The actual cause of this behavior is something often overlooked.

The default option for the line configuration "transport preferred" is telnet. This means that if you enter just "1.2.3.4" at the command line, that's the same as typing "telnet 1.2.3.4". Likewise, typing "google.com" is the same as typing "telnet google.com". So when you enter a string that doesn't match up with any known command (usually a typo like "confgi"), this is the same as typing "telnet confgi" so DNS resolution is attempted on that string ("confgi") for the purpose of telneting to that supposed host. Which won't work -- but you need to wait for the DNS query to timeout (as you most likely don't have a DNS resolver configured -- so it actually broadcasts out a query).

As noted, if DNS resolution is turned off, the router won't even attempt to resolve "confgi" so the command "telnet confgi" will quickly fail, rather than slowly timeout trying to perform DNS resolution.

Turning off DNS lookup will sidestep this issue, but a better fix is to configure "transport preferred none" so that the attempted telnet connection never even occurs. If I want to try connecting to another box, I have no problem actually typing "telnet" or "ssh."

Edit: Separate from this particular discussion, it's worth noting that DNS resolution is generally turned off not only for this reason, but also because several "show" commands (like "sh users") will attempt to resolve IPs to names, and it will try to several DNS queries, slowly failing on each one, as the command's output is generated.

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If this is for ES, use the asset and identifies framework to populate that with valid DNS entries, and use that instead. If not, you would basically need to dump your entire DNS into an index using an on prem forwarder, then pull that data into a lookup in the Cloud. I have done this before using ldapsearch and Active Directory. More on reddit.com

config t ! ip domain-name ip name-server a.a.a.a b.b.b.b c.c.c.c d.d.d.d ! default ip domain-lookup ! line console 0 transport preferred none exit ! line aux 0 transport preferred none exit ! line vty 0 15 transport preferred none end write mem What does this do? By default theere is a default transport of "ssh" or "telnet" assigned to the vty interfaces. This means if you type a command that IOS doesn't immediately recognize it assumes you intended to pass that "word" to the default transport so you could SSH to something. We are changing that behavior so there is no default transport method. It will no longer pass a typo to the SSH process, which means it won't try to do a DNS lookup on it. But, since we didn't use no ip domain-lookup the switch can still perform a DNS lookup when it needs to. That's the big difference. no ip domain-lookup means you can't use a DNS name as a syslog destination, or as an NTP server which can be annoying. More on reddit.com

1 - ip domain-lookup allows the router to try to resolve names to IP. e.g. with it enabled you can run ping google.com from the router and it will try to query the IP for google.com. If no ip domain-lookup is added, you wouldn't be able to ping anything by name, you'd only be able to ping by IP 2 - If you disable ip domain-lookup, the router is limited to using any records that were manually added to it as hosts (your command #6). You can have multiple nameservers, if they were being overridden that may be a limitation of Packet Tracer. On real gear you can have multiple 3 - This sets a domain for the router itself, typically your organizations domain-name if you have one. This is used when generating self-signed crypto keys, but it also used if you're trying to access a resource by name while not using the FQDN (same behavior as Windows or other operating systems). e.g. if you set ip domain-name company.com, and then ping mail, the router will automatically do a lookup for mail.company.com 4 - Domain list is similar to domain-name, but allows for entering multiple domains that will be tried in order. e.g you could add company.com, company.net, and company.org, and the router would try to find the requested resource in company.com first, then .net, then .org 5 - Likely a limitation of PT, this is if you want the router to function as a DNS Server for other clients on the network 6 - Correct, this is basically adding a manual record so that the router would not need to query anything else to resolve it 7 - A DNS Client is just the software that enables looking up DNS records. If you didn't have a DNS client running, everything would need to be done against IP addresses only More on reddit.com