Acess list questions

hawaz

Is there a rule whether to assign inbound or outbound access list to an interface ?

1/one documentation says that u mostly assign outbound execpt on telnet
2/another says depends entirely on the network and or protocol

What about the rule assign access list to an interface close to destination if extended and close to source if standard .

I need some clarification.

thanks in advance.

M_Boyd

Cool just did this topic a couple of days ago although anyone feel free to correct me if I am wrong on this. Can help you with one part ....

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Extended access lists should be placed nearest the source

Standard access lists should be placed at the destination

The reason for this is because standard access lists only use the source port whilst the extended access lists use source and destination ports so you are best placing at the source.

arracapuns

Hi guys,

Yes, this is an interesting topic...

M_Boyd, you are pretty right in what you say, but I may say that you mistake port addresses with IP addresses when you refer to standard access lists.

-Standard access list can check part, or the whole IP source Address. (not ports)

-Extended access lists can check part, or the whole IP source and destination addresses, source and destination port numbers, protocols (tcp, udp, icmp, igrp igmp and others), IP TOS, IP precedende (According to CCNA certification guide by Wendell Odom)

I would add that Extended lists should be placed not only near to the source, but also as INBOUND traffic. The reason is that with extended lists you can specify in high detail the destination, and therefore discard the packet as soon as possible and BEFORE it wastes routing resources. It makes no sense applying it to OUTBOUND traffic and have your router busy with traffic that you know is going to be discarded.

Please, notice that this is not a statement, but my own opinion. Anyway, there can be an scenario in which this logic simply does not apply. If someone of you can think of such an scenario, please let me know...

I hope this is somehow clarifying for you, hawaz.

Good luck.