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• VMWare use of Gratuitous ARP REPLY

  - by trs80

  I have an ESXi cluster that hosts several Windows Server VMs and around 30 Windows workstation VMs. Packet captures show a high number of ARP replies of the form: -sender_ip: VM IP -sender_mac: VM virtual MAC -target_ip: 0.0.0.0 -target_mac: Switch interface MAC The specific addresses aren't really a concern -- they're all legitimate and we're not having any problems with communications (most of the questions surrounding GARP and VMWare have to do with ping issues, a problem we don't have). I'm looking for an explanation of the traffic pattern in an environment that functions as expected. So the question is why would I see a high number of unsolicited ARP replies? Is this a mechanism VMWare uses for some purpose? What is it? Is there an alternative? EDIT: Quick diagram: [esxi]--[switch vlan]--[inline IDS]--[fw]--(rest of network) The IDS is complaining about these unsolicited ARPs. Several IDS vendors trigger on ARP replies without a prior request, or for ARP replies that have a target IP of 0.0.0.0. The target MAC in these replies is the VLAN interface on the switch. Capture points: -The IDS grabs the offending packets -The FW can see the same ones -A VM on the ESXi host does not see these, although there is an ARP request for a specific IP on the ESXi host that has source_ip=0.0.0.0 and source_mac=[switch vlan interface]. I can't share the captures, unfortunately. Really I'm interested in finding out if this is normal for an ESXi deployment.

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• Configure linux machine as bridge/switch and end device

  - by leemes

  At my home, I have two desktop PCs in two rooms. The router / DSL modem is in one of these rooms. Now I want to configure a home server (having 2 LAN ports, running 24/7) in the corridor between the two rooms, using only one LAN cable at each door. This gives me the following physical configuration: (door) (door) .----/-/----. .-----/-/----------._ FritzBox | | | .----´´ DSL Router PC1 Server | PC2 As just said, the server has 2 network interfaces and is running Ubuntu. What I need now is a network configuration which enables both the server and PC1 to connect to the router. I think the server needs to serve as a bridge or switch. Currently, all computers are configured having static IP addresses. If I'm understanding it correctly, a bridge / switch doesn't have its own IP address, but as the server needs to be configured as an own end device, it needs to have one. My first question is, do I have to configure both interfaces separately, giving both the same static IP address? My next question is, how do I bridge the two physical networks into one? I have basic understanding (but am always confused again and again) of bridges and switches, but I don't know how to configure it in software. I only know that it's possible to do so :) The third question is: Is it possible to configure this in a way that network packets from/to PC1 to/from the router only go through hardware or only consume low CPU in the server? Can you help me? Thanks in advance!

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• Network topology for both direct and routed traffic between two nodes

  - by IndigoFire

  Despite it's small size, this is the most difficult network design problem I've faced. There are three nodes in this network: PC running Windows XP with an internal WiFi adapter.Base station with both WiFi and a Wireless Modem (WiModem)Mobile device with both WiFi and WiModem The modem is a low-bandwidth but high-reliability connection. We'd like to use WiFi for high-bandwidth stuff like file transfers when the mobile is nearby, and the modem for control information. Here's the tricky part: we'd like the wifi traffic to go directly from the mobile to the PC, as rebroadcasting packets on the same WiFi channel takes up double the bandwidth. We can do that with a manual configuration by giving the both the PC and the base station two IP addresses for their WiFi interfaces: one on a subnet shared with the mobile, and one on their own subnet. The routes on the PC are set up so that any traffic going to the mobile via WiModem goes through the secondary IP address so that return traffic from the mobile also goes through the WiModem. Here's what that looks like: PC WiFi 1: 192.168.2.10/24 WiFi 2: 192.168.3.10/24 Default route: 192.168.2.1 Base Station WiFi 1: 192.168.2.1/24 WiFi 2: 192.168.3.1/24 WiModem: 192.168.4.1/24 Mobile WiFi: 192.168.3.20/24 WiModem: 192.168.4.20/24 We'd like to move to having the base station automatically configure the mobile and PC, as the manual setup is problematic when you start having multiple mobiles and PCs. This means that the PC can only have 1 IP address and needs to be treated as being pretty simple. Is it possible to have a setup driven by DHCP on the base station that is efficient with bandwidth?

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• TCP dies on a Linux laptop

  - by Roman Cheplyaka

  Once in several days I have the following problem. My laptop (Debian GNU/Linux testing) suddenly becomes unable to work with TCP connections to the internet. The following things continue to work fine: UDP (DNS), ICMP (ping) — I get instant response TCP connections to other machines in the local network (e.g. I can ssh to a neighbour laptop) everything is ok for other machines in my LAN But when I try TCP connections from my laptop, they time out (no response to SYN packets). Here's a typical curl output: % curl -v google.com * About to connect() to google.com port 80 (#0) * Trying 173.194.39.105... * Connection timed out * Trying 173.194.39.110... * Connection timed out * Trying 173.194.39.97... * Connection timed out * Trying 173.194.39.102... * Timeout * Trying 173.194.39.98... * Timeout * Trying 173.194.39.96... * Timeout * Trying 173.194.39.103... * Timeout * Trying 173.194.39.99... * Timeout * Trying 173.194.39.101... * Timeout * Trying 173.194.39.104... * Timeout * Trying 173.194.39.100... * Timeout * Trying 2a00:1450:400d:803::1009... * Failed to connect to 2a00:1450:400d:803::1009: Network is unreachable * Success * couldn't connect to host * Closing connection #0 curl: (7) Failed to connect to 2a00:1450:400d:803::1009: Network is unreachable Restarting the connection and/or reloading the network card kernel module doesn't help. The only thing that helps is reboot. Clearly something is wrong with my system (everything else works fine), but I have no idea what exactly. I don't know how to reproduce this, but as I said, it happens every several days. My setup is a wireless router that is connected to the ISP via PPPoE. Any advice?

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• Monitoring instantaneous network throughput at one second intervals?

  - by Shaddi

  For a testing setup I have, I need to monitor the throughput through a "router"* at regular intervals of around 5 seconds or less (sub-second intervals would be very nice, but not required). Ideally, I would be able to generate a file which contained both the number of bytes and packets seen during each interval. I will eventually be generating a time-series of throughput from this data. On a previous setup using an older version of FreeBSD, there was a tool called "bpfmon" which gave me this information. However, I need to do this under a modern version of Linux (namely, Ubuntu 11.04). I have looked at both iptraf and iftop, but these do not appear to provide the resolution I need, nor do they seem to easily allow scraping the data I need. I understand iptables statistics may be able to give me what I'm after, but the examples I've seen of this seem to rely on repeatedly reading and resetting traffic counters, which seems like it could give inaccurate as read/reset is not an atomic operation. I already capture a tcpdump trace of the traffic I'm interested in on the link I want to monitor, so I am open to approaches which simply parse that. I feel like this must be a common problem though, so I am hoping there will be a standard "best practice" tool for accomplishing this. *I say "router" in quotes because I am really talking about a machine with two bridged NICs through which all the traffic I'm interested in passes.

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• Packet flooding while configuring a Debian L2TP/IPSec client?

  - by Joseph B.

  I'm currently at my wits end trying to configure an L2TP over IPSec VPN connection on my Debian using openswan and xl2tp box connecting to a server of unknown configuration. I've managed to successfully establish the connection and everything appears to be working well until I attempt to set the VPN connection as my default route, at which point I see a massive flood of packets simultaneously being transmitted (on the tune of ~1.5 GB in about 2min) until the server drops my connection. Prior to this network traffic on all my interfaces is minimal. According to iftop the majority of this traffic appears to be coming out of port 12, although I can't seem to figure out how to finger a specific process. If I instead just route traffic destined for 74.0.0.0/8 through it I'm able to access Google's servers through the VPN without issue. My xl2tp.conf file is: [lac vpn-nl] lns = example.vpn.com name = myusername pppoptfile = /etc/ppp/options.l2tpd.client My options.l2tpd.client file is: ipcp-accept-local ipcp-accept-remote refuse-eap require-mschap-v2 noccp noauth idle 1800 mtu 1410 mru 1410 usepeerdns lock name myusername password mypassword connect-delay 5000 And my routing table looks like: Destination Gateway Genmask Flags Metric Ref Use Iface 10.5.2.1 * 255.255.255.255 UH 0 0 0 ppp0 10.0.50.0 * 255.255.255.0 U 0 0 0 eth0 10.50.0.0 * 255.255.0.0 U 0 0 0 eth0 10.0.0.0 * 255.255.0.0 U 0 0 0 eth0 192.168.0.0 * 255.255.0.0 U 0 0 0 eth0 loopback * 255.0.0.0 U 0 0 0 lo default * 0.0.0.0 U 0 0 0 ppp0 I'm seeing absolutely nothing in auth.log and syslog during this time and can't seem to find any other log files it might be writing to. Any suggestions would be appreciated!

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• Windows Server doesn't connect to a network share

  - by Dmitriy N. Laykom

  Windows Server doesn't connect to a network share. Network share is working. Blockquote Pinging 109.123.146.223 with 32 bytes of data: Reply from 109.123.146.223: bytes=32 time<1ms TTL=63 Reply from 109.123.146.223: bytes=32 time<1ms TTL=63 Reply from 109.123.146.223: bytes=32 time<1ms TTL=63 Ping statistics for 109.123.146.223: Packets: Sent = 3, Received = 3, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms net view \shareaddress Blockquote System error 53 has occurred. The network path was not found. When I connected the network share I observed this error message: Blockquote \ "Mapped disk letter" refers to a location that is unavailable. It could be on a hard drive on this computer, or on a network. Check to make sure that the disk is properly inserted, or that you are connected to the Internet or your network, and then try again. If it still cannot be located, the information might have been moved to a different location The network share was mounted via Group Policy. Perchance anyone knows how I can avoid this error? When the OS has been restored from the disk problem has been solved

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• pdns-recursor allocates resources to non-existing queries

  - by azzid

  I've got a lab-server running pdns-recursor. I set it up to experiment with rate limiting, so it has been resolving requests openly from the whole internet for weeks. My idea was that sooner or later it would get abused, giving me a real user case to experiment with. To keep track of the usage I set up nagios to monitor the number of concurrent-queries to the server. Today I got notice from nagios that my specified limit had been reached. I logged in to start trimming away the malicious questions I was expecting, however, when I started looking at it I couldn't see the expected traffic. What I found is that even though I have over 20 concurrent-queries registered by the server I see no requests in the logs. The following command describes the situation well: $ sudo rec_control get concurrent-queries; sudo rec_control top-remotes 22 Over last 0 queries: How can there be 22 concurrent-queries when the server has 0 queries registered? EDIT: Figured it out! To get top-remotes working I needed to set ################################# # remotes-ringbuffer-entries maximum number of packets to store statistics for # remotes-ringbuffer-entries=100000 It defaults to 0 storing no information to base top-remotes statistics on.

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• Can't ping localhost/or reach locally hosted domain

  - by Ian

  I can't reach a locally hosted domain, and in testing I have discovered I can't ping localhost or the actual IP either. OS is Windows7 64bit, Pro. DNS works, I can ping others on my network, they can ping me, and they can reach the hosted domain. The ONLY problem I have found is that I can't reach the locally hosted domains! C:\Users\ianipconfig /all Windows IP Configuration Host Name . . . . . . . . . . . . : leda Primary Dns Suffix . . . . . . . : Node Type . . . . . . . . . . . . : Hybrid IP Routing Enabled. . . . . . . . : No WINS Proxy Enabled. . . . . . . . : No DNS Suffix Search List. . . . . . : hcs Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : hcs Description . . . . . . . . . . . : Atheros AR8121/AR8113/AR8114 PCI-E Ethern et Controller Physical Address. . . . . . . . . : 00-23-54-7C-E2-2A DHCP Enabled. . . . . . . . . . . : No Autoconfiguration Enabled . . . . : Yes IPv4 Address. . . . . . . . . . . : 192.168.0.12(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.0.1 DNS Servers . . . . . . . . . . . : 192.168.0.1 NetBIOS over Tcpip. . . . . . . . : Enabled Ethernet adapter VirtualBox Host-Only Network #2: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : VirtualBox Host-Only Ethernet Adapter #2 Physical Address. . . . . . . . . : 08-00-27-00-88-4A DHCP Enabled. . . . . . . . . . . : No Autoconfiguration Enabled . . . . : Yes Autoconfiguration IPv4 Address. . : 169.254.205.215(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.0.0 Default Gateway . . . . . . . . . : NetBIOS over Tcpip. . . . . . . . : Enabled C:\Users\ianping localhost Pinging leda [127.0.0.1] with 32 bytes of data: Request timed out. Request timed out. Request timed out. Request timed out. Ping statistics for 127.0.0.1: Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), C:\Users\ianping coachmaster.leda.hcs Pinging coachmaster.leda.hcs [192.168.0.12] with 32 bytes of data: Request timed out. Request timed out. Request timed out. Request timed out. Ping statistics for 192.168.0.12: Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), C:\Users\ian I can reach a hosted VM in VirtualBox and the VM can browse the hosted sites. I've removed Zone Alarm and disabled Windows Firewall - same results. So how can I browse my locally hosted sited? What could be blocking it? Thanks Ian

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• How can I monitor network traffic?

  - by WIndy Weather

  I have a home network with about 10 devices including BluRay player [netflix] and both windows and linux machines. I need to collect network traffic statistics so that if questions come up about how much traffic I'm using I have the answer independent of my ISP. I've looked at DD-WRT, but I see that even buying a new router that will be supported is a problem since I might get the wrong version of the hardware. I have a DIR-655 and a DIR-501 - neither of which is supported. I don't mind buying new hardware, but it looks like a crap-shoot to get one that will work. DD-WRT looks like a bad solution unless someone knows of a place to get a router that is guaranteed to work. Does someone know of an arduino or other SBC solution? I have plenty of NAT routers already, so I just need traffic statistics for external traffic. The network is GBit Ethernet inside and Cable / soon to be DSL outside. The DIR-655 only gives me "packets", not bytes transferred oddly enough. Thanks, ww

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• How to Monitor Network in Medium-Sized Company?

  - by Kyle Lowry

  I work at a medium sized company (100+ employees). An issue that has been cropping up is network performance, internet access in particular. We have about 70 or more computers, a mix of Mac OS X and Windows XP & 7 machines. We have several servers (Exchange server, PC file servers, MS SQL, Blackberry, FTP, Mac server, etc). There are four main switches, a SonicWall firewall, and probably a couple routers in the server room with a dozen or so more scattered around the building. The network structure has grown organically over a number of years; and, as far as I know, there really isn't a monitoring solution in place. When we experience network issues (slow connections, dropped packets, and so on), our general solution is to power cycle some hardware or go around to each employee and ask them if they are uploading/downloading any large files. This is really inefficient and time consuming, and it does not allow us to monitor the network, tackling potential problems proactively. I would like to find a solution that would allow me to monitor network usage company-wide in real time, with detail going down to the individual computer, ideally. Given the hodgepodge of equipment and operating systems, what would be the best way to set up some kind of monitoring solution? Hardware, software, restructuring our network architecture?

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• Server Intermittently Inaccessible Externally (but Accessible Internally Continuously)

  - by nicorellius

  I have a CRM on a server on a network. We have a static IP and another server outward facing. We use port-forwarding to map to the CRM, so that when you go to the IP or the FQDN, you get to the CRM: xxx.xxx.xxx.xxx crm.example.com Internally, we can access the CRM by going to crm or crm.example.com Lately, I've been noticing that accessing the server from outside the network times out or gives 503, bad gateway. During that time, I can also SSH (different port, so this works) into the outward facing computer and access the server just fine. I have a robot monitoring the site and indeed via HTTP monitoring the site is going down periodically. I looked through the Apache server access and error logs and nothing stuck out at me so I'm a bit confused as to what could be going on. I also searched the access logs for 503 and found nothing. When I run tracert from outside the network, it appears the packets basically make it through the wider area servers (Comcast city and county servers) and end up dropping at the CRM server's front step. I'm tempted to replace the server because it is older and underpowered but it would be nice to know what is going on. Any ideas what to do next?

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• Apache Virtual Hosts behind Cisco Router

  - by Theo

  I'm setting up an Apache 2.2 Ubuntu web server for internal services that is also supposed to be accessed from outside our LAN. Our LAN has a single external IP that is the external IP of our RV042 Cisco router. We have set up several A records on our external DNS server that point to this IP. Our internal DNS server resolve the same records to the internal IP of our web server, so computers from inside the network can access them using the same address as if they were outside. We forwarded the router's external 80 port to our web server's 80 port. I have set up one Virtual Host for each domain name in our list, and my httpd.conf is something like this: ServerName web.domain.com NameVirtualHost *:80 <VirtualHost *:80> ServerName alfresco.domain.com <Proxy *> Order deny,allow Allow from all </Proxy> ProxyPass /alfresco http://localhost:8080/alfresco ProxyPassReverse /alfresco http://localhost:8080/alfresco ProxyPass /share http://localhost:8080/share ProxyPassReverse /share http://localhost:8080/share </VirtualHost> <VirtualHost *:80> ServerName crm.domain.com DocumentRoot /var/www/sugarcrm </VirtualHost> Now, this works if we are in our LAN. However, if we are outside of our LAN we reach our web server's default page saying: It Works! This is the default web page for this server. But we can't reach the virtual hosts, as if the domain name is not being preserved when the router forward the packets to the web server. Am I doing something wrong? How can I check what is going on? What should be the settings to make this work from outside?

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• Windows 2008 R2 DNS cant resolve own SOA

  - by user46742

  We have two Domain Controllers for our network. They both run DHCP, DNS, and ADS. They are both VM's sitting on MS Hyper V Server 2008 on separate physical hosts. We had our primary DC go down a week ago. I upgraded an already existing VM to Primary DC and built a new VM for the secondary. Both DNS servers are running and the SOA is configured correctly for Primary DC 1. However when I run the best practice analyzer it states the server cannot resolve it's own SOA. Check the configuration in the adapter. I checked and they are configured properly. I also went through the DNS entries thoroughly and made sure there was no records of the previous DC that went down. NSLOOKUP resolves the domain and primary dc fine. I also checked the firewalls on the machines and our physical firewall for any deny packets. Any suggestions? I appreciate any help!

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• Can next hop address be same as destination address?

  - by Raj

  Like if host address is 100.0.0.1 and next hop address is 100.0.0.2 and destination ip address is also 100.0.0.2 Is this a valid use case? Any real life usage? <dest ip> <next hop> ip route 100.0.0.2 255.255.255.255 100.0.0.2 weight 1 next-hop-vrf GlobalRouter Above is the command on a router inside a VRF. 100.0.0.2 is pingable from host. 100.0.0.1 & 100.0.0.2 are an ip address assigned to a VLAN on host & destination respectively. On a linux box, Such configuration is valid. [root]# netstat -r -n Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 55.55.55.55 55.55.55.55 255.255.255.255 UGH 0 0 0 eth0 [root]# ip route show 55.55.55.55 via 55.55.55.55 dev eth0 As per my understanding, If a destination IP is reachable (i.e in the same subnet of host IP) we dont need a next hop. I came across one application for using next hop for destination IP in same subnet (i.e for VPN) See this: Will packets send to the same subnet go through routers? If next hop != destination IP but they are in same subnet as that of host, is a valid scenario for VPN, then i am wondering what are the applications of next_hop==dest_ip & subnet same as host? This is my first post in Super User. Extremely happy with the quick and warm response.

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• Cannot connect to MySQL on RDS (Amazon Web Services) from my laptop

  - by Bruno Reis

  I'm having some trouble connecting to a MySQL 5.1 server on an RDS instance on AWS from my laptop. The detailed description of the problem is here: https://forums.aws.amazon.com/thread.jspa?messageID=323397 In short: I have 2 MySQL servers, both with the same db configuration and firewall (security group) configuration. One of them works fine: I can connect to it from my EC2 instances (ie, from inside the AWS cloud) and from my laptop. The other one doesn't: I can connect from my EC2 instances but not from my laptop. The symptom: a connection attempt from my laptop just hangs, and then times out, as if there was a firewall blocking me (ie, silently dropping my SYN packets). I must say that everything has been working fine for a very long time, and this problem began suddenly, 3 days ago, without any modifications to DB parameters or the security groups. My current analysis of the situation: The firewall (ie, security group) cannot be the problem: both MySQL servers share the same firewall configuration -- I can connect to one of them but not to the other. Later on, I even added a rule to allow inbound connections from 0.0.0.0/0 (ie, I turned off the firewall), and nothing. Oh, I also created a new, fresh security group and changed this instance's SG to the new one (to which I first added my ip address, and then 0.0.0.0/0) but still nothing. The credentials cannot be the problem: I use the same from my laptop and from my EC2 instances -- and the user (which is what Amazon calls master user), in the database, has a host of '%'. MySQL is not blocking my IP due to, say, too many failed connection attemps: I've FLUSH HOSTS on the database, and also I tried to connect using many different source IP addresses, even from all around the world through a VPN proxy service. What could I be missing? I'm asking here because it's been about 36 hours since I've posted on AWS forums but got no answer at all over there... someone here might have a solution! Any input is really appreciated, I'm out of ideas. Thanks!

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• MSMQ on Win2008 R2 won't receive messages from older clients

  - by Graffen

  I'm battling a really weird problem here. I have a Windows 2008 R2 server with Message Queueing installed. On another machine, running Windows 2003 is a service that is set up to send messages to a public queue on the 2008 server. However, messages never show up on the server. I've written a small console app that just sends a "Hello World" message to a test queue on the 2008 machine. Running this app on XP or 2003 results in absolutely nothing. However, when I try running the app on my Windows 7 machine, a message is delivered just fine. I've been through all sorts of security settings, disabled firewalls on all machines etc. The event log shows nothing of interest, and no exceptions are being thrown on the clients. Running a packet sniffer (WireShark) on the server reveals only a little. When trying to send a message from XP or 2003 I only see an ICMP error "Port Unreachable" on port 3527 (which I gather is an MQPing packet?). After that, silence. Wireshark shows a nice little stream of packets when I try from my Win7 client (as expected - messages get delivered just fine from Win7). I've enabled MSMQ End2End logging on the server, but only entries from the messages sent from my Win7 machine are appearing in the log. So somehow it seems that messages are being dropped silently somewhere along the route from XP or 2003 to my 2008 server. Does anyone have any clues as to what might be causing this mysterious behaviour? -- Jesper

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• PFSence VPN Routing

  - by SvrGuy

  We use PFSense firewalls at three installations with the following LAN networks: 1.) Datacenter #1: 10.0.0.0/16 2.) Datacenter #2: 10.1.0.0/16 3.) HQ: 10.2.0.0/16 All of these locations are linked via an IPSEC tunnel that works properly. Hosts in any of the above networks can communicate with hosts in any other of the above networks. Now, for our laptops etc. we established a road warrior network 10.3.0.0/16 and have implemented OpenVPN to link the laptops etc. to Datacenter #1. This works great too, so our laptops can connect and communicate with any host in Datacenter #1 (anything on 10.0.0.0/16) The problem is the laptops can't communicate with any hosts that Datacenter #1 can reach by its IPSEC tunnel to Datacenter #2 (and/or the HQ for that matter). Does anyone know what to do configuration wise on the PFSense box in Datacenter #1 to configure to route packets received on the OpenVPN tunnel to Datacenter #2 over the IPSEC tunnel? It could be a setting on the OpenVPN or some sort of static route or some such. Any ideas?

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• Linux Centos 6 becomes unavailable from time to time - OS&network issue

  - by adoado0

  I am encountering following problem. There is one server (DL160 G5) running Centos 6.3 with default kernel 2.6.32-220.2.1.el6.x86_64 - at this point I'd like to add that issue appeared also at older version - 6.1 and older kernel (do not remember exactly which version). There is cPanel installed and from time to time it becomes unavailable (network connection). What I've checked is (via KVMoIP): load average is completely normal it does not lack memory or disk space when problem occurs no console notifications checked all access logs and there is no sign that it can be caused by a client script cannot even access local interface (127.0.0.1) or main IP address running tcpdump I can only see packets arriving to server - no responses all services seem to be running properly (mail,sql,http,ssh) checked crontab and all clients' crontabs too network port utilisation is low ( up to several Mbits) arriving packet rate is low - hundreds per second (according to tcpdump) console (via kvmoip) works fine, no lags there is no conntrack at this server there is no ipv6 at this server flushing iptables, unloading modules does not resolve problem restarting network does not resolve problem, no errors appear it also occurs when two sepearate networks are configured (and multiple gateways) as well as one IP, one default gw and one network is configured - so it seems network configuration independent it seems to repeat randomly (load,packet rate,bandwith usage,load independent) checked server with different rootkit detection tools - it seems to be clean server has been rebooted, it did not change anything there are no interface errors it apperas randomly can be once a week or several times per day It usually works fine after 1-15 minutes. What I can also check? It is definitely OS issue - there is traffic at interface only in one direction when problem occurs, can not even ping loopback. Any ideas? Recommended checks? Anything I did not checked above.

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• What causes a switch port to receive data not destined for it?

  - by user1693454

  We are having an intermittent fault which is effecting one of our control systems on one of our HP Procurve switches. For some reason, this PLC (10mbit port - 192.168.6.56) which is attached directly to the HP Switch intermittantly start's receiving data which is not destined for it. The data is being sent from a Thecus NAS with latest firmware (192.168.6.218) to a physical IBM Server running Win2003R2 and SAP (192.168.6.225). The problem does not just send to this server, it has been to other physical servers in the past too, but always from the Thecus NAS. I am using a monitor port to wireshark what is going in/out of the PLC - normally there would be about 1mb in/out per 2 or 3 minutes - only a server asking the state of the coils. When the problem occurs, there is a flood of data being put onto the PLC line - in this captured instance, about 67mb in less than a minute. Due to this, there is no way that the PLC can be queried as the port is effectively DOSed, in turn killing part of our factory. I know that having Production on the same vlan as IT is not a good idea - I agree, however it cannot be changed at the moment (will have to wait 3 months), as well as the problem has only started happening in the last 3 months. Here is a screen cap of one of the packets being sent from the Thecus NAS which was captured from the PLC port on the HP Switch: And there are over 700 of these in this one 1024kb file. If anyone has any idea on what could be going on, some help would be greatly appreciated. If you need to know anything more, let me know! Cheers!

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• 2 Computers, same network, different outgoing speeds when uploading to internet?

  - by user117339

  I have 2 work machines in my office, a PowerMac G5 and a MacBook Air. Both behind an IPCop firewall. The PowerMac is connected through a gigabit switch, the MacBook Air is connected through a Netgear 802.11g access point that is then plugged into the gigabit switch. There is also a FreeNAS box, both machines are able to read and write files to it at close to their pipe speeds. The main problem is when I am trying to upload files to the internet at large. The G5 is only hitting 0.1 - 0.25 Mbps. The Macbook is able to hit 2-3 Mbps. The setup (G5 / IPCop / Network) has been the same for 5 years. The issues with the internet speed started about 3 months ago. I hadn't tested on the Macbook at this point. I had complained to the ISP, they said their modem needed a firmware update, did that nothing changed. Reset IPCop, turned off squid, etc. No changes. The ISP switched the office over to a better plan with a theoretical 6 Mbps up, still no change. At this point I tried testing the Macbook, and lo and behold there's the speed. But why? I have tried changing out everything, cables, switches, using another ethernet port on the G5, wiping the system, using DHCP, using manual IPs, changing DNS servers, etc. Nothing works. I figured that if there was something horribly wrong with the network, then internally I would find a similar issue, but that is perfect. iperf, ping, etc show no dropped packets and near saturation of the internal network. I'm at a loss as to what the heck is going on. Any ideas would be appreciated! Below are some screenshots of speedtest.net: G5: Macbook Air:

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• Linux as a gateway (no NAT)

  - by Hugo

  I'm trying to configure a linux server as a gateway/router, but I can't get it to work, and all information I've managed to find is NAT-related. I have a public IP block for the gateway and devices behind it, so I want the gateway to simply route packets to the internet - again: no NATing! I've managed to get the gateway to access the internet successfully (that was just a matter of configuring the IP and GW), and the computers behind it can communicate with it. [EDIT: more info] This is actually an IPv6 block (2800:40:403::0/48) (but I've found that most utilities and instructions can be easily adapted from IPv4 to IPv6 with little hastle). The server has too ports: wan: 2800:40:403::1/48 lan: 2800:40:403::3/48 One of the computers behind it is connected to it via a switch; 2800:40:403::7/48 The wan interface on the server can ping6 www.google.com without issues. The lan interface on the server and the client can mutually ping each other without issues (as well as SSH, etc). I've tried setting the server as a default gateway for the client, with no luck: client # route -A inet6 add default gw 2800:40:403::3 dev eth1 server # cat /proc/sys/net/ipv6/conf/all/forwarding 1 I don't want any filtering/firewalling/etc, just plain routing. Thanks.

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• Snort not detecting outgoing traffic

  - by Reacen

  I'm using Snort 2.9 on windows server 2008 R2 x64, with a very simple configuration that goes like this: # Entire content of Snort.conf: alert tcp any any -> any any (sid:5000000; content:"_secret_"; msg:"TRIGGERED";) # command line: snort.exe -c etc/Snort.conf -l etc/log -A console Using my browser, I send the string "_secret_" in the url to my server (where Snort is located). Example: http://myserver.com/index.php?_secret_ Snort receives it and throws an alert, it works, no problem ! But when I try something like this : <?php // (index.php) header('XTest: _secret_'); // header echo '_secret_'; // data ?> If I just request http://myserver.com/index.php, it does not work or detect anything from the outgoing traffic even though the php file is sending the same string both in headers and in data, with no compression/encoding or whatsoever. (I checked using Wireshark) This looks to me like a Snort problem. No matter what I do it only detects receiving packets. Did anyone ever face this sort of problems with Snort ? Any idea how to fix it ?

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• Transfer iptables rules to another server (almost) real time

  - by MrShunz

  I'm running 2 cPanel servers with ConfigServer Security & Firewall plugin. One of the functions of the plugin is to block via iptables (temporarily and/or permanently) IPs which fail various authentications (POP3/IMAP, SMTP, FTP, webmail, mod_security and such). Now, i'd like to push those IP blocks to the border router to drop packets as soon as possible (and doing so protecting the other machines on the network). Keep in mind that after N failed logins IP is blocked for 5 minutes, then re-allowed. If multiple bans occours in an hour IP is blocked permanently and should be unlocked "by hand". So I need a near realtime solution. What I'm looking for is a better way than firing some cronjobs both on cPanels and border router to: dump the rules to file transfer the file to border router (via scp/sftp) load the rules from the file in the border router I'm aware that I will need some scripts to parse and modify the rules as cPanels have one ethernet interface and some aliases while border router has two ehternet interfaces and some loopbacks. All machines involved use Linux. EDIT as per @pjmorse comment. The plugin consists of a bunch of perl and config files. The part I'm intrested in is a process which scans logfiles (lfd) and installs iptables rules (and sends an alert email). Fact is, it upgrades quite often (one or two times a week) and itself is 7000 lines of perl so I'm not comfortable on tampering with it.

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• Route outbound connections from local network through VPN

  - by Sharkos

  I have a server A running OpenVPN, an OpenVPN client B (a rooted Android phone as it happens) and a third party C (a laptop, tablet etc.) tethered to B. B can use the VPN to access the internet via A; C can use the tethered connection WITHOUT the VPN to access the internet via B. However, with the VPN on B active, I cannot load information from the internet on C. A appears to log similar traffic inbound and outbound when B or C attempt to load a webpage, say, but the VPN on device B reports no inbound traffic when the connection originated from C. Where should I look for packets being dropped, and what ip rules should I use to make sure they are passed back through the VPN and into the local network B <- C? (I'll obviously post whatever further information is needed.) Further info Without VPN: root@android:/ # ip route default via [B's External Gateway] dev rmnet0 [B's External Subnet] dev rmnet0 proto kernel scope link src [B's External IP] [B's External Gateway] dev rmnet0 scope link 192.168.43.0/24 dev wlan0 proto kernel scope link src 192.168.43.1 With VPN: root@android:/ # ip route 0.0.0.0/1 dev tun0 scope link default via [B's External Gateway] dev rmnet0 [B's External Subnet] dev rmnet0 proto kernel scope link src [B's External IP] [B's External Gateway] dev rmnet0 scope link [External address of A] dev tun0 scope link 128.0.0.0/1 dev tun0 scope link 172.16.0.0/24 dev tun0 scope link 172.16.0.8/30 dev tun0 proto kernel scope link src 172.16.0.10 192.168.43.0/24 dev wlan0 proto kernel scope link src 192.168.43.1 192.168.168.0/24 dev tun0 scope link

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