Proxy ARP

息抜き(眠すぎる)にネットに転がるWorkbookとかをやる
Static route (specified only outgoing interface)

Router1#sh arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  8.8.8.8                 0   Incomplete      ARPA
Internet  192.168.12.1            -   5018.0001.0000  ARPA   GigabitEthernet0/0

・めっちゃコンフィグ少なくて、その中にあんまり見慣れないproxy-arpが入ってたらそら気になるよなってことで

Router2#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#int gi0/0
Router(config-if)#ip proxy-arp

Router#sh arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  8.8.8.8                 1   5018.0002.0000  ARPA   GigabitEthernet0/0
Internet  192.168.12.1            -   5018.0001.0000  ARPA   GigabitEthernet0/0

Router#ping 8.8.8.8
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 3/7/13 ms

Adding a static route to an Ethernet or other broadcast interface (for example, ip route 0.0.0.0 0.0.0.0 Ethernet 1/2) will cause the route to be inserted into the routing table only when the interface is up. This configuration is not generally recommended. When the next hop of a static route points to an interface, the router considers each of the hosts within the range of the route to be directly connected through that interface, and therefore it will send Address Resolution Protocol (ARP) requests to any destination addresses that route through the static route.

Chapter: IP Routing Protocol-Independent Commands: A through R

The practical implication of configuring the ip route 0.0.0.0 0.0.0.0 ethernet 1/2 command is that the router will consider all of the destinations that the router does not know how to reach through some other route as directly connected to Ethernet interface 1/2. So the router will send an ARP request for each host for which it receives packets on this network segment. This configuration can cause high processor utilization and a large ARP cache (along with memory allocation failures). Configuring a default route or other static route that directs the router to forward packets for a large range of destinations to a connected broadcast network segment can cause your router to reload.

Chapter: IP Routing Protocol-Independent Commands: A through R

・ネクストホップがある⇒ネクストホップ宛てにARP
・I/Fでのスタティック⇒宛先にARP、つまりProxy ARPで代理応答してくれないとARP解決できない
・引用したCCOには、デフォルトルートをI/Fにするとえげつない量のARPを送信する（なぜなら宛先が0.0.0.0/0だから）のでやめようねってことも書いてる