HTTP Browsing

[ihoskins]

I have a client that was recently bought out by another company. The other company has its own IT dept and came down and setup a PIX to do VPN back to its offices. After that happened the users on the local network are unable to http browse to many of the webpages. They can ping and resolve names on the internet, but when browsing to them, it gives a page cannot be displayed after timing out.

The config looks like this:

PIX Version 6.3(1)
interface ethernet0 auto
interface ethernet1 auto
nameif ethernet0 outside security0
nameif ethernet1 inside security100
enable password RzJy8UGUdGeazLOG encrypted
passwd C9jBOvy.OAcr2ROt encrypted
hostname Calsgf1
domain-name stemilt.com
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
access-list 101 permit icmp any any echo-reply
access-list 101 permit icmp any any source-quench
access-list 101 permit icmp any any unreachable
access-list 101 permit icmp any any time-exceeded
access-list 101 permit tcp any host 66.81.2.243 eq smtp
access-list 101 permit udp any any eq isakmp
access-list 101 permit esp any any
access-list nonat permit ip 192.168.1.0 255.255.255.0 192.168.32.0
255.255.255.0
access-list nonat permit ip 192.168.1.0 255.255.255.0 192.168.48.0
255.255.255.0
access-list nonat permit ip 192.168.1.0 255.255.255.0 10.1.2.0 255.255.255.0
access-list 110 permit ip 192.168.1.0 255.255.255.0 192.168.32.0
255.255.255.0
access-list 110 permit ip 192.168.1.0 255.255.255.0 192.168.48.0
255.255.255.0
pager lines 24
mtu outside 1400
mtu inside 1400
ip address outside 66.81.2.243 255.255.255.248
ip address inside 192.168.1.2 255.255.255.0
ip audit info action alarm
ip audit attack action alarm
ip local pool ithelocalpool 10.1.2.10-10.1.2.254
pdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 0 access-list nonat
nat (inside) 1 0.0.0.0 0.0.0.0 0 0
static (inside,outside) tcp 66.81.2.243 smtp 192.168.1.17 smtp netmask
255.255.255.255 0 0
access-group 101 in interface outside
route outside 0.0.0.0 0.0.0.0 66.81.2.242 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
sysopt connection permit-ipsec
sysopt ipsec pl-compatible
crypto ipsec transform-set myset esp-3des esp-md5-hmac
crypto dynamic-map dynmap 40 set transform-set myset
crypto map mymap 30 ipsec-isakmp
crypto map mymap 30 match address 110
crypto map mymap 30 set peer 207.66.193.25
crypto map mymap 30 set transform-set myset
crypto map mymap 40 ipsec-isakmp dynamic dynmap
crypto map mymap interface outside
isakmp enable outside
isakmp key ******** address 207.66.193.25 netmask 255.255.255.255 no-xauth
no-config-mode
isakmp identity address
isakmp policy 30 authentication pre-share
isakmp policy 30 encryption 3des
isakmp policy 30 hash md5
isakmp policy 30 group 2
isakmp policy 30 lifetime 1800
isakmp policy 40 authentication pre-share
isakmp policy 40 encryption des
isakmp policy 40 hash md5
isakmp policy 40 group 2
isakmp policy 40 lifetime 86400
vpngroup vpn3000 address-pool ithelocalpool
vpngroup vpn3000 dns-server 192.168.1.17
vpngroup vpn3000 wins-server 192.168.1.17
vpngroup vpn3000 default-domain 192.168.1.17
vpngroup vpn3000 idle-time 1800
vpngroup vpn3000 password ********
telnet 0.0.0.0 0.0.0.0 inside
telnet timeout 5
ssh 0.0.0.0 0.0.0.0 outside
ssh 207.66.193.16 255.255.255.240 inside
ssh timeout 60
console timeout 0
terminal width 80
Cryptochecksum:94fe3e39aa7ebb5af77543317a320979
Calsgf1#


Any help would be appreciated.

 

[ihoskins]

The MTU size was totally off...

The commands to specify the Maximum Transmission Unit (MTU) or maximum packet size are found on lines 43 through 45. The default values are 1,500 bytes for Ethernet and 8,192 bytes for Token Ring. These values can be modified if necessary. The minimum value is 64 bytes and the maximum value is 65,536 bytes. The PIX supports Path MTU Discover and will send ICMP “packet too big” messages if a large packet is sent with the Don’t Fragment bit set. In most environments, the default MTU values should work fine.

--
Ian Hoskins

 

[pabica]

The "many of the web pages" and "after timing out" are classical symptopms of an MTU problem...

What happens is that many of the larger pages well send back packets larger than the (in this case) 1400 bytes..

You can confirm this diagnosis by finding one of the sites that times out... lets assume that it is

http://www.abcdef.com...

and on the same machine, bring up a command window and at the DOS prompt type "telnet

http://www.abcdef.com

80" and then type "get"... this should bring up an http error from the remote web server... if it does, then the MTU is too small and large packets are never making it back from the remote server... the telnet test will bring back small packets and verify connectivity to port 80 on the remote server...

sometimes, admins will set this value to 1400 to allow room for the VPN encryption overhead...

Thanks,
Bill...
pabica@bellsouth.net