the hostname in terminal is bogon,is that normal?

Lets start with something basic. Bash prompt could be adjusted upon customizing bash profile files. Bash prompts are the ones you see on the left hand side of a terminal screen, it repeats every time after a command finishes or Enter key is pressed, it may show but no limited to, hostname, username with $ at the end. All that are defined by Bash Prompt Escape Sequences. Here is a basic Bash support escapes for a quick reference: http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/bash-prompt-escape-sequences.htmlHere is a more detailed doc: http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/ There are so many online resources available also.

Bash profile are pure text files, you may put bash commands in to run when a Bash window launching, this may answer your question why the prompt changes upon network status.

Comes to OS X system, it maybe a little bit complicated, as the Terminal came with OS X has default OS X customized global profiles that apply to all users, the file /etc/profile and maybe /etc/bashrc as well. Users may have their own profile files, which located in ~/etc/profile.

You may get system online documents by running:

man bash

BTW, there are some online generators, like http://ezprompt.net/ or http://bashrcgenerator.com/. they are WYSIWYG program.

This may not answer your question directly, as we don't know how your system have been customized and what file or where has been changed. If you want more detailed instruction, it's better start to provide more details, picture is always bonus.

<经过版主编辑>