Name resolution tries to convert some of the numerical address values into a human readable format. There are two possible ways to do these conversions, depending on the resolution to be done: calling system/network services (like the gethostname() function) and/or resolve from Wireshark specific configuration files. For details about the configuration files Wireshark uses for name resolution and alike, see Appendix B, Files and Folders.
The name resolution feature can be enabled individually for the protocol layers listed in the following sections.
Name resolution can be invaluable while working with Wireshark and may even save you hours of work. Unfortunately, it also has its drawbacks.
- Name resolution will often fail. The name to be resolved might simply be unknown by the name servers asked, or the servers are just not available and the name is also not found in Wireshark’s configuration files.
- 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. Each time you open a capture file it may look “slightly different” simply because you can’t connect to the name server (which you could connect to before).
- DNS may add additional packets to your capture file. You may see packets to/from your machine in your capture file, which are caused by name resolution network services of the machine Wireshark captures from.
- Resolved DNS names are cached by Wireshark. This is required for acceptable performance. However, if the name resolution information should change while Wireshark is running, Wireshark won’t notice a change in the name resolution information once it gets cached. If this information changes while Wireshark is running, e.g. a new DHCP lease takes effect, Wireshark won’t notice it.
Name resolution in the packet list is done while the list is filled. If a name can be resolved after a packet is added to the list, its former entry won’t be changed. As the name resolution results are cached, you can use → to rebuild the packet list with the correctly resolved names. However, this isn’t possible while a capture is in progress.
Try to resolve an Ethernet MAC address (e.g. 00:09:5b:01:02:03) to something more “human readable”.
ARP name resolution (system service): Wireshark 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, Wireshark 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 neither ARP or ethers returns a result, Wireshark tries to convert the first 3 bytes of an ethernet address to an abbreviated manufacturer name, which has been assigned by the IEEE (e.g. 00:09:5b:01:02:03 → Netgear_01:02:03).
Try to resolve an IP address (e.g. 216.239.37.99) to something more “human readable”.
DNS/concurrent DNS name resolution (system/library service): Wireshark will ask the operating system (or the concurrent DNS library), to convert an IP address to the hostname associated with it (e.g. 216.239.37.99 → www.1.google.com). The DNS service is using synchronous calls to the DNS server. So Wireshark will stop responding until a response to a DNS request is returned. If possible, you might consider using the concurrent DNS library (which won’t wait for a name server response).
![[Warning]](wsug_graphics/warning.svg) | Warning |
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Enabling network name resolution when your name server is unavailable may significantly slow down Wireshark while it waits for all of the name server requests to time out. Always use concurrent DNS resolution. |
DNS vs. concurrent DNS: 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 concurrent DNS 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 concurrent DNS service works a bit differently. It will also ask the DNS server, but it won’t wait for the answer. It will just return to Wireshark in a very short amount of time. The actual (and the following) address fields won’t show the resolved name until the DNS server returns an answer. As mentioned above, the values get cached, so you can use → to “update” these fields to show the resolved values.
hosts name resolution (hosts file): If DNS name resolution failed, Wireshark will try to convert an IP address to the hostname associated with it, using a hosts file provided by the user (e.g. 216.239.37.99 → www.google.com).