ASA 5505 as a "modem"

[deca24]

Hey all,

So I am trying to figure out an issue I am having. My ISP recently notified me that modem rental will be going up starting the first of the year. I have fiber optics to my house. Right now the setup is:

ONT box (fiber converter) -->DHCP - modem - static external/30 -->static external/30 - ASA 5505 - internal range (router mode)-->L3 switch (internal VLAN routing).

What I would like to get to is: ONT --> ASA --> L3 switch.

One thing I have figured out is that I COULD eliminate the modem by plugging in a firewall/router and going from there I was able to get to the Internet and such.

The problem I currently have is that I have a static IP address. The modem pulls a WAN IP from DHCP, with the internal IP being one part of a /30 IP address. So right at the moment I am trying to figure out how to get the ASA to pull the DHCP from the ONT box and still keep my static IP in play.

Thoughts? Suggestions?

Thank you all!

Scott

[Masoud Pourshabanian]

Hello,

As I understood, your modem is getting a public /30 IP address from ONT and your ASA another /30 from modem which is currently used in your network.  And you are translating your private internal IP addresses to the IP address on the ASA interface by using PAT.

After connecting ASA to ONT, ASA will receive an IP address from ONT. Then you need to change your NAT configuration. In your NAT statement, instead of using interface IP(ONT), you can use your static IP address.

Just to mention, you do not need to set your current static IP address on the interface. You need to just add it in the NAT statement.

You also need to change ASA default route toward ONT.

I hope I understood your question correctly.

Masoud

[deca24]

Hi Masoud,

Thank you for your reply. Currently the modem is getting a DHCP from the ONT box, with the internal interface on the modem being one side of my static /30 IP. The outside interface of my ASA is the other side of the /30 IP.

At this moment the ONT box is really just a converter. The ISP is currently running a DHCP server that seems to have a lease expiration of 58 minutes.

I have uploaded a PDF hoping to clear up that my description may have caused.

I guess what I am really not sure of is how to deal with the static IP address when I cut out the modem. If I didnt have the static IP, this would be a no-brainer and easy to do.

Since I run my own website, Exchange and such to play with, I would like to keep my static IP.

Thoughts? Suggestions?

Thank you!

Scott

[Masoud Pourshabanian]

Hello,

Does exchange has a private IP address and has been published by ASA using static NAT?

If yes, you need to change ASA static IP address on external interface to DHCP and change the ASA default route toward to ISP.

and a little change in your NAT statement based on your current configuration.

If you share you config, I can explain more.

Masoud

[deca24]

Masoud,

Exchange does have a private IP and traffic is passed via port fowarding.

ASA Config:
ASA5505# sh run
: Saved
:
ASA Version 8.2(5)
!
hostname ASA5505
domain-name DOMAINNAME.COM
enable password  encrypted
passwd  encrypted
names
!
interface Ethernet0/0
 description ISP Modem
 switchport access vlan 2
!
interface Ethernet0/1
 shutdown
!
interface Ethernet0/2
 description  Internal
 switchport access vlan 11
!
truncated
!
interface Vlan1
 shutdown
 no nameif
 no security-level
 no ip address
!
interface Vlan2
 nameif outside
 security-level 0
 ip address 125.125.125.125 255.255.255.252
!
interface Vlan11
 nameif inside
 security-level 100
 ip address 10.1.1.1 255.255.255.224
!
interface Vlan21
 no nameif
 security-level 100
 no ip address
!
interface Vlan31
 no nameif
 security-level 100
 no ip address
!
interface Vlan51
 no nameif
 security-level 100
 no ip address
!
interface Vlan101
 no nameif
 security-level 100
 no ip address
!
!
time-range RDP-inbound
 periodic weekdays 7:15 to 16:45
!
banner exec This is a private network. If you have not been given explicit permission to be on this device, disconnect immediately!
banner login This is a private network. If you have not been given explicit permission to be on this device, disconnect immediately!
ftp mode passive
clock timezone EST -5
clock summer-time EDT recurring
dns domain-lookup inside
dns server-group DefaultDNS
 name-server SERVER1
 name-server SERVER2
 domain-name DOMAINNAME
same-security-traffic permit intra-interface
object-group network mail
 network-object host SERVER
object-group network webserver
 network-object host SERVER
access-list inside_nat0_outbound extended permit ip 10.1.0.0 255.255.240.0 IP 255.255.255.248
access-list Outside_access_in extended permit tcp host IP interface outside eq 3389
access-list Outside_access_in extended permit tcp any interface outside eq smtp
access-list Outside_access_in extended permit tcp any interface outside eq www
access-list Outside_access_in extended permit tcp any interface outside eq https
access-list Outside_access_in extended permit ip host IP any
access-list New-Group_splitTunnelAcl standard permit 10.1.0.0 255.255.240.0
access-list inside_access_in extended permit ip host IP any
access-list Outbound extended permit tcp host SERVER any eq smtp
access-list Outbound extended deny tcp any any eq smtp
access-list Outbound extended permit ip any any
access-list global_mpc extended permit ip any any
pager lines 24
logging enable
logging trap notifications
logging asdm informational
logging host inside SERVER
logging permit-hostdown
no logging message 106015
no logging message 313001
no logging message 313008
no logging message 106023
no logging message 710003
no logging message 106100
no logging message 302015
no logging message 302014
no logging message 302013
no logging message 302018
no logging message 302017
no logging message 302016
no logging message 302021
no logging message 302020
flow-export destination inside SERVER 9991
mtu outside 1500
mtu inside 1500
ip local pool VPN-IPs IP-IP mask 255.255.255.248
ip verify reverse-path interface outside
icmp unreachable rate-limit 1 burst-size 1
icmp deny any echo-reply outside
asdm image disk0:/asdm-645.bin
asdm history enable
arp timeout 14400
nat-control
global (outside) 10 interface
nat (inside) 0 access-list inside_nat0_outbound
nat (inside) 10 IP 255.255.255.255
nat (inside) 10 192.168.80.0 255.255.255.248
nat (inside) 10 10.1.0.0 255.255.240.0
static (inside,outside) tcp interface 3389 IP 3389 netmask 255.255.255.255
static (inside,outside) tcp interface smtp IP smtp netmask 255.255.255.255
static (inside,outside) tcp interface www IP www netmask 255.255.255.255
static (inside,outside) tcp interface https IP https netmask 255.255.255.255
access-group Outside_access_in in interface outside
access-group Outbound in interface inside
!
router eigrp 5
 no auto-summary
 network 10.1.1.0 255.255.255.224
 network IP 255.255.255.248
 network IP 255.255.255.252
!
router rip
 network IP
 version 2
!
route outside 0.0.0.0 0.0.0.0 IP 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
aaa authentication ssh console LOCAL
http server enable 8080
http 10.1.X.X 255.255.255.255 inside
http 10.X.X.X 255.255.255.255 inside
http 10.X.X.X 255.255.255.255 inside
http X.X.X.X 255.255.255.255 inside
http X.X.X.X 255.255.255.255 outside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec transform-set ESP-3DES-SHA esp-3des esp-sha-hmac
crypto ipsec transform-set ESP-AES-256-MD5 esp-aes-256 esp-md5-hmac
crypto ipsec transform-set ESP-DES-SHA esp-des esp-sha-hmac
crypto ipsec transform-set ESP-DES-MD5 esp-des esp-md5-hmac
crypto ipsec transform-set ESP-AES-192-MD5 esp-aes-192 esp-md5-hmac
crypto ipsec transform-set ESP-3DES-MD5 esp-3des esp-md5-hmac
crypto ipsec transform-set ESP-AES-256-SHA esp-aes-256 esp-sha-hmac
crypto ipsec transform-set ESP-AES-128-SHA esp-aes esp-sha-hmac
crypto ipsec transform-set ESP-AES-192-SHA esp-aes-192 esp-sha-hmac
crypto ipsec transform-set ESP-AES-128-MD5 esp-aes esp-md5-hmac
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
crypto dynamic-map SYSTEM_DEFAULT_CRYPTO_MAP 65535 set pfs group1
crypto dynamic-map SYSTEM_DEFAULT_CRYPTO_MAP 65535 set transform-set ESP-AES-128-SHA ESP-AES-128-MD5 ESP-AES-192-SHA ESP-AES-192-MD5 ESP-AES-256-SHA ESP-AES-256-MD5 ESP-3DES-SHA ESP-3DES-MD5 ESP-DES-SHA ESP-DES-MD5
crypto map outside_map 65535 ipsec-isakmp dynamic SYSTEM_DEFAULT_CRYPTO_MAP
crypto map outside_map interface outside
crypto ca trustpoint _SmartCallHome_ServerCA
 crl configure
crypto ca certificate chain _SmartCallHome_ServerCA
 certificate ca 6ecc7aa5a7032009b8cebcf4e952d491
-Truncated-
  quit
crypto isakmp enable outside
crypto isakmp policy 10
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400
crypto isakmp policy 65535
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400
telnet timeout 5
ssh X.X.X.X 255.255.255.255 outside
ssh X.X.X.X 255.255.255.255 inside
ssh X.X.X.X 255.255.255.255 inside
ssh X.X.X.X 255.255.255.255 inside
ssh X.X.X.X 255.255.255.255 inside
ssh X.X.X.X 255.255.255.255 inside
ssh timeout 30
console timeout 10
management-access inside
threat-detection basic-threat
threat-detection statistics access-list
threat-detection statistics host number-of-rate 3
threat-detection statistics tcp-intercept rate-interval 30 burst-rate 400 average-rate 200
ntp server X.X.X.X source inside prefer
webvpn
group-policy New-Group internal
group-policy New-Group attributes
 dns-server value X.X.X.X
 vpn-tunnel-protocol IPSec
 split-tunnel-policy tunnelspecified
 split-tunnel-network-list value New-Group_splitTunnelAcl
 default-domain value ebbs.us
username sworks password rZHtLTteBnX1edzp encrypted privilege 15
username sebbing password aVPcVVXENmaXU.Ix encrypted privilege 15
username sebbing attributes
 vpn-group-policy New-Group
 vpn-access-hours none
 vpn-simultaneous-logins 3
 vpn-idle-timeout 30
 vpn-session-timeout none
 vpn-filter none
 ipv6-vpn-filter none
 vpn-tunnel-protocol IPSec l2tp-ipsec svc webvpn
 password-storage disable
 group-lock none
username buddy password QRqHo6j2jCymU1dT encrypted privilege 0
username buddy attributes
 vpn-group-policy New-Group
tunnel-group New-Group type remote-access
tunnel-group New-Group general-attributes
 address-pool VPN-IPs
 default-group-policy New-Group
tunnel-group New-Group ipsec-attributes
 pre-shared-key *****
!
class-map global-class
 match any
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 ip-options
  inspect netbios
  inspect rsh
  inspect rtsp
  inspect skinny
  inspect esmtp
  inspect sqlnet
  inspect sunrpc
  inspect tftp
  inspect sip
  inspect xdmcp
  inspect icmp
 class global-class
  flow-export event-type all destination X.X.X.X
!
service-policy global_policy global
smtp-server X.X.X.X
prompt hostname context
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:d41d8cd98f00b204e9800998ecf8427e
: end

I understand that if I were to drop the static from the loop, this would be an easy fix. However, with needing to keep the static IP is what is making it difficult.

Thank you.

Thoughts? Suggestions?

Scott

[Masoud Pourshabanian]

Hello,

There might be more involved because I do not have ASA with OS the same version as yours to test it.

interface Vlan2
 nameif outside
 security-level 0
 ip address dhcp


current
global (outside) 10 interface
nat (inside) 0 access-list inside_nat0_outbound
nat (inside) 10 IP 255.255.255.255
nat (inside) 10 192.168.80.0 255.255.255.248
nat (inside) 10 10.1.0.0 255.255.240.0

next
global (outside) 10 125.125.125.125 255.255.255.252
nat (inside) 0 access-list inside_nat0_outbound
nat (inside) 10 IP 255.255.255.255
nat (inside) 10 192.168.80.0 255.255.255.248
nat (inside) 10 10.1.0.0 255.255.240.0


current
static (inside,outside) tcp interface 3389 IP 3389 netmask 255.255.255.255
static (inside,outside) tcp interface smtp IP smtp netmask 255.255.255.255
static (inside,outside) tcp interface www IP www netmask 255.255.255.255
static (inside,outside) tcp interface https IP https netmask 255.255.255.255

next
static (inside,outside) tcp 125.125.125.125 3389 IP 3389 netmask 255.255.255.255
static (inside,outside) tcp 125.125.125.125 smtp IP smtp netmask 255.255.255.255
static (inside,outside) tcp 125.125.125.125  www IP www netmask 255.255.255.255
static (inside,outside) tcp 125.125.125.125  https IP https netmask 255.255.255.255

current
route outside 0.0.0.0 0.0.0.0 IP 1

next
route outside 0.0.0.0 0.0.0.0 [your ISP ip] 1