Thanks for the reply and the links Aki, good to know the installation steps. As per your below comments and install steps, I was under the impression that the proxy setup that I used during the OS install will only apply for installation and proxy configuration will clear up after the OS install. But, when I do the 'apt update', still trying to resolve the old proxy. Please see the below output, where 'xxx.xxxx.xxx' is my old proxy address. I manage to find config under /etc/apt/apt.conf, have updated the proxy address and am now able to resolve and able to do the 'apt update'. About setting up the system-wide proxy, I couldn't the setup info (unless I missed it) in the Debian handbook apart from the Squid proxy setup. But I'm not looking to set up a Squid proxy on this machine, I'm looking to leverage the existing proxy server in my environment to access the internet. So, I set up the proxy at /etc/profile.d/proxy.sh and appears to be working.
~$ sudo apt update
[sudo] password for debadmin:
Err:1
http://security.debian.org/debian-security bullseye-security InRelease
Could not resolve 'xxx.xxxx.xxx'
Err:2
http://deb.debian.org/debian bullseye InRelease
Could not resolve 'xxx.xxxx.xxx'
Err:3
https://dl.google.com/linux/chrome/deb stable InRelease
Could not resolve 'xxx.xxxx.xxx'
Err:4
http://deb.debian.org/debian bullseye-updates InRelease
Could not resolve 'xxx.xxxx.xxx'
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
W: Failed to fetch
http://deb.debian.org/debian/dists/bullseye/InRelease Could not resolve 'xxx.xxxx.xxx'
W: Failed to fetch
http://security.debian.org/debian-secur ... /InRelease Could not resolve 'xxx.xxxx.xxx'
W: Failed to fetch
http://deb.debian.org/debian/dists/bull ... /InRelease Could not resolve 'xxx.xxxx.xxx'
W: Failed to fetch
https://dl.google.com/linux/chrome/deb/ ... /InRelease Could not resolve 'xxx.xxxx.xxx'
W: Some index files failed to download. They have been ignored, or old ones used instead.
~$