what is the basic rules for ACLs?

Answer Posted / vikram pratap singh

These basic rules should be followed when creating and
applying access lists:

One access list per protocol per direction.
Standard IP access lists should be applied closest to the
destination.
Extended IP access lists should be applied closest to the
source.
Use the inbound or outbound interface reference as if
looking at the port from inside the router.
Statements are processed sequentially from the top of list
to the bottom until a match is found, if no match is found
then the packet is denied.
There is an implicit deny at the end of all access lists.
This will not appear in the configuration listing.
Access list entries should filter in the order from
specific to general. Specific hosts should be denied first,
and groups or general filters should come last.
Never work with an access list that is actively applied.
New lines are always added to the end of the access list.
A no access-list x command will remove the whole list. It
is not possible to selectively add and remove lines with
numbered ACLs.
Outbound filters do not affect traffic originating from the
local router.
There are many show commands that will verify the content
and placement of ACLs on the router.

The show ip interface command displays IP interface
information and indicates whether any ACLs are set.

The show access-lists command displays the contents of all
ACLs on the router.

show access-list 1 shows just access-list 1.

The show running-config command will also reveal the access
lists on a router and the interface assignment information.

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