4.2.2.1
4.2.2.3
4.2.2.4
4.2.2.5

all work.. To see who servers they are just look at the PTR

[homer]$ dig -x 4.2.2.2

; <<>> DiG 9.2.4 <<>> -x 4.2.2.2

;; ANSWER SECTION:
2.2.2.4.in-addr.arpa. 86254 IN PTR vnsc-bak.sys.gtei.net.
1.2.2.4.in-addr.arpa. 86265 IN PTR vnsc-pri.sys.gtei.net.
3.2.2.4.in-addr.arpa. 86247 IN PTR vnsc-lc.sys.gtei.net.
4.2.2.4.in-addr.arpa. 86252 IN PTR vnsc-pri-dsl.genuity.net.
5.2.2.4.in-addr.arpa. 86400 IN PTR vnsc-bak-dsl.genuity.net.