[strongSwan] strongswan/L2TP and NAT-T transport with both NATed

[Ulysse 31]

2010/11/22 Ulysse 31 <ulysse31 at gmail.com>:
> Hi all,
>
> I have a strongswan with L2TP working with XP roadwarrior clients/ osx
> clients and iphone on one gateway with a public IP.Had to enable
> --enable-nat-transport but it works great.
> Now I have a second configuration, which is like :
>
>     <client>
>          |
> <NAT Gateway>
>          |
>   <Internet >
>          |
> <NAT Gateway (cisco ASA 5505)>
>          |
> <Strongswan Server>
>          |
>    <LAN>
>
> It is the almost the same configuration, the main big difference comes
> from the strongswan server that is NATed. The cisco ASA as no VPN
> feature enable, it is used like a simple NAT gateway, redirecting one
> public IP to the internal IP using a static NAT. all IP (TCP/UDP), esp
> and AH protocol is allowed. here is the first example of configuration
> used :
>
> config setup
>       plutodebug="control"
>       strictcrlpolicy=no
>       overridemtu=1410
>       nat_traversal=yes
>       charonstart=no
>       plutostart=yes
>
> conn L2TP
>    authby=psk
>    pfs=no
>    auto=add
>    rekey=no
>    type=tunnel
>    left=yy.yy.yy.yy                      # Internal private IP
>    leftnexthop=XX.XX.XX.XX      # External IP address
>    leftprotoport=17/1701
>    leftfirewall=yes
>    right=%any
>    rightprotoport=17/%any
>    rightsubnetwithin=0.0.0.0/0
>    rightfirewall=yes
>    esp=aes128-sha1
>    ike=aes128-sha-modp1024
>    forceencaps=yes
>
> Here is what I got in the logs (the aa.aa.aa.aa is the IP public
> address of the client, and bb.bb.bb.bb is its private address) :
>
>
> ---
> Nov 20 11:51:35 src@<stronswanserv> pluto[26142]: "L2TP"[2]
> aa.aa.aa.aa:4500 #4: cannot respond to IPsec SA request because no
> connection is known for
> XX.XX.XX.XX/32===yy.yy.yy.yy:4500:17/1701…aa.aa.aa.aa:4500[bb.bb.bb.bb]:17/%any==={bb.bb.bb.bb/32}
> Nov 20 11:51:38 src@<stronswanserv> pluto[26142]: "L2TP"[2]
> aa.aa.aa.aa:4500 #4: Quick Mode I1 message is unacceptable because it
> uses a previously used Message ID 0xfb7bef8d (perhaps this is a
> duplicated packet)
> Nov 20 11:51:38 src@<stronswanserv> pluto[26142]: "L2TP"[2]
> aa.aa.aa.aa:4500 #4: sending encrypted notification INVALID_MESSAGE_ID
> to aa.aa.aa.aa:4500
> Nov 20 11:51:38 src@<stronswanserv> pluto[26142]: | next event
> EVENT_NAT_T_KEEPALIVE in 13 seconds
> The "Quick Mode I1 message is unacceptable" is repeated several times
> ( retries from client ) and the ISAKMP is never established, then it
> times out.
> ---
>
>
> So next I tried with adding "leftsubnet=XX.XX.XX.XX/32" on the conn
> L2TP config. which allowed me to establish ISAKMP, but then I have on
> the logs :
>
>
> ---
> Nov 20 11:52:58 src@<stronswanserv> pluto[26339]: |
> preparse_isakmp_policy: peer requests PSK authentication
> ...
> Nov 20 11:52:58 src@<stronswanserv> pluto[26339]: "L2TP"[1]
> aa.aa.aa.aa #4: responding to Main Mode from unknown peer aa.aa.aa.aa
> Nov 20 11:52:59 src@<stronswanserv> pluto[26339]: "L2TP"[1]
> aa.aa.aa.aa #4: NAT-Traversal: Result using RFC 3947: both are NATed
> Nov 20 11:52:59 src@<stronswanserv> pluto[26339]: "L2TP"[1]
> aa.aa.aa.aa #4: Peer ID is ID_IPV4_ADDR: 'bb.bb.bb.bb'
> Nov 20 11:52:59 src@<stronswanserv> pluto[26339]: "L2TP"[2]
> aa.aa.aa.aa #4: deleting connection "L2TP" instance with peer
> aa.aa.aa.aa {isakmp=#0/ipsec=#0}
> Nov 20 11:52:59 src@<stronswanserv> pluto[26339]: "L2TP"[2]
> aa.aa.aa.aa:4500 #4: sent MR3, ISAKMP SA established
> Nov 20 11:52:59 src@<stronswanserv> pluto[26339]: "L2TP"[2]
> aa.aa.aa.aa:4500 #4: ignoring informational payload, type
> IPSEC_INITIAL_CONTACT
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: "L2TP"[2]
> aa.aa.aa.aa:4500 #5: NAT-Traversal: received 2 NAT-OA. using first,
> ignoring others
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: "L2TP"[2]
> aa.aa.aa.aa:4500 #5: responding to Quick Mode
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: |
> kernel_alg_esp_auth_keylen(auth=2, sadb_aalg=3): a_keylen=20
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: |
> install_inbound_ipsec_sa() checking if we can route
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: | route owner of
> "L2TP"[2] aa.aa.aa.aa:4500 unrouted: NULL; eroute owner: NULL
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: | add inbound eroute
> aa.aa.aa.aa/32:57947 -> XX.XX.XX.XX/32:1701 =>
> tun.10000 at yy.yy.yy.yy:17
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: | inserting event
> EVENT_RETRANSMIT, timeout in 10 seconds for #5
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: | next event
> EVENT_NAT_T_KEEPALIVE in 6 seconds
> ...
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: "L2TP"[2]
> aa.aa.aa.aa:4500 #4: ignoring informational payload, type
> INVALID_HASH_INFORMATION
> Nov 20 11:53:00 src@<stronswanserv> pluto[26339]: "L2TP"[2]
> aa.aa.aa.aa:4500 #4: received Delete SA payload: deleting ISAKMP State
> #4
> ---
>
>
> I have tried different flags on the conn settings that may helped me
> (forceencaps=yes, type=transport instead of type=tunnel ). I really
> don't see why does it act like this on this machine. this machine (the
> strongswan server) is quite particular, since it runs a devil-linux
> distribution (livecd), that i had to rebuild in order to add the
> --enable-nat-transport on the strongswan script build, it uses
> strongswan 4.2.16, is there a way to check if the binary is really
> with the --enable-nat-transport ?
> Does someone have an hint on what I can do in order to make it work ?
> please help !
>
> --
> Ulysse31
>

Hi again,

I really need help, if somebody has some ideas ...
If somebody needs more logs/outputs/informations, please let me know.
Thanks again.


-- 
Gomes do Vale Victor
Ingénieur Systèmes, Réseaux et Securité