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Host record creates reverse but not forward

Authority
Posts: 36
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Hello,

 

According to the Infoblox RESTful Web API guide, creation of a host record means creating an A record and a PTR record. Instead of creating both A and PTR separately, we create a host record. I've found that sometimes the host record creates only the reverse (PTR record) and not the forward (A record).

 

My questions are -

1. Are there any specific conditions when adding a host record might create either forward or reverse and not both?

2. Under what circumstances does a host record create only the reverse and not the forward?

3. Under what circumstances (if this is a valid case) does a host record create only the forward and not the reverse?

4. What can I do to make sure that a host record creates both forward and reverse?

 

Thank you for your help.

Re: Host record creates reverse but not forward

[ Edited ]
Adviser
Posts: 132
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@TSaikia wrote:

 

According to the Infoblox RESTful Web API guide, creation of a host record means creating an A record and a PTR record.

That's not quite true. A host record is its own type of object, distinct from a A record object or a PTR record object. (You can see this if you create both host records and A records for a particular domain. A Web API call to return host record objects will return only the host records, while a WAPI call to return A record objects will return only the A records.)

 

What happens is that if you do a DNS query for an A record for a fully-qualified domain name and there's a host record for that FQDN, then the Infoblox DNS server will return a response as if there were an actual A record. The response will contain the (IPv4) address listed in the host record for that FQDN. (If there are multiple addresses listed in the host record then multiple A records will be included in the response.) A similar thing happens when you query PTR records and there's a host record referencing the address in question.

 

So when you write "sometimes the host record creates only the reverse (PTR record) and not the forward (A record)" I presume you mean that if you do an nslookup or dig command that sometimes you can get a correct PTR response but not an A response. (Or vice versa, nslookup/dig might return an A record but no PTR record.)


My questions are -

1. Are there any specific conditions when adding a host record might create either forward or reverse and not both?

2. Under what circumstances does a host record create only the reverse and not the forward?

3. Under what circumstances (if this is a valid case) does a host record create only the forward and not the reverse?

4. What can I do to make sure that a host record creates both forward and reverse?


 

I would check to see that a) the relevant forward-mapping and reverse-mapping zones are defined in the Infoblox system, b) there is at least one Infoblox grid member listed as a nameserver for each of the two zones, and c) the zones have been delegated properly such that the Infoblox grid member(s) are in fact authoritative for the zones from the point of view of the systems trying to resolve the name. If any of these are not done then you might see the situations you describe.

 

For example, suppose you have a host record for FQDN foo.example.com with IPv4 address 192.168.0.1. Then you need to make sure that the zones foo.example.com and 0.168.192.in-addr.arpa are both defined in the Infoblox system, and that both zones have at least one Infoblox grid member listed as a nameserver for the zone. You also need to make sure that zone delegation is done such that the relevant DNS query actually is sent to the Infoblox grid member acting as a nameserver.

 

If you can't figure out what went wrong I suggest you contact Infoblox support and have them assist you with troubleshooting.

 

Frank

 

 

 

 

Re: Host record creates reverse but not forward

Authority
Posts: 36
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Thank you for the reply, Frank. However, I didn't really understand this statement -

 

"if you do a DNS query for an A record for a fully-qualified domain name and there's a host record for that FQDN, then the Infoblox DNS server will return a response as if there were an actual A record"

 

Say, if we have a host record for FQDN test.example.com (no separate A record for this FQDN), then if I run a web api like,

 -X GET https://w.x.y.z/wapi/v1.1/record:a -d name=test.example.com

 

I'll get a response but it'll contain the host IP even though I queried an A record?

Re: Host record creates reverse but not forward

GHorne Community Manager
Community Manager
Posts: 254
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No, that API query will return a null result as there is no A record by that name.

 

You would have to query the /record:host namespace to get a result

Re: Host record creates reverse but not forward

Authority
Posts: 36
12291     0

Yes, I thought so but what does this statement by Frank mean?

 

"if you do a DNS query for an A record for a fully-qualified domain name and there's a host record for that FQDN, then the Infoblox DNS server will return a response as if there were an actual A record"

Re: Host record creates reverse but not forward

Adviser
Posts: 213
12291     0

It means that if you query the DNS server for the hostname, you will get an "A" record response back from the DNS server.  You may be confusing the underlying DNS protocol query from the API query.  The API query is specific in that you must request the record:host object type for HOST objects as they will not return when you make an API query for A records.

 

DNS at the protocol level, on the other hand, is completely different as there are no such things as a "host" object construct like what Infoblox uses.  Instead, the DNS version of a "host" is the A or, quite possibly, AAAA record type.

Re: Host record creates reverse but not forward

Authority
Posts: 36
12291     0

I get it now, I think Smiley Happy

Thank you. I'll summarize it so you could correct me in case I go wrong somewhere -

1. HOST record for FQDN test.example.com is created in Infoblox. Say, the IP is 1.2.3.4.

2. If a reverse zone 4.3.in-addr.arpa.net is defined and a grid member is assigned as it's nameserver, then a PTR record is created in the DNS level.

Additionally, if example.com is defined and a grid member is assigned to serve as it's nameserver, then an A record will be created in the DNS level.

3. If either zone or nameserver isn't defined/assigned, then the respective record will not be created in the DNS level.

Re: Host record creates reverse but not forward

Adviser
Posts: 213
12291     0
That’s correct.

Re: Host record creates reverse but not forward

Authority
Posts: 36
12291     0

Wonderful..... I had 1 more question. If you could shed some light on what this statement means in Frank's resolution, it'll be great.

 

"You also need to make sure that zone delegation is done such that the relevant DNS query actually is sent to the Infoblox grid member acting as a nameserver"

 

Does this mean, while we are querying (dig etc.) the FQDN, it has to be done against the nameserver (which is the grid member assigned to that zone)?

Re: Host record creates reverse but not forward

Adviser
Posts: 213
12291     0
Not necessarily…BUT, if the zone you are using, such as example.com, does not ultimately get you to one of the Infoblox appliances, then the resolution could be wrong or inaccurate. In this case, there is an actual example.com domain owned and registered by someone else. Since you can define anything you like on Infoblox, you need to make sure the query for your target name gets you to your Infoblox environment.

Most of the time you wouldn’t use something someone else already owns but that’s what Frank’s “catch-all” description is about. He’s covering all of the bases.

Re: Host record creates reverse but not forward

Adviser
Posts: 132
12291     0

What Don said :-)

 

Frank

Re: Host record creates reverse but not forward

Authority
Posts: 36
12291     0

Thank you so much for the explanation Smiley Happy

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