Cisco Pix Inside Interface to Vlan Interface Traffic Problem

Posted on 2006-11-19
Last Modified: 2013-11-16
I am trying to connect to devices on a lower security level interface (vlan20 - from my inside interface (  and I am having problems.  I don't understand how to get the traffic to flow using nat. acl, etc....

Any help would be very much appreciated.


Here is my current pix config:

PIX Version 6.3(3)
interface ethernet0 100full
interface ethernet1 100full
interface ethernet2 100full
nameif ethernet0 outside security0
nameif ethernet1 inside security100
nameif ethernet2 vlan20 security4
fixup protocol dns maximum-length 512
fixup protocol ftp 21
fixup protocol h323 h225 1720
fixup protocol h323 ras 1718-1719
fixup protocol http 80
fixup protocol rsh 514
fixup protocol rtsp 554
fixup protocol sip 5060
fixup protocol sip udp 5060
fixup protocol skinny 2000
fixup protocol smtp 25
fixup protocol sqlnet 1521
fixup protocol tftp 69
pager lines 24
logging on
logging timestamp
logging buffered debugging
logging trap debugging
logging host inside
mtu outside 1500
mtu inside 1500
mtu vlan20 1500
ip address outside x.x.x.x
ip address inside
ip address vlan20
ip audit info action alarm
ip audit attack action alarm
arp timeout 14400
global (outside) 1 interface
global (vlan20) 2 interface
nat (inside) 1 0 0
nat (vlan20) 1 0 0
route outside x.x.x.x 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00
timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00
timeout uauth 0:05:00 absolute
aaa-server TACACS+ protocol tacacs+
aaa-server RADIUS protocol radius
aaa-server LOCAL protocol local
no snmp-server location
no snmp-server contact
snmp-server community public
no snmp-server enable traps
floodguard enable
telnet timeout 5
ssh inside
ssh timeout 30
console timeout 0
terminal width 80

Question by:cgkuehn
LVL 28

Expert Comment

ID: 17976935
Given your current configuration posted above, you need to add a nat statement to match the global statement that you have applied for your vlan20 interface.  You have:

global (vlan20) 2 interface

which means you need to add something like the following for traffic from the inside interface to be translated correctly on the vlan20 interface:

nat (inside) 2 0 0

It is the same command as your "nat (inside) 1" statement that you already have, but you need to specify a "2" instead so that it matches up with the "global (vlan20) 2" statement.  This will allow all source traffic from traffic coming into the inside interface to be translated using PAT to the vlan20 interface IP address ( when going to any device on that vlan20 interface.

Hope this helps...
LVL 20

Accepted Solution

calvinetter earned 500 total points
ID: 17977125
 I wouldn't bother with nat & global statements in this situation.  When letting your inside network access another local network directly attached to your PIX, it's much easier to accomplish this via a static NAT which disables NAT between your inside interface & the other interface, eg:

static (inside,vlan20) netmask
clear xlate   <- important to run this after the command above

  So, traffic from the 192.168.111.x subnet will appear as such on the 'vlan20' interface/network, without NAT happening; depending on what's attached to this interface (router, layer-3 switch?) you might need to set a static route on the other device so it knows how to reach the 192.168.111.x subnet (unless the PIX interface is it's default gateway).  And you don't need to setup any ACLs if all you care about is hosts on the 'inside' network initiating traffic to the 'vlan20' network.

  But, going by the name 'vlan20' - what's the overall setup? Is the PIX 'vlan20' interface connected to a port on a switch, with the port a member of VLAN 20?  ie, switchport configured like just another VLAN port that a PC would attach to?

LVL 51

Expert Comment

by:Keith Alabaster
ID: 17977483
I would agree with Calvinetter. Let the traffic just route normally to the vlan20 from the inside.
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Author Comment

ID: 17982473
Thanks for your comments!

I have both (inside and vlan20) interfaces going into the same switch 2940 (not layer-3) and those ports are configured for their respective vlans, so this will not work with this setup.....right?

I have an old 2610 w/6 ethernet (not FE), do you think I could make that work with my current setup?

In the meantime I have set up a remote VPN on the pix (vlan20 interface) and I am having that give out an inside address and that seems to work alright.  What do you think would be my best bet?

Thanks again!
LVL 20

Expert Comment

ID: 17985082
>...both (inside and vlan20) interfaces going into the same switch...those ports are configured for their respective vlans
   This may work between those 2 subnets as long as traffic isn't trying to enter/exit the same interface on the PIX (ie "U-turn") - PIX 7.x or a router will allow that.  
   But, if you've got other VLANs that you need to route between, then either a layer-3 switch, a router or upgrading your PIX (if 515 or above) to 7.x would be better suited for this.  Though a 2610 isn't really powerful enough for routing between multiple VLANs, especially with heavy traffic & also it doesn't have FE ports.

   You *could* turn your ethernet2 interface into a trunk port & change its port on the switch to also trunk but that's needless complication on your PIX, especially if trying to allow VPN traffic in.  
   Your best bet is to just get a layer-3 switch if possible - which is ideally suited for this, minimum 3560.  Next best would be to upgrade the PIX to 7.x if it's got current SmartNet support.  Regardless, I strongly advise upgrading your PIX to *at least* 6.3(5), if not 7.x, even if you do get a L3 switch.  6.3(5) has many bug- & some security fixes.

>I have set up a remote VPN on the pix ...give out an inside address..
   Don't set your VPN IP pool to anything that overlaps any of your internal subnets.  But VPN issues are best left for a separate post in the VPN TA.   Let's deal with the VLAN situation first.  VPN is yet another reason to upgrade your PIX.


Author Comment

ID: 17988061
I am going to upgrade the PIX to 7.x and get a L3 switch.

Thanks for all your suggestions.

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