Default Gateway on a 3750 for IP Phone?

Unanswered Question
Jun 18th, 2007

All, we have 2 locations with 2 differnt IP Scheme. Loc 1 has IP Address 10.7.0.0 for Data and 10.101.0.0 for Voice, Location 2 has IP Address 10.8.0.0 for Data and 10.101.0.0 for Voice. Both locations are sharing the Voice VLAN. Does the switch need to have a default gateway in order for the IP phone to know where the call manager is at to get its ip address?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
mohammedmahmoud Mon, 06/18/2007 - 11:17

Hi,

If this switch is a layer 3 switch, then it can use a default route to the other LAN, but if it is a layer 2 switch then the default gateway is used by the switch itself for remote management and not for routing transit traffic, can you elevate more about your topology.

HTH,

Mohammed Mahmoud.

rwamstutz Mon, 06/18/2007 - 11:34

Mo, thank you for your reply.

The two locations are seperate divisions, but they share the same phone system. Voice VLAN traffic is sent across the Fiber line. Data is sent across the WAN. On each of the 3750's at both facilities, there is a VLAN 230 called VOICE.

So my question, when an 7940 IP phone is connected to the network, how does it know to get its IP Address from the DHCP server on the CCM? Cause since its connected, it looks for a DHCP server, how would it know if it needed to get it from the Data VLAN on the Voice VLAN?

mohammedmahmoud Mon, 06/18/2007 - 11:39

Hi,

You'll need ip helper command on the VLAN SVI interface of the IP Phones on the remote location to be able for the DHCP request to reach the DHCP server on the other end (the CCM).

HTH,

Mohammed Mahmoud.

rwamstutz Mon, 06/18/2007 - 11:49

Wouldnt this command forward all DHCP requests to the CCM box? We only want Phones to get their IP Addresses from the CCM without affecting the PCs.

mohammedmahmoud Mon, 06/18/2007 - 12:01

Hi,

No, since the remote PCs and the remote IP Phones belongs to different VLANs, thus there are 2 SVI interfaces, one for each, and since you are going to apply this command only under the IP Phones SVI interface it will only let the IP phones reach the CCM and not the PCs.

HTH,

Mohammed Mahmoud.

rwamstutz Mon, 06/18/2007 - 12:10

Ok, so you recommend we use:

ip helper-address anything else?

Once I enter this command, can I remove the default-gateway on the switch (the default gateway on the switch, is the Voice vlan Ip address of the switch that is directy connected to the CCM.)

mohammedmahmoud Mon, 06/18/2007 - 12:21

Hi,

Yes, you are right regrading the ip helper command, but as for the default gateway, if you are talking about the "default-gateway" command then it is of no need as long as "ip routing" is enabled on the switch, but you'll need static routing for the Voice IPs over the WAN links on both sides as they are 2 different IP subnets, in order for they to inter-communicate.

HTH,

Mohammed Mahmoud.

Actions

This Discussion