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Fespino1
Beginner

ACLs to block traffic between interfaces on same cisco router

Hello,

 

I'm trying to come up with a couple of ACLs to block traffic in the same router from two of its interfaces (if possible). The only purpose of this router is for internet access only that will be used for one of our wlans. One interface is for us to manage it and the only subnet that needs access to the router. No other communication to the router should exist. Below is the a very simplified example. For example, 10.253.0 subnet will be used for one of our wlans and the router is also the dhcp server for this subnet and we will be using public dns servers. The snapshot below is just an example to simplify scenario. For the management example,10.64.192. subnet should be the only subnet with access to manage this router. Also, the traffic between these two subnets should be blocked so 10.253.0.1 should only have access to the internet. and 10.64.192. will be for management only. We don't want users from the this wlan to have any internal access so I'm trying to block traffic both ways. Is this possible using ACLs in the router?

Both connections to the switch from the router are access ports and the gateway for the management address is on a core (L3). The gateway for the wlan is on the router.

I've been playing with packet tracer but im not getting the results i want. this snapshot is simplified i'm not testing it directly from the router, I have desktops to test communication between subnets in my real packet tracer file FYI

 

cisco.PNG

1 ACCEPTED SOLUTION

Accepted Solutions
Georg Pauwen
VIP Expert

Hello,

 

you can use simple access list like in the example below. Traffic from subnet 10.53.0.0/24 to 10.64.192.0/24 is blocked, the rest is allowed:

 

access-list 101 deny ip 10.253.0.0 0.0.0.255 10.64.192.0 0.0.0.255
access-list 101 permit ip 10.253.0.0 0.0.0.255 any
!
interface GigabitEthernet0/0
description 10_253_0_0_Subnet
ip access-group 101 in

View solution in original post

5 REPLIES 5
Georg Pauwen
VIP Expert

Hello,

 

you can use simple access list like in the example below. Traffic from subnet 10.53.0.0/24 to 10.64.192.0/24 is blocked, the rest is allowed:

 

access-list 101 deny ip 10.253.0.0 0.0.0.255 10.64.192.0 0.0.0.255
access-list 101 permit ip 10.253.0.0 0.0.0.255 any
!
interface GigabitEthernet0/0
description 10_253_0_0_Subnet
ip access-group 101 in

View solution in original post

Hello @Georg Pauwen thank you for the quick response, I just noticed I forgot to add the interfaces in this example.  Another thing I think I need to clarify is that the router should only have access to what I'm calling the mgmt subnet in this example and the wlan subnet while also not allowing communication between the two. So in your example, if im using g0/0 as the 10.253.0.0/16 this is where I'm placing this acl right? And let's say I use g0/1 as the 10.64.192.0/23 subnet interface do I need to accomplish what I need? Sorry for not being clear hope this can help explaining better 

mlund
Rising star

Hi

Another option is to create an vrf, if the router supports it, and move the interface for vlan10 and the isp interface into that vrf.

In that way you have separated the router into 2 logical routers with there own routingtables.

/Mikael

@mlund Hey thank you I will pass this option to the senior eng and see what he thinks. Unfortunately, I think they want to have the 3 physical interfaces at this moment but it is a good option I appreciate it. 

Fespino1
Beginner

@Georg Pauwen Hey I tested the ACLs and it worked I now have communication between hosts in the same subnet only. I used two acls one for each interface. I appreciate it