Packet Traversal
The following image and table show a large ICMP packet traversing from ECU 1 to ECU 2, passing through the edge devices and the WireGuard tunnel.
The packet gets fragmented due to the MTU size of the WireGuard tunnel, which is set to 1542 bytes at the WireGuard interface wt0.
Packet Traversal Example
Packet Traversal Table
The table shows the packet traversal from ECU 1 to ECU 2, including the time, source and destination IP addresses, protocol, frame size, interface names and additional information about the packets. This example illustrates how the ICMP echo request is fragmented and reassembled as it traverses through the network interfaces and edge devices.
| # | Time | Source | Destination | Protocol | Size | Device | Interface ID | Interface name | Info |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 2.547363 | 10.0.0.1 | 10.0.0.2 | ICMP | 1514 | ECU 1 | 0 | vlan@eth0 | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 2 | 2.547365 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | ECU 1 | 1 | eth0 | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 3 | 2.547465 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | edge1 | 2 | enx | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 4 | 2.547465 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | edge1 | 3 | br-opendut | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 5 | 2.547521 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | edge1 | 4 | gre | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 6 | 2.547555 | 10.0.0.1 | 10.0.0.2 | ICMP | 1542 | edge1 | 5 | wt0 | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 7 | 2.547682 | 192.168.0.1 | 192.168.0.2 | IPv4 | 1514 | edge1 | 6 | end0 | Fragmented IP protocol (proto=UDP 17, off=0, ID=6ab0) [Reassembled in #8] |
| 8 | 2.547697 | 192.168.0.1 | 192.168.0.2 | WireGuard | 146 | edge1 | 6 | end0 | Transport Data, receiver=0x527A7C12, counter=277, datalen=1552 |
| 9 | 2.547739 | 192.168.0.1 | 192.168.0.2 | IPv4 | 1514 | edge2 | 7 | end0 | Fragmented IP protocol (proto=UDP 17, off=0, ID=6ab0) [Reassembled in #10] |
| 10 | 2.547739 | 192.168.0.1 | 192.168.0.2 | WireGuard | 146 | edge2 | 7 | end0 | Transport Data, receiver=0x527A7C12, counter=277, datalen=1552 |
| 11 | 2.547837 | 10.0.0.1 | 10.0.0.2 | ICMP | 1542 | edge2 | 8 | wt0 | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 12 | 2.547837 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | edge2 | 9 | gre | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 13 | 2.547837 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | edge2 | 10 | br-opendut | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 14 | 2.547896 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | edge2 | 11 | enx | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 15 | 2.547896 | 10.0.0.1 | 10.0.0.2 | ICMP | 1518 | ECU 2 | 12 | eth0 | Echo (ping) request id=0x5285, seq=0/0, ttl=64 |
| 16 | 2.547896 | 10.0.0.1 | 10.0.0.2 | ICMP | 1514 | ECU 2 | 13 | vlan@eth0 | Echo (ping) request id=0x5285, seq=0/0, ttl=64 (reply in 14) |
| 17 | 2.547959 | 10.0.0.2 | 10.0.0.1 | ICMP | 1514 | ECU 2 | 13 | vlan@eth0 | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 (request in 13) |
| 18 | 2.547959 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | ECU 2 | 12 | eth0 | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 19 | 2.547959 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | edge2 | 11 | enx | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 20 | 2.547959 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | edge2 | 10 | br-opendut | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 21 | 2.547969 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | edge2 | 9 | gre | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 22 | 2.547989 | 10.0.0.2 | 10.0.0.1 | ICMP | 1542 | edge2 | 8 | wt0 | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 23 | 2.548052 | 192.168.0.2 | 192.168.0.1 | IPv4 | 1514 | edge2 | 7 | end0 | Fragmented IP protocol (proto=UDP 17, off=0, ID=6507) [Reassembled in #24] |
| 24 | 2.548060 | 192.168.0.2 | 192.168.0.1 | WireGuard | 146 | edge2 | 7 | end0 | Transport Data, receiver=0x010151F4, counter=110, datalen=1552 |
| 25 | 2.548134 | 192.168.0.2 | 192.168.0.1 | IPv4 | 1514 | edge1 | 6 | end0 | Fragmented IP protocol (proto=UDP 17, off=0, ID=6507) [Reassembled in #26] |
| 26 | 2.548134 | 192.168.0.2 | 192.168.0.1 | WireGuard | 146 | edge1 | 6 | end0 | Transport Data, receiver=0x010151F4, counter=110, datalen=1552 |
| 27 | 2.548307 | 10.0.0.2 | 10.0.0.1 | ICMP | 1542 | edge1 | 5 | wt0 | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 28 | 2.548307 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | edge1 | 4 | gre | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 29 | 2.548307 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | edge1 | 3 | br-opendut | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 30 | 2.548388 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | edge1 | 2 | enx | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 31 | 2.548488 | 10.0.0.2 | 10.0.0.1 | ICMP | 1518 | ECU 1 | 1 | eth0 | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
| 32 | 2.548489 | 10.0.0.2 | 10.0.0.1 | ICMP | 1514 | ECU 1 | 0 | vlan@eth0 | Echo (ping) reply id=0x5285, seq=0/0, ttl=64 |
Remarks:
- The interface ID corresponds to the numbers in the image above.
- The ICMP packet is sent from ECU 1 at
10.0.0.1to ECU 2 at10.0.0.2. - The packet is fragmented at the edge device due to the MTU size of the network interfaces that connect the edge devices. See steps 7-10 and 23-26.
- The packet request reaches the destination ECU 2 in step 16.
Overhead analysis
The packet sent by the DuT has 1518 bytes, consisting of a standard ethernet frame with 1514 bytes and VLAN tag with 4 bytes.
This packet exceeds the MTU of 1500 bytes at the edge device.
In this case there are two packets sent between the edge devices with 146 bytes and 1514 bytes.
The overhead of OpenDuT can therefore be computed as follows: (1514 + 146) - 1518 = 142 Bytes
Breakdown:
- GRE encapsulation overhead: 24 bytes
- Fragmentation due to MTU limit (requires a second packet with IPv4 header and Ethernet frame): 34 bytes
- Encapsulation in another Ethernet frame (WireGuard tunnel): 34 bytes
- WireGuard encryption overhead: 1592 bytes (WireGuard packet) - 1542 bytes (original payload) = 50 bytes
Thus: 1660 - 50 - 34 - 34 - 24 = 1518 bytes