Monday, February 23, 2009

Sun M-Series Enterprise Unix Servers And DSCP - Why?

SPECIAL NOTE: Friday's post on the absorption of knowledge was written on Blogspot in IE7 and suffered from some horrible display problems on FireFox and other browsers. It has been completely retooled. Apologies for any inconvenience that post caused. Even though I write some goofy rants, missing text wasn't supposed to be part of that post's intentionally cryptic style. Thanks :) - Mike

Hey there,

Today, we're going to look at DSCP (The Domain to Service processor Communication Protocol) and why it was introduced with the newer M series Enterprise servers from Sun. The first time I ran into it, I thought approximately the following: All right, here's something else that can make my life more complicated ;) Now, not only do I have to hop onto a private network (added security at work) to connect to the service processor (SP), but then I have to be sure that an entirely separate network is functioning correctly in order for me to connect to a domain on my machine if I want to get there directly from the SP. I'm naturally negative, but I keep it inside until I've given myself the time to realize that things are either not as bad or better than I initially assumed, which goes a long way toward maintaining good relationships with other human beings ;)

DSCP, although it "is" another layer of complication, is actually a pretty good idea. In essence, it's an attempt at damage control and resource sharing (which almost never works entirely), on par with earlier "HUGE" Sun computers, which does a pretty decent job at a relatively low cost. And, I use the word "cost" in reference to the amount of work you have to put into getting it all set up and working correctly. It's practically free, in that respect, so kudos (The plural, pronounced kyu-doze) to Sun for adding a little extra protection and making it an additon to an existing model that doesn't encumber the admin or user to a noticeable degree. Once it's set up, it may as well be non-existent. ...unless you have problems with it, but that's a general rule when it comes to anything.

Inter-process communication on the 6800/6900, etc boxes was handled pretty decently as well, but didn't really lay ground for the possiblity of scaling easily in the future. On those boxes, shared memory (for example) was "stuck" to a single SP, so if you had multiple SP's, you essentially had multiple machines, each alienated from the other with regards to system resources. The 6800/6900's were, as one would expect, worse in this regard than the 15k-and-up models (check out the price tags. Some times it can be an indicator of quality. Is the difference in ease of sharing worth it? Depends on your situation)

The 15k-and-up servers ran physical ethernet from the service processor(s) to the domain controllers (whereas, if I forgot to mention above, the older mailbox-architecture was imbedded and much more difficult to "change"). This setup made it slightly easier to re-allocate resources since you basically had a MAN setup on your Sun system (Maintenance Area Network for those of us who still care ;). Since the MAN operated at the application layer of the stack, all you had to do to scale up when you added a new product or application was assign a new TCP port. And that was that: Sharing made much simpler. There's a lot of nitty-gritty behind it all, but who wants to read about that? If you do, check out and go nuts ;)

So, now, we've made it all the way up to the almost-present (we'll just consider it the "now" for now ;) and the M-Series servers. Since the MAN configuration of the 15k-and-up servers worked out so beneficially, that concept was guaranteed to be built in to the next generation of Enterprise computers. The one big drawback, from an architectural perspective, was the fact that the 15k-and-up servers had a whole bunch of externally exposed cables patched all over the place to maintain that separate MAN network (lots of ways to goof that up). The DSCP is Sun's way of taking care of that issue while maintaining the extended reliablity (and security) introduced with the MAN concept.

DSCP reproduces the 15k-and-up MAN using shared RAM, a pseudo-serial driver and PPP. To the user, this means all the benefits of a MAN, without all of the cords ;) Actually, it's a very nice implementation of physical-to-virtual transformation. And, as we all know, in about 10 to 15 years, we'll all be virtual and the only people left alive on the planet earth will be maintenance technicians ;)

The best thing about DSCP is how incredibly complicated it is to set up. Just kidding ;) It's actually incredibly simple. So simple that, if you're like me, you're wondering when a monkey is going to be able to start doing your job ;) Assuming an unlimited amount of Domains attached to a service processor, setup of DSCP is as simple as this:

XSCF> setdscp -i -m
Commit these changes to the database? [y|n] : y

or, even simpler:

XSCF> setdscp
DSCP network [ ] >
DSCP netmask [ ] >
XSCF address [ ] >
Domain #00 address [ ] >
Domain #01 address [ ] >

These examples are from an M4000 with only 2 domains, but the flavour stays the same on the larger boxes in the series. The only thing you really have to worry about (just like your MAN networks) is that you pick a network that doesn't get used. Generally, as shown above, using a non-routable network is best practice. Although I accidentally typed a 24-bit netmask for a class C IP (and used 1 for the network instead of 0), it doesn't really make a difference.

Of course, displaying the information is just as simple (should you forget):

XSCF> showdscp

DSCP Configuration:


Location Address
---------- ---------
Domain #00
Domain #01

The key benefit, aside from the easier resource sharing that carries over from the MAN days, is the extra protection each domain is provided. Assuming an exploit is commited against one domain, whoever's gotten onto your box and screwed up that configuration will have to work harder to get to the other connected domains, since they'll have to go through the XSCF to get there. There is no absolute direct connection between domains. Although, since I know somebody out there is thinking this, it "is" still possible to attack all the domains on an M-Series machine at once; just not in an overt fashion. For instance (and I'm not encouraging this behaviour in any way whatsover) if you can create a situation whereby the administrator needs to power-cycle his/her M-Series server to restore functionality to the exploited domain, you've just brought all of the domains down in one fell swoop.

And, in closing, if you can't get to the XSCF to check out the DSCP configuration and you have the proper privilege and access to a domain hosted on an M-Series server, you can obtain that same information using the prtdscp command. Even more convenient, you can SSH (assuming you've set it up) directly from your domain to the DSCP IP using a command similar to:

host # ssh `prtdscp -s`

If you work somewhere that can afford it, enjoy the convenience :)


, Mike

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