diff --git a/geofw/src/main.rs b/geofw/src/main.rs
index 65cbf02..3a2d795 100644
--- a/geofw/src/main.rs
+++ b/geofw/src/main.rs
@@ -1,3 +1,5 @@
+mod maxmind;
+
 use anyhow::Context as _;
 use aya::{
     maps::{Queue, RingBuf},
@@ -6,12 +8,7 @@ use aya::{
 use clap::Parser;
 use log::{debug, warn};
 use maxminddb::geoip2;
-use std::{
-    fs::File,
-    io::Write,
-    net::{IpAddr, Ipv4Addr, Ipv6Addr},
-    os::{fd::AsRawFd, unix::io::FromRawFd},
-};
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
 use tokio::signal;
 
 #[derive(Debug, Parser)]
@@ -22,6 +19,11 @@ struct Opt {
 
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
+    let maxmind_db = maxmind::MaxmindDB::new("./geofw/GeoLite2-City.mmdb");
+    println!("{:?}", maxmind_db);
+    maxmind_db.read_binary_search_tree();
+    return Ok(());
+
     let opt = Opt::parse();
 
     env_logger::init();
@@ -93,7 +95,7 @@ async fn main() -> anyhow::Result<()> {
                 response
                     .push(result as u8, 0)
                     .expect("error in writing result to queue");
-                println!("wrote {} for {:?}", result, addr);
+                // println!("wrote {} for {:?}", result, addr);
             }
         }
     });
diff --git a/geofw/src/maxmind.rs b/geofw/src/maxmind.rs
new file mode 100644
index 0000000..e5ca2b7
--- /dev/null
+++ b/geofw/src/maxmind.rs
@@ -0,0 +1,310 @@
+use std::{
+    cmp::Ordering,
+    collections::HashMap,
+    fmt::{Debug, Formatter, Result as FmtResult},
+    fs::File,
+    io::Read,
+    net::Ipv4Addr,
+};
+
+const METADATA_SECTION_START: &[u8] = &[
+    0xab, 0xcd, 0xef, 0x4d, 0x61, 0x78, 0x4d, 0x69, 0x6e, 0x64, 0x2e, 0x63, 0x6f, 0x6d,
+];
+
+pub struct MaxmindDB {
+    metadata: Metadata,
+    data: Vec<u8>,
+}
+
+#[derive(Debug, Default)]
+struct Metadata {
+    node_count: u32,
+    record_size: u16,
+    binary_tree_section_start: usize,
+    data_section_start: usize,
+    metadata_section_start: usize,
+}
+
+#[derive(Debug, PartialEq, Clone)]
+enum Data {
+    String(String),
+    Double(f64),
+    Bytes(Vec<u8>),
+    U16(u16),
+    U32(u32),
+    Map(HashMap<String, Data>),
+    I32(i32),
+    U64(u64),
+    U128(u128),
+    Array(Vec<Data>),
+    DataCache,
+    End,
+    Boolean(bool),
+    Float(f32),
+}
+
+impl Debug for MaxmindDB {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
+        f.write_fmt(format_args!("{:?}", self.metadata))
+    }
+}
+
+impl MaxmindDB {
+    pub fn new(path: &str) -> Self {
+        let mut data = vec![];
+        {
+            let mut file = File::open(path).expect("error in opening file");
+            file.read_to_end(&mut data)
+                .expect("error in reading contents of file");
+        }
+
+        let position = data
+            .windows(METADATA_SECTION_START.len())
+            .rev()
+            .position(|x| x == METADATA_SECTION_START)
+            .unwrap();
+        let metadata_start = data.len() - position;
+        let mut db = Self {
+            metadata: Metadata::default(),
+            data: data.to_vec(), // TODO: Change this ?
+        };
+
+        let m = db.read_metadata(metadata_start);
+        println!("metadata = {:?}", m);
+        let Data::U16(record_size) = *m.get("record_size").unwrap() else {
+            unreachable!()
+        };
+        let Data::U32(node_count) = *m.get("node_count").unwrap() else {
+            unreachable!()
+        };
+        db.metadata = Metadata {
+            binary_tree_section_start: 0,
+            data_section_start: ((record_size as usize * 2) / 8) * node_count as usize + 16,
+            metadata_section_start: metadata_start,
+            record_size,
+            node_count,
+        };
+
+        db
+    }
+
+    fn read_metadata(&self, metadata_start: usize) -> HashMap<String, Data> {
+        let (Data::Map(map), _) = self.read_data(metadata_start) else {
+            unreachable!()
+        };
+        map
+    }
+
+    pub fn read_binary_search_tree(&self) {
+        // Only support 28bit format for now
+        assert_eq!(self.metadata.record_size, 28);
+
+        let node_size = self.metadata.record_size as usize * 2 / 8;
+        let mut node = 96;
+        let mut ip = Ipv4Addr::new(139, 84, 164, 110).to_bits();
+
+        let mut i = 0;
+        while i < 32 && node < self.metadata.node_count {
+            let bit = ip & 0x80000000;
+            ip <<= 1;
+
+            let n = &self.data[node as usize * node_size..(node as usize * node_size) + node_size];
+            node = if bit == 0 {
+                u32::from_be_bytes([n[3] & 0b1111_0000, n[0], n[1], n[2]])
+            } else {
+                u32::from_be_bytes([n[3] & 0b0000_1111, n[4], n[5], n[6]])
+            };
+
+            i += 1;
+        }
+
+        if node == self.metadata.node_count {
+            println!("not found!");
+        } else {
+            let data_section_offset = node - self.metadata.node_count;
+            let data = self
+                .read_data(self.metadata.data_section_start + data_section_offset as usize - 16);
+
+            println!("{:?}", data);
+        }
+    }
+
+    fn read_data(&self, read_offset: usize) -> (Data, usize) {
+        // println!("read offset: {}", read_offset);
+        let data = &self.data[read_offset..];
+        let (data_type, length, read) = Self::read_data_meta(data);
+
+        // println!("{} {} {}", data_type, length, read);
+
+        match data_type {
+            1 => {
+                // println!("read = {:?}", read + read_offset);
+                // let data = &data[read..];
+                let s = (data[0] >> 3) & 0x3;
+                let v = data[0] & 0b0000_0111;
+
+                let pointer = match s {
+                    0 => u32::from_be_bytes([0, 0, v, data[1]]),
+                    1 => u32::from_be_bytes([0, v, data[1], data[2]]) + 2048,
+                    2 => u32::from_be_bytes([v, data[1], data[2], data[3]]) + 526336,
+                    3 => u32::from_be_bytes([data[1], data[2], data[3], data[4]]),
+                    _ => unreachable!(),
+                };
+
+                let (data, _) = self.read_data(self.metadata.data_section_start + pointer as usize);
+                (data, s as usize + 1 + 1)
+            }
+            2 => {
+                let value = &data[read..read + length];
+
+                (
+                    Data::String(String::from_utf8_lossy(value).to_string()),
+                    read + length,
+                )
+            }
+            3 => {
+                assert_eq!(length, 8);
+                let s = &data[read..read + length];
+                let num = f64::from_be_bytes([s[0], s[1], s[2], s[3], s[4], s[5], s[6], s[7]]);
+
+                (Data::Double(num), read + length)
+            }
+            4 => {
+                todo!("reached data field???");
+            }
+            5 => {
+                let slice = &data[read..read + length];
+                let number = match *slice {
+                    [] => 0,
+                    [a] => a as u16,
+                    [a, b] => (a as u16) << 8 | b as u16,
+                    _ => unreachable!(),
+                };
+
+                (Data::U16(number), read + length)
+            }
+            6 => {
+                let slice = &data[read..read + length];
+                let number = match *slice {
+                    [] => 0,
+                    [a] => a as u32,
+                    [a, b] => (a as u32) << 8 | b as u32,
+                    [a, b, c] => (a as u32) << 16 | (b as u32) << 8 | c as u32,
+                    [a, b, c, d] => {
+                        (a as u32) << 24 | (b as u32) << 16 | (c as u32) << 8 | d as u32
+                    }
+                    _ => unreachable!(),
+                };
+
+                (Data::U32(number), read + length)
+            }
+            7 => {
+                let mut map = HashMap::with_capacity(length);
+                // length is number of elements
+                let mut length = length;
+                let mut read = read;
+
+                while length > 0 {
+                    let (key, r) = self.read_data(read_offset + read);
+                    read += r;
+                    let (value, r) = self.read_data(read_offset + read);
+                    read += r;
+
+                    let Data::String(key) = key else {
+                        unreachable!()
+                    };
+
+                    map.insert(key, value);
+                    length -= 1;
+                }
+
+                (Data::Map(map), read)
+            }
+            8 => {
+                let slice = &data[read..read + length];
+                let number = match *slice {
+                    [] => 0,
+                    [a] => a as i32,
+                    [a, b] => (a as i32) << 8 | b as i32,
+                    [a, b, c] => (a as i32) << 16 | (b as i32) << 8 | c as i32,
+                    [a, b, c, d] => {
+                        (a as i32) << 24 | (b as i32) << 16 | (c as i32) << 8 | d as i32
+                    }
+                    _ => unreachable!(),
+                };
+
+                (Data::I32(number), read + length)
+            }
+            9 => {
+                let slice = &data[read..read + length];
+                let number = slice.iter().enumerate().fold(0, |acc, (i, &byte)| {
+                    acc | ((byte as u64) << (8 * (slice.len() - i - 1)))
+                });
+
+                (Data::U64(number), read + length)
+            }
+            10 => {
+                let slice = &data[read..read + length];
+                let number = slice.iter().enumerate().fold(0, |acc, (i, &byte)| {
+                    acc | ((byte as u128) << (8 * (slice.len() - i - 1)))
+                });
+
+                (Data::U128(number), read + length)
+            }
+            11 => {
+                let mut read = read;
+                let mut out = vec![];
+                let mut length = length;
+
+                while length > 0 {
+                    let (value, r) = self.read_data(read_offset + read);
+                    read += r;
+                    length -= 1;
+                    out.push(value);
+                }
+
+                (Data::Array(out), read)
+            }
+            12 => {
+                todo!("reached data cache container");
+            }
+            13 => (Data::End, read_offset),
+            14 => {
+                todo!("reached boolean");
+            }
+            15 => {
+                assert_eq!(length, 4);
+                let s = &data[read..read + length];
+                let num = f32::from_be_bytes([s[0], s[1], s[2], s[3]]);
+
+                (Data::Float(num), read + length)
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    fn read_data_meta(data: &[u8]) -> (u8, usize, usize) {
+        let mut read = 0;
+        let data_type = if data[0] >> 5 == 0 {
+            read += 1;
+            data[1] + 7
+        } else {
+            data[0] >> 5
+        };
+
+        let length = data[0] & 0b000_11111;
+
+        let (length, r) = match length {
+            0..29 => (length as usize, 1),
+            29 => (29 + data[1] as usize, 2),
+            30 => (285 + data[1] as usize + data[2] as usize, 3),
+            31 => (
+                65821 + data[1] as usize + data[2] as usize + data[3] as usize,
+                4,
+            ),
+            _ => unreachable!(),
+        };
+
+        (data_type, length, read + r)
+    }
+}
diff --git a/run.sh b/run.sh
index eaf29a5..6077259 100755
--- a/run.sh
+++ b/run.sh
@@ -3,4 +3,6 @@
 set -e
 set -o pipefail
 
-RUST_LOG=info cargo run --config 'target."cfg(all())".runner="sudo -E"'
+RUST_LOG=info cargo run
+
+# RUST_LOG=info cargo run --config 'target."cfg(all())".runner="sudo -E"'