Handling User Grown Machines on a Large Network?

matth asks: "Recently with the outbreak of the MSBLASTER worm and the startup of the college semester here in the US we've been hit by a big problem here where I work. Many students are bringing in machines from home, often times infected. The infections are so bad that they bring the whole network to a crawl. Yes, you can install ACLs on edge routers and put a router between the dorms and the rest of your network, but it still brings the dorm to a crawl. You can make sure people install the patches, but what if someone re-installs Windows, or brings in another machine, and what about NEXT year? From the Slashdot community, how have sysadmins out there dealt with this? How can you manage each machine in a network such as a college, where people are bringing their own machines in from the outside? ACLs on routers... but what about for the segmented network?"

Comments

Deny them DNS services

[eaglesnax]

I think this was one of the approaches Stanford was going to take. No DNS for your machine until you get it checked out by their IT department.

Chris

Here is what we do

[Anonymous Coward]

In our residence halls, we have about 7500 people. What we have done is make a series of VLANs, centrally administered by VMPS. We have the regular VLAN for a building's users, a quarantine VLAN, and a blackhole VLAN. As we detect users that are infected, we move them to the quarantine VLAN where we have colocated a quarantine webserver via an 802.1q trunk. This server provides them with all the patches, av software and latest DATs. Once installed, the resident "signs" with their campus ID to verify that they have installed the various fixes, and they are moved back. If someone languishes in the quarantine VLAN for too long, we move them to the blackhole VLAN (which is essentially a defined VLAN that isn't trunked anywhere so VMPS can still legally place them there).

This segmentation has helped dramatically. At one point, we were blocking nearly 800,000 icmp echo requests outbound/sec across all interfaces. Now? around 1k/sec. And that's over the last week.

Now if I could just get past the residents who:
1. Don't fix themselves because it was too much to read.
2. Don't know how to use a web browser
3. Don't know what a scroll bar is (!!!)
4. Don't contact us for help, but instead go to the President and Provost's offices.

Hang in there, segmentation helps dramatically.

Re:You could just...

[Jon Abbott]

Case in point -- back in 2000, even though I had about four years Linux experience by then, I managed to bring down Internet access for an entire dorm (about 900 students) for a week.

It all started when I helped a friend install Linux on his new computer. Unfortunately, in addition to installing a DHCP client on his machine, I had accidentally flagged the DHCP server to install as well. What happened was that the DHCP server software on his new Linux box was challenging the Windows DHCP server that the dorm was using, and his machine won -- even though his DHCP server wasn't properly configured to hand out IP addresses to other clients. So, all of these other 900 students would turn on their computers, which would send out a DHCP request, and they would get a response from his computer instead of the real DHCP server, thus causing their computers to give up trying to connect to the network. Ironically enough, his computer connected to the internet fine, as it was the only one connecting to the real DHCP server (I guess that explains his super-fast connection during that week).

Anyway, we had no idea that any of this was happening until we headed back to his dorm room one day, and found three network services guys looking in bewilderment at the computer (they had never used anything but Windows, so they had no idea how to fix it). They claimed that it took them a week to isolate the problem to his machine. They explained what was happening, and it then hit me that the DHCP server was also running on his machine, so I logged in, apt-get removed it, and the problem was immediately fixed. Not in their eyes though, as they made us talk to the head guy at network services... He gave us fair warning that if we did that again, our access to the network would be revoked (and rightly so!).

The obvious moral of the story is, whereas most OSes give you just enough rope to tie a knot, Linux gives you enough rope to hang about 900 people. :^)