24 DNS/BIND: Tracking Domain Names and Addresses in .NET Make ean13+2 in .NET 24 DNS/BIND: Tracking Domain Names and Addresses

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830 24 DNS/BIND: Tracking Domain Names and Addresses using visual studio .net toincoporate ean-13 supplement 5 in web,windows application USPS Intelligent Mail The second format is .net vs 2010 GS1-13 more readable because of its layout and the comments. The at symbol (@) at the start of the SOA resource record stands for the zone name (also called the origin) as specified in the named.

conf file. Because the named.conf file specifies the zone name to be zach.

net, you could rewrite the first line as follows:. IN SOA ns. mgs@sobell.

com. (. The host utility ret .net framework EAN13 urns something closer to the first format with each of the times specified in seconds:. $ host -t soa SOA mgs\ 03111 28800 7200 2419200 86400 TXT Text Associates a character string with a domain. The Name field holds the domain name. The data field can contain up to 256 characters and must be enclosed within quotation marks. TXT records can contain any arbitrary text value.

As well as general information, they can be used for things such as public key distribution. Following is a TXT resource record that specifies a company name:. IN TXT "Sob European Article Number 13 for .NET ell Associates Inc.

". DNS Queries and Responses Queries A DNS query has thre e parts: 1. Name Domain name, FQDN, or IP address for reverse name resolution 2. Type Type of record requested (page 827) 3.

Class Always IN for Internet class Most DNS servers store in cache memory the query responses from other DNS servers. When a DNS server receives a query, it first tries to resolve the query from its cache. If that attempt fails, the server may query other servers to get an answer.

Because DNS uses cache, when you make a change to a DNS record, the change takes time sometimes a matter of days to propagate throughout the DNS hierarchy. A DNS message sent in response to a query can hold the following records: Header record Information about this message Query record Repeats the query Answer records Resource records that answer the query Authority records Resource records for servers that have authority for the answers Additional records Additional resource records, such as NS records The dig utility does not consult /etc/nsswitch.conf (page 475) to determine which server to query.

The following example uses dig to query a DNS server. The +all option causes dig to query for all records..

Cache Responses Introduction to DNS 831 $ dig +all m ; <<>> DiG 9.7.

0-P1 <<>> +all ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51842 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 3 ;; QUESTION SECTION: ;


com. ;; ADDITIONAL SECTION: ns1. ns2. ns3. .



156. 50715 50715 50715. IN IN IN NS NS NS 78819 78819 78819. IN IN IN A A A 91.189.94.

173 91.189 UPC-13 for .NET .

94.219 209.6.

3.210. Reverse Name Resolution In addition to norma EAN-13 for .NET l or forward name resolution, DNS provides reverse name resolution (also referred to as inverse mapping or reverse mapping) so you can look up domain names given an IP address. Because resource records in the forward DNS database are indexed hierarchically by domain name, DNS cannot perform an efficient search by IP address on this database.

DNS implements reverse name resolution by means of special domains named (IPv4) and (IPv6).

Resource records in these domains have Name fields that hold IP addresses; the records are indexed hierarchically by IP address. The Data fields hold the FQDNs that correspond to these IP addresses. Reverse name resolution can verify that someone is who he says he is or at least is from the domain he says he is from.

In general, it allows a server to retrieve and record the domain names of the clients it provides services to. For example, legitimate mail contains the domain of the sender and the IP address of the sending machine. A mail server can verify the stated domain of a sender by checking the domain associated with the IP address.

Reverse name resolution can also be used by anonymous FTP servers to verify that a domain specified in an email address used as a password is legitimate. For example, to determine the domain name that corresponds to the IP address 82.211.

81.150 in Figure 24-5 on the next page, a resolver would query DNS for information about the domain named 150.81.

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