HP 635n HP Jetdirect Print Servers - Practical IPv6 Deployment for Printing an - Page 23

If it cannot, it must timeout before moving to another IP address.

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address and begins the FTP connection on it. What happens when a given protocol is supported over IPv4 but not IPv6? What would the behavior be? Let's look at a trace where we are trying to open a telnet connection to mfp3.remote.example.internal. HP Jetdirect does not support telnet on IPv6. Here we can see that the DNS query behaves as before and the IPv6 address is selected as before. However, when the connection is attempted over IPv6, the TCP connection is RESET (RST) indicating that this port is not supported. The FTP client tries a couple more times (rather persistently). Rather than quit altogether, the client changes to use IPv4 and a connection is then accepted. This process of gathering all the IP addresses associated with a name and then trying each IP address until a "good one" is found for a particular service is extremely important to understand. It is a fundamental part of every application that claims to be IP Neutral. Unfortunately, each application must implement these changes and some applications may not do it correctly. This could lead to performance issues. Be sure to try more than one application when troubleshooting these types of problems to try and eliminate network issues versus application issues. An example of a networking issue would be where DNS contains an AAAA record that describes a host. However, IPv6 is not network routable from all locations of the site network. When a Vista client resolves the name and gets an IPv6 address and begins to try and contact it, the client is assuming that the IPv6 address can be reached over the network. If it cannot, it must timeout before moving to another IP address. If all applications are timing out because of IPv6 reachability issues, application performance could drop to unacceptable levels. In the example above, the switch from IPv6 to IPv4 due to Telnet not being supported over IPv6 happens in about one second, because the Telnet server is able to return a TCP RST and inform the client immediately. Let's look at a case where we have a DNS records indicating IPv4 and IPv6 addresses, but only connectivity over IPv4. The host is on the IPv4 network 192.168.0/24 and the IPv6 network of 2001:db8::/64 and is trying to reach mfp3.remote.example.internal. Here we can see that there is a 21 second delay (as opposed to one second) when IPv6 reachability is an issue. You can also see in this trace how the DNS query goes over IPv6 but asks for both IPv4 and IPv6 records. Keep in mind that once a non link local IPv6 address is configured on Vista clients and Vista clients are part of an Active Directory Integrated DNS environment, IPv6 addresses will automatically appear 23

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address and begins the FTP connection on it.
What happens when a given protocol is supported
over IPv4 but not IPv6?
What would the behavior be?
Let’s look at a trace where we are trying to
open a telnet connection to mfp3.remote.example.internal.
HP Jetdirect does not support telnet on
IPv6.
Here we can see that the DNS query behaves as before and the IPv6 address is selected as before.
However, when the connection is attempted over IPv6, the TCP connection is RESET (RST) indicating
that this port is not supported.
The FTP client tries a couple more times (rather persistently).
Rather
than quit altogether, the client changes to use IPv4 and a connection is then accepted.
This process of gathering all the IP addresses associated with a name and then trying each IP address
until a “good one” is found for a particular service is extremely important to understand.
It is a
fundamental part of every application that claims to be IP Neutral.
Unfortunately, each application
must implement these changes and some applications may not do it correctly.
This could lead to
performance issues.
Be sure to try more than one application when troubleshooting these types of
problems to try and eliminate network issues versus application issues.
An example of a networking
issue would be where DNS contains an AAAA record that describes a host.
However, IPv6 is not
network routable from all locations of the site network.
When a Vista client resolves the name and
gets an IPv6 address and begins to try and contact it, the client is assuming that the IPv6 address can
be reached over the network.
If it cannot, it must timeout before moving to another IP address.
If all
applications are timing out because of IPv6 reachability issues, application performance could drop
to unacceptable levels.
In the example above, the switch from IPv6 to IPv4 due to Telnet not being
supported over IPv6 happens in about one second, because the Telnet server is able to return a TCP
RST and inform the client immediately.
Let’s look at a case where we have a DNS records indicating
IPv4 and IPv6 addresses, but only connectivity over IPv4.
The host is on the IPv4 network
192.168.0/24 and the IPv6 network of 2001:db8::/64 and is trying to reach
mfp3.remote.example.internal.
Here we can see that there is a 21 second delay (as opposed to one second) when IPv6 reachability
is an issue.
You can also see in this trace how the DNS query goes over IPv6 but asks for both IPv4
and IPv6 records.
Keep in mind that once a non link local IPv6 address is configured on Vista clients and Vista clients
are part of an Active Directory Integrated DNS environment, IPv6 addresses will automatically appear