Name resolution tries to resolve some of the numerical address values to human readable names. There are two possible ways to do this conversations, depending on the resolution to be done: calling system/network services (like the gethostname function) and/or evaluate from Ethereal specific configuration files. If there are both features available, Ethereal will first try the system services and then fall back to it's own configuration files. XXX - is this really true? For details about the configuration files Ethereal uses for name resolution and alike, see Appendix A, Configuration (and other) Files and Folders.
However, be prepared that this conversion often will fail, e.g. the name to be resolved might simply be unknown by the servers asked and not found in the configuration files.
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You may see packets to/from your machine in your capture file, which are caused by name resolution network services (e.g. DNS packets). |
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The resolved names are not stored in the capture file or somewhere else, so the resolved names might not be available if you open the capture file later or on a different machine. |
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The name resolution in the packet list is done while the list is filled. If a name could be resolved after a packet was added to the list, that entry won't be changed. As the name resolution results are cached, you can use "View/Reload" to rebuild the packet list, this time with the correctly resolved names. |
The name resolution feature can be en-/disabled separately for the following protocol layers (in brackets):
ARP name resolution (system service) Ethereal will ask the operating system to convert an ethernet address to the corresponding IP address (e.g. 00:09:5b:01:02:03 -> 192.168.0.1).
Ethernet codes (ethers file) If the ARP name resolution failed, Ethereal tries to convert the ethernet address to a known device name, which has been assigned by the user using an ethers file (e.g. 00:09:5b:01:02:03 -> homerouter).
Ethernet manufacturer codes (manuf file) If both ARP and ethers didn't returned a result, Ethereal tries to convert the first 3 bytes of an ethernet address to an abbreviated manufacturer name, which has been assigned by the IETF (e.g. 00:09:5b:01:02:03 -> Netgear_01:02:03).
DNS/ADNS name resolution (system/library service) Ethereal will ask the operating system (or the ADNS library), to convert an IP address to the hostname associated with it (e.g. 65.208.228.223 -> www.ethereal.com). The DNS service is using synchronous calls to the DNS server. So Ethereal will stop responding until a response to a DNS request is returned. If possible, you might consider using the ADNS library (which won't wait for a network response).
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Enabling network name resolution when your name server is unavailable may significantly slow down Ethereal while it waits for all of the name server requests to time out. Use ADNS in that case. |
DNS vs. ADNS here's a short comparison: Both mechanisms are used to convert an IP address to some human readable (domain) name. The usual DNS call gethostname() will try to convert the address to a name. To do this, it will first ask the systems hosts file (e.g. /etc/hosts) if it finds a matching entry. If that fails, it will ask the configured DNS server(s) about the name.
So the real difference between DNS and ADNS comes when the system has to wait for the DNS server about a name resolution. The system call gethostname() will wait until a name is resolved or an error occurs. If the DNS server is unavailable, this might take quite a while (several seconds). The ADNS service will work a bit differently. It will also ask the DNS server, but it won't wait for the answer. It will just return to Ethereal in a very short amount of time. XXX - what does happen with the actual address field at that run? Will the response be ignored for that field?
hosts name resolution (hosts file) If DNS name resolution failed, Ethereal will try to convert an IP address to the hostname associated with it, using an hosts file provided by the user (e.g. 65.208.228.223 -> www.ethereal.com).
ipxnet name resolution (ipxnets file) XXX - add ipxnets name resolution explanation.