pg_hba.conf issue

Hi friends,

We have a product with Postgres 8.1 integrated for installations on
Windows. The standard pg_hba.conf configuration going in the package is

# TYPE DATABASE USER CIDR-ADDRESS METHOD

# IPv4 local connections:
host all all 127.0.0.1/32 trust
# IPv6 local connections:
#host all all ::1/128 trust
#host all all 172.21.42.121/24 trust
host all all 172.21.51.56/24 trust

While this works at most of the locations, we have a peculiar error coming
up at 2-3 locations. The error reads:

no pg_hba.conf entry for host "::1" , user "crisil" , database "crisil" ,
SSL off "

Can someone give any clue on why could this be coming up? We do not intend
to use SSL either. Our analysis shows this problem gets resolved if the
entry for ::1/128 is uncommented but we would like to understand in which
scenario is this entry needed.

Regards,
Ritu
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