topic Re: pix behind dsl modem...help! in Network Security

pix behind dsl modem...help!

mjsully — Fri, 21 Feb 2020 07:19:31 GMT

I am trying to setup a PIX 501 firewall that sits behind a DSL modem on a home network that consists of three PC's. I have the PIX setup as a dhcp server for the inside interface. It seems to be assigning addresses ok to the PC's. I can ping an outside ip from within the PIX, but I cannot access any web pages via a browser from any of the computers on the LAN. I can see the dns info, so that looks like its ok. when I try to connect to the internet, the firewall logs the following "710005: UDP request discardedfrom10.0.1.104/137toinside:10.255.255.255/netbios-ns" and thats it.

firewall is setup as below. please help. thanks

interface ethernet0 auto

interface ethernet1 100full

nameif ethernet0 outside security0

nameif ethernet1 inside security100

enable password xxxxx

passwd xxxxx

hostname pixfirewall

fixup protocol ftp 21

fixup protocol h323 h225 1720

fixup protocol h323 ras 1718-1719

fixup protocol http 80

fixup protocol ils 389

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

names

pager lines 24

logging on

logging buffered debugging

mtu outside 1500

mtu inside 1500

ip address outside pppoe setroute

ip address inside 10.0.1.100 255.0.0.0

ip audit info action alarm

ip audit attack action alarm

pdm history enable

arp timeout 14400

global (outside) 1 interface

nat (inside) 1 0.0.0.0 0.0.0.0 0 0

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:

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 10.0.0.0 255.0.0.0 inside

telnet timeout 5

ssh timeout 5

console timeout 0

vpdn group DSL request dialout pppoe

vpdn group DSL localname xxxx

vpdn group DSL ppp authentication pap

vpdn username xxxx password *********

dhcpd address 10.0.1.102-10.0.1.110 inside

dhcpd lease 3600

dhcpd ping_timeout 750

dhcpd enable inside

terminal width 80

Re: pix behind dsl modem...help!

mostiguy — Sat, 03 Apr 2004 08:54:55 GMT

can you crank up debug logging for pppoe? what outside ip can you ping? are you getting an external ip address from your isp?

Re: pix behind dsl modem...help!

mjsully — Sat, 03 Apr 2004 15:31:33 GMT

I found that if I manually specify a set of dns servers using the "dhcpd dns" command, that I can browse the internet. still not sure why the dhcp wasn't getting this automatically. I could ping any valid outside address from the FW all along, and I could enter the ip address of a site in the browser instead of the hostname and it would work fine. would like to know why the dns wasn't getting through automatically, if anyone has any thoughts? at least it is working though. thanks

Re: pix behind dsl modem...help!

guydestefano — Mon, 05 Apr 2004 22:28:39 GMT

Please forgive this post since I am not an expert or have any expierience in the PIX 501. Three weeks ago, I purchased a PIX 501 and tried to install it with two desktop and one laptop computer to safely share the Internet. Thru much help with the ARS networking board and this particular forum, everything works super. The pix shares 3 computers and also one access point for wireless laptop. The only differences between yours and my config are listed below. If you have already found the answer, that's great. I am only saying below works for me. Good Luck, it was very stressful until the final instruction made it work.

hostname pixfirewall

--------------> domain-name ciscopix.com

fixup protocol ftp 21

pager lines 24

--------------> icmp permit any unreachable outside

logging on

aaa-server LOCAL protocol local

--------------> http server enable

--------------> http 192.168.1.0 255.255.255.0 inside

no snmp-server location

dhcpd ping_timeout 750

--------------> dhcpd auto_config outside

dhcpd enable inside

Re: pix behind dsl modem...help!

sskillin — Mon, 05 Apr 2004 23:20:33 GMT

In this case, the PIX is both a DHCP client and a DHCP server. As a DHCP client, it was recieving DNS info from your ISP and could probably resolve things just fine. Your inside computers, however, are relying on THEIR DHCP server (in this case, the PIX) to provide them with all the info they need. So yes, "dhcpd dns" must be set in order for your client computers to get all of their info.