Ethernet Switches & Routers

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New Contributor
Posts: 2
Registered: ‎07-27-2010

Problem with DHCP & VoIP on FGX-648P-PoE

I have a L2 only 648P-PoE uplinked to a CIsco 2821XM router via 0/1/1 and to a second semi-managed switch via 0/1/2. The router has several VLANs, including a Cisco Call Manager VLAN (VLAN 6). Routing between VLANs is working. A Cisco Call Manager on a Windows 2000 server is also on the switch. Simple pinging works. However, my Cisco 7960 VoIP phones cannot get DHCP info from the Call Manager. The DHCP service is running and configured and is on port 0/1/39 (untagged vlan 6)

Running Wireshark on both the DHCP server port and a VoIP phone port shows DHCP requests from the phone, but they don't appear to be arriving at the server port.

I'm new to Brocade, but have experience with Cisco 3550/3560 L2/L3 switches. I've looked through the lengthy online config document as well as my FNCNE study guide, but can't see what I'm doing wrong. Any help/suggstions would be appreciated. Thanks!

Here's my switch config:

ver 04.3.01T7e1

module 1 fgs-48-port-management-module

!
!
!
!

vlan 1 name DEFAULT-VLAN by port

loop-detection

!

vlan 6 name VoIP by port

tagged ethe 0/1/1 to 1/1/2 ethe 0/1/5 to 0/1/38 ethe 0/1/40

untagged ethe 0/1/39 ethe 0/1/41

uplink-switch ethe 0/1/1 to 0/1/2

!

vlan 40 name VLAN40 by port

tagged ethe 0/1/1 to 0/1/2

uplink-switch ethe 0/1/1 to 0/1/2

!

vlan 42 name VLAN42

tagged ethe 0/1/1 to 0/1/2 ethe 0/1/5 to 0/1/6 ethe 0/1/9 to 0/1/15

uplink-switch ethe 0/1/1 to 0/1/2

!

<snip>  <several more VLANs - all similarly configured>

!
!
!
!
!

hostname SWITCH-POE

ip dhcp snooping vlan 6

ip address 192.168.24.111 255.255.255.0

no ip dhcp-client enable

ip default-gateway 192.168.24.110

cdp run

fdp run

interface ethernet 0/1/5

dual-mode 42

inline power

voice-vlan 6

!

interface ethernet 0/1/6

dual-mode 42

inline power

voice-vlan 6

!

<snip>

interface ethernet 0/1/38

dual-mode 50

inline power

voice-vlan 6

!

interface ethernet 0/1/40

inline power

!

<snip>

!
!
!
!
!
!
end

Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: Problem with DHCP & VoIP on FGX-648P-PoE

Hi Frank,

     Have a read of the below.

BootP/DHCP relay parameters

The following parameters control the Layer 3 Switch’s forwarding of BootP/DHCP requests:

Helper address – The BootP/DHCP server’s IP address. You must configure the helper address on the interface that receives the BootP/DHCP requests from the client. The Layer 3 Switch cannot forward a request to the server unless you configure a helper address for the

server.

Gateway address – The Layer 3 Switch places the IP address of the interface that received the BootP/DHCP request in the request packet’s Gateway Address field (sometimes called the Router ID field). When the server responds to the request, the server sends the response as a unicast packet to the IP address in the Gateway Address field. (If the client and server are directly attached, the Gateway ID field is empty and the server replies to the client using a unicast or broadcast packet, depending on the server.)

By default, the Layer 3 Switch uses the lowest-numbered IP address on the interface that receives the request as the Gateway address. You can override the default by specifying the IP address you want the Layer 3 Switch to use.

From you can see that it is the job of the router to receive and forward requests to the DHCP server.  You will need to configure this on the Cisco sine you are using layer 2 only code on the FGS.

New Contributor
Posts: 2
Registered: ‎07-27-2010

Re: Problem with DHCP & VoIP on FGX-648P-PoE

MsChipp:

Thank you for your help. My understanding is that the IP helper address is only required if the DHCP/BootP server is on a different subnet than the DHCP client. I'll try it.

I discovered that my problem was the use of the "uplink-switch" command, which appears to block broadcasts from going to all the hosts in a subnet and instead sends the broadcast only out the ports defined in the uplink-switch command. Once I removed that command my DHCP server began receiving and responding to DHCP messages. I do have some other issues with my VoIP phones and Call Manager, but I don't think they're related to my Foundry switch.

I do have one small issue, however. I cannot ping the Foundry switch itself, although I can ping through it and I can ping other devices that are on that same subnet (192.168.24.xxx/24, please see config above). Anyone have any thoughts?

Again, thanks for your help. We're getting a mix of Cisco and Foundry devices now, so I think I'll be adding a FNCNE to my bag.

Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: Problem with DHCP & VoIP on FGX-648P-PoE

To configure a designated management VLAN, enter commands such as the following.

FastIron(config)#vlan 10 by port

FastIron(config-vlan-10)#untag ethernet 1/1 to 1/4

FastIron(config-vlan-10)#management-vlan

Thanks

Michael Schipp

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