I have a Cisco 871 router at one of my client sites. (they purchased the router from me and I sent them the router with a basic configuration on it). When they connect it after hours clients get the proper IP addresses and dhcp configuration however are unable to access the internet.
We are connecting their ISP supplied router to Gigabitethernet0. They have a static address. I have been through the confiration many times and am thinking I am missing something so simple.
I would remove the commands ip nat enable as they are not necessary in your setup
Have you tried with a PC connected to ISP router, to see if the ISP router attempts to assign an IP address via DHCP?
From the cisco router console can you ping an internet address like 220.127.116.11?
the default static route relies on IP proxy ARP enabled on the ISP router
>>> ip route 0.0.0.0 0.0.0.0 GigabitEthernet0
This is not a good configuration for several reasons.
You should find out what is the IP address of the ISP router and use it as IP next-hop. The main reason is that with this configuraton the ARP table could become really big as it would try to resolve by ARP every destination instead of resolving only the IP next-hop.
Besides this, if IP proxy ARP is disabled on the ISP router your router cannot go anywhere as any ARP request attempt gets no answer from ISP router.
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