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feat: rebase static IP on gateway change

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Codex
2026-06-28 20:56:20 +08:00
parent b0a397a16b
commit da1cf3c9e7
3 changed files with 227 additions and 1 deletions
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220
watchdog/network-watchdog.sh
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@@ -3,6 +3,8 @@
# Network watchdog for the CUPS print server.
# Default behavior: when connectivity checks fail repeatedly, switch the
# configured interface back to DHCP so the box can regain network access.
# If DHCP reveals a different gateway, the script can rebuild the static IP
# with the new network prefix while keeping the old host octet.
#
# Edit /etc/cups-watchdog/network-watchdog.conf to set STATIC_IP,
# STATIC_PREFIX, STATIC_GATEWAY and STATIC_DNS. You can also run:
@@ -20,9 +22,12 @@ STATIC_IP=""
STATIC_PREFIX="24"
STATIC_GATEWAY=""
STATIC_DNS="114.114.114.114 223.5.5.5"
STATIC_HOST_OCTET=""
PING_TARGETS="223.5.5.5 114.114.114.114"
FAIL_THRESHOLD=3
DHCP_AFTER_FAILURE=1
REBASE_STATIC_ON_GATEWAY_CHANGE=1
REBASE_WAIT_SECONDS=20
LOG_FILE="/var/log/cups-watchdog/network.log"
MAX_LOG_SIZE_KB=256
@@ -71,6 +76,56 @@ detect_interface() {
ip route show default 2>/dev/null | awk '{print $5; exit}'
}
current_ipv4_for_interface() {
local iface="$1"
ip -4 -o addr show dev "$iface" scope global 2>/dev/null | awk '{split($4, a, "/"); print a[1]; exit}'
}
current_prefix_for_interface() {
local iface="$1"
ip -4 -o addr show dev "$iface" scope global 2>/dev/null | awk '{split($4, a, "/"); print a[2]; exit}'
}
current_gateway_for_interface() {
local iface="$1"
local gateway
gateway="$(ip route show default dev "$iface" 2>/dev/null | awk '{print $3; exit}')"
if [ -z "$gateway" ]; then
gateway="$(ip route show default 2>/dev/null | awk '{print $3; exit}')"
fi
echo "$gateway"
}
last_octet() {
local ip="$1"
case "$ip" in
*.*.*.*) echo "${ip##*.}" ;;
*) echo "" ;;
esac
}
prefix24() {
local ip="$1"
case "$ip" in
*.*.*.*) echo "${ip%.*}" ;;
*) echo "" ;;
esac
}
valid_host_octet() {
local octet="$1"
case "$octet" in
''|*[!0-9]*) return 1 ;;
esac
[ "$octet" -ge 1 ] 2>/dev/null && [ "$octet" -le 254 ] 2>/dev/null
}
nm_connection_for_interface() {
local iface="$1"
nmcli -t -f NAME,DEVICE con show --active 2>/dev/null | awk -F: -v iface="$iface" '$2 == iface {print $1; exit}'
@@ -141,6 +196,70 @@ configure_dhcp() {
fi
}
set_config_value() {
local key="$1"
local value="$2"
local tmp_file
if [ ! -f "$CONFIG_FILE" ]; then
mkdir -p "$(dirname "$CONFIG_FILE")" 2>/dev/null || true
: > "$CONFIG_FILE" 2>/dev/null || return 1
fi
tmp_file="${CONFIG_FILE}.tmp.$$"
if grep -q "^${key}=" "$CONFIG_FILE" 2>/dev/null; then
awk -v key="$key" -v value="$value" '
BEGIN { q = sprintf("%c", 34) }
$0 ~ "^" key "=" { print key "=" q value q; next }
{ print }
' "$CONFIG_FILE" > "$tmp_file" && mv "$tmp_file" "$CONFIG_FILE"
else
printf '%s="%s"\n' "$key" "$value" >> "$CONFIG_FILE"
fi
chmod 600 "$CONFIG_FILE" 2>/dev/null || true
}
wait_for_dhcp_network() {
local iface="$1"
local i=0
local ip
local gateway
while [ "$i" -lt "${REBASE_WAIT_SECONDS:-20}" ]; do
ip="$(current_ipv4_for_interface "$iface")"
gateway="$(current_gateway_for_interface "$iface")"
if [ -n "$ip" ] && [ -n "$gateway" ]; then
echo "$ip $gateway"
return 0
fi
i=$((i + 1))
sleep 1
done
return 1
}
candidate_ip_in_use() {
local iface="$1"
local candidate_ip="$2"
local current_ip="$3"
[ "$candidate_ip" = "$current_ip" ] && return 1
if command -v arping >/dev/null 2>&1; then
# arping duplicate-address detection returns success when no reply is seen.
arping -D -I "$iface" -c 2 -w 3 "$candidate_ip" >/dev/null 2>&1
[ "$?" != "0" ] && return 0
return 1
fi
if ping -c 1 -W 1 "$candidate_ip" >/dev/null 2>&1; then
return 0
fi
return 1
}
configure_static_nmcli() {
local iface="$1"
local conn
@@ -243,6 +362,105 @@ configure_static() {
fi
}
rebase_static_after_dhcp() {
local iface="$1"
local dhcp_state
local dhcp_ip
local dhcp_gateway
local dhcp_prefix
local host_octet
local base_prefix
local candidate_ip
local old_static_ip="$STATIC_IP"
local old_static_gateway="$STATIC_GATEWAY"
local old_static_prefix="$STATIC_PREFIX"
local old_static_dns="$STATIC_DNS"
local current_dns
[ "${REBASE_STATIC_ON_GATEWAY_CHANGE:-1}" = "1" ] || return 0
if [ -z "${STATIC_IP:-}" ] || [ -z "${STATIC_GATEWAY:-}" ]; then
log_msg "skip static rebase: STATIC_IP or STATIC_GATEWAY is empty"
return 0
fi
dhcp_state="$(wait_for_dhcp_network "$iface" 2>/dev/null || true)"
if [ -z "$dhcp_state" ]; then
log_msg "skip static rebase: DHCP did not provide an IP and gateway in time"
return 0
fi
dhcp_ip="$(echo "$dhcp_state" | awk '{print $1}')"
dhcp_gateway="$(echo "$dhcp_state" | awk '{print $2}')"
if [ "$dhcp_gateway" = "$STATIC_GATEWAY" ]; then
log_msg "DHCP gateway is still $dhcp_gateway; keep DHCP recovery without rebasing static IP"
return 0
fi
host_octet="${STATIC_HOST_OCTET:-$(last_octet "$STATIC_IP")}"
if ! valid_host_octet "$host_octet"; then
log_msg "skip static rebase: invalid STATIC_HOST_OCTET '$host_octet'"
return 0
fi
base_prefix="$(prefix24 "$dhcp_ip")"
[ -n "$base_prefix" ] || base_prefix="$(prefix24 "$dhcp_gateway")"
if [ -z "$base_prefix" ]; then
log_msg "skip static rebase: cannot derive IPv4 /24 prefix from DHCP state"
return 0
fi
candidate_ip="${base_prefix}.${host_octet}"
if candidate_ip_in_use "$iface" "$candidate_ip" "$dhcp_ip"; then
log_msg "skip static rebase: candidate $candidate_ip appears to be in use; staying on DHCP"
return 0
fi
dhcp_prefix="$(current_prefix_for_interface "$iface")"
STATIC_IP="$candidate_ip"
STATIC_GATEWAY="$dhcp_gateway"
STATIC_PREFIX="${dhcp_prefix:-$STATIC_PREFIX}"
current_dns="$(grep -E '^nameserver ' /etc/resolv.conf 2>/dev/null | awk '{print $2}' | head -n2 | tr '\n' ' ')"
STATIC_DNS="${current_dns:-$STATIC_DNS}"
log_msg "gateway changed from $old_static_gateway to $STATIC_GATEWAY; rebasing static IP from $old_static_ip to $STATIC_IP/$STATIC_PREFIX"
configure_static
sleep 3
if connectivity_ok; then
set_config_value "STATIC_IP" "$STATIC_IP" || true
set_config_value "STATIC_GATEWAY" "$STATIC_GATEWAY" || true
set_config_value "STATIC_PREFIX" "$STATIC_PREFIX" || true
set_config_value "STATIC_DNS" "$STATIC_DNS" || true
set_config_value "STATIC_HOST_OCTET" "$host_octet" || true
set_config_value "PING_TARGETS" "$STATIC_GATEWAY 223.5.5.5 114.114.114.114" || true
log_msg "static rebase succeeded: $STATIC_IP via $STATIC_GATEWAY"
return 0
fi
STATIC_IP="$old_static_ip"
STATIC_GATEWAY="$old_static_gateway"
STATIC_PREFIX="$old_static_prefix"
STATIC_DNS="$old_static_dns"
log_msg "static rebase to $candidate_ip failed connectivity check; falling back to DHCP"
configure_dhcp
}
recover_after_failure() {
local iface
local fallback_iface
fallback_iface="$(detect_interface)"
configure_dhcp || return 1
iface="$(detect_interface)"
[ -n "$iface" ] || iface="$fallback_iface"
if [ -z "$iface" ]; then
log_msg "skip static rebase: network interface not found after DHCP recovery"
return 1
fi
rebase_static_after_dhcp "$iface"
}
connectivity_ok() {
local iface
local gateway
@@ -288,7 +506,7 @@ check_network() {
log_msg "connectivity failed ($fail_count/$FAIL_THRESHOLD)"
if [ "$fail_count" -ge "$FAIL_THRESHOLD" ] && [ "$DHCP_AFTER_FAILURE" = "1" ]; then
configure_dhcp
recover_after_failure
echo 0 > "$count_file"
fi
}