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I was configuring Standard ACL on router 1841 on Cisco Packet Tracer with the help of command access-list 1 permit 172.16.40.3 0.0.0.0 and access-list 1 deny 172.16.40.4 0.0.0.0 and then I applied this ACL to interface f0/0 which should have allowed the host 172.16.40.3 and blocked the host 172.16.40.4 instead it blocked the entire network 172.16.40.0 network not a single host can ping to the 172.16.10.1 router even the neighbour routers are not able to ping to 172.16.10.1 router. What should I do to solve this problem?

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1

You need to use wildcards. What you did permits 172.16.40.3 to talk to 0.0.0.0 (invalid address) and the implied deny any any blocks anything else.

Try

permit 172.16.40.3/32 0.0.0.0/0
deny 172.16.40.4/32 0.0.0.0/0
permit any any

or

permit 172.16.40.3 0.0.0.0 0.0.0.0 255.255.255.255
deny 172.16.40.4 0.0.0.0 0.0.0.0 255.255.255.255
permit any any
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  • Thank-you so much mate
    – user60845
    Sep 7, 2019 at 14:08
  • I tried what you suggested to me but the router is not recognising /32 and /0 mask I think that's the old syntax.
    – user60845
    Sep 7, 2019 at 14:32
  • @user60845 I've added the lengthy wildcard syntax as well.
    – Zac67 ♦
    Sep 7, 2019 at 17:36
  • Tired that too again it's a old syntax 😣
    – user60845
    Sep 8, 2019 at 5:28
  • Hey man problem solved I was applying the ACL on inbound connection that's why it was not letting other devices to communicate to the router. As I applied the ACL on outbound connection the problem solved. Thank-you very much for replying I really appreciate that 😊👍
    – user60845
    Sep 8, 2019 at 7:24

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