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Queries in .NET Draw Code 128A in .NET Queries

Queries using visual studio .net toencode barcode code 128 in asp.net web,windows application ASP.NET Web Application Framework Iterative query There are two types of D NS queries: iterative and recursive.1 An iterative query sends a domain name to a DNS server and asks the server to return either the IP address of the domain or the name of the DNS server that is authoritative for the domain or one of its parents: The server does not query other servers when seeking an answer. Nameservers typically send each other iterative queries.

A recursive query sends a domain name to a DNS server and asks the server to return the IP address of the domain: The server may need to query other servers to get the answer. Both types of queries can fail, in which case the server returns a message saying it is unable to locate the domain. When a client, such as a browser, needs the IP address that corresponds to a domain name, the client queries a resolver.

Most resolvers are quite simple and require a DNS server to do most of the work: That is, they send recursive queries. The. Recursive query 1. There is a third type of query that is not covered in this book: inverse. An inverse query provides a domain name given a resource record.

Reverse name resolution (page 783), not an inverse query, is used to query for a domain name given an IP address.. 778 24 DNS/BIND: Tracking Domain Names and Addresses 2. Do you know the addre ss of ftp.site1.

example.com. 1.

Do you know the address of ftp.site1.example.

com. 3. No, but DNS server 1 should.

. Root DNS server Authorit Code128 for .NET ative server for com Authoritative server for example.com Authoritative server for site1.

example.com. Resolver Client s primary DNS server 4. Do you know the address of ftp.site1.example.com. 5. No, but DNS server 2 should. 6. Do you know the addre .NET ANSI/AIM Code 128 ss of ftp.

site1.example.com.

7. No, but DNS server 3 should. 10.

Yes, here it is.. 8. Do you know the address of ftp.site1.example.com. 9. Yes, here it is. Figure 24-4. A recursive query that starts several iterative queries to find the answer resolver communicates wi Visual Studio .NET code 128c th a single DNS server, which can perform multiple iterative queries in response to the resolver s recursive query. All DNS servers must answer iterative queries.

DNS servers can also be set up to answer recursive queries. A DNS server that is not set up to answer recursive queries treats a recursive query as though it is an iterative query. In Figure 24-4, the resolver on a client system is trying to discover the address of the server ftp.

site1.example.com.

on the network with the DNS layout shown in Figure 24-3 on page 777. The resolver on the client sends a recursive query to its primary DNS server. This server interrogates the root server and one additional server for each zone until it receives an answer, which it returns to the resolver on the client.

In practice, the query would not start with the root server because most servers usually have the location of the authoritative nameserver for the com. domain stored in cache (memory)..

Servers There are three main typ VS .NET barcode standards 128 es of DNS servers: primary (master), secondary (slave), and caching-only. A primary master server, also called a primary server or master server, is the authoritative server that holds the master copy of zone data.

It copies information from the zone or master file, a local file that the server administrator maintains. For security and efficiency, a primary master server should provide iterative answers only. A primary master server that provides recursive answers is more easily subverted by a DoS attack (page 1080) than one that provides iterative answers only.

Slave servers, also called secondary servers, are authoritative and copy zone information from the primary master server or another slave server.. Introduction to DNS 779 On some systems, when in Code 128 for .NET formation on the primary master server changes, the primary master server sends a message to the slave servers. When a slave receives such a message, it uses a process called zone transfer to copy the new zone information from the master server to itself.

DNS caches, also called caching-only servers, are not authoritative. These servers store answers to previous queries in cache (memory). When a DNS cache receives a query, it answers it from cache if it can.

If the DNS cache does not have the answer in cache, it forwards the query to an authoritative server. It is possible but for reasons of security not recommended for the same server to be the primary master server (authoritative) for some zones and a DNS cache for others. When the same server acts as both a DNS cache and a master server, if a malicious local user or malfunctioning resolver on the local network floods the DNS cache with more traffic than it can handle (a DoS attack), users may be prevented from accessing the public servers that the primary master server handles.

Conversely, if the authoritative server is compromised, the attacker can subvert all traffic leaving the network..
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