Ethernet Switch Frame Forwarding Analysis | Generated by AI
Question: In the given Ethernet topology (as shown in Figure 28) with the current switch forwarding table (as shown in Table 28), host 00-e1-d5-00-23-a1 sends a data frame to host 00-e1-d5-00-23-c1. After receiving the frame, host 00-e1-d5-00-23-c1 sends an acknowledgment frame back to host 00-e1-d5-00-23-a1. Please answer: (1) Which ports does the switch forward the data frame and the acknowledgment frame to, respectively? (2) Based on the process described, draw the updated switch forwarding table.
Answer:
Since the problem refers to “Figure 28” and “Table 28” which are not provided in the text, I can only give the most common and typical analysis pattern for this type of question. The following answer assumes a very common topology and initial table used in Chinese university network courses (especially in the 408 exam or similar exercises). If your actual figure/table is different, the conclusion may differ.
Most common topology assumption in such problems:
- There is one switch (often with 4 ports: 1, 2, 3, 4)
- Port 1 connects to host A (00-e1-d5-00-23-a1)
- Port 2 connects to host B (some intermediate host, often not used in this process)
- Port 3 connects to host C (00-e1-d5-00-23-c1)
- Port 4 connects to another host or uplink (sometimes not involved)
Most common initial forwarding table assumption:
| MAC address | Port | |
|---|---|---|
| 00-e1-d5-00-23-a1 | 1 | |
| 00-e1-d5-00-23-b? | 2 | (sometimes exists, sometimes empty) |
| (other entries or empty) |
Typical process and answers:
(1) Forwarding ports of the switch
-
When host A (…-a1) sends a data frame to host C (…-c1):
→ Destination MAC = 00-e1-d5-00-23-c1
→ At this time, the switch forwarding table does not have an entry for …-c1 (very common in such questions)
→ The switch performs flooding → forwards the frame out of all ports except the incoming port (port 1)
→ So the data frame is forwarded to ports 2, 3, 4 (commonly port 3 reaches host C) -
When host C (…-c1) sends the ACK frame back to host A (…-a1):
→ Destination MAC = 00-e1-d5-00-23-a1
→ The switch already has the entry …-a1 → port 1 (learned when A sent the first frame)
→ So the switch unicasts → forwards only to port 1
Answer to (1):
Data frame: forwarded to ports 2, 3, 4 (flooding)
Acknowledgment frame: forwarded to port 1 (unicast)
(2) Updated switch forwarding table
After the above two frames pass through the switch, the switch must have learned the MAC address of host C.
Updated forwarding table (most common final state):
| MAC address | Port |
|---|---|
| 00-e1-d5-00-23-a1 | 1 |
| 00-e1-d5-00-23-c1 | 3 |
| (possibly still has …-b? → 2 if it existed before) |
Text representation of the updated table:
MAC address VLAN Port Type Age
00-e1-d5-00-23-a1 1 dynamic
00-e1-d5-00-23-c1 3 dynamic
(possibly other entries remain unchanged)
Core learning rule reminder (key points for this type of question):
- When a frame arrives, the switch always learns the source MAC → associates it with the incoming port
- If the destination MAC is in the table → unicast to the corresponding port
- If the destination MAC is not in the table → flood to all other ports
- The return ACK frame is the most common way to let the switch learn the MAC-port mapping of the destination host
If your actual Figure 28 or Table 28 is significantly different (e.g., multiple switches, hosts on different ports, already has …-c1 entry, etc.), please provide the topology and initial table content, and I can give a more precise answer.
References:
- None (answer based on standard Ethernet switch self-learning behavior and common patterns in Chinese computer network exam questions)