I am trying to replace existing fedora core4 server with most equivalent redhat. Can you suggest me most appropriate one. Server is used for names resolution.

I understand what you're asking, but I can't give a direct answer (without doing a lot of digging).

FC4 was released in June 2005 [1]. RHEL4 was released in February 2005, while RHEL5 was released in March 2007 [2]. Since Fedora features are sometimes merged into newer RHEL after lots of testing, it seems most likely that certain software component versions in FC4 are the same as - or superseded by - software component versions in RHEL5.

However, I could be mistaken, and you'll want to dig up FC4 release and maintenance documentation (containing software versions) and compare that with RHEL5 release docs and errata (also containing software versions). If all you care about is, e.g., BIND versions, that should make your search a lot quicker.

When performing major OS upgrades, be sure to take good backups and keep them in a safe place even after a successful upgrade. (So that you can refer back to them if eccentricities are discovered in new software versions after a period of time.)

[1] http://en.wikipedia.org/wiki/Fedora_Core
[2] http://www.redhat.com/security/updates/errata/

Redhat FC 4 : glibc-2.3.5 , kernel 2.6.11

Redhat EL4.x / Redhat CentOS 4.x : glibc-2.3.4 , kernel 2.6.9

Redhat EL5.x / Redhat CentOS 5.x : glibc-2.5 , kernel 2.6.18

EL5 is based on FC6

Thankyou Members for your time and great efforts. I'am sure , need to do a lot of homework before I start this activity.

Perhaps this will help as well

http://kbase.redhat.com/faq/docs/DOC-3079