not cloning github private repo through ssh , although it can clone bitbucket snd gitlab private repo.

Do you have any firewalls or proxies in between?

If so, check those. You could use traceroute to see where the break is.

No, I dont have any firewall and proxies in between. And by using traceroute after 13 hops only *** comes upto 255.

traceroute -m255 github.com
traceroute to github.com (192.30.253.113), 255 hops max, 60 byte packets
 1 192.168.108.254 (192.168.108.254) 3.249 ms 3.224 ms 3.203 ms
 2 192.168.1.2 (192.168.1.2) 0.495 ms 0.492 ms 0.514 ms
 3 10.111.116.1 (10.111.116.1) 3.567 ms 43.600 ms 43.584 ms
 4 10.111.116.1 (10.111.116.1) 3.035 ms 2.992 ms 3.351 ms
 5 14.141.116.69.static-delhi.vsnl.net.in (14.141.116.69) 3.925 ms 4.287 ms 4.267 ms
 6 172.23.183.121 (172.23.183.121) 30.087 ms 172.29.250.33 (172.29.250.33) 28.354 ms 28.758 ms
 7 ix-ae-1-3.thar2.njy-newark.as6453.net (66.198.70.33) 221.207 ms 207.973 ms 219.678 ms
 8 if-ae-11-14.tcore2.nto-new-york.as6453.net (63.243.186.5) 226.802 ms if-ae-11-14.tcore2.nto-new-york.as6453.net (63.243.216.5) 212.938 ms if-ae-14-2.tcore2.nto-new-york.as6453.net (63.243.186.16) 226.592 ms
 9 63.243.216.14 (63.243.216.14) 217.780 ms 221.911 ms 226.549 ms
10 216.156.16.132.ptr.us.xo.net (216.156.16.132) 234.515 ms 234.521 ms 223.455 ms
11 te-4-2-0.rar3.chicago-il.us.xo.net (207.88.12.137) 223.020 ms 216.525 ms 217.684 ms
12 207.88.13.115.ptr.us.xo.net (207.88.13.115) 218.345 ms 233.351 ms 227.396 ms
13 209.48.43.110 (209.48.43.110) 217.766 ms 223.831 ms 209.48.43.106 (209.48.43.106) 216.725 ms
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noo