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Voice over IP across WAN


I have a non-Cisco VOIP solution on my LAN which I want to use for one of our branch office as well. Here is my current design and overall topology to help you answer my questions:

LAN Information:

1. The VOIP Server and IP Phones are on their own VLAN (10.4.x.x /20)

2. The data traffic is segmented by several Vlans

a. VLan 1 = 172.16.0.x /20 default

b. VLan 2 = 172.16.24.x /21 Voice VLan

c. VLan 3 = 172.16.32.x /21 Data

d. VLan 4 = 172.16.40.x./21 Data

Note: the reason for the Vlans to have different subnet mask and network IDs is that I am in the process of sub netting VLan 1 into several and smaller Vlans, and I don’t want to overlap IP addresses.

3. All Vlans are routed by a Layer 3 switch (L3switch1)

4. L3switch1 has a default route to a router (router1)

5. Router1 has a default route to the firewall. It also has a route to the L3switch1 for each VLan configured on the L3 switch.

6. At the exception of VLan 1, all over VLan interfaces on the L3switch1 are configured with an IP helper-address pointing to a DHCP server on VLan 1.

WAN Information:

1. From L3switch1, I have a router (router1) connected to our branch office router (router2) via a dedicated line.

2. Router1 and 2 have one Ethernet and one serial interface.

Note: The routers are configured with an IP address at the interface level. No sub-interface is configured.

3. Router2 is configured with a DHCP pool to provide IP addresses to the computers at the branch office and points every PC to resolve name queries to a DNS server on VLan 1 at the main office.

4. Of course, the branch office PCs are on a different network = 172.16.16.x /20

5. The branch office switch is a 2900 (24 ports)

VOIP Information:

1. Special configuration needed to be done to allow voice and data traffic to go through one port on the access switch. We turned 802.1q on between the L3switch1 ports to each access switches.

2. All ports on the access switches are set as trunk (802.1q) ports only allowing the voice VLan and the appropriate data VLan, so the IP phones get one IP address from the voice VLan and the PC plugged into the phone gets an IP address from a different VLan.

3. The DHCP server is configured to assign an IP address from the Voice VLan to phone and an IP Address from a data VLan the PCs.


1. How should I configure my equipment to allow my IP phones in the branch to get an IP address from the voice VLan configured at and have my PCs connected get an IP address from a data VLan?

2. Is it possible to advertise the main office’s Vlans to the branch office network equipment (router and switch)?

I would appreciate any help and/or pointers that could help me configure this setup

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