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Execute the nslookup command to check the DNS but receive the false outcome as the result of inputting un-standard FQDN

Publication Date:  2012-10-23 Views:  77 Downloads:  0
Issue Description
Version: All versions.
The problem description:
Use the nslookup command onsite to detect whether the DNS can resolve the domain name correctly. Execute the nslookup, search the IP corresponding to the ITA host whose name is vds-ita-1, and find that the IP is wrong, this mislead us onsite to consider that the DNS can’t resolve the domain name correctly. But, in fact, the actual service is normal.
Alarm Information
None.
Handling Process
1. Execute the command onsite: nslookup vds-ita-1.huawei.com, then receive a false IP address.
2. It’s not a FQDN in the command: “vds-ita-1.huawei.com”, it’s not ended with a “.”.
3. Modify the command as to: “nslookup vds-ita-1.huawei.com.”, then tests it and receives the right address of ITA.
4. Execute the command: nslookup vds-ita-1, it also receives the right IP.
5. What is the IP through executing “nslookup vds-ita-1.huawei.com”? To answer this question we need to check the configurations of DNS.
a) Open the DNS server’s “DNS Manager”, select “View>Advanced”.
b) At the left navigation tree, successively display the nodes: “DNS > computer name > Forward Lookup Zones”, click the node “huawei.com” and the entire hosts’ information are shown at the right window.
c) We find that there is not only a “vds-ita-1” but also a “vds-ita-1.huawei.com” whose IP is the false one we receive at the step 1.
d) Confirm that the host record “vds-ita-1.huawei.com” is useless, it may be a added record, delete it and execute the command “nslookup vds-ita-1.huawei.com” to search, we can also receive the right address.
Root Cause
1. Fully qualified domain name (FQDN) is a special domain name whose ending is a “.”, for example “vds-ita-1.huawei.com.” is a FQDN.
2. In the common network applications, we can omit the ending dot of the FQDN; however the DNS can’t omit this dot casually. The ending dot of FQDN represents the root of DNS, as it , the FQDN can express an absolute route. For instance, “vds-ita-1.huawei.com.” can represent the host named vds-ita-1 in the domain of huawei.com which is a com sub-domain in the root of DNS.
3. If the DNS detects a domain name is not a FQDN, for satisfying the FQDN standard it will add the current region name to the end of that domain name. For example, in the domain of “huawei.com”, DNS will look “vds-ita-1” as “vds-ita-1.huawei.com.”, look “vds-ita-1.huawei.com”as“vds-ita-1.huawei.com.huawei.com.”
4. If there isn’t any conflicting host name, the two commands will search the same outcome, contrarily, if there are some conflicting host names, for instance there are two host “vds-ita-1” and “vds-ita-1.huawei.com”, they will search the different outcomes.
Suggestions
None.

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