How to add second network of addresses in a Cisco PIX 506e

Posted on 2006-10-19
Last Modified: 2013-11-16
Thanks to the help on this site, I was able to get my new PIX 506e setup at our remote office.
The office has Cable internet going to PIX 506e, using DHCP from provider.  We then have an HP ProCurve 2524 to hook up the user workstations.  I am using the PIX as the DHCP server on the network and using IPs 192.168.10.x.
We have a second seperate network (10.0.x.x) hooked up to a seperate switch that our developers use in the labs.  Is there a way to add those systems in the 10.0.x.x network to my switch, but not have access to and from the internet.  We mainly need some users on the 192.168.10.x network to be able to see and connect to those 10.0.x.x systems, which are mostly Linux boxes.   Below is my PIX config and thanks so much in advance:

PIX Version 6.3(5)
interface ethernet0 auto
interface ethernet1 auto
nameif ethernet0 outside security0
nameif ethernet1 inside security100
enable password JfkQFW23RBBo0F9M encrypted
passwd JfkQFW23RBBo0F9M encrypted
hostname NYPIX
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 http 8080
fixup protocol pptp 1723
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 history errors
mtu outside 1500
mtu inside 1500
ip address outside dhcp setroute
ip address inside
ip audit info action alarm
ip audit attack action alarm
pdm location inside
pdm logging informational 100
pdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 1 0 0
timeout xlate 0:05:00
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 sip-disconnect 0:02:00 sip-invite 0:03:00
timeout uauth 0:05:00 absolute
aaa-server TACACS+ protocol tacacs+
aaa-server TACACS+ max-failed-attempts 3
aaa-server TACACS+ deadtime 10
aaa-server RADIUS protocol radius
aaa-server RADIUS max-failed-attempts 3
aaa-server RADIUS deadtime 10
aaa-server LOCAL protocol local
http server enable
http inside
no snmp-server location
no snmp-server contact
snmp-server community public
no snmp-server enable traps
no floodguard enable
telnet inside
telnet timeout 30
ssh inside
ssh timeout 30
console timeout 0
dhcpd address inside
dhcpd lease 3600
dhcpd ping_timeout 750
dhcpd domain
dhcpd auto_config outside
dhcpd enable inside
terminal width 80
: end

Question by:WPC479
  • 3
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LVL 79

Expert Comment

ID: 17767531
Well -- yes and no
Yes, you can put a different subnet on the same wire and they won't be able to go out through the PIX fw
No, you can't talk between the two different subnets without some layer 3 device to route between the subnets
No, you can't use the PIX to route between the subnets unless you set up VLAN interfaces and trunk between the switch and the PIX
You could simply add an additional ip address only on those PC's that you want to talk to this new 10.x.x. subnet, but I don't think they can simultaneously be dhcp clients. Manually assign then a primary IP address in the 192.168.10.x range and give them an additional address in the 10.0.0.x subnet

Author Comment

ID: 17768302

How do I configure the 10.x subnet in the PIX config to make sure they are blocked from the outside world.
LVL 79

Accepted Solution

lrmoore earned 125 total points
ID: 17768795
By *not* including them in the nat statement, and not having any interface of the pix in the 10.x subnet you can be 100% sure that no 10.x traffic will ever go through the PIX to the outside world.

nat (inside) 1 0 0  <== does *not* include 10.x.x.x


Author Comment

ID: 17797036
Someone mentioned to me that instead of adding the 10.0.0.x address to the NIC, that I should set up a route between the 192.168.10.x and the 10.0.0.x networks.  How would I do that with the PIX?  And most importantly, the 10.0.0.x needs to be invisible both ways with the outside world of the PIX.

LVL 79

Expert Comment

ID: 17797310
You can't setup a route between the two networks without having some layer3 routing device to route between them. Given that your PC's all point to the PIX inside IP as their default gateway, then the PIX would have to know about this network and route back to it. But - the PIX can't do that anyway.
The only way you could make that work would be to setup VLAN's on your switch, create VLAN subinterfaces on the PIX, set up complex rules for what can/cant talk to each other, and this would still violate your requirement that this network be invisible to the PIX.
Given that you are sharing the same layer2 space with 2 different layer3 addresses, the only practical  solution is to simply add a secondary IP on any system that you want to talk to both networks and the PIX never gets involved in any way. If it does see any traffic sourced from the 10.x.x.x network (and it will because of simple things like Netbios broadcasts) it simply disregards it because it has no rules to tell what to do with it.


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