Firewall drops packets as "Bounce back traffic detected" when pinging secondary DMZ Subnet

03/26/2020 44 15385

DESCRIPTION:

Multiple networks are connected to a single physical interface which is configured as DMZ. When we try to access the secondary subnet from main DMZ subnet, firewall drops as "Bounce back traffic detected"

RESOLUTION:

1. Navigate to Network | Interfaces; configure an interface as DMZ with Static IP. In this case, we have configured X4 as DMZ with IP address 192.168.0.10, Subnet: 255.255.255.0 
   
2. We have one more network which is connected to the same switch without any VLANs. In this case, we have secondary network as 2.2.2.0/24
3. In order for the 2.2.2.0 to go online through SonicWall, SonicWall should know how to reach it. Hence , we create a Static ARP for the network and Static Route as follows:
   • Navigate to Network | ARP
   • click Add under Static ARP and enter any one IP in the network which is going to act as gateway for that subnet.

 Now, the SonicWall will publish MAC address of X4 to 2.2.2.1

1. Navigate to Network | Routing and click Add.

Source: Any Destination: 2.2.2.0 / 24 (Create address object for 2.2.2.0 of type DMZ) Service: Any Gateway: 0.0.0.0 Interface: X4 Metric: 1 Disable Route when interface is disconnected: Checked Click Ok.

Now, the computers of network 2.2.2.0 should have gateway as 2.2.2.1
From any computer of 192.168.0.x, try to ping the computer in 2.2.2.x.

Ping will fail and if we do capture on SonicWall, we will see Drop Code as "Bounce traffic detected / drop bounce same link pkt".
  

1. Navigate to System | Packet Monitor 
2. click Configure, go to Monitor Filter tab and configure as follows:
   • Ether type: IP
   • IP type: ICMP
   • Source IP: 192.168.0.246
   • Rest all fields should be blank
   • Under Display Filter, all fields should be blank
   • Under Advanced Monitor filter, enable all checkboxes. Click Ok.
   • Click Clear and Start Capture.

From the computer, 192.168.0.246, try to ping 2.2.2.10.
In Packet Monitor, refresh the page and we can see the packets getting dropped by firewall.

NOTE: This behavior is only on DMZ Interfaces. In LAN Interface, with correct ARP and route, traffic will flow without any drops.

To resolve this:

1. Login to SonicWall.
2. On address bar, instead of main.html, use diag.html and hit enter. (For example, https://x.x.x.x/diag.html)
3. Click Internal Settings.
4. Under "Routing and Network Settings" heading, enable the checkbox "Enable ICMP Redirect on DMZ zone"
5. Click Accept on top and Click Close.
   
6. Now try to ping 2.2.2.x, we can see successful pings.
    

Resolution for SonicOS 6.5 and Later

SonicOS 6.5 was released September 2017. This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 and later firmware.

1. Navigate to the Manage tab and click Network | Interfaces; configure an interface as DMZ with Static IP. In this case, we have configured X4 as DMZ with IP address 192.168.0.10, Subnet: 255.255.255.0 
   
2. We have one more network which is connected to the same switch without any VLANs. In this case, we have secondary network as 2.2.2.0/24
3. In order for the 2.2.2.0 to go online through SonicWall, SonicWall should know how to reach it. Hence, we create a Static ARP for the network and Static Route as follows:
   • Navigate to the Manage tab 
   • Click Network | ARP
   • Click Add under Static ARP and enter any one IP in the network which is going to act as gateway for that subnet.

 Now, the SonicWall will publish MAC address of X4 to 2.2.2.1

1. Navigate to the Manage tab
2. Click Network | Routing and click Add.

Source: Any Destination: 2.2.2.0 / 24 (Create address object for 2.2.2.0 of type DMZ) Service: Any Gateway: 0.0.0.0 Interface: X4 Metric: 1 Disable Route when interface is disconnected: Checked Click Ok.

Now, the computers of network 2.2.2.0 should have gateway as 2.2.2.1
From any computer of 192.168.0.x, try to ping the computer in 2.2.2.x.

Ping will fail and if we do capture on SonicWall, we will see Drop Code as "Bounce traffic detected / drop bounce same link pkt".
  

1. Navigate to the Investigate tab
2. Click Packet Monitor 
3. Click Configure, go to Monitor Filter tab and configure as follows:
   • Ether type: IP
   • IP type: ICMP
   • Source IP: 192.168.0.246
   • Rest all fields should be blank
   • Under Display Filter, all fields should be blank
   • Under Advanced Monitor filter, enable all checkboxes. Click Ok.
   • Click Clear and Start Capture.

From the computer, 192.168.0.246, try to ping 2.2.2.10.
In Packet Monitor, refresh the page and we can see the packets getting dropped by firewall.

NOTE: This behavior is only on DMZ Interfaces. In LAN Interface, with correct ARP and route, traffic will flow without any drops.

To resolve this:

1. Login to SonicWall.
2. On address bar, instead of main.html, use diag.html and hit enter. (For example, https://x.x.x.x/diag.html)
3. Click Internal Settings.
4. Under "Routing and Network Settings" heading, enable the checkbox "Enable ICMP Redirect on DMZ zone"
5. Click Accept on top and Click Close.
   
6. Now try to ping 2.2.2.x, we can see successful pings.