For changing the host header (and more), check out Alternate Access Mappings. You will find this under the Operations tab and Global Configuration section. Click "Edit Public URLs" and be sure to have the correct web application selected before you make any changes.
Scenario:If you have developed the sharepoint site with url http://xyz:47089 and later you have mapped with any public IP(Header will be change) then you will be able to access only home page but you can not access other resources and page that is bindup with link, In this case,you can change URL by Alternate access mappings.
Solution:
Step[1] : Open Sharepoint Central Admin & go to Operations tab
Step[2] : Under Global configuration heading select Alternate access mappings.
Step[3] : Select the desired web application i.e. [http://xyz:47089] (in this example)
Step[4] : On Edit Internal URLs page set the change the value of [http://xyz1:47089] to"[http://15.12.0.89:47089]".
Step[5] : Now this site[http://15.12.0.89:47089] will be accessible throughout the intranet from any domain.
Note: The same you can map with Public IP for e.g. 15.12.0.89 and you just need to provide windows authetication to this site
