1- Where your example says ipv3, it should probably read ipv4.
2- Here's one other way to accomplish this without using sudo -s:
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward
Now, the explanation for this problem is as follows. The original command has this structure:
$ sudo echo 1 > /proc/sys/net/ipv4/ip_forward
^^^ Part 1 ^^ ^^^^ Part 2 ^^^^
Part 1 runs as sudo, BUT you're then trying to redirect output to a file. The redirection itself "runs" as an unprivileged user, that's why it has no permission to write to the file.
The solution I propose does the "echo" as an unprivileged user, but then pipes that to the "tee" command, which we run through sudo. Thus, tee will be run as root and will be able to write to the file.
Tee basically takes standard input and writes it to both a file and stdout. This is commonly used to write to a file while also getting the output on-screen. If you want to know more about tee, check the man page.