Access list

Hi,

I have 2 cisco routers. A and B.

A must able to initiate TCP connections to B and be able to receive packets in response to its own connections.  

But B can't initialize TCP connections to A.

How do i configure that in the excesslist?

Thank you.
AgeOfWarsAsked:
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AgeOfWarsAuthor Commented:
Sorry.

I meant I have 2 computers, A and B connected to one router.

PC A must be able to initiate TCP connections to B and be able to receive packets in response to its own connections.  

But PC B alone can't initialize TCP connections to A.

how do I configure the accesslist

Thank you


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grbladesCommented:
Hi AgeOfWars,
Create an access list which only permits established connections back to computer A :-
access-list 101 permit tcp any any established
access-list 101 deny ip any any

Then apply this access-list in the outbound direction on the interface computer A connects to.
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AgeOfWarsAuthor Commented:
Hi GrBlades,

I have 2 questions)

1)
Can you briefly explain the use of TCP and IP in the sentence. I know what they means but I don't really get it.

2)
Say, PC A is connected to Router port 1 and B is connected to router port 2. When a packet travels from PC A to PC B, the accesslist will activate becuase it is applied to port 1. my question is when a packet travelling from PC B to PC A, it will go through port 1, route to port 2 and to PC A, will the accesslist applied on port 1 be activated?
if yes, which will be the outbound and inbound port?

Thank you.
Ian
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grbladesCommented:
1) The TCP keyword means the line only matches TCP type packets. This is required in order to use the 'established' keyword. This like therefore permits all TCP replies back to PC A but does not allow any new connections to it from other machines.
The IP keyword basically means any IP traffic. This line basically sais to deny anything else.

2) The access-list is applied to the outbound direction so when traffic goes from PC A it goes into the port so does not go through the access-list. The reply from PC B does go out of that port so gets checked against the access-list.
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AgeOfWarsAuthor Commented:
Thanks!
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Networking Protocols

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