1. Configure a PC as a DHCP server. Cloud terminals can obtain IP addresses through DHCP. Configure the S7700 as a DHCP server, only the desktop PCs can obtain IP addresses.
The test result indicates that the devices are incompatible.
2. Capture the packets exchanged during IP address obtaining when the S7700 functions as a DHCP server.
The following figure shows the captured packets.
Figure 4-1 Packets captured during IP address obtaining
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OFFER packets; however, the S7700 did not receive the packets returned by cloud terminals.
3. Capture DHCP packets when the original DHCP server is used and when the S7700 is used as the DHCP server.
The following figure shows the DHCP OFFER packet returned by the non-Huawei DHCP server.
Figure 4-2 DHCP OFFER packet returned by the non-Huawei DHCP server
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The following figure shows DHCP OFFER packet returned by the S7700.
Figure 4-3 DHCP OFFER packet returned by the S7700
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Compare the Option fields in two DHCP OFFER packets. The DHCP OFFER packet returned by the non-Huawei DHCP server has more options than the DHCP OFFER packet returned by the S7700. These missing options are not configured on the S7700, and the Option 55 field in the DHCP DISCOVER packet does not request these options.
4. Confirm with the customer whether these options are required. If cloud terminals need to check these options, add these options on the S7700.
Add options as follows:
dns-list x.x.114.133
nbns-list x.x.114.133
domain-name dd
option 7 ip-address 192.168.1.1
force insert option 7 15 44 //The option 55 field in the DHCP DISCOVER packet sent by clients does not request options 7, 15, and 44. Run the command to insert these options forcibly.
5. After the configuration is modified, cloud terminals still fail to obtain IP addresses from the S7700. Continue to compare the two DHCP OFFER packets.
The following figure shows the DHCP OFFER packet returned by the non-Huawei DHCP server.
Figure 4-4 DHCP OFFER packet returned by the non-Huawei DHCP server
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The following figure shows DHCP OFFER packet returned by the S7700.
Figure 4-5 DHCP OFFER packet returned by the S7700
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The UDP checksum in the DHCP packets sent by S7700 is 0000. According to RFC, UDP checksum with the value being 0000 does not need to be checked. There is a possibility that the cloud terminals still checked the UDP checksum with the value being 0000, causing an error in packet checking. As a result, the cloud terminals do not process the packets sent from the S7700.
