Many macOS users of Juniper's Network Connect VPN client encounter this frustrating scenario: after an abrupt VPN disconnection (due to network drops, system sleep, or crashes), the network interface becomes unresponsive with errors like:

ping: sendto: Cannot allocate memory
ifconfig en0 down/up commands fail to restore connectivity

The manual IPv4 toggle works because it forces the network stack to:

• Release all DHCP leases and IP assignments
• Clear kernel-level networking buffers
• Reinitialize TCP/IP stack components

Here's the equivalent command sequence for the GUI reset process:

# Disable IPv4
networksetup -setv4off "Wi-Fi"

# Verify interface state
ifconfig en0 | grep "status:"

# Re-enable DHCP (or your preferred config)
networksetup -setdhcp "Wi-Fi"

# Alternative for manual config:
# networksetup -setmanual "Wi-Fi" 192.168.1.100 255.255.255.0 192.168.1.1

Save this as vpnreset.sh:

#!/bin/bash

INTERFACE="Wi-Fi"
LOG="/tmp/vpnreset.log"

echo "$(date) - Resetting $INTERFACE" >> $LOG

# Capture pre-state
ifconfig en0 >> $LOG 2>&1
networksetup -getinfo "$INTERFACE" >> $LOG 2>&1

# Reset sequence
networksetup -setv4off "$INTERFACE" >> $LOG 2>&1
sleep 2
networksetup -setdhcp "$INTERFACE" >> $LOG 2>&1

# Verify restoration
ping -c 2 8.8.8.8 >> $LOG 2>&1
echo "$(date) - Reset complete. Ping exit code: $?" >> $LOG

For stubborn cases, add these commands before the networksetup calls:

# Flush DNS
dscacheutil -flushcache

# Remove all routes
route -n flush

# Reset firewall (may require sudo)
pfctl -F all

Create ~/Library/LaunchAgents/local.vpnreset.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>local.vpnreset</string>
    <key>ProgramArguments</key>
    <array>
        <string>/bin/bash</string>
        <string>-c</string>
        <string>/path/to/vpnreset.sh</string>
    </array>
    <key>WatchPaths</key>
    <array>
        <string>/var/run/pppconfd</string>
    </array>
</dict>
</plist>

Load with launchctl load ~/Library/LaunchAgents/local.vpnreset.plist

To simulate VPN crashes for testing:

# Force kill VPN process
pkill -9 ncui

# Or simulate network drop
sudo ifconfig en0 down
sleep 5
sudo ifconfig en0 up

---

When Juniper Networks' VPN client terminates unexpectedly (due to WiFi drops, system sleep, or forced closure), it often leaves macOS network interfaces in a corrupted state where basic networking commands fail with memory allocation errors:

$ ping google.com
ping: sendto: Cannot allocate memory

Standard interface resets prove ineffective:

$ sudo ifconfig en0 down
$ sudo ifconfig en0 up
# Still broken

$ sudo route -n flush
# No improvement

Even DNS cache flushing (though unrelated) fails to resolve the core issue.

The only reliable solution involves manually toggling IPv4 settings through System Preferences, which is cumbersome for developers needing frequent VPN access.

Here's the equivalent terminal solution using macOS's networksetup utility:

# Get current IPv4 method for the interface (usually en0 or en1)
CURRENT_METHOD=$(networksetup -getinfo "Wi-Fi" | grep "IPv4:" | awk '{print $2}')

# Disable IPv4 temporarily
sudo networksetup -setv4off "Wi-Fi"

# Restore original configuration
sudo networksetup -setv4$CURRENT_METHOD "Wi-Fi"

Save this as vpn_reset.sh:

#!/bin/bash

INTERFACE="Wi-Fi" # Change to your network service name
LOG_FILE="$HOME/vpn_reset.log"

{
    echo "$(date) - Resetting network configuration"
    
    # Capture current state
    OLD_IP=$(ifconfig en0 | grep "inet " | awk '{print $2}')
    OLD_METHOD=$(networksetup -getinfo "$INTERFACE" | grep "IPv4:" | awk '{print $2}')
    
    # Reset sequence
    networksetup -setv4off "$INTERFACE"
    sleep 2
    networksetup -setv4$OLD_METHOD "$INTERFACE"
    
    # Verify restoration
    NEW_IP=$(ifconfig en0 | grep "inet " | awk '{print $2}')
    if [ "$OLD_IP" != "$NEW_IP" ]; then
        echo "Warning: IP address changed from $OLD_IP to $NEW_IP"
    fi
    
    echo "Reset completed successfully"
} >> "$LOG_FILE" 2>&1

For systems with both Ethernet and WiFi:

#!/bin/bash

reset_interface() {
    local interface=$1
    local service_name=$2
    
    echo "Processing $service_name ($interface)"
    CURRENT_METHOD=$(networksetup -getinfo "$service_name" | grep "IPv4:" | awk '{print $2}')
    
    networksetup -setv4off "$service_name"
    sleep 1
    networksetup -setv4$CURRENT_METHOD "$service_name"
    
    ifconfig $interface down
    sleep 1
    ifconfig $interface up
}

reset_interface "en0" "Wi-Fi"
reset_interface "en1" "Ethernet"

Make the script executable and create a launchd plist for automatic recovery:

chmod +x ~/vpn_reset.sh
sudo cp ~/vpn_reset.sh /usr/local/bin/

Create /Library/LaunchDaemons/com.user.vpnreset.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.user.vpnreset</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/bin/vpn_reset.sh</string>
    </array>
    <key>StartInterval</key>
    <integer>300</integer>
    <key>RunAtLoad</key>
    <true/>
</dict>
</plist>

Check the reset operation with:

tail -f ~/vpn_reset.log
ifconfig en0 | grep "status:"
networksetup -getinfo "Wi-Fi"