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• How does Subnetting Work?

  - by Kyle Brandt

  How does Subnetting Work, and How do you do it by hand or in your head? Can someone explain both conceptually and with several examples? Server Fault gets lots of subnetting homework questions, so we could use an answer to point them to on Server Fault itself. What is classless routing and why is class-based routing obsolete? If I have a network, how do I figure out how to split it up? If I am given a netmask, how do I know what the network Range is for it? Sometimes there is a slash followed by a number, what is that number? Sometimes there is a subnet mask, but also a wildcard mask, they seem like the same thing but they are different? Someone mentioned something about knowing binary for this? What is NAT (Network Address Translation). Not looking for links to other sites (unless maybe you have one post with a bunch of good ones). I already know how to subnet, I just thought it would be nice if Server Fault had a generic subnetting answer.

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• Help, my CentOS servers keep going down , No route to host after a random uptime

  - by user249071

  Hello , I have a couple of Centos linux servers, that have a very simple task, they run nginx + fastcgi for php , and some NFS mounts between them, readonly They have some RPC commands to start some downloading processes with wget, nothing fancy , from a main server, but their behavior is very unstable, they simply go down, we tried to monitor ram , processor usage, even network connections, they don't load up so much, max network connections up to... 250 max, 15% processor usage and memory , well, doesn't even fill up, 2.5GB from 8GB max , I have no ideea why can a linux server go down like that, they aren't even public servers, no domain names installed no public serving, for sites. The only thing that I've discovered was that if i didn't restart the network service every couple of hours or so... the servers were becoming very slow, starting apps very slow, but not repoting a high usage of resources...Maybe Centos doesn't free the timeout connections, or something like that...It's based on Red Hat right? I'm not a linux expert , but I'm sure that there are a few guys out there that can easily have an answer to this , or even have some leads to what i can do ... I haven't installed snort, or other things to view if we have some DOS attacks, still the scheduled script that restarts the network each hour should put the system back online, and it doesn't.... Thank you in advance

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• Slackware - Assigning routes (IP address ranges) to one of many network adapters

  - by Dogbert

  I am using a Slackware 13.37 virtual machine within VirtualBox (current). I currently have a number of Ubuntu VMs on a single server, along with this Slackware VM. All VMs have been set up to use "Internal Network" mode, so they are all on a private LAN, and can see each other (ie: share files amongst themselves), but they remain private from the outside world. On on the these VMs (the Slackware one), I need to be able to grant it access to both this private network, and the internet at large. The first suggestion I found for handling this is to add another virtual network adapter to the VM, then set it to NAT. This results in the Slackware VM having the following network adapter setup: -NIC#1: Internal Network -NIC#2: NAT I want to set up the first network adapter (NIC#1) to handle all traffic on the following subnets: 10.10.0.0/255.255.0.0 192.168.1.0/255.255.255.0 And I want the second virtual network adapter (NIC#2) to handle everything else (ie: internet access). May I please have some assistance in setting this up on my Slackware VM? Additionally, I have searched for similar questions on SuperUser and Stackoverflow, but they all seem to pertain to my situation (ie: they all refer to OSX, or Ubuntu via the use of some UI-based tool). I'm trying to do this on Slack specifically via the command-line. Thanks!

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• Strange Behaviour with Unicode Characters in Windows

  - by open_sourse

  Ok, I do not know if this is a programming question, but it certainly is a technical one so I am asking it here. I was working on some internationalization stuff in my PHP code, and in order to ensure that my generated HTML shows up Unicode correctly based on the encoding and stuff I decided to add some Chinese text to my PHP page, which then echoes it into the browser to complete my test case. So I went into google and typed "Chinese", copied the first Chinese text that the search returned (which was ??/??). I then copied it into Notepad++ which is my editor, and to my surprise showed up as boxes similar to [][]/[][]. So I thought the encoding in Notepad++ was messed up and I changed the encoding to UTF-8 and UCS, neither worked. I did it fresh in a newly encoded file, still I got the boxes. The same content when I paste into Google and StackOverFlow (like I did in this posting) shows up correct Chinese! I even opened up Windows Clipboard Viewer and the content is represented in the Clipboard as boxes! I tried pasting it into Windows Explorer address bar and using to rename a file to, but I still get boxes. But it shows up correctly when pasted into my Chrome Browser address bar! Is this a Windows issue? Since I am able to paste it correctly in SO, the data in memory should be encoded correctly right? But if that is the case why does it show up as boxes in the Clipboard Viewer? I am confused here...By the way I am using Windows XP with SP3. (I am asking this question here, even if it is not programmatic, because it is preventing me from running my programming test cases..)

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• ldap-authentication without sambaSamAccount on linux smb/cifs server (e.g. samba)

  - by umlaeute

  i'm currently running samba-3.5.6 on a debian/wheezy host to act as the fileserver for our department's w32-clients. authentication is done via OpenLDAP, where each user-dn has an objectclass:sambaSamAccount that holds the smb-credentials and an objectclass:shadowAccount/posixAccount for "ordinary" authentication (e.g. pam, apache,...) now we would like to dump our department's user-db, and instead use authenticate against the user-db of our upstream-organisation. these user-accounts are managed in a novell-edirectory, which i can already use to authenticate using pam (e.g. for ssh-logins; on another host). our upstream organisation provides smb/cifs based access (via some novell service) to some directories, which i can access from my linux client via smbclient. what i currently don't manage to do is to use the upstream-ldap (the eDirectory) to authenticate our institution's samba: i configured my samba-server to auth against the upstream ldap server: passdb backend = ldapsam:ldaps://ldap.example.com but when i try to authenticate a user, i get: $ smbclient -U USER \\\\SMBSERVER\\test Enter USER's password: Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.6.6] tree connect failed: NT_STATUS_ACCESS_DENIED the logfiles show: [2012/10/02 09:53:47.692987, 0] passdb/secrets.c:350(fetch_ldap_pw) fetch_ldap_pw: neither ldap secret retrieved! [2012/10/02 09:53:47.693131, 0] lib/smbldap.c:1180(smbldap_connect_system) ldap_connect_system: Failed to retrieve password from secrets.tdb i see two problems i'm having: i don't have any administrator password for the upstream ldap (and most likely, they won't give me one). i only want to authenticate my users, write-access is not needed at all. can i go away with that? the upstream ldap does not have any samba-related attributes in the db. i was under the impression, that for samba to authenticate, those attributes are required, as smb/cifs uses some trivial hashing which is not compatible with the usual posixAccount hashes. is there a way for my department's samba server to authenticate against such an ldap server?

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• Combine multiple rows into one

  - by Jim

  I am trying to combine multiple rows of data into one. Column A contains the value on which the groupings will be based -- rows whose Column A values match will be combined into one row. My range extends from column A through X so I need a matching row of data to start in column Y. Example: +--------------+ ¦ 1001 ¦ A ¦ C ¦ ¦ 1001 ¦ B ¦ D ¦ ¦ 1002 ¦ A ¦ E ¦ ¦ 1002 ¦ B ¦ F ¦ ¦ 1002 ¦ C ¦ G ¦ +--------------+ Desired Result: +------------------------------+ ¦ 1001 ¦ A ¦ C ¦ B ¦ D ¦ ¦ ¦ ¦ 1002 ¦ A ¦ E ¦ B ¦ F ¦ C ¦ G ¦ +------------------------------+ The VBA code I am currently using is not taking the entire contents of the matched row. It is only taking the data in the 2nd column and moving it up. VBA Code: Sub Mergeitems() Dim cl As Range Dim rw As Range Set rw = ActiveCell Do While rw <> "" ' for each row in data set ' find first empty cell on row Set cl = rw.Offset(0, 1) Do While cl <> "" Set cl = cl.Offset(0, 1) Loop ' if next row needs to be processed... Do While rw = rw.Offset(1, 0) cl = rw.Offset(1, 1) ' move the data Set cl = cl.Offset(0, 1) ' update pointer to next blank cell rw.Offset(1, 0).EntireRow.Delete xlShiftUp ' delete old data Loop ' next row Set rw = rw.Offset(1, 0) Loop End Sub

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• Can Spotlight or Media Browser index metadata contained in iPhoto or Aperture in Mac OS X?

  - by jaydles

  It seems silly to go to all the trouble to assign "Face" data to thousands of photos, but not make it possible to use that data to locate them outside of that application. Is there any way to get Spotlight or Media Browser in OSX (Snow Leopard) to index and recognize metadata (Faces, Places, etc.) contained in iPhoto or Aperture? I know that that metadata is stored in the "library" database for Aperture/iphoto, rather than on the actual files (which is too bad). And I can even potentially see why it might create challenges for spotlight to use it, since spotlight is presumably a file index system, not a media organizer, but surely the media browser used across the other OSX apps is intended to use it? The media browser's whole purpose seems to be to let you easily locate and reference the items you organize in one of the ilife apps (iphoto or Aperture, in this case) from the others (say, imovie, or Mail). It's particularly vexing since the photo app on the iphone sorts by faces by default. Additionally, the mac-based media browser does access smart albums and folders, so you could establish a workaround by creating a smart album for each "face" or place, or tag, and access them that way, but it seems like there must be an easier way. Am I missing something?

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• terminal-window viewer for tab-delimited files in *nix?

  - by khedron

  I work with a lot of tab-delimited data files, with varying columns of uncertain length. Typically, the way people view these files is to bring them down from the server to their Windows or Mac machine, and then open them up in Excel. This is certainly fully-featured, allowing filtering and other nice options. But sometimes, you just want to look at something quickly on the command line. I wrote a bare-bones utility to display the first<n>lines of a file like so: --- line 1 --- 1:{header-1} 2:{header-2} 3:... --- line 2 --- 1:{data-1} 2:{data-2} 3:... This is, obviously, very lame, but it's enough to pipe through grep, or figure out which header columns to use "cut -f" on. Is there a *nix-based viewer for a terminal session which will display rows and columns of a tab-delimited file and let you move the viewing window over the file, or otherwise look at data? I don't want to write this myself; instead, I'd just make a reformatter which would replace tabs with spaces for padding so I could open the file up in emacs and see aligned columns. But if there's already a tool out there to do something like this, that'd be great! (Or, I could just live with Excel.)

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• Cisco ASA user authentication options - OpenID, public RSA sig, others?

  - by Ryan

  My organization has a Cisco ASA 5510 which I have made act as a firewall/gateway for one of our offices. Most resources a remote user would come looking for exist inside. I've implemented the usual deal - basic inside networks with outbound NAT, one primary outside interface with some secondary public IPs in the PAT pool for public-facing services, a couple site-to-site IPSec links to other branches, etc. - and I'm working now on VPN. I have the WebVPN (clientless SSL VPN) working and even traversing the site-to-site links. At the moment I'm leaving a legacy OpenVPN AS in place for thick client VPN. What I would like to do is standardize on an authentication method for all VPN then switch to the Cisco's IPSec thick VPN server. I'm trying to figure out what's really possible for authentication for these VPN users (thick client and clientless). My organization uses Google Apps and we already use dotnetopenauth to authenticate users for a couple internal services. I'd like to be able to do the same thing for thin and thick VPN. Alternatively a signature-based solution using RSA public keypairs (ssh-keygen type) would be useful to identify user@hardware. I'm trying to get away from legacy username/password auth especially if it's internal to the Cisco (just another password set to manage and for users to forget). I know I can map against an existing LDAP server but we have LDAP accounts created for only about 10% of the user base (mostly developers for Linux shell access). I guess what I'm looking for is a piece of middleware which appears to the Cisco as an LDAP server but will interface with the user's existing OpenID identity. Nothing I've seen in the Cisco suggests it can do this natively. But RSA public keys would be a runner-up, and much much better than standalone or even LDAP auth. What's really practical here?

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• Delayed internet access

  - by Joel Coel

  When I (and presumably my users) first start up or log in to my computer I can't get internet access until several minutes after logging in. Internet pages like serverfault.com will time out. During this time I can access internal web servers. Sometimes pinging the gateway seems to fix the problem. I'm using Windows 7 on this machine with wifi, and the problem seems limited to the wifi network, which is on a separate vlan. The wired network does not share the problem, but I know it's not the wifi connection itself because the internal sites work. The wifi access point is attached to a 3Com 4200 switch, with the port set for vlan 2 untagged, vlan 1 tagged. The 4200 has a fiber connection to a 3Com 4900SX fiber switch that acts almost as a router here. The fiber connection is vlan 1 untagged vlan 2 tagged at both ends. The gateway is then attached to a different 4200 (vlan 1 untagged, vlan 2 tagged) that has a similar fiber connection to the 4900SX. vlan 2 has 192.168.8.0/22 IPs, vlan 1 has 10.1.0.0/16 IPs. The 4900SX has an interface for both vlans (10.1.1.1/192.168.8.1), as does the gateway (10.1.1.5/192.168.8.5). There is one dchp server for both vlans on the same switch as the gateway. It chooses a dhcp scope based on the interface used by the 4900sx to forward the dhcp request. There is also a network access list on the 4900sx set to deny all vlan2 traffic to any 10.1.x.x host, with exceptions made for a few servers, including dhcp, 4900sx, and the gateway. I think that about covers it. Any ideas on why internet access would be delayed like this?

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• WAN Optimization for Small Office/Home Office

  - by TiernanO

  I have been reading up on WAN optimization for the last while, mostly out of interest of speeding up my own internet connections, but also to speed up the office internet connection. At home, I have 2 cable modems plugged into a RouterBoard RB750, which load balances the connections. In the office, we have a single connection into a NetGear router. Most of the WAN Optimization products I have seen, seem to be prohibitively expensive, but also seem to be based on the idea of having multiple branches around the world. What I am looking for, ideally, is as follows: software install: I am "guessing" I need to install it in 2 places: one in the office or house, and one in "the cloud". any connections going to, say, The US (we are in Europe, but our backup's live in the US currently, which would be something important to speed up) would be "tunnelled" though the Optimizer. If downloading or uploading large files, open multiple connections between both "the cloud" and the optimizer... This is where a lot of speed could be gained. finally, for items not compressed, they would be compressed on the cloud side of things, also items that are already on the optimizer could be not sent again. kind of like RSync or Proxy servers... So, is there something that can be done? Is it available using off the shelf components (some magic script with SSH, Squid, Linux and duct tape) or is it something that needs to be purchased? or even an Open Source Project that does 90% of what i am asking?

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• Cheap Solution for Routing a Toll Free Number to a Standard POTS Number

  - by VxJasonxV

  I do some technical work for an Internet Radio Show/Podcast, and need to fix something that has been broken for a while. The hosts have a Skype-In number to take listener calls, and for convenience sake, I bought and paid for a toll free number for a period of time. I used to use Asterlink for routing calls, but they folded and sent my number to OneBox, but they're ridiculously expensive by comparison. I'm looking for a cheap solution for this one simple task. Forward toll free calls to a skype-in number. The definition of cheap is as cheap or cheaper than Asterlink was. I paid something like $2 a month, and then the termination/call rate, which was a fraction of a sent for termination, and only whole cents after some serious time on the call. A $20 preload lasted me months at a time. I don't want to be upsold too, I want a simple web based management screen (CDR/stats are fun!), and obviously, it needs to be reliable. What vendors out there are you a fan of that solves this need?

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• iptables, blocking large numbers of IP Addresses

  - by Twirrim

  I'm looking to block IP addresses in a relatively automated fashion if they look to be 'screen scraping' content from websites that we host. In the past this was achieved by some ingenious perl scripts and OpenBSD's pf. pf is great in that you can provide it nice tables of IP addresses and it will efficiently handle blocking based on them. However for various reasons (before my time) they made the decision to switch to CentOS. iptables doesn't natively provide the ability to block large numbers of addresses (I'm told it wasn't unusual to be blocking 5000+), and I'm a bit cautious over adding that many rules into an iptable. ipt_recent would be awesome for doing this, plus it provides a lot of flexibility for just severely slowing down access, but there is a bug in the CentOS kernel that is stopping me from using it (reported, but awaiting fix). Using ipset would entail compiling a more up-to-date version of iptables than comes with CentOS which whilst I'm perfectly capable of doing it, I'd rather not do from a patching, security and consistency perspective. Other than those two it looks like nfblock is a reasonable alternative. Is anyone aware of other ways of achieving this? Are my concerns about several thousand IP addresses in iptables as individual rules unfounded?

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• What's a good solution for file-tagging in linux?

  - by julien

  I've been looking for a way to tag my files and search/filter them based on those tags. Here are my (updated) requirements : any file readable by the user can be tagged freely a user can search for files matching one or several tags files can be moved around without losing the previously associated tags the system could be backed up easily no dependencies on any desktop environment if any gui is involved, there must be a cli fallback I've been hoping for some basic filesystem & coreutils hackery to handle this, but I haven' thought about this hard enough yet. Meanwhile I'll review beagle and metatracker, which have been mentionned here, and see how they perform. Ok so beagle has huge gnome dependencies, and tracker is okish, but still has some dependencies I don't like... Been doing some more research, and the way to go could very well be extended file attributes. That's a native solution for most recent filesystems, but they aren't very well supported yet (most coreutils destroys them by default, cp for example needs the -a flag to preserve them). Would like to hear some thoughts on using them while I try my hand at some hacks myself, eventhough this might warrant a new question.

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• Securing NTP: which method to use?

  - by Harry

  Can someone good at NTP configuration please share which method is the best/easiest to implement a secure, tamper-proof version of NTP? Here are some difficulties... I don't have the luxury of having my own stratum 0 time source, so must rely on external time servers. Should I read up on the AutoKey method or should I try to go the MD5 route? Based on what I know about symmetric cryptography, it seems that the MD5 method relies on a pre-agreed set of keys (symmetric cryptography) between the client and the server, and, so, is prone to man-in-the-middle attack. AutoKey, on the other hand, does not appear to work behind a NAT or a masquerading host. Is this still true, by the way? (This reference link is dated 2004, so I'm not sure what is the state of art today.) 4.1 Are public AutoKey-talking time servers available? I browsed through the NTP book by David Mills. The book looks excellent in a way (coming from the NTP creator after all), but the information therein is also overwhelming. I just need to first configure a secure version of NTP and then may be later worry about its architectural and engineering underpinnings. Can someone please wade me through these drowning NTP waters? Don't necessarily need a working config from you, just info on which NTP mode/config to try and may be also a public time server that supports that mode/config. Many thanks, /HS

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• Permanent fix for unicode characters not displaying correctly (as boxes)

  - by Chase

  Please read this entire message before replying. First I know how to fix the issue on a temporary basis. I am looking for a permanent fix. I work with foreign language files a lot. Unfortunately sometimes all the unicode characters in windows explorer, notepad, and other places (as rendered by windows, probably GDI) do not display correctly. That is they display as square blocks, where as they had just been displaying correctly. There are countless methods to temporarily correct the issue. But again, I want a way to permanently resolve the issue. What I have tried: The silly "Hide fonts based on language settings". This setting only applies to what fonts you see in the fonts folder and font dropdowns. It doesn't disable foreign fonts (doesn't work, or if it does, it is temporary). Deleting the font cache file and rebooting (works.. usually, temporary solution). Changing my locale and then back (sometimes works, temporary solution). Rebooting my PC and getting lucky (50-50 chance, temporary solution). Changing my keyboard input/adding foreign keyboard (temporary solution that only seems to work once). Reinstalling windows (temporary solution, sometimes lasts a few months though, I have done this 7 times across 3 computers) What I have not tried: Buying Windows Ultimate and installing the interface packs. This is not a solution. I can't read Japanese/Chinese and I do not want my interface in those languages. What I will not do: Switch to a different brand operating system (unix, linux, mac os x) Switch to an older version of windows (Windows Vista, XP, 2000, etc). So can anyone recommend a permanent fix for the problem?

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• 4.4.1 Timeout in 10 minute intervals SMTP on batch email jobs

  - by TEEKAY

  I am running a job that uses SMTP and it can run in excess of an hour, emailing the entire time. It's not my code but a workflow based app so I just get a form to configure the mail server, subj, msg, etc and can't see it's implementation. I know it is .NET and SmtpClient. I have been seeing 4.4.1 timeouts every 10 minutes being reported by the application as the response from the server. The # of emails in those 10 minute sessions are variable, between 100 and below 150 which leads me to ask about the 10 minute timeout time specifically. I have found there are several exchange properties (though I don't know what version they are running) that set timeout limits. (http://technet.microsoft.com/en-us/library/bb232205%28v=exchg.150%29.aspx) Would those values for ConnectionInactivityTimeOut and ConnectionTimeout be the controlling the timeouts? and finally I would like to ask if exchange considers the consistent connection(s) it kept receiving from the same source as one continuous connection and cause the timeout each 10 minutes and cause the timeout? I am using a static ip of the mail server. Thanks if anyone can shed any light on my problem. EDIT - It is my belief that the library is just keeping the connections around and isn't wrapped in any cleanup code or using statement. That said, I still haven't made any progress on this issue in the last year and just requeue the failed ones as I see them.

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• lenovo x1 carbon windows 8 frequent wifi disconnect issue

  - by hIpPy

  I'm having frequent wifi disconnects on my Lenovo X1 Carbon Touch laptop. I got this laptop 2 months back and it has been happening ever since about 3-5 times a day and 10 times a week on average. I've Frontier Fios internet. Power connected or not does not matter. Once I get disconnected, I try below to connect again in that order: turn Airplane mode on and off, troubleshoot network problems windows troubleshooter), restart the laptop I'd find that the WiFi adapter would get disabled and sometimes windows troubleshooting would help but more than often I'd end up restarting the laptop. A week back, I upgraded my wifi network adapter drivers (now Intel, version 15.5.6.48, 10/3/2012). I still get disconnected frequently but turning Airplane mode on and off gets me connected again. So the driver update did help. Windows 8 is updated. None of the other devices (nexus, iphone phones, nexus7, ipad tablets) would have wifi issues when my laptop would get disconnected. config: Intel(R) Centrino(R) Advanced-N 6205 (WiFi network adapter) Microsoft Windows 8 Pro Microsoft Windows [Version 6.2.9200] x64-based PC LENOVO System Model: 3443CTO X1 Carbon Touch I recently noticed this log message When I got disconnected in event viewer: Your computer was not assigned an address from the network (by the DHCP Server) for the Network Card with network address 0x[XXXXXXXXXXXX]. The following error occurred: 0x79. Your computer will continue to try and obtain an address on its own from the network address (DHCP) server. Any idea?

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• Manual Http error response code in non-existent folder via routing

  - by Slytherin

  Apache server running on ubuntu-like linux I am getting unexpected behaviour when i try to manually send error response. If my .htaccess is responsible for the error response , then appropriate error document is loaded and displayed , with according response code in browser console. However , if my router is origin of the response code , then i get blank screen , but correct response code. .htaccess looks like this RewriteEngine On # RewriteBase / RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule !\.(css|js|icon|zip|rar|png|jpg|gif|pdf)$ index.php [L] ErrorDocument 404 /err/404.html ErrorDocument 403 /err/403.html ErrorDocument 500 /err/500.html part of my router that sends the response is the following header("HTTP/1.1 403 Forbidden"); trying this format didnt help either header("HTTP/1.1 403 Forbidden", TRUE, 403); I also tried HTTP/1.0. Furthermore i was thinking that maybe relative path to error page might be an issue , but discarded this idea after attempting to access a document that is forbidden via .htaccess EDIT I should also point out , this scenario happens when URL for not-existing article is requested. Is it possible that Server is looking for a .htaccess file in a folder based on URL ? Eg: domain/blog/non-existent , is server looking for blog folder ? I am specifically asking this because there is no blog folder

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• Preventing endless forwarding with two routers

  - by jarmund

  The network in quesiton looks basically like this: /----Inet1 / H1---[111.0/24]---GW1---[99.0/24] \----GW2-----Inet2 Device explaination H1: Host with IP 192.168.111.47 GW1: Linux box with IPs 192.168.111.1 and 192.168.99.2, as well as its own route to the internet. GW2: Generic wireless router with IP 192.168.99.1 and its own route to the internet. Inet1 & Inet2: Two possible routes to the internet In short: H has more than one possible route to the internet. H is supposed to only access the internet via GW2 when that link is up, so GW1 has some policy based routing special just for H1: ip rule add from 192.168.111.47 table 991 ip route add default via 192.168.99.1 table 991 While this works as long as GW2 has a direct link to the internet, the problem occurs when that link is down. What then happens is that GW2 forwards the packet back to GW1, which again forwards back to GW2, creating an endless loop of TCP-pingpong. The preferred result would be that the packet was just dropped. Is there something that can be done with iptables on GW1 to prevent this? Basically, an iptables-friendly version of "If packet comes from GW2, but originated from H1, drop it" Note1: It is preferable not to change anything on GW2. Note2: H1 needs to be able to talk to both GW1 and GW2, and vice versa, but only GW2 should lead to the internet TLDR; H1 should only be allowed internet access via GW2, but still needs to be able to talk to both GW1 and GW2. EDIT: The interfaces for GW1 are br0.105 for the '99' network, and br0.111 for the '111' network. The sollution may or may not be obnoxiously simple, but i have not been able to produce the proper iptables syntax myself, so help would be most appreciated. PS: This is a follow-up question from this question

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• Customer site is out of IP addresses, they want to go from /24 to /12 netmask... Bad idea?

  - by ewwhite

  One of my client sites called to ask me to change the subnet masks of the Linux servers I manage there while they re-IP/change the netmask of their network based on a 10.0.0.x scheme. "Can you change the server netmasks from 255.255.255.0 to 255.240.0.0?" You mean, 255.255.240.0? "No, 255.240.0.0." Are you sure you need that many IP addresses? "Yeah, we never want to run out of IP addresses." A quick check against the Subnet Cheat Sheet shows: a 255.255.255.0 netmask, a /24 provides 256 hosts. It's clear to see that an organization can exhaust that number of IP addresses. a 255.240.0.0 netmask, a /12 provides 1,048,576 hosts. This is a small < 200-user site. I doubt that they'd allocate more than 400 IP addresses. I suggested something that provides fewer hosts, like a /22 or /21 (1024 and 2048 hosts, respectively), but was unable to give a specific reason against using the /12 subnet. Is there anything this customer should be concerned about? Are there any specific reasons they shouldn't use such an incredibly large mask in their environment?

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• High-performance Academic Server [closed]

  - by PHPsmith

  Suppose I want to build a server for the university's academic interests. The server is dedicated only to a site, where users (students and lecturers) just view and fill the academic data. But at a time (e.g. once a semester), about 12,000 students will access the site simultaneously. Due to limitation of resources, I have to build the server using free software (except for the operating system Windows 7, the university has been prepared). The hardware is also limited to the usual 4-core computers (eg, Ivy Bridge Intel Core i7-3770) with approximately 16GB of memory (DDR3 1600 MHz), equipped with an RJ-45 port (Intel 82 579 Gigabit Ethernet). With all these limitations, I have to choose the software (web server, database, etc) are appropriate for this purpose is achieved. I decided to create a site in PHP. Please help me by answering the following questions based on your expertise. (my prime candidate software to consider after googling) Web server which is faster & stable & secure, when implemented and optimized for PHP? And why? (nginx) PHP accelerator which is faster & stable & compatible with the selected web server? And why? (APC with Zend Optimizer+) Database which is faster & stable & secure, when implemented and optimized for selected web server and selected PHP accelerator? (MySQL) Are there any errors that have been or will be happening from my condition is? If there is, please enlighten me? Is there anything else I need to know in order to achieve this goal? If there is, please enlighten me? I understand that the performance also depends on the implementation of source-code program, so I assume it will create a site with the best efficiency (e.g. using AJAX).

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• Does SNI represent a privacy concern for my website visitors?

  - by pagliuca

  Firstly, I'm sorry for my bad English. I'm still learning it. Here it goes: When I host a single website per IP address, I can use "pure" SSL (without SNI), and the key exchange occurs before the user even tells me the hostname and path that he wants to retrieve. After the key exchange, all data can be securely exchanged. That said, if anybody happens to be sniffing the network, no confidential information is leaked* (see footnote). On the other hand, if I host multiple websites per IP address, I will probably use SNI, and therefore my website visitor needs to tell me the target hostname before I can provide him with the right certificate. In this case, someone sniffing his network can track all the website domains he is accessing. Are there any errors in my assumptions? If not, doesn't this represent a privacy concern, assuming the user is also using encrypted DNS? Footnote: I also realize that a sniffer could do a reverse lookup on the IP address and find out which websites were visited, but the hostname travelling in plaintext through the network cables seems to make keyword based domain blocking easier for censorship authorities.

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• Routing public IPs (each a /32) through a VPN to another server

  - by Lee S

  Hopefully the title makes sense; I have a server currently in a colo facility, with many IP addresses routed to it. They are individual IPs and not in a contiguous block. Due to vastly improved connectivity (fibre) at home I am slowly bringing my infrastructure in-house for managability and eventually, cost savings. What I would like to do though is use the IP addresses allocated to my existing server, at home. I have an IP block allocated to me on my new ISP connection, but for a couple of reasons I'd like to make use of the colo ones for now: Ease of transition - lots of domains, dns, hard-coded IPs in programs, etc. Connectivity fallback. If my primary line goes down and switches to fallback 1 (dsl) or fallback 2 (4G), I lose access to the ISP-allocated IP block of IPs that are only presented on the primary WAN interface. What I'd like to achieve is my home virtualisation server (Proxmox/Debian-based) "dials in" to the colo server in the colo facility (also Proxmox/Debian) via VPN or similar, and gets to make use of the IP addresses that currently terminate on the colo box. If the primary connection to my ISP goes down and one of the fallback routes kicks in, the VPN tunnel will just time out and then be re-established on the backup connection instead. I'm sure this is doable, but I have no idea how. I'm not afraid to get my hands dirty, I just don't really know where to start?

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• Having trouble with a workaround, for booting from a usb stick, using grub and a minimal linux kernel to load usb drivers

  - by s hanley

  I'm trying to boot from a usb stick. I formatted it to fat32, and later to ext2, and installed dsl on it using unetbootin, and later the usb install guide on dsl wiki (http://www.damnsmalllinux.org/wiki/index.php/Install_to_USB_From_within_Linux). The bios doesn't have a setting for booting from usb. Grub doesn't "see" the usb drive when I use the root and find commands, explained in (http://www.damnsmalllinux.org/wiki/index.php/USB_Booting). This happens even when I set boot from floppy at the top of the boot order. However, my usb keyboard is recognised by the bios and by grub. How can it recognise the keyboard but not the usb drive? Also, the usb led does flash even before grub starts up, so surely something must be happening usb-wise? I am now following an ubuntu guide to booting from a USB stick, using a hdd-based, minimal linux kernel to supply the usb drivers. But I'm having difficulty adapting it to other OSes (slax/dsl/aptosid). I believe I have to alter the initrd.gz file to include usb drivers and then copy that file along with vmlinuz to a partition on my hdd. But, what's the grub command for the kernel line supposed to look like? From the ubuntu example it's: title USB FLASH DRIVE root (hd0,6) kernel /boot/usb-boot/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper noprompt cdrom-detect/try-usb=true persistent initrd /boot/usb-boot/initrd.lz boot Should mine just be: title USB FLASH DRIVE root (hd0,6) kernel /boot/usb-boot/vmlinuz cdrom-detect/try-usb=true initrd /boot/usb-boot/initrd.lz boot

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