I've long since deleted the OP's message, but figured I would share our experiences having been using TACACS+ with our Cisco hardware for a couple of years. Originally deployed for the need and want of controlling multiple users across several devices, and to safely control 3rd party read, or reverse-telnet access to the very few nodes that may need it, without needing to mess around with parser views on every device. To that end it's worked just fine without complaint. Note: We're using shrubbery.net's tac_plus. The per-command authorization does slow some nodes down slightly, but nothing as severe as a few seconds each It does work out to about 1 command per (1000ms / Node to AAA RTT) as you'd expect. Eg; The worst I've seen on a ~200ms link, copy/paste lump-of-config will work out to about the expected 4-5 commands/second. Devices running v15 seem to speed this up somehow, not sure if they multiplex commands under the hood, or if I'm just crazy. I've never looked into it that closely for lack of interest and time. There is a stupid gotcha when dealing with the command authorization in the TACACS configuration. If you permit 'johndoe' a 'show ip bgp .*', and he is also a member of a group with subsequent show commands, the show commands in the 'group' config block are completely ignored. This makes some scenarios tricky. We utilize a local root, unprivileged user with unique credentials across each device. It's possible to configure Cisco's AAA to prevent the local user login while AAA is up / reachable. Generally, we are of the opinion that if our nodes cannot reach the AAA server, we have bigger problems that would necessitate a senior administrator with access to the local root user credentials anyway. Otherwise, a TACACS server can be setup in literally minutes and the configuration required is minuscule and easy to backup safely. A note on the local root user. By far and away, the worst possible scenario is not AAA going down / becoming entirely unreachable, but instead when experiencing network instability. Having experienced this scenario for a few very frustrating hours, the experience is along the lines of; - Enter a pile of commands. Some fail (wile AAA is briefly up), some succeed (while AAA is down). - Swear at your console, and repeat until the problem(s) are resolved. Our workaround was; Add your backup / root user with full privileges to your TACACS backend, with _no_ password. This denies them access when AAA is running as there is no password to authenticate against, but prevents "Authorization failed!" when the AAA server is briefly available in the middle of your diags / trying to resolve the connectivity problem. For the Unix admins; The TACACS binary itself, is awful - It has no status exit codes. The process cannot be monitored or controlled safely by way of something like DJB's daemontools, even with the fg_helper hack - at least I've not managed to succeed to date and have given up. To that end, we have a hacked together script to assist with safely reloading configs and such that parses stdout and stderr to decide what to do. Eg; trying to gracefully restart TACACS with a broken config will cause the daemon to exit - not awesome. All that said, I have heard a lot of praise from an enterprise in my neck of the woods who shelled out for Cisco's TACACS+ VM Appliance. If you have the money it's supposedly worth it especially for the AD hooks. I hope this provides some insight to those that may need it. ________________________________________ From: NANOG [nanog-bounces@nanog.org] On Behalf Of Colton Conor [colton.conor@gmail.com] Sent: Monday, December 29, 2014 9:28 AM To: Michael Douglas Cc: NANOG Subject: Re: The state of TACACS+ Glad to know you can make local access only work if TACAS+ isn't available. However, that still doesn't prevent the employee who know the local username and password to unplug the device from the network, and the use the local password to get in. Still better than our current setup of having one default username and password that everyone knows. On Mon, Dec 29, 2014 at 9:38 AM, Michael Douglas <Michael.Douglas@ieee.org> wrote:
In the Cisco world the AAA config is typically set up to try tacacs first, and local accounts second. The local account is only usable if tacacs is unavailable. Knowledge of the local username/password does not equate to full time access with that credential. Also, you would usually filter the incoming SSH sessions to only permit a particular management IP range; the local credential, or tacacs credential, shouldn't be usable from any arbitrary network.
On Mon, Dec 29, 2014 at 10:32 AM, Colton Conor <colton.conor@gmail.com> wrote:
Scott,
Thanks for the response. How do you make sure the failsafe and/or root password that is stored in the device incase remote auth fails can't be accessed without having several employees engaged? Are there any mechanisms for doing so?
My fear would be we would hire an outsourced tech. After a certain amount of time we would have to let this part timer go, and would disabled his or her username and password in TACAS. However, if that tech still knows the root password they could still remotely login to our network and cause havoc. The thought of having to change the root password on hundreds of devices doesn't sound appealing either every time an employee is let go. To make matters worse we are using an outsourced firm for some network management, so the case of hiring and firing is fairly consistent.
On Mon, Dec 29, 2014 at 9:22 AM, Scott Helms <khelms@zcorum.com> wrote:
Colton,
Yes, that's the 'normal' way of setting it up. Basically you still have to configure a root user, but that user name and password is kept locked up and only accessed in case of catastrophic failure of the remote authentication system. An important note is to make sure that the fail safe password can't be accessed without having several people engaged so it can't be used without many people knowing.
Scott Helms Vice President of Technology ZCorum (678) 507-5000 -------------------------------- http://twitter.com/kscotthelms --------------------------------
On Mon, Dec 29, 2014 at 10:15 AM, Colton Conor <colton.conor@gmail.com
wrote:
We are able to implement TACAS+. It is my understanding this a fairly old protocol, so are you saying there are numerous bugs that still need to be fixed?
A question I have is TACAS+ is usually hosted on a server, and networking devices are configured to reach out to the server for authentication. My question is what happens if the device can't reach the server if the devices network connection is offline? Our goal with TACAS+ is to not have any default/saved passwords. Every employee will have their own username and password. That way if an employee gets hired/fired, we can enable or disable their account. We are trying to avoid having any organization wide or network wide default username or password. Is this possible? Do the devices keep of log of the last successful username/password combinations that worked incase the device goes offline?
On Sun, Dec 28, 2014 at 5:02 PM, Robert Drake <rdrake@direcpath.com> wrote:
Picking back up where this left off last year, because I apparently only work on TACACS during the holidays :)
On 12/30/2013 7:28 PM, Jimmy Hess wrote:
Even 5 seconds extra for each command may hinder operators, to the extent it would be intolerable; shell commands should run almost instantaneously.... this is not a GUI, with an hourglass. Real-time responsiveness in a shell is crucial --- which remote auth should not change. Sometimes operators paste a buffer with a fair number of commands, not expecting a second delay between each command --- a repeated delay, may also break a pasted sequence.
It is very possible for two of three auth servers to be unreachable, in case of a network break, but that isn't necessary. The "response timeout" might be 5 seconds, but in reality, there are cases where you would wait longer, and that is tragic, since there are some obvious alternative approaches that would have had results that would be more 'friendly' to the interactive user.
(Like remembering which server is working for a while, or remembering that all servers are down -- for a while, and having a 50ms timeout, with all servers queried in parallel, instead of a 5 seconds timeout)
I think this needs to be part of the specification.
I'm sure the reason they didn't do parallel queries was because of both network and CPU load back when the protocol was drafted. But it might be good to have local caching of authentication so that can happen even when servers are down or slow. Authorization could be updated to send the permissions to the router for local handling. Then if the server dies while a session is open only accounting would be affected.
That does increase the vendors/implementors work but it might be doable in phases and with partial support with the clients and servers negotiating what is possible. The biggest drawback to making things like this better is you don't gain much except during outages and if you increase complexity too much you make it wide open for bugs.
Maybe there is a simpler solution that keeps you happy about redundancy but doesn't increase complexity that much (possibly anycast tacacs, but the session basis of the protocol has always made that not feasible). It's possible that one of the L4 protocols Saku Ytti mentioned, QUIC or MinimaLT would address these problems too. It's possible that if we did the transport with BEEP it would also provide this, but I'm reading the docs and I don't think it goes that far in terms of connection assurance.
-- -JH
So, here is my TACACS RFC christmas list:
1. underlying crypto 2. ssh host key authentication - having the router ask tacacs for an authorized_keys list for rdrake. I'm willing to let this go because many vendors are finding ways to do key distribution, but I'd still like to have a standard (https://code.google.com/p/openssh-lpk/ for how to do this over LDAP in UNIX) 3. authentication and authorization caching and/or something else