Cisco – Importance of DHCP option 12, client host name

ciscodhcpNetworknetworking

The main purpose of a DHCP server is to provide dynamic configuration for a group of hosts (mainly IP, Gateway and DNS). There are several options that can also be sent.

Option 12 (client hostname), which is supported by Cisco devices, doesn't make sense to me. I tried it. I set this option ON and set the value to "Tom". Then you can see that all hosts got the same name, which is "Tom".

In which scenarios would I need to set all hosts to the same exact name? What is the importance of such a thing?

Best Answer

You wouldn't set this option on the whole scope. Rather, you'd set it for a reserved address, so that a specific host gets a defined IP address and a defined host name.

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Well I managed to figure this out.

The bottom line is:

Using authentication-key-chains uses the "TCP Enhanced Authentication Option"
Using authentication-key uses the "TCP MD5 Signature Option"

From https://datatracker.ietf.org/doc/html/draft-bonica-tcp-auth-06

12.4.  Backwards Compatibility

   On any particular TCP connection, use of the TCP Enhanced
   Authentication Option precludes use of the TCP MD5 Signature Option.

You simply cannot mix the two different TCP options.

Cisco ASA 5505 stop passing traffic randomly

The issue has been resolved! I have tried to analyze non-working hosts ARP tables and found ASA's MAC address change. Decreased ASA's log verbosity to Warning level, rebooted it and got a message during boot

IP address collision detected between host 192.168.0.1 at f80f.4197.a18d and interface inside

So found host with the MAC noted. Despite it has different IP address and it is separate point to investigate, host's disconnection immediately resolves the issue.

Best Answer

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