The below table shows a sample of a packet filter firewall rule$-$set for an imaginary network of IP

address that range from $192\mathrm{.}168\mathrm{.}1\mathrm{.}0$ to $192\mathrm{.}168\mathrm{.}1\mathrm{.}254.$

a$)$ Describe the effect of rules $1,2,3,$ and $4.$

Sample Packet Filter Firewall Ruleset

b$)$ Write rules for having the below effects.

Allow External Users to send email in $($SMTP Port#: $25).$

Allow External Users to access WWW server $($HTTP Port#: $80).$

Everything not previously allowed is explicitly denied.