Hi Ondrej,
I am sorry for replying lately.
The primary problem I see with your configuration is the way you have configured your default route. You have basically pointed out the Vlan3 interface, without telling the router who the next hop is. This way of configuring default routes (or any static route in general) works fine only with point-to-point interfaces, such as PPP links or similar connections. However, it may not work properly with multi-access interfaces such as Ethernet where there can be multiple routers reachable over that interface. The router now assumes that the entire internet is directly connected to your Vlan3 interface (just have a look at your show ip route output - it will tell you that the 0.0.0.0/0 is directly connected), and acts accordingly: It simply tries to ARP for every packet's destination, just the way it would do with any destination in a directly connected network. Obviously, the entire internet is not directly connected to your Vlan3 interface, so the destinations do not hear your router's ARP requests, and that is why the internet connection may fail. Sometimes it may work because the upstream router at the ISP may have its Proxy ARP function turned on - the Proxy ARP function allows a router to answer ARP queries looking for any address to which the router knows a route. However, it is a best practice to have Proxy ARP deactivated, and it seems that your provider has done just that. Even if the Proxy ARP was active at your ISP's router, relying on it would create huge ARP traffic, sloppy performance, excessively large ARP tables and in worst cases, memory exhaustion on your router and intermittent reloads.
To sum it up shortly: Whenever defining a static route out an Ethernet or any other multi-access interface, always use the next hop IP address if possible, and avoid creating static routes defined using egress interfaces only.
This issue has been discussed many times on this forum but it keeps popping again and again so that's why I am so outspoken about this :)
This is the set of commands I recommend pasting into your configuration that will correct the configuration:
no ip default-gateway
no ip route 0.0.0.0 0.0.0.0 Vlan3
ip route 0.0.0.0 0.0.0.0 192.168.0.1
I see you have used the ip default-gateway command. This command can be quite confusing. The fact is that this command has an effect only if the device has IP routing deactivated - in other words, if the device does not operate as an IP router and does not have a routing table. On routers, this command is practically useless because you want your routers to do IP routing so you almost never turn off the IP routing function on them. So while you have configured it, your router ignores it because its routing is still active and it uses its routing table to direct packets. That is why I am removing this command along with the incorrect static default route, and I am replacing it with an explicit default route directed to 192.168.0.1. Please try out these commands.
Just to complete the thought, the ip default-gateway would be used on switches that do not perform routing - for these, this is the only way of defining a default gateway, as they do not have a routing table.
If these modifications do not work then I will need further diagnostic output from your router - the full outputs of the following commands:
show ip route
show ip interface brief
ping 192.168.0.150
ping 192.168.0.1
Thanks!
Best regards,
Peter
