Fix macOS corrupted routing table

macos-network-flush-routing-table.sh

#!/usr/bin/env bash
#
# ## The Problem
#
#    Can't assign requested address
#
# It occurs when macOS's TCP stack routing table has become corrupted.
#
# ## Reproducing
#
# I have experienced this issue frequently when using Surge or ClashX:
#
# * changing networks while having the Enhanced Mode enabled.
# * putting the device to sleep and waking it up to a different network.
#
# Related problems:
#
# * https://discussions.apple.com/thread/3792069
# * http://codefromabove.com/quickies/osx-cant-assign-requested-address-code49/
# * https://www.expressvpn.com/support/troubleshooting/log-items/unable-to-connect-cant-assign-requested-address-code49/
#
# ## The Solution
#
# To fix it, the routing table should be flushed. There are two
# available methods:
#
# * reboot - seems stupid, because I have to reopen all the existing
#   applications and documents.
# * use this script - preferred.
#

PATH=/bin:/sbin

# This is the outbound interface to Internet.
# Use ifconfig -L to figure out which interface corresponds to WiFi/Ethernet:
#
# * en0 is Ethernet, typically.
# * en0 is WiFi on MacBook without hardware Ethernet.
#
INTERFACE=en0

echo "taking $INTERFACE down..."
ifconfig "$INTERFACE" down
sleep 2

echo "flushing the routing table..."
route -n flush
sleep 2

echo "taking $INTERFACE up..."
ifconfig "$INTERFACE" up