A new Automatic Teller Machine (ATM) switch (IBAHN) is introduced to the Head office LAN where all braches are connected. The new ATM switch consists of 56 virtual interfaces and each virtual interface represents an ATM to AS 400 system by ATM switch. We have experienced that the number of ATM increases, the corresponding MAC address of the ATM switch for its interfaces including primary interface is assigned with router MAC address ( 172.17.1.2 pls refer attached diaram) gradually resulting all packets destined to ATM switch terminated at the router interface.
Also we have tried with deleting arp cache but it still assigned the router fast Ethernet MAC address for ATM switch. Therefore ATM switch did not get the AS 400 response and ATM switch keep on sending the SYN packets. We have monitored the arp broadcast and it only ask from several interfaces the rest of the MAC address is already determine incorrectly by the router ( Assigned router MAC address again)
From this arp on snoibndr output it follows that it's actually not the router, but host 00:13:D4:83:D6:3B. MAC range starting from 00:13:D4 is not Cisco range, but ASUSTEK. Since you say all this addresses belong to your "iBAHN" system, there's no problem here.
The problem is actually different: you use 'ip unnumbered FastEthernet 0/0' on your serial interfaces. As soon as you have serial link up, your router now has two interfaces belonging to the same 192.168.12.204/28 subnet. This is not valid configuration. You need to either use different subnets or enable bridging. Each has advantages and disadvatnages, but generally routing using different subnets would be easier to support.
If router claims IP addresses that belong to other systems (that is router responds with its own MAC address to ARP requests about IP of other systems), then it's proxy-arp at work. Proxy-arp may be good or bad thing depending on your topology, addressing scheme, routing, NAT, firewall rules.
Could you please ammend your diagram with IP addresses and mask of each involved system and interface? Also, could you please post 'sh arp' from the router and 'sh run int ' and for interfaces e0, e1 and WAN interface from it?
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