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[–]_chrisjhartCCNA R&S 7 points8 points  (4 children)

Using the interface as the next-hop address in a static route is not considered to be a best practice because your device will attempt to ARP for every IP address that is to be routed for that interface.

For example, if I configure ip route 192.168.0.0 0.0.0.255 Gi0/1, then my device forwards a packet for 192.168.0.10. The device will ARP for the owner of 192.168.0.10. If it needs to forward a packet for 192.168.0.15, it will also ARP for that. This is perfectly normal behavior if the 192.168.0.0/24 network is directly connected to Gi0/1 - however, if Gi0/1 is a point-to-point link between two routers, and 192.168.0.0/24 is actually directly connected to another interface on the opposite router, then we're needlessly ARPing for a wide range of IP addresses when all of them need to be forwarded to only a single IP.

This problem gets much, much worse with default static routes, especially when connected to the internet. If I configure ip route 0.0.0.0 0.0.0.0 Gi0/1, then my device will ARP for every single unknown IP address out of my Gi0/1 WAN interface and store the results in the ARP cache. In even the smallest networks, this can result in a massively-bloated ARP cache and cause delays on the router's data plane, increasing the amount of time it takes for the router to forward a packet.

Let me know if you have more questions!

[–]tolegittoshit2A+/N+/CCNA 0 points1 point  (0 children)

nice break down there sir.

[–]a_cute_epic_axisJust 'cause it ain't in my flair doesn't mean I don't have certs 0 points1 point  (0 children)

Also this will fail if you're trying to go more than one hop away and proxy-arp isn't enabled.

[–]karjune01A+, Network+[S] 0 points1 point  (1 child)

Thanks for the very detailed response. Keith was indeed talking about ARP for the network on the connected line.

[–]_chrisjhartCCNA R&S 1 point2 points  (0 children)

You're welcome!