stranger domain

[Frank Y.F. Luo]

I was doing a name checking for some domains, say, kean.edu

My name server could not resolve it

$host kean.edu
;; connection timed out; no servers could be reached

but my ISP's name sever (xxx.xx.xx.xx) can

$host kean.edu xxx.xxx.xxx.xxx
Using domain server:
Name: xxx.xxx.xxx.xx

kean.edu has address 131.125.1.105

However, when I turned on trace, it stops at the one point ( the name server
of kean.edu)

$dig +trace @xxx.xx.xx.xx  kean.edu

; <<>> DiG 9.2.4rc6 <<>> +trace @xxx.xxx.xxx.xxx kean.edu
;; global options:  printcmd
.                       195497  IN      NS      C.ROOT-SERVERS.NET.
.                       195497  IN      NS      D.ROOT-SERVERS.NET.
.                       195497  IN      NS      E.ROOT-SERVERS.NET.
.                       195497  IN      NS      F.ROOT-SERVERS.NET.
.                       195497  IN      NS      G.ROOT-SERVERS.NET.
.                       195497  IN      NS      H.ROOT-SERVERS.NET.
.                       195497  IN      NS      I.ROOT-SERVERS.NET.
.                       195497  IN      NS      J.ROOT-SERVERS.NET.
.                       195497  IN      NS      K.ROOT-SERVERS.NET.
.                       195497  IN      NS      L.ROOT-SERVERS.NET.
.                       195497  IN      NS      M.ROOT-SERVERS.NET.
.                       195497  IN      NS      A.ROOT-SERVERS.NET.
.                       195497  IN      NS      B.ROOT-SERVERS.NET.
;; Received 436 bytes from xxx.xx.xx.xx#53 in 35 ms

edu.                    172800  IN      NS      A3.NSTLD.COM.
edu.                    172800  IN      NS      C3.NSTLD.COM.
edu.                    172800  IN      NS      D3.NSTLD.COM.
edu.                    172800  IN      NS      E3.NSTLD.COM.
edu.                    172800  IN      NS      G3.NSTLD.COM.
edu.                    172800  IN      NS      H3.NSTLD.COM.
edu.                    172800  IN      NS      L3.NSTLD.COM.
edu.                    172800  IN      NS      M3.NSTLD.COM.
;; Received 299 bytes from 192.33.4.12#53(C.ROOT-SERVERS.NET) in 46 ms

kean.edu.               172800  IN      NS      ASTRO1.kean.edu.
kean.edu.               172800  IN      NS      ASTRO2.kean.edu.
;; Received 100 bytes from 192.5.6.32#53(A3.NSTLD.COM) in 36 ms

dig: Couldn't find server 'ASTRO1.kean.edu': Name or service not known

Any idea about this strange thing? Thanks in advance.