Re: Problems with SMTP port forwarding on ASA 5505

shampton10 · ‎01-26-2013

Cannot telnet to port 25 to test for SMTP traffic. Packet trace indicates that the packet is dropped by the implicit rule, but I have tried an access rule specifically for SMTP, and the trace appears to skip the rule and drop the packet when it hits the implicit default drop rule. Can anyone help? Here is my configuration:

ASA Version 8.2(5)
!
hostname XXXXXXXXXXXXXXXXX
enable pXXXXXXXXXXXXXXXXXXXXX encrypted
passwd XXXXXXXXXXXXXXXXXX encrypted
names
name XXX.XXX.XXX.74 DNI-HOST1
name XXX.XXX.XXX.184 DNI-HOST2
name 192.168.1.2 Server
!
interface Ethernet0/0
switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
!
interface Ethernet0/3
!
interface Ethernet0/4
!
interface Ethernet0/5
!
interface Ethernet0/6
!
interface Ethernet0/7
!
interface Vlan1
nameif inside
security-level 100
ip address 192.168.1.1 255.255.255.0
!
interface Vlan2
nameif outside
security-level 0
ip address XXX.XXX.XXX.130 255.255.255.248
!
ftp mode passive
clock timezone CST -6
clock summer-time CDT recurring
object-group service rdp tcp
port-object eq 3389
access-list INBOUND extended permit icmp any any time-exceeded
access-list INBOUND extended permit icmp any any echo-reply inactive
access-list INBOUND extended permit icmp any any
access-list INBOUND extended permit tcp any any eq smtp
access-list INBOUND extended permit tcp any any eq https
access-list INBOUND extended permit tcp any eq 3389 any object-group rdp
pager lines 24
logging enable
logging buffered warnings
logging asdm informational
mtu inside 1500
mtu outside 1500
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 1 192.168.1.0 255.255.255.0
static (inside,outside) tcp interface smtp Server smtp netmask 255.255.255.255
access-group INBOUND in interface outside
route outside 0.0.0.0 0.0.0.0 XXX.XXX.XXX.129 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
timeout floating-conn 0:00:00
dynamic-access-policy-record DfltAccessPolicy
http server enable
http 192.168.1.0 255.255.255.0 inside
http DNI-HOST2 255.255.255.255 outside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
crypto ca trustpoint _SmartCallHome_ServerCA
crl configure
crypto ca certificate chain _SmartCallHome_ServerCA
certificate ca [REDACTED]
quit
telnet 192.168.1.0 255.255.255.0 inside
telnet timeout 5
ssh 206.190.255.0 255.255.255.0 outside
ssh DNI-HOST2 255.255.255.255 outside
ssh DNI-HOST1 255.255.255.255 outside
ssh timeout 5
console timeout 0
management-access inside

threat-detection basic-threat
threat-detection statistics access-list
threat-detection statistics tcp-intercept rate-interval 30 burst-rate 400 average-rate 200
webvpn
username Administrator password XXXXXXXXXXXXXXXXXXXX encrypted
!
class-map inspection_default
match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
parameters
message-length maximum client auto
message-length maximum 512
policy-map global_policy
class inspection_default
inspect dns preset_dns_map
inspect ftp
inspect h323 h225
inspect h323 ras
inspect rsh
inspect rtsp
inspect esmtp
inspect sqlnet
inspect skinny
inspect sunrpc
inspect xdmcp
inspect sip
inspect netbios
inspect tftp
inspect ip-options
!
service-policy global_policy global
prompt hostname context
no call-home reporting anonymous
call-home
profile CiscoTAC-1
no active
destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
destination address email callhome@cisco.com
destination transport-method http
subscribe-to-alert-group diagnostic
subscribe-to-alert-group environment
subscribe-to-alert-group inventory periodic monthly
subscribe-to-alert-group configuration periodic monthly
subscribe-to-alert-group telemetry periodic daily
Cryptochecksum:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
: end

Karsten Iwen · ‎01-26-2013

Your ACL and NAT should work. Please send the output of the packet-tracer-command:

packet-tracer input outside tcp 1.2.3.4 1234 XXX.XXX.XXX.130 25

And better change the ACL:

no access-list INBOUND extended permit tcp any any eq smtp

access-list INBOUND extended permit tcp any XXX.XXX.XXX.130 eq smtp

These ACEs are wrong or not needed:

access-list INBOUND extended permit tcp any any eq https

access-list INBOUND extended permit tcp any eq 3389 any object-group rdp

For icmp/ping replys configure icmp-inspection:

policy-map global_policy

class inspection_default

inspect icmp

--

Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

techinneed · ‎01-26-2013

I agree with "Karsten" on the ACL\ACE changes.

What I would also check, is the email server. I only know Exchange servers. On the Exchange server, there is an SMTP protocol "Virtual Server" where you can configure what IP addresses are allowed to perform "SMTP Relay" to it. You should indicate which SMTP Relay Servers' IP and\or IP Networks are allowed for relay. You should not have your Email\SMTP in an open relay setup, for obviously reasons.

I use an external 3rd-Party vendor for Spam filtering and they provide me with a list of hosts and networks that represent their relay servers. I then add them to my ASA and Exchange server as only possible hosts that can relay to my server.

Not sure how you are setup, but I figure I share my experience.

Hope this helps!

shampton10 · ‎01-27-2013

Thanks. I made the suggested changes, here are the results of packer-tracer:

ASA# packet-tracer input outside tcp 1.2.3.4 1234 XXX.XXX.XXX.130 25

Phase: 1
Type: UN-NAT
Subtype: static
Result: ALLOW
Config:
static (inside,outside) tcp interface smtp Server smtp netmask 255.255.255.255
match tcp inside host Server eq 25 outside any
static translation to XXX.XXX.XXX.130/25
translate_hits = 0, untranslate_hits = 3
Additional Information:
NAT divert to egress interface inside
Untranslate XXX.XXX.XXX.130/25 to Server/25 using netmask 255.255.255.255

Phase: 2
Type: ACCESS-LIST
Subtype: log
Result: ALLOW
Config:
access-group INBOUND in interface outside
access-list INBOUND extended permit tcp any host XXX.XXX.XXX.130 eq smtp
Additional Information:

Phase: 3
Type: IP-OPTIONS
Subtype:
Result: ALLOW
Config:
Additional Information:

Phase: 4
Type: INSPECT
Subtype: inspect-smtp
Result: ALLOW
Config:
class-map inspection_default
match default-inspection-traffic
policy-map global_policy
class inspection_default
inspect esmtp _default_esmtp_map
service-policy global_policy global
Additional Information:

Phase: 5
Type: HOST-LIMIT
Subtype:
Result: ALLOW
Config:
Additional Information:

Phase: 6
Type: NAT
Subtype: rpf-check
Result: ALLOW
Config:
static (inside,outside) tcp interface smtp Server smtp netmask 255.255.255.255
match tcp inside host Server eq 25 outside any
static translation to XXX.XXX.XXX.130/25
translate_hits = 0, untranslate_hits = 3
Additional Information:

Phase: 7
Type: NAT
Subtype: host-limits
Result: ALLOW
Config:
static (inside,outside) tcp interface smtp Server smtp netmask 255.255.255.255
match tcp inside host Server eq 25 outside any
static translation to XXX.XXX.XXX.130/25
translate_hits = 0, untranslate_hits = 3
Additional Information:

Phase: 8
Type: IP-OPTIONS
Subtype:
Result: ALLOW
Config:
Additional Information:

Phase: 9
Type: FLOW-CREATION
Subtype:
Result: ALLOW
Config:
Additional Information:
New flow created with id 24392, packet dispatched to next module

Result:
input-interface: outside
input-status: up
input-line-status: up
output-interface: inside
output-status: up
output-line-status: up
Action: allow

I'm not all that experienced with translating these results, but on the surface, it appears to be passing traffic. However, I still cannt telnet to the public IP using port 25. I am using Putty as my telnet client and it doesn't generate an error. At no time am I able to interact with the prompt in the putty window. The putty window just closes abruptly after about 10 seconds. Does the line in Phase 7 containing 'untranslate_hits=3' have anything to do with my issue?

Here is the new config:

NUGENT-ASA# show run
: Saved
:
ASA Version 8.2(5)
!
hostname NUGENT-ASA
enable password XXXXXXXXXXXXXXXXXXXX encrypted
passwd XXXXXXXXXXXXXXXXXX encrypted
names
name XXX.XXX.XXX.74 DNI-HOST1
name XXX.XXX.XXX.184 DNI-HOST2
name 192.168.1.2 Server
!
interface Ethernet0/0
switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
!
interface Ethernet0/3
!
interface Ethernet0/4
!
interface Ethernet0/5
!
interface Ethernet0/6
!
interface Ethernet0/7
!
interface Vlan1
nameif inside
security-level 100
ip address 192.168.1.1 255.255.255.0
!
interface Vlan2
nameif outside
security-level 0
ip address XXX.XXX.XXX.130 255.255.255.248
!
ftp mode passive
clock timezone CST -6
clock summer-time CDT recurring
object-group service rdp tcp
port-object eq 3389
access-list INBOUND extended permit icmp any any time-exceeded
access-list INBOUND extended permit icmp any any echo-reply inactive
access-list INBOUND extended permit icmp any any
access-list INBOUND extended permit tcp any host XXX.XXX.XXX.130 eq smtp
pager lines 24
logging enable
logging buffered warnings
logging asdm informational
mtu inside 1500
mtu outside 1500
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 1 192.168.1.0 255.255.255.0
static (inside,outside) tcp interface smtp Server smtp netmask 255.255.255.255
static (outside,inside) tcp interface smtp Server smtp netmask 255.255.255.255
access-group INBOUND in interface outside
route outside 0.0.0.0 0.0.0.0 XXX.XXX.XXX.129 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
timeout floating-conn 0:00:00
dynamic-access-policy-record DfltAccessPolicy
http server enable
http 192.168.1.0 255.255.255.0 inside
http DNI-HOST2 255.255.255.255 outside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
crypto ca trustpoint _SmartCallHome_ServerCA
crl configure
crypto ca certificate chain _SmartCallHome_ServerCA
certificate ca [REDACTED]
quit
telnet 192.168.1.0 255.255.255.0 inside
telnet timeout 5
ssh 206.190.255.0 255.255.255.0 outside
ssh DNI-HOST2 255.255.255.255 outside
ssh DNI-HOST1 255.255.255.255 outside
ssh timeout 5
console timeout 0
management-access inside
dhcpd dns 8.8.8.8 4.2.2.2
!
dhcpd address 192.168.1.100-192.168.1.131 inside
dhcpd dns 8.8.8.8 4.2.2.2 interface inside
!

threat-detection basic-threat
threat-detection statistics access-list
threat-detection statistics tcp-intercept rate-interval 30 burst-rate 400 average-rate 200
webvpn
username Administrator password XXXXXXXXXXXXXXXXXXXXXXX encrypted
!
class-map inspection_default
match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
parameters
message-length maximum client auto
message-length maximum 512
policy-map global_policy
class inspection_default
inspect dns preset_dns_map
inspect ftp
inspect h323 h225
inspect h323 ras
inspect rsh
inspect rtsp
inspect esmtp
inspect sqlnet
inspect skinny
inspect sunrpc
inspect xdmcp
inspect sip
inspect netbios
inspect tftp
inspect ip-options
inspect icmp
!
service-policy global_policy global
prompt hostname context
no call-home reporting anonymous
call-home
profile CiscoTAC-1
no active
destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
destination address email callhome@cisco.com
destination transport-method http
subscribe-to-alert-group diagnostic
subscribe-to-alert-group environment
subscribe-to-alert-group inventory periodic monthly
subscribe-to-alert-group configuration periodic monthly
subscribe-to-alert-group telemetry periodic daily
Cryptochecksum:XXXXXXXXXXXXXXXXXXXXXXXXXXX
: end

shampton10 · ‎01-27-2013

I guess my issue is not specific to SMTP. I'm also working on a rule to allow RDP (port 3389). The packer-tracer results are the same, but I cannot connect from outside using RDP.

Karsten Iwen · ‎01-27-2013

Configure a more verbose logging and show us if there is any logging for your traffic (""show logging").

logging buffered 6

Have you tested that you have connectivity to your ASA at all? Can you ping the public IP from your Client? And you are really using the ASA interface-IP for your test as that is the IP that has the translation configured?

--
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

shampton10 · ‎01-27-2013

There was a rule set in ASDM to allow ICMP traffic, but it was disabled. When I enabled that rule (see below), everything started working.

access-list INBOUND extended permit icmp any any echo-reply

Doesn't make a whole lot of sense to me that SMTP and RDP traffic would just work after enabling it, but it does. I don't like it, so I would like to clean it up.

And yes, I am using the public IP, connected from a different network over the internet.