1721 Internet Access

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Oct 17th, 2005
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I am trying to setup a network using a Cisco 1721 router and 1924 Switch with two VLANs. I have the 1721 default gateway set to my networks default gateway, and the switch is pointing to the interface of the router on the same VLAN. The problem is that whenever I try to access any internet resources from the router it won't connect. Even trying to send a ping to http://www.google.com won't work.


If from within the router I do a ping http://www.google.com it will connect to my DNS server, and resolve the address. After that I just get five periods telling me that it can't reach the host.


If I try the same ping from within Windows I get a response from the router that the host is unreachable. It seems as if the router isn't sending the packets back out to the internet gateway for some reason. I am only using the built in LAN interface on the router with two subinterfaces defined for the VLAN switching.


Am I missing something here? Any ideas of what my problem might be? Thanks in advance for any help.

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ankurbhasin Mon, 10/17/2005 - 11:36
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Hi erik,


Where do you terminate the internet line? Is it via serial interface if yes do you have a default route pointing to the next hop ip address.


It will be good it you just paste your router "sh run"


Regards,


Ankur

Richard Burts Mon, 10/17/2005 - 11:53
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I am curious about the statement that Eric made:

I have the 1721 default gateway set to my networks default gateway

We need to know whether he meant that he has a default route or did he really mean that he had configured the default-gateway on the router. Configuring a default-gateway is one of the options in configuring the router, but it does not establish a default route in general operation.


default-gateway on the Cisco router is used in situations where the router is acting as an IP host and not as a router. As far as I know there are two situations where the router acts as an IP host rather than as a router. The first is if you have configured "no ip routing" and the second is if you have done a rom boot. Otherwise the default-gateway command does not supply a default route.


So I agree that seeing the show running-config and perhaps a show ip route will be necessary for us to understand and solve the issue here.


HTH


Rick

ComputerErik Mon, 10/17/2005 - 18:00
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Thanks guys, I got it figured out. What Rick said got me checking, and I found that indeed the default-gateway had been set, but that no default route had been set in the routing table. I just added a default route to the table and it now seems to be working fine.


Just FYI this is on a home network with a cable internet connection. The cable connects to a computer acting as a router/firewall, and then to my switch.

Richard Burts Mon, 10/17/2005 - 20:38
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Erik


I am glad that we were able to help you resolve your issue. I find that it is not uncommon to become confused about the relationship between default-gateway and default route. I believe that configuring default-gateway on the router is a good practice (to act as insurance in those few situations where the router may be acting as an IP host rather than acting as a router). But having a default route is much more important than having a default-gateway.


I encourage you to continue your participation in the forums.


HTH


Rick

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