fixup protocol icmp error - Please explain 3

[fraustbyte]

Can someone please explain this in detail? Thanks

 

[NetworkGhost]

There are several types of ICMP messages that are generated for different reasons. Most see are ICMP Type 3 (Destination Unreachable). Alot of times you need these ICMP messages to be kicked back to you for proper transport for situations such as PATH MTU-D. This is important both for troubleshooting and if your machine does not receive the ICMP messages your traffic may not flow correctly. You'll see this alot with https through IPSEC tunnels. The ICMP fixup forwards the ICMP error message to the destination host. Normally the PIX will block and log.

Free Firewall/Network/Systems Support-

http://firewalls.ath.cx

 

[Supergrrover]

This is most useful for traceroutes that timeout at each hop along the way. The router that decrements the count to 0 will generate an icmp error packet and send it back to the originator. Since the outgoing packet and the router that returns the error have different IPs the firewall will drop them because there isn't an entry in the temporary ACL for that IP.

This line tells the ASA/PIX to create and entry in a table and watch the conversation so that it can expect returned packets and NAT them back through the internal host.


Brent
Systems Engineer / Consultant
CCNP, CCSP

 

[fraustbyte]

Thanks to both of you for the explanations. Just to round out my understanding why is this not part of the default configuration? Are there situations when you wouldn't want this kind of traffic coming back to the originator inside the private network?

 

[rkstephen]

Hello,

I have a PIX 506E firewall in place behind a DMZ router. I'm trying to get outside web e-mail access running for our 'on-the-road' staff. I have an ip available 63.227.76.80 with yssmail.yss.ames.ia.us as the url for which I intend to use to point the users to sign in to our inside Exchange server. The Exchange server is Exchange 2003 with web e-mail running on the inside. I'm having trouble getting through the firewall to access the web e-mail on our Exchange server. I have included the config of the PIX firewall. Can anyone tell me what statements I need to include. 192.168.0.109 is the Exchange server. Thanks.

rkstephen

PIX Version 6.3(1)
interface ethernet0 auto
interface ethernet1 auto
nameif ethernet0 outside security0
nameif ethernet1 inside security100
enable password 8iJJ9bxLMjdUe1Yl encrypted
passwd 8iJJ9bxLMjdUe1Yl encrypted
hostname pixfirewall
domain-name yss.yss.ames.ia.us
clock timezone CST -6
clock summer-time CDT recurring
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
name 192.168.0.109 mail
access-list outside_in permit tcp any host 63.227.76.67 eq smtp
access-list outside_in permit icmp any host 63.227.76.65 echo-reply
access-list outside_in permit icmp any host 63.227.76.65 source-quench
access-list outside_in permit icmp any host 63.227.76.65 unreachable
access-list outside_in permit icmp any host 63.227.76.65 time-exceeded
access-list yssgroup_splitTunnelAcl permit ip 192.168.107.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.108.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.109.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.121.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.123.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.124.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.125.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.126.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.127.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.128.0 255.255.255.0 192.1
access-list yssgroup_splitTunnelAcl permit ip 192.168.0.0 255.255.255.0 192.168
access-list nonat permit ip 192.168.0.0 255.255.255.0 192.168.5.0 255.255.255.2
access-list nonat permit ip 192.168.107.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.108.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.109.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.121.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.123.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.124.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.125.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.126.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.127.0 255.255.255.0 192.168.5.0 255.255.255
access-list nonat permit ip 192.168.128.0 255.255.255.0 192.168.5.0 255.255.255
access-list outside_cryptomap_dyn permit ip any 192.168.5.0 255.255.255.224
pager lines 24
logging on
mtu outside 1500
mtu inside 1500
ip address outside 63.227.76.65 255.255.255.192
ip address inside 192.168.0.1 255.255.255.0
ip audit info action alarm
ip audit attack action alarm
ip local pool VPNPOOL 192.168.5.1-192.168.5.25
pdm location 192.168.17.0 255.255.255.0 inside
pdm location 192.168.18.0 255.255.255.0 inside
pdm location 192.168.19.0 255.255.255.0 inside
pdm location 192.168.21.0 255.255.255.0 inside
pdm location 192.168.23.0 255.255.255.0 inside
pdm location 192.168.24.0 255.255.255.0 inside
pdm location 192.168.25.0 255.255.255.0 inside
pdm location 192.168.107.0 255.255.255.0 inside
pdm location 192.168.121.0 255.255.255.0 inside
pdm location 192.168.108.0 255.255.255.0 inside
pdm location 192.168.125.0 255.255.255.0 inside
pdm location 192.168.124.0 255.255.255.0 inside
pdm location 192.168.109.0 255.255.255.0 inside
pdm location 192.168.123.0 255.255.255.0 inside
pdm location 192.168.126.0 255.255.255.0 inside
pdm location 192.168.127.0 255.255.255.0 inside
pdm location 192.168.128.0 255.255.255.0 inside
pdm location 192.168.26.0 255.255.255.0 inside
pdm location 192.168.27.0 255.255.255.0 inside
pdm location 192.168.28.0 255.255.255.0 inside
pdm location 192.168.0.101 255.255.255.255 inside
pdm location mail 255.255.255.255 inside
pdm logging informational 100
pdm history enable
arp timeout 14400
global (outside) 10 63.227.76.68
nat (inside) 0 access-list nonat
nat (inside) 10 0.0.0.0 0.0.0.0 0 0
static (inside,outside) 63.227.76.67 mail netmask 255.255.255.255 0 0
access-group outside_in in interface outside
route outside 0.0.0.0 0.0.0.0 63.227.76.66 1
route inside mail 255.255.255.255 192.168.0.1 1
route inside 192.168.17.0 255.255.255.0 192.168.0.242 1
route inside 192.168.18.0 255.255.255.0 192.168.0.241 1
route inside 192.168.19.0 255.255.255.0 192.168.0.244 1
route inside 192.168.21.0 255.255.255.0 192.168.0.254 1
route inside 192.168.23.0 255.255.255.0 192.168.0.254 1
route inside 192.168.24.0 255.255.255.0 192.168.0.254 1
route inside 192.168.25.0 255.255.255.0 192.168.0.254 1
route inside 192.168.26.0 255.255.255.0 192.168.0.254 1
route inside 192.168.27.0 255.255.255.0 192.168.0.254 1
route inside 192.168.28.0 255.255.255.0 192.168.0.254 1
route inside 192.168.107.0 255.255.255.0 192.168.0.254 1
route inside 192.168.108.0 255.255.255.0 192.168.0.241 1
route inside 192.168.109.0 255.255.255.0 192.168.0.244 1
route inside 192.168.121.0 255.255.255.0 192.168.0.254 1
route inside 192.168.123.0 255.255.255.0 192.168.0.254 1
route inside 192.168.124.0 255.255.255.0 192.168.0.254 1
route inside 192.168.125.0 255.255.255.0 192.168.0.254 1
route inside 192.168.126.0 255.255.255.0 192.168.0.254 1
route inside 192.168.127.0 255.255.255.0 192.168.0.254 1
route inside 192.168.128.0 255.255.255.0 192.168.0.254 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
http server enable
http 192.168.0.101 255.255.255.255 inside
no snmp-server location
no snmp-server contact
snmp-server community public
no snmp-server enable traps
tftp-server inside 192.168.0.110 /ciscotftp
floodguard enable
sysopt connection permit-ipsec
crypto ipsec transform-set ESP-3DES-MD5 esp-3des esp-md5-hmac
crypto dynamic-map outside_dyn_map 20 match address outside_cryptomap_dyn
crypto dynamic-map outside_dyn_map 20 set transform-set ESP-3DES-MD5
crypto map outside_map 65535 ipsec-isakmp dynamic outside_dyn_map
crypto map outside_map client authentication LOCAL
crypto map outside_map interface outside
isakmp enable outside
isakmp policy 20 authentication pre-share
isakmp policy 20 encryption 3des
isakmp policy 20 hash md5
isakmp policy 20 group 2
isakmp policy 20 lifetime 86400
vpngroup yssgroup address-pool VPNPOOL
vpngroup yssgroup dns-server 192.168.0.101
vpngroup yssgroup wins-server 192.168.0.101
vpngroup yssgroup default-domain yss.ames.ia.us
vpngroup yssgroup split-tunnel yssgroup_splitTunnelAcl
vpngroup yssgroup idle-time 1800
vpngroup yssgroup password ********
telnet 192.168.0.101 255.255.255.255 inside
telnet 192.168.0.234 255.255.255.255 inside
telnet timeout 5
ssh 0.0.0.0 0.0.0.0 outside
ssh timeout 5
console timeout 0
username ddenton password e1n42Gxju3IRFBag encrypted privilege 2
username bschrader password epJpxNlwxorF70Hk encrypted privilege 2
username sramus password A9PcgDs1zBR0y5B0 encrypted privilege 2
username rstephen password pxG5WOHc57nmwNpq encrypted privilege 15
username jhaglund password cLKNVdPhb24qJ/7A encrypted privilege 2
username qcisupport password 9bMl6LmTqGqx4wmh encrypted privilege 2
username spaul password DtED.ycTU3irHCe9 encrypted privilege 2
username darringdale password CkXy08NTxGqBHy5e encrypted privilege 2
username adtran password s/dvJdub2ZmNsKdt encrypted privilege 15
username kmcomber password qAsZUktlfJGOZByV encrypted privilege 2
username tbowman password 01xFwMLRvf8EeGd4 encrypted privilege 2
username ecarlson password fl19rrLa6c7DNFY0 encrypted privilege 2
username cdunnwald password 3xLkLev5HItgXH21 encrypted privilege 2
username softforce password 03lkRg/dR7ReXsvq encrypted privilege 2
username tjohanson password DRfZ4RUFZKdyEuad encrypted privilege 2
terminal width 80
banner exec All actions are logged. Unauthorized users will be prosecuted.
banner login All actions are logged. Unauthorized users will be prosecuted.
Cryptochecksum:04ca9229056bc93c2cf7ff3e7dd6c3d8
: end