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learning destination MAC if default route uses interface and not next-hop IP

I have a router with the following configuration:

service password-encryption ! hostname suse_class ! ip subnet-zero ! no ip domain-lookup ! interface FastEthernet0/0 ip address 192.168.100.254 255.255.255.0 no shutdown no ip proxy-arp ip nat inside duplex auto speed auto ! interface FastEthernet1/0 ip address 10.0.0.1 255.255.255.128 ip access-group inboundfilters in ip access-group outboundfilters out no ip proxy-arp ip nat outside no shutdown duplex auto speed auto ! ! ip nat pool suseclass 10.0.0.1 10.0.0.1prefix-length 29 ip nat inside source list 1 pool suseclass overload no ip classless no ip forward-protocol udp tftp no ip forward-protocol udp domain no ip forward-protocol udp time no ip forward-protocol udp tacacs ip route 0.0.0.0 0.0.0.0 FastEthernet1/0 no ip http server ! ! ip access-list extended inboundfilters evaluate traffic ip access-list extended outboundfilters permit tcp any any reflect traffic permit udp any any reflect traffic permit icmp any any reflect traffic access-list 1 permit 192.168.100.0 0.0.0.255 ! line con 0 exec-timeout 0 0 logging synchronous line aux 0 line vty 0 4 login

The question I have is since I used the interface (fa1/0) in my default route statement instead of the next-hop IP address how does this router find out the MAC address for the router on the 10.0.0.0/25 network that my router is forwarding traffic to out of fa1/0?

Reply to
Brad
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10.0.0.0/25 > network that > my router is forwarding traffic to out of fa1/0?

It doesn't. It arps for the destination IP address in the outbount packet and the upstream router responds it it is configured for proxy-arp.

pointing a static to an interface is a BAD idea; you will want to chane it to the next hop IP address ( and clear the routers ARP cache (use shut/no shut if necessary).

Reply to
Merv

Thanks for the reply. That makes sense. If the other router had proxy arp disabled I guess my router would be unable to communicate to the outside world?

I did notice that the arp cache was huge, but besides that why is it such a bad idea?

Reply to
Brad

That is why it is abad idea, that ARP cache has to be scanned continually by the router. Change to use the next IP hop and it you control the next hop router disable proxy arp on it also.

Reply to
Merv

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