I have an 891 router and I am configuring a static default pointing out one of the WAN links. The problem is, specifying a next hop of the wan interface (Fa8 in this case) does not work. However, specifying a next hop of DHCP works perfectly.
ip route 0.0.0.0 0.0.0.0 fastethernet8 (no work)
ip route 0.0.0.0 0.0.0.0 dhcp (works)
Why would this be?
I think the reason for the default route statement with a physical interface not working is that the upstream router is not sending any proxy-arp for the ip addresses you are requesting arp for.
In simple words, If you set up a default route to physical interface and you are trying to reach 220.127.116.11 , your router will look into its routing table and will not find any route for it other than a default route pointing to Fethernet 8, so it will think that 18.104.22.168 is directly connected to it from that interface and will try ARP for 22.214.171.124 , having not recieve anything than from the upstream router ( which is not sending any proxy-arp ) it will just drop it as it will not be able to make a frame for that address 126.96.36.199.
hope i am making any sense here