GSSAPI auth and NAT Problems

[Oliver Loch]

Hi,

what OS / Kerberos version is running on your laptop?

Try to enable the GSSAPI* options in the client and server config files.

Also check if you can disable the "trust dns" option on the ssh client.

The machine should try to get a ticket for the public ip/name and not for the system behind it, so the tickets won't match.

KR,

Oliver 

Am 01.08.2012 um 15:09 schrieb Jörg Herzinger <bowser at fstph.at>:

> Hi, I am trying to get GSSAPI auth to work and the problem ist that my
> kerberos server and the ssh server I want to connect to are behind a nat.
> My setup looks like this:
> 
> my_laptop -------- virtual_machine_host ----- kerberos & ssh server
> (any ip here)    128.131.XX.YY - 10.0.0.1     10.0.0.2 & 10.0.0.3
> 
> Port forwads are done by iptables on my virtual-machine-host. Port 22 ist
> forwarded to my ssh server. I can get a kerberos ticket easily on my
> laptop:
> joerg at laptop ~ % kinit joerg
> Password for joerg at REAML.AT:
> joerg at laptop ~ % klist -af
> Ticket cache: FILE:/tmp/krb5cc_1000
> Default principal: joerg at REALM.AT
> 
> Valid starting     Expires            Service principal
> 08/01/12 09:34:39  08/01/12 23:34:39  krbtgt/REALM.AT at REALM.AT
> 	renew until 08/02/12 09:35:00, Flags: FPRI
> 	Addresses: (none)
> 
> Connecting to my virtual machine host with gssapi auth also works like
> expected but when I try to connect to my ssh server gssapi fails (No valid
> Key exchange context) and I am prompted for a password. Connecting via ssh
> from my kerberos server to my ssh server internally works too.
> The stange thing i found is that even with NO host keytab on my ssh server
> I do get a ticket when trying to connect.
> 
> joerg at laptop ~ % kinit joerg
> Password for joerg at REALM.AT:
> joerg at laptop ~ % klist -af
> Ticket cache: FILE:/tmp/krb5cc_1000
> Default principal: joerg at REALM.AT
> 
> Valid starting     Expires            Service principal
> 08/01/12 09:46:42  08/01/12 23:46:42  krbtgt/REALM.AT at REALM.AT
> 	renew until 08/02/12 09:47:03, Flags: FPRI
> 	Addresses: (none)
> joerg at blackmini ~ % ssh root at virtual-machine-host
> Warning: Permanently added 'virtual-machine-host,128.131.XX.YY' (ECDSA) to
> the list of known hosts.
> Password:
> 
> 130 joerg at laptop ~ % klist -af
> Ticket cache: FILE:/tmp/krb5cc_1000
> Default principal: joerg at REALM.AT
> 
> Valid starting     Expires            Service principal
> 08/01/12 09:46:42  08/01/12 23:46:42  krbtgt/REALM.AT at REALM.AT
> 	renew until 08/02/12 09:47:03, Flags: FPRI
> 	Addresses: (none)
> 08/01/12 09:46:57  08/01/12 23:46:42  host/virtual-machine-host@
> 	renew until 08/02/12 09:47:03, Flags: FPRT
> 	Addresses: (none)
> 08/01/12 09:46:57  08/01/12 23:46:42  host/virtual-machine-host at REALM.AT
> 	renew until 08/02/12 09:47:03, Flags: FPRT
> 	Addresses: (none)
> 
> I already read a lot about address less tickets and "rdns=no", but all
> this seems way outdated. The config option "extra_addresses" looks
> promising but I didn't have success with this either. I am working on
> ubuntu laptop 11.04 and ssh server is Debian Squeeze.
> Any ideas or further suggestions on what I could try to get this working?
> This would be quite important for me.
> 
> thanks,
>    Jörg
> 
> 
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