Nope, as long as routing is fine between the two sites, the helpers on the vlanl interfaces should be enough. I would also tend to agree with Arne that it would be good to have a dhcp at the local site, this way you aren't rely in that T1 circuit to be up for dhcp. If the link goes down, then no dhcp.
LVL 79

Accepted Solution

lrmoore earned 250 total points
ID: 36485798
Both the Cisco 2811 and the 3560G switch are perfectly cabable of providing DHCP to the local PC's/ Phones.
I highly recommend keeping DHCP local. I'm assuming that the 2811 will be SRST router in case T1 fails, to provide local dialtone? If yes, then DHCP must be provided locally!

Author Comment

ID: 36485913
No SRST will be configured. We want to provide them service but it's just not mission critical to be up 24/7.  

I'm thinking of just letting the 3560 do the dhcp. But like Soulja mentioned they should at least have DHCP if the T1 line is down.

For the sake of VOIP will have I have to make each interface from the 3560 remote site to the 2851 at HQ all trusted interfaces?

Author Comment

ID: 36488852
I will start a new question for the VOIP side. Thanks all.

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