@thrig has the right answer based on your desire to do this solely within .ssh/config
One might also consider using a function with defaults to make other tunnel commands quick (especially if the tunnel does not change but only the host).
sshn() {
# set your desired host and port forwarding as default
# and allow them to be passed in if you should need it
host="${1:-devdb}"
port="${2:-1234:127.0.0.1:1234}"
# now all you have to do is `sshn` and it will connect
echo "executing ssh -N $host -L $port"
ssh -N "$host" -L "$port"
}
Here are three examples of it in use:
with no args the defaults specified in the function are used:
$ sshn
executing -N devdb -L 1234:127.0.0.1:1234
with tunnel default, run on a different host:
$ sshn host2
executing ssh -N host2 -L 1234:127.0.0.1:1234
with both defaults, run a full one-off to a new host/tunnel:
$ sshn host3 12345:127.0.0.1:12345
executing ssh -N host3 -L 12345:127.0.0.1:12345