Odem Book Error standard ACLs?

steele84

I'm sure I'm in the wrong here but I cannot figure out why the following logic would work? Wouldn't the source IP address in the packets from Host 10.1.1.1 have a source IP of S0/0/0 interface on R1 (R1 is the one on the left) therefore not being able to match the cmd in the ACL? pages in the book 615-616



Here is the text relating too this example:
"For example, Figure 22-9 repeats the same ACL shown earlier in Figure 22-7. The first line of that ACL matches the specific host address 10.1.1.1. If that ACL exist on router R2, placing that ACL as an inbound ACL on R2's S0/0/1 interface can work, because packets sent by host 10.1.1.1 on the left side of the figure can enter R2's S0/0/1 interface. However, if R2 enables ACL 1 on it F0/0 interface, for inbound packets, the ACL will never match a packet with source IP address 10.1.1.1, because packets sent by host 10.1.1.1 will never enter that interface. Packets sent by 10.1.1.1 will exit R2's F0/0 interface, but never enter it, just because of the network topology.

Gallager00

No that logic will work. I think I understand where you are getting confused. Layer 3 header stays the same but Layer 2 header does not.

When a route receives a packet, it removes the old layer 2 header info in the packet and places the new layer 2 header.

atorven

That example is trying to highlight the differences between applying an access list inbound vs outbound.

steele84

Ah yes I'm thinking layer 2! Thanks for clarifying, over thinking things studying way to long at once! Thanks!!