CBS350 - One directional ACLs

[bwv656]

Dear Cisco Community,

I have two VLANs on my CBS350-24T-4X

• VLAN 10 - 192.168.10.0
• VLAN 30 - 192.168.30.0

And I want VLAN 10 to access VLAN 30
but I want to block VLAN 30 accessing VLAN 10.

VLAN 10 -----ALLOW---->>> VLAN 30

VLAN 10 <<<----BLOCK----- VLAN 30

I've tried several things and also followed this Cisco YouTube video but it blocks signal from both directions.
When I ping from 192.168.10.7 to 192.168.30.33 I get Request timeout.

When I ping from 192.168.30.33 to 192.168.10.7 I get Request timeout.

Here are my settings. Any help would be very much appreciated!! 
Thank you so much in advance.

[TJ-20933766]

If you create an ACL that blocks traffic sourced from VLAN 30 that is destined for VLAN 10 and apply the ACL to the VLAN 30 interface in the inbound direction, your desired goal would be met; however, you would still not be able to ping. If you were on a computer in VLAN 10 and pinged a computer on VLAN 30 that was running a packet capture, you would see the incoming echo request followed by the echo reply. The computer in VLAN 10 would never receive the echo reply because the ACL would be blocking it. So traffic is in fact making it from VLAN 10 to VLAN 30 but traffic from VLAN 30 is not making it back to VLAN 10.

Now if you are wanting VLAN 10 to be able to initiate a connection with a computer in VLAN 30 and allowing the return traffic (able to receive the echo replies) while denying any computer in VLAN 30 from initiating a connection with any device in VLAN 10, you would not be able to accomplish this with an ACL. This is what a stateful packet filter does which is commonly seen in firewalls.

Does this answer your question?

[bwv656]

Thank you so much for the detailed explanation!!!

I was very confused about the difference between ACLs and FireWalls. But after reading your explanation, everything makes perfect sense now. 

Looks like, I need to do this via FireWall in my Router, not this switch. And I have two questions relate d to this. hopefully, you can answer this for me.

With the limitations you mentioned above, L3 switches with ACLs are faster at handling signals compared to handling via FireWalls in the router, right?

And my current router is EdgeRouter Lite and let's say I have 10 computers in my entire network. Do you think this small router is able to handle this FireWall traffic without slowing down?

[paul driver]

Hello

---

@bwv656 wrote:

Dear Cisco Community,

I have two VLANs on my CBS350-24T-4X

• VLAN 10 - 192.168.10.0
• VLAN 30 - 192.168.30.0

And I want VLAN 10 to access VLAN 30
but I want to block VLAN 30 accessing VLAN 10.

VLAN 10 -----ALLOW---->>> VLAN 30

VLAN 10 <<<----BLOCK----- VLAN 30

---

Having never had any exposure to this switch model so i cannot say if you can do this within the GUI, So do you have access to the cli?

The following example should perform the above request for tcp traffic, udp is classless it so cannot be filtered on established traffic


ip access-list extended Vl10-Vl30
permit icmp 192.168.30.0 0.0.0.255 any echo-reply
deny icmp 192.168.30.0 0.0.0.255 any echo
permit tcp 192.168.30.0 0.0.0.255 any established
deny tcp 192.168.30.0 0.0.0.255 any
permit ip any any

int vlan 10
ip access-group Vl10-Vl30 out

[bwv656]

Thank you so much for the answer. But I have a quick question before I try anything. Above CLI commands you posted are for IOS only right? The switch I have is the new CBS 350 switches, basically a face-lifted version of old SG350s. Please correct me if I am wrong but IOS commands are not compatible with these switches, right? Especially the ACLs commands.

[TJ-20933766 · Accepted solution]

-The access list shown by Paul will allow UDP traffic to be initiated from VLAN 30 to VLAN 10 which does not conform to the requirements of the original post which is why I mentioned using a stateful packet filter such as the one in your EdgeRouter Lite.

-As to your question about slowing down, you will likely not see any kind of speed degradation.

-As for your question about ACL CLI syntax, according to: https://www.cisco.com/c/dam/en/us/td/docs/switches/lan/csbms/350_/cli_guide/CLI_Tesla_Sx350_2_2_5.pdf it looks to be similar to IOS but some minor differences so if you were wanting to block traffic as mentioned in your original post, the syntax would be:

ip access-list extended NO-ACCESS-TO-VLAN10
 deny ip any 192.168.10.0 0.0.0.255

interface vlan 30
 service-acl input NO-ACCESS-TO-VLAN10 default-action permit-any

[bwv656]

Thank you so much once again for taking the time to write this detailed answer!!! You really helped me to understand the whole thing.

As you suggest I will use the EdgeRouter for managing the traffic. And I am so glad about this because I was starting to think managing ACLs felt not as intuitive as managing Firewall rules. At least for me.

Thanks again for your crystal clear answers!! Happy New Year!! 

[paul driver]

Hello @TJ-20933766  

The acl you propose will not allow traffic initiated from vlan 10 whatsoever not even tcp.

Now if your going to incorporate a router for the inter lan routing then your have options open up other than using a firewall

features such as:

DACL

CBAC

ZBFW

All of which won’t require a designated firewall but will allow you to deny traffic one way and allow the other!

However if this switch is the L3 for the lan then naturally the above isn’t viable with a router or firewall unless you move the L3 for those two vlans off the switch and onto a router /firewall and filter from their

[bwv656]

Paul, thank you so much for providing the extra information. Since I don't have a CISCO router. I only have Cisco Switches at home (CBS350-24T-4X and SG200). So those features you listed are out of reach for me. But in the future, I will consider them when I upgrade my router. For now, I will stick with the Firewall in my router and go from there. Thanks again for providing the detailed answers today and hope you have a wonderful 2021!! Happy New Year!!