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can you please help me decode a MX Record like this

1w    IN    MX   10  mail.example.com
      IN    MX   20  mail2.example.net

what is IN in above two records and since in second record there is no update time mentioned, as per my understanding it takes the value from TTL value of the zone file, but is TTL Value a mandatory for zone file ? if not what what is ttl value for second record.

I am fairly new to email tech hence might be asking some basic questions hence would appreciate if you can point me in right direction.

Muds
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1 Answers1

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"IN" is the "class" for the rdata value (the address in this record). Which defines different ways to access that information. It isn't an MX specific item and it's almost universally uses IN for Internet these days since most other options are obsolete. See section 3.2.4 in https://www.rfc-editor.org/rfc/rfc1035.

CLASS fields appear in resource records. The following CLASS mnemonics and values are defined:

IN 1 the Internet

CS 2 the CSNET class (Obsolete - used only for examples in some obsolete RFCs)

CH 3 the CHAOS class

HS 4 Hesiod [Dyer 87]

So it's unrelated to TTL. A TTL's default will vary depending on your DNS provider. I think the 1w is the max TTL, so no individual records can have a TTL that is greater than that max.

Community
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John Brandenburg
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  • thanks for the clarification John, 1w is the max assumed right coz i have seen examples with 3w, so in light of that if i do not mention any figure what is the default , is it only what is set by provider or is there any standard as well ? – Muds Jan 11 '18 at 17:44