Figure 311 TCP Session Disconnect

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Summafy pane-

Frame 132 starts the TCP disconnect with the FIN flag from the router. Hosta ACKs in frame 133 and says, "Hey, I am a l so fin i shed ," in frame 134 (FIN). The routdr gives the fina I ACK in the last frame. A 4-w ay d^conn ect like this is common.

Next I want yo a to thnnk outsi de the box a little. Wlcat wou Id have happened if the default gateway was not configured on the host or if the router was not local in the preceding testing? You can give me the number oae phrase that most support pe ople g i ve, wR ch is , itelepends; as usual, however, I'll crinde at th at answer. In many cases, however, that is the best answer. Actually, the packets may still get to their destination assuming proxyARP is enabled on the router and thyt hosta wil! ARP fo a nonlocal destin ations.

Proxy ARP helps hosts reach remote subnets without configuring routing or a default gateway. Configuring the host with a emaller sub^o mask would make the host ARP for everything and thus send all packets via the router. The router just replies to the host with its MAC address assuming that it is configured to accept and respond to proxy ARP. Obviously, there are security and ovefhead disa dvantages to proxy ARP. The Cisco !OS intetface co mmRnd no ip proxy-arp turns this off1 and is shown in Example 3-28.

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