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New Member

VLAN Problem

I have just Created a new VLAN on a 4507 and I am getting Ip addresses. The problem that I am having is that I can't hit the internet. Any Idea? I am thinking it might have to deal with DNS because DHCP is working fine?

6 REPLIES

Re: VLAN Problem

Hi Zimm,

Are you able to ping any internet ip address like yahoo or some other public ip. If yes that it will be a DNS issue but if not that means you are not able to leave your network even.

So you have to check you routing between new vlan and your internet connection.

If you can explain you topology little bit might be we can help you!!

Regards,

Ankur

Hall of Fame Super Silver

Re: VLAN Problem

Matt

If the VLAN is working so that you have connectivity and if DHCP is working so that PCs connected in the new VLAN are being assigned IP addresses but you can not get to the Internet then there are several things that you should check that might be the problem:

- what default gateway is being assigned to the PCs? (is it the IP address on the VLAN on the 4507)?

- can the PCs in the new VLAN ping their default gateway?

- can PCs on the new VLAN access resources within your organization's network?

- Is it possible that the subnet of the new VLAN is not being advertised so that remote resources do not have a route for response traffic?

- Is it possible that you are doing NAT at the edge of your network connecting to the Internet and the NAT is not recognizing the addresses of the new VLAN as something that should be translated?

HTH

Rick

New Member

Re: VLAN Problem

I am not able to Ping internet ip addresses. I think that it is not being advertised so that remote resources do not have a route for response traffic. How would I go to resolve this issue. Also I am able to hit resources on the inner network just not the internet.

New Member

Re: VLAN Problem

What are you using for a pass through for internet connectivity? A pix or some other type of appliance or something like Microsoft ISA Server? I would check the routing from that device to your new subnet.

Josh

Hall of Fame Super Silver

Re: VLAN Problem

Matt

If you are not able to ping to Internet resources by IP address then it takes any question of being a DNS issue out. In troubleshooting it is good to be able to eliminate some of the possibilities.

I am not clear from your response what is the answer to the question that I asked about whether the PCs on the new VLAN are able to access resources within the organization network. If the PCs are able to access things that are several hops away, it shows that their network is being advertised within the organization network.

So one followup question would be: can the PCs on the new VLAN ping to the device that is the gateway to the Internet for your network?

I believe that there are several possible causes of this problem that we need to investigate:

- it could be a problem of routing within your network. We need to verify whether the PCs can get to the network edge.

- it could be a problem of routing in the Internet. We need to verify if the Internet has routes back to the new VLAN. (Is there any possibility that the addressing on the new VLAN is different from the addressing of the rest of your network?)

- it could be a problem of doing NAT or PAT at the network edge and the new addresses not being properly translated.

If you could provide a few specifics (IP addressing of the new VLAN, IP addressing of the organization network, if NAT/PAT are being done) it might help us to find answers to your problem.

HTH

Rick

New Member

Re: VLAN Problem

Well i figured out the problem and fixed it. It was a PIX issue. It wouldn't let the subnet route out. Thanks for all your helps.

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