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cisco vlan isolation

Posted on 2015-02-23
Medium Priority
Last Modified: 2015-11-10
I need to create a acl list that will apply to my guest vlan that is already setup for wifi,  I uses aerohive.  What i need is to apply a vlan to a switch port so i can plug a computer in and isolate that computer form the whole network except dhcp requests from a internal server.   Out bound and inbound i do not need a port restrictions from the internet

so my vlan in question is vlan 23   ip range it uses is

How do i do it...


I have seen lots of articles on this but not the definitive answer and commands to enter.
Question by:ckness

Accepted Solution

rgorman earned 668 total points
ID: 40627036
Just so I am clear on what you want to do...

Your guest VLAN 23 is configured to use subnet so I am assuming the gateway for the hosts on that network would be something like  Also, what mask are you using?  I am also assuming you have as the IP address for the VLAN interface on that switch and it is configured to allow routing.  What is the switches default route currently?  I would assume it would be another VLAN that the Internet router is connected to and the LAN IP of that router.  I would also assume you have the routing working so your regular LAN traffic routes through a VLAN interface on the same switch before routing to the VLAN where the Internet router is.  If it is setup that way (3 VLAN's) then it should be fairly easy to add an ingress access list to the VLAN 23 interface that denies traffic from source to your LAN subnet but add exceptions for DHCP/BOOTP.  You may also want to block LAN to through an ingress access list on the LAN VLAN interface.
LVL 31

Assisted Solution

Predrag earned 668 total points
ID: 40627464
To block all access VLAN 23 to any of your networks you can use this ACL. But in this case other members of VLAN 23 can access to each VLAN  23 host. No need for more configuration - DHCP works. Basically you deny access to any private address space from that VLAN.

access-list 100 deny ip
access-list 100 deny ip
access-list 100 deny ip
access-list 100 permit ip any any

int vlan 23
ip access-group 100 in

Is that all you need or you want to isolate that host from other hosts on VLAN 23 too?

Assisted Solution

Matt earned 664 total points
ID: 40627565
This is an example from one of my clients - Guest with limitations.

LAN, mask, gateway

interface Vlan23
 description Guest LAN
 ip address
 ip access-group GUEST_access_in in

ip access-list extended GUEST_access_in
 remark ACL for VLAN GUEST
 remark Block traffic to private networks
 deny   ip
 deny   ip
 deny   ip
 deny   ip
 deny   ip
 deny   ip
 deny   ip
 deny   ip
 deny   ip
 remark Allowed DHCP
 permit udp any any eq bootps
 remark Allowed traffic
 permit tcp any eq www
 permit tcp any eq 443
 permit tcp any eq ftp-data
 permit tcp any eq ftp
 permit tcp any eq 22
 permit tcp any eq 465
 permit tcp any eq 587
 permit tcp any eq 993
 permit tcp any eq 995
 permit udp any eq domain
 permit udp any eq ntp
 remark Allowed outside VPN
 remark VPN-> PPTP
 permit tcp any eq 1723
 permit gre any
 remark VPN-> L2TP - IPSec
 permit udp any eq isakmp
 permit udp any eq non500-isakmp
 remark VNC
 permit tcp any eq 5900
 remark Apple
 permit tcp eq 5223
 permit udp range 16384 16403
 remark Amazon
 permit tcp eq 5223
 permit tcp eq 5223
 permit tcp eq 5223
 permit tcp eq 4244
 permit tcp eq 5242
 permit tcp eq 5242
 permit tcp eq 5242
 permit tcp eq 5242
 permit tcp eq 5242
 permit tcp eq 5223
 permit tcp eq 4244
 remark Facebook
 permit tcp object-group FACEBOOK gt 1024 log
 remark Android Market
 permit tcp any eq 5228
 permit udp any eq 5228
 remark XMPP
 permit tcp any eq 5222
 remark Allowed traffic for Web Services Dynamic Discovery
 permit udp host eq 3702
 remark UPnP
 permit udp host eq 1900
 remark Viber
 permit tcp any eq 4244
 permit tcp any eq 5242
 permit udp any eq 5243
 permit udp any eq 7985
 remark ICMP traffic
 permit icmp any echo
 permit icmp any echo-reply
 remark Blocked traffic
 deny   ip any any log

Expert Comment

by:Daniel Sheppard
ID: 40628931
I am confused as to what you are attempting to accomplish here, you mention ACL and in the same sentence you mention you need to apply a VLAN to a specific port.

In isolating a specific port from the rest of a layer 2 network, it really isn't possible to do it (unless you block it with a layer 2 ACL and filter by MAC addresses, but then you can't achieve the second requirement of allowing DHCP).

You can filter at the router, however anything connected to the same network segment (subnet) can still access that computer unless you are using Cisco's private Vlan functionality.

IF you are blocking at the router, the above configurations will work.  IF you need more fine grained control, I would recommend moving to a separate VLAN for your device.

Author Comment

ID: 41221966
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