diff --git a/README.md b/README.md
index 247c467..b7ca04a 100644
--- a/README.md
+++ b/README.md
@@ -2,9 +2,9 @@
 
 [General description in English ↓](#introduction)
 
-## Oracle 云服务器重装 Debian
+## VPS 网络重装 Debian 10 脚本
 
-**暂不支持 Oracle Linux 作为原系统。创建新机器时请选择 Ubuntu 系统模板。**
+**暂不支持 Oracle Linux 作为原系统。创建新机器时请选择 Ubuntu 20.04 或 18.04 系统模板。**
 
 下载脚本：
 
@@ -15,13 +15,14 @@ curl -fLO https://raw.githubusercontent.com/bohanyang/debi/master/debi.sh && chm
 运行脚本：
 
 ```
-sudo ./debi.sh --cdn --network-console --ethx --bbr --user root --password <这里设置 root 密码>
+sudo ./debi.sh --cdn --network-console --ethx --bbr --user root --password <新系统用户密码>
 ```
-* ❗ **Oracle ARM 架构还需要添加 `--bpo-kernel` 参数，以安装新版 5.10 内核，否则系统可能无法启动**
-* 以上命令选项开启了 BBR；设置了网卡名称形式是 `eth0` 而不是 `ens3` 这种。
-* 不加 `--password` 选项会提示输入密码。
-* （可选）添加 `--cloud-kernel` 参数，以安装空间占用较小的内核，但可能会导致 UEFI 启动的机器（如 Oracle、Azure 及 Hyper-V、Google Cloud 等）VNC 黑屏。BIOS 启动的普通 VPS 则没有此问题。
-* 默认使用 UTC 时区，中国时区请加 `--timezone Asia/Shanghai`
+
+* `--bbr` 开启 BBR
+* `--ethx` 网卡名称使用传统形式，如 `eth0` 而不是 `ens3`
+* `--cloud-kernel` 安装占用空间较小的 `cloud` 内核，但可能会导致 UEFI 启动的机器（如 Oracle、Azure 及 Hyper-V、Google Cloud 等）VNC 黑屏。BIOS 启动的普通 VPS 则没有此问题。
+* 默认时区为 UTC，添加 `--timezone Asia/Shanghai` 可使用中国时区。
+* 默认使用 Debian 官方 CDN 镜像源（deb.debian.org），添加 `--china` 可使用阿里云镜像源。
 
 如果没有报错可以重启：
 
@@ -37,7 +38,7 @@ sudo shutdown -r now
 
 ## Introduction
 
-This script is written to reinstall a VPS/virtual machine to Debian 10 Buster.
+This script is written to reinstall a VPS/virtual machine to minimal Debian 10.
 
 ## Should Work On
 
@@ -103,10 +104,10 @@ Otherwise, you can run this command to revert all changes made by the script:
  * `--dns '8.8.8.8 8.8.4.4'` (Default IPv6 DNS: `2001:4860:4860::8888 2001:4860:4860::8844`)
  * `--hostname <string>` FQDN hostname (includes the domain name), e.g. `server1.example.com`
  * `--network-console` Enable the network console of the installer. `ssh installer@ip` to connect
- * `--version 10` Supports: `9`, `10`, `11`, `stretch`, `buster`, `bullseye`
- * `--suite buster` **For normal cases, please use `--version` instead.** e.g. `stretch`, `buster`, `bullseye`, `sid`, `oldstable`, `stable`, `testing`, `unstable`
+ * `--version 11` Supports: `9`, `10`, `11`, `stretch`, `buster`, `bullseye`
+ * `--suite bullseye` **For normal cases, please use `--version` instead.** e.g. `stretch`, `buster`, `bullseye`, `sid`, `oldstable`, `stable`, `testing`, `unstable`
  * `--release-d-i` d-i (Debian Installer) for the released versions: 10 (buster) and 9 (stretch)
- * `--daily-d-i` Use latest daily build of d-i (Debian Installer) for the unreleased versions: 11 (bullseye) and sid (unstable)
+ * `--daily-d-i` Use latest daily build of d-i (Debian Installer) for the unreleased version: 11 (bullseye), sid (unstable)
  * `--mirror-protocol http` or `https` or `ftp`
  * `--https` alias to `--mirror-protocol https`
  * `--mirror-host deb.debian.org`
diff --git a/debi.sh b/debi.sh
index 99ba4a2..676af1f 100755
--- a/debi.sh
+++ b/debi.sh
@@ -74,19 +74,100 @@ download() {
     fi
 }
 
+set_security_archive() {
+    case $suite in
+        stretch|oldstable|buster|stable)
+            security_archive="$suite/updates"
+            ;;
+        bullseye|testing)
+            security_archive="$suite-security"
+            ;;
+        sid|unstable)
+            security_archive=''
+            ;;
+        *)
+            err "Unsupported suite: $suite"
+    esac
+}
+
+set_daily_d_i() {
+    case $suite in
+        stretch|oldstable|buster|stable)
+            daily_d_i=false
+            ;;
+        bullseye|testing|sid|unstable)
+            daily_d_i=true
+            ;;
+        *)
+            err "Unsupported suite: $suite"
+    esac
+}
+
+set_suite() {
+    suite=$1
+    set_daily_d_i
+    set_security_archive
+}
+
+set_debian_version() {
+    case $1 in
+        9|stretch|oldstable)
+            set_suite stretch
+            ;;
+        10|buster|stable)
+            set_suite buster
+            ;;
+        11|bullseye|testing)
+            set_suite bullseye
+            ;;
+        sid|unstable)
+            set_suite sid
+            ;;
+        *)
+            err "Unsupported version: $1"
+    esac
+}
+
+has_cloud_kernel() {
+    case $suite in
+        stretch|oldstable)
+            [ "$architecture" = amd64 ] && [ "$bpo_kernel" = true ] && return
+            ;;
+        buster|stable)
+            [ "$architecture" = amd64 ] && return
+            [ "$architecture" = arm64 ] && [ "$bpo_kernel" = true ] && return
+            ;;
+        bullseye|testing|sid|unstable)
+            [ "$architecture" = amd64 ] || [ "$architecture" = arm64 ] && return
+    esac
+
+    local tmp; tmp=''; [ "$bpo_kernel" = true ] && tmp='-backports'
+    echo "Warning: No cloud kernel is available for $architecture/$suite$tmp." 1>&2
+    
+    return 1
+}
+
+has_backports() {
+    case $suite in
+        stretch|oldstable|buster|stable|bullseye|testing) return
+    esac
+
+    echo "Warning: No backports kernel is available for $suite." 1>&2
+
+    return 1
+}
+
 ip=
 netmask=
 gateway=
 dns='8.8.8.8 8.8.4.4'
 hostname=
 network_console=false
-suite=buster
-daily_d_i=false
+set_debian_version 10
 mirror_protocol=http
 mirror_host=deb.debian.org
 mirror_directory=/debian
 security_repository=http://security.debian.org/debian-security
-security_archive=buster/updates
 account_setup=true
 username=debian
 password=
@@ -154,42 +235,11 @@ while [ $# -gt 0 ]; do
             network_console=true
             ;;
         --version)
-            case $2 in
-                9|stretch)
-                    suite=stretch
-                    daily_d_i=false
-                    security_archive=stretch/updates
-                    ;;
-                10|buster)
-                    suite=buster
-                    daily_d_i=false
-                    security_archive=buster/updates
-                    ;;
-                11|bullseye)
-                    suite=bullseye
-                    daily_d_i=true
-                    security_archive=bullseye-security
-                    ;;
-                *)
-                    err "Unsupported version: $2"
-            esac
+            set_debian_version "$2"
             shift
             ;;
         --suite)
-            suite=$2
-            case $2 in
-                bullseye|testing)
-                    daily_d_i=true
-                    security_archive="$suite-security"
-                    ;;
-                sid|unstable)
-                    daily_d_i=true
-                    security_archive=''
-                    ;;
-                *)
-                    daily_d_i=false
-                    security_archive="$suite/updates"
-            esac
+            set_suite "$2"
             shift
             ;;
         --release-d-i)
@@ -349,19 +399,8 @@ done
 [ -z "$kernel" ] && {
     kernel="linux-image-$architecture"
 
-    [ "$cloud_kernel" = true ] && {
-        [ "$architecture" != amd64 ] && [ "$architecture" != arm64 ] &&
-        err 'Cloud kernel is only available for amd64 (x86_64) and arm64 (aarch64) architectures'
-
-        kernel="linux-image-cloud-$architecture"
-    }
-
-    [ "$bpo_kernel" = true ] && {
-        [ "$suite" != buster ] && [ "$suite" != stretch ] &&
-        err 'Backports kernel is only available for 10 (buster) and 9 (stretch)'
-
-        install="$kernel/$suite-backports $install"
-    }
+    [ "$cloud_kernel" = true ] && has_cloud_kernel && kernel="linux-image-cloud-$architecture"
+    [ "$bpo_kernel" = true ] && has_backports && install="$kernel/$suite-backports $install"
 }
 
 [ -n "$authorized_keys_url" ] && ! download "$authorized_keys_url" /dev/null &&