Is is a legacy thing when I keep seeing references to applying settings to vty lines 0 4, as opposed to 0 15? I thought that until I noticed that some of the configurations I have seen have separate entries for 0 4 and 5 15.
VTY lines are usually used for creating out-of-band management sessions to devices. If a password is not supplied on a vty line, that line cannot be used for managing the device. In some cases administrators may decide to let junior staff to use lines 0 - 4 and senior staff to use lines 5 - 15. This could be one of several possibilities for having separate configurations. You could also have different passwords on each vty line.
Arvind provides an interesting commentary on vty lines. But my interpretation of the original question is a bit different.
In traditional IOS there were 5 lines for vty (line vty 0 4) to support remote access. In recent versions (and perhaps differing by feature set) there are 16 lines vty 0 15. Even if you configure all 16 lines exactly the same (same password, same login properties, same transport protocol, etc) the output of show run/show start will separate lines 0 4 and lines 5 15. I assume this is some legacy effect in the parser and does not have any operational impact.
Both you and Arvind answered my question, thanks. Unfortunately the system allowed me to rate Arvind's post, but not yours. It allows me to submit it, but then returns to an un-rated message. Sorry... probably a PEBKAC error. :( Either that or it's not updating my browser and I just gave you about 20 more points. Thanks again to both of you.
I appreciate the thought and the effort to attempt to rate. The most important thing is that your question was answered.