1. Unfortunately in South Asia a caste system was established amongst Muslims and "legitimized" by corrupt rulers and Mullahs e.g. fatwa jalandari.
It was a combination of converted Brahmins or others trying to retain their caste/race status by "Islamizing" it, and also of conquering races such as Afghans, Turks, Arabs etc stating a native Indian convert could not marry from them.
2. Caste is quite strong amongst Indian Muslims, in fact the legendary Dr Ambedkar apparently said he felt it was in some ways worse amongst Indian Muslims than Hindus (obviously I am not sure in what context he said it because Hindu "higher castes" will at times murder "lower-caste" Hindus for petty things).
3. Pakistanis have it but to a much lesser extent but they do have very strong tribal divisions and hierarchy which remind one of Hindu Brahmin casteism.
4. Bangladesh has it the least.
However caste racism/discrimination is practised amongst our Hindu community with the "higher" caste Bangladeshi Hindus dominating any opportunities/quotas/resources allocated to the Hindu community as a whole.
This should be outlawed in the People's Republic of Bangladesh and our government, media and civil society should actively combat caste discrimination.