ACL Inbound vs Outbound

I think I understand ACLs, except the inbound vs outbound. In my mind it seems like inbound should be for traffic coming into the LAN and outbound should be going out to the WAN, but alas its not that.

So, if I am understanding correctly, inbound and outbound is from the perspective of the sending device.

Device A sends traffic though Router 1 and Router 2 to get to Device B.
Router 1 Ethernet 0 is the inbound interface and Router 1 Serial 0/0 is the outbound interface, while Router 2 Serial 0/0 is the inbound interface and Router 2 Ethernet 0 is the outbound interface. Am I understanding this correctly?

Thanks everyone!

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Comments

phobophile

It's all based on the direction of the traffic. Not one interface is going to be specifically be an INBOUND only, or OUTBOUND only interface.

Using your example, when traffic is going from HostA to HostB, the ethernet interface on Router1 would be viewed as an INCOMING interface (from the view of the router). When the flow of traffic then goes from HostB to Host A, then that ethernet interface on Router1 would be an OUTGOING interface, since traffic is leaving Router1 out that interface. Hope that makes sense.

MrBrian

michaelcox wrote: »

I think I understand ACLs, except the inbound vs outbound. In my mind it seems like inbound should be for traffic coming into the LAN and outbound should be going out to the WAN, but alas its not that.

So, if I am understanding correctly, inbound and outbound is from the perspective of the sending device.

Device A sends traffic though Router 1 and Router 2 to get to Device B.
Router 1 Ethernet 0 is the inbound interface and Router 1 Serial 0/0 is the outbound interface, while Router 2 Serial 0/0 is the inbound interface and Router 2 Ethernet 0 is the outbound interface. Am I understanding this correctly?

Thanks everyone!

Well funny enough you can place access lists, and I'll use the interfaces you gave in your example, in/out on any interface you want...

Inbound or Outbound on Ethernet 0... also
Inbound or Outbound on Serial 0/0

If you add an ACL to an interface, any packets needing to go through that interface will be filtered through the ACL if it's going in the direction configured by you... just think of the packet flow hop by hop and mess around with it in a lab/simulator for awhile and you'll see. HTH!

michaelcox

phobophile wrote: »

It's all based on the direction of the traffic. Not one interface is going to be specifically be an INBOUND only, or OUTBOUND only interface.

Using your example, when traffic is going from HostA to HostB, the ethernet interface on Router1 would be viewed as an INCOMING interface (from the view of the router). When the flow of traffic then goes from HostB to Host A, then that ethernet interface on Router1 would be an OUTGOING interface, since traffic is leaving Router1 out that interface. Hope that makes sense.

it does, thank you.