What is your favourite "hack" in networking?

I will list some hre:

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- /31 masks

- On Cisco routers, change SSH using NAT as per example below:

interface loopback 1

ip address 169.254.255.255 255.255.255.255

ip nat inside

interface Gi0/0

desc [outside interface]

ip address a.b.c.d 255.255.255.y

ip nat outside

ip nat inside source static tcp 169.254.255.255 22 interface Gi0/0 54321

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