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• RPCSS kerberos issues on imaged Windows workstations

  - by sysadmin1138

  While doing some unrelated troubleshooting I came across a set of Event Log entries that have me concerned. Machine Name: labcomputer82 Source: Security-Kerberos Event ID: 4 Event Description: The Kerberos client received a KRB_AP_ERR_MODIFIED error from the server labcomputer143$. The target name used was RPCSS/imagemaster4.ad.domain.edu. This indicates that the target server failed to decrypt the ticket provided by the client. This can occur when the target server principal name (SPN) is registered on an account other than the account the target service is using. Please ensure that the target SPN is registered on, and only registered on, the account used by the server. This error can also happen when the target service is using a different password for the target service account than what the Kerberos Key Distribution Center (KDC) has for the target service account. Please ensure that the service on the server and the KDC are both updated to use the current password. If the server name is not fully qualified, and the target domain (AD.DOMAIN.EDU) is different from the client domain (AD.DOMAIN.EDU), check if there are identically named server accounts in these two domains, or use the fully-qualified name to identify the server. There are three machine names used in this message. It's generated on labcomputer82, it's attempting to talk to another lab workstation called labcomputer143, and the service in question (RPCSS) refers to the name of the machine that this machine was imaged from (and possibly also that of labcomputer143, I'm not sure). The thing that has me raising both eyebrows is that the machine named labcomputer82 is attempting to use an SPN of RPCSS/imagemaster4.ad.domain.edu. The SPN attribute on the computer object in AD looks just fine. It has all the names it should have. Of the over 3,000 computer objects in our AD domain, somewhere around 1,700 of the are computer-lab seats that are frequently imaged. If we're doing something wrong, I'd like to know in time to get our procedures modified (and people retrained) for fall quarter. But if this is normal for imaged machines, I'll just continue ignoring these.

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• New AD-DC in a new Site is refusing cross-site IPv4 connections

  - by sysadmin1138

  We just added a new Server 2008 (sp2) Domain Controller in a new Site, our first such config. It's over a VPN gateway WAN (10Mbit). Unfortunately it is displaying a strange network symptom. Connections to the SMB ports (TCP/139 and TCP/445) are being actively refused... if the connection is coming in on pure IPv4. If the incoming connection is coming by way of the 6to4 tunnel those connections establish and work just fine. It isn't the Firewall, since this behavior can be replicated with the firewall turned off. Also, it's actually issuing RST packets to connection attempts; something that only happens with a Windows Firewall if there is a service behind a port and the service itself denies access. I doubt it's some firewall device on the wire, since the server this one replaced was running Samba and access to it from our main network functioned just fine. I'm thinking it might have something to do with the Subnet lists in AD Sites & Services, but I'm not sure. We haven't put any IPv6 addresses in there, just v4, and it's the v4 connections that are being denied. Unfortunately, I can't figure this out. We need to be able to talk to this DC from the main campus. Is there some kind of site-based SMB-level filtering going on? I can talk to the DC's on campus just fine, but that's over that v6 tunnel. I don't have access to a regular machine on that remote subnet, which limits my ability to test.

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• Barriers to IPv6 deployment: addressing

  - by sysadmin1138

  There are several things that are keeping IPv6 deployment from being a topic of active discussion here at my work. There are the usual technical issues, but one non-technical one appears to be a major stumbling block on the path to actually getting a deployment project going. Addresses, memorizing of. Specifically, IPv4 addresses are comprehensible, and IPv6 addresses just look like a big long string of hex. The human mind has real trouble memorizing lists of more than 7-8 items, and an IPv4 address (192.168.231.148) has four items in it which makes it easy for us to memorize. A fully populated IPv6 address has not only 8 sections, but each section has 4 hex digits in it. IPv6 addresses were not designed for memorization. To the technician who knows that the DNS server is at 192.168.42.42 (or more likely "42.42", since the company prefix is likely memorized), the idea of memorizing an IPv6 address fills them with dread. Which in turn makes them much less enthusiastic about participating in an IPv6 deployment project. Because of how our network works we're not fully dynamic in terms of v4 addressing. We have several to many subnets that are entirely statically assigned for a variety of reasons, chief among them being that the overhead of static DHCP assignments is perceived as being too great. Also, some devices still aren't smart enough to pull DNS addresses out of DHCP while also having a static assignment, and therefore require manually configured DNS settings. Therefore, some v6 address memorization will have to be done. We're not under any mandate to get v6 out the door, so we don't have pressure from the top. However, it is time to start prepping our infrastructure to handle IPv6 even if we don't convert wholesale. For those of you who have been in IPv6-land for a while, what short-cut methods do you use to discuss or keep track of subnets and specific/critical IP addresses? If I can help reduce some of the dread surrounding IPv6 we might get the project going.

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• Implementing an isolated guest WLAN via IPSec VPN on Windows

  - by sysadmin1138

  We are attempting to set up a guest WLAN network that is isolated from the rest of our network. This is proving difficult due to a couple of technical reasons. My first choice was to use a separate VLAN, on which our Firewall's handy WLAN port would handle DHCP, DNS and the network isolation we need. Unfortunately, due to the fact that our main office and our Internet connection itself are in different locations connected by way of a Metro Ethernet connection, I'm at the mercy of our ISP for VLAN transit. They won't pass a second VLAN between our two sites. And my hardware doesn't support 802.1ad "Q-in-Q", which would also solve this problem. So I can't use the VLAN method for isolation. At least not without spending money. As our Firewall can handle IPSec site-to-site VPN connections, I hope it is possible to connect a Server 2008R2 (standard) server I have in the office location to the WLAN and provide gateway services to the firewall. Thusly: Unfortunately, I don't know if it is possible to connect the two this way. The firewall has a pretty flexible IPSec/L2TP implementation (I've used it to connect iPads in the wild), but is neither Kerberized or supports NTLM. The Connection Security Rules view on the Windows server seems to get close to what I think needs to be done, but I'm failing on figuring out how to get it to do what I need it to do. Is this even possible, or do I need to pursue alternate solution?

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• MongoDB and datasets that don't fit in RAM no matter how hard you shove

  - by sysadmin1138

  This is very system dependent, but chances are near certain we'll scale past some arbitrary cliff and get into Real Trouble. I'm curious what kind of rules-of-thumb exist for a good RAM to Disk-space ratio. We're planning our next round of systems, and need to make some choices regarding RAM, SSDs, and how much of each the new nodes will get. But now for some performance details! During normal workflow of a single project-run, MongoDB is hit with a very high percentage of writes (70-80%). Once the second stage of the processing pipeline hits, it's extremely high read as it needs to deduplicate records identified in the first half of processing. This is the workflow for which "keep your working set in RAM" is made for, and we're designing around that assumption. The entire dataset is continually hit with random queries from end-user derived sources; though the frequency is irregular, the size is usually pretty small (groups of 10 documents). Since this is user-facing, the replies need to be under the "bored-now" threshold of 3 seconds. This access pattern is much less likely to be in cache, so will be very likely to incur disk hits. A secondary processing workflow is high read of previous processing runs that may be days, weeks, or even months old, and is run infrequently but still needs to be zippy. Up to 100% of the documents in the previous processing run will be accessed. No amount of cache-warming can help with this, I suspect. Finished document sizes vary widely, but the median size is about 8K. The high-read portion of the normal project processing strongly suggests the use of Replicas to help distribute the Read traffic. I have read elsewhere that a 1:10 RAM-GB to HD-GB is a good rule-of-thumb for slow disks, As we are seriously considering using much faster SSDs, I'd like to know if there is a similar rule of thumb for fast disks. I know we're using Mongo in a way where cache-everything really isn't going to fly, which is why I'm looking at ways to engineer a system that can survive such usage. The entire dataset will likely be most of a TB within half a year and keep growing.

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• Encryption of OS X to Windows SMB traffic and password

  - by Brian

  I connected to a Windows Server 2008 R2 shared folder from a Mac OS X Mountain Lion computer over the Internet using this command: mount -t smbfs //user@server/path/to/share local_folder Is traffic encrypted by default? What settings do I look at (if any) to know whether it was encrypted? If it wasn't encrypted, what's the easiest way to encrypt it? Was the password I typed at the command line encrypted? Update: sysadmin1138 has addressed the password question. Does anyone know how I can tell if the traffic itself is being encrypted?

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