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• SNMP Access on Ubuntu

  - by javano

  I am trying to use SNMP to monitor a machine locally on its self and remotely. This is the snmpd.conf (Ubuntu 8.04.1): # sec.name source comunity com2sec readonly 1.2.3.4 nicenandtight com2sec readonly 5.6.7.8 reallysafe group MyROGroup v1 readonly group MyROGroup v2c readonly group MyROGroup usm readonly view all included .1 view system included .iso.org.dod.internet.mgmt.mib-2.system access MyROGroup "" any noauth exact all none none syslocation my house syscontact me <[email protected]> exec .1.3.6.1.4.1.2021.7890.1 distro /usr/bin/distro smuxpeer .1.3.6.1.4.1.674.10892.1 includeAllDisks 95% 1.2.3.4 is the local machines IP and everything is working locally. 5.6.7.8 is the remote machine and initially I am just trying to touch SNMPD with snmpwalk from the remote machine; snmpwalk -v 2c -c reallysafe 1.2.3.4 Timeout: No Response from 1.2.3.4 I have added to iptables as the very first rule; -A INPUT -p udp -m udp --dport 161 -j ACCEPT With such a loose iptables rule I can't see why I can't even touch the SNMPD on that Uubuntu Machine. There are more specific rules further down the table but as I couldn't connect I added the above. TCPDump shows the UDP packets coming in. What could be going wrong here?

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• Small TCP Window on WAN between 2 Locations

  - by Brent

  Site A: Denver datacenter. 60MBPS. Site B: Chicago. 100MBPS. ICMP pings: Packets: Sent = 176, Received = 176, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 74ms, Maximum = 94ms, Average = 75ms File transfer between sites that never goes past ~7MBPS: Windows Update download at 60MBPS+: Site to site: IPSec VPN using two Cisco 5520's. CPU at 3-4% and lots of memory to spare. The latency between to two sites is very acceptable so I can't see an issue why it is performing so slow when transferring between the two sites. I have found that any type of transfer (FTP, HTTP, Windows file shares) will never go above ~7MBPS. When the WAN was first setup, I was able to get transfers at 50-60MBPS, which is what is expected due to the WAN connection at the Site A at 60MBPS. Then a few days later, I was not able to get anything going faster than ~7MBPS. Is there a upstream router between Denver and Chicago causing this? I want to take the blame away from our setup as downloads from Windows Update go blazing fast and for the first few days after the site to site VPN came up, I was transferring VM images at 50-60MBPS. Our stack: HP P2000 MSA - HP C7000 Chassis - HP Flex-10 - Cisco Gigabit switch - Cisco ASA - WAN

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• Intermittent extrememly long response times when downloading documents

  - by pap

  I have a Java web application running om Tomcat 7 with an Apache httpd 2.2 fronting with mod_jk/AJP. One part of the application is serving files (up to 4mb size). Now, normally this all runs very smooth with stable, low response-times. However, in rare instances (<0.1% of downloads), the downloadtime will go beyond 1 minute. After activating the ThreadStuckValve in Tomcat, I can see that the long responses seem to be stuck at org.apache.tomcat.jni.Socket.sendbb(Native method) i.e network I/O. At most, these long-running downloads take 5 minutes, which I strongly suspect is because of the default 300 second timout in Apache 2.2 (http://httpd.apache.org/docs/2.2/mod/core.html, "TimeOut directive"). To me, this looks like network problems. The Apache timeout (if that is what is kicking in at the 5 minute mark) indicates that ACK packets are not being transmitted correctly. My questions are what could be causing this? Closed browser at receiving end but socket not signaled as closed properly? Packet loss or some other network failure in transit? Where would I start troubleshooting this? We're running Tomcat and Apache on Windows server 2008-R2 in a vmware virtualized server.

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• Server 2003 and XP Client; Why are HTTP connections being silently dropped.

  - by Asa Yeamans

  On my network, my edge-router, a windows 2003 r2 server router with all the latest updates, will drop packets, but only under specific circumstances. I have troubleshot and isolated it down to the most simple configuration i can. There is NO NAT involved. Only fully-public IP addresses. No Firewalls are running either, all ahve been disabled. no packet filters on any interfaces anywhere either. I have a single Windows XP virtual machine and my edge-router(the windows 2003 r2 server, and also a virtual machine) running on a windows 2008 x64 r2 system (running virtual server 2005 as i dont have Intel-VT compatible chip yet). The edge router can access any external http site just fine, no issues. However the windows XP machine is only able to access certain sites. These work: www.google.com www.txstate.edu www.workintexas.com www.thedailywtf.com . These Dont: www.yahoo.com www.utexas.edu en.wikipedia.org slashdot.org www.bing.com. I have removed all possibility of DNS issues by connecting with net-cat from the XP box and sending GET /\r\nHost: \r\n\r\n and that connection replicates the issue as well. The network setup: My statically assigned IP block: x.x.x.168/29 DSL Modem -----PPPoE Connection---- x.x.x.169[EdgeRouter] [EdgeRouter]x.x.x.170 -----Virtual Ethernet----- x.x.x.174 [Test2] Test2's Default gateway is x.x.x.170 and test2 can ping any and every valid, accessible, public IP address with no packet loss what-so-ever. If i connect directly over PPPoE from test2 (the XP box) everything works just fine... Im at my wits end, i have NO IDEA whats causing this.

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• Monitor mode 802.11 captures on OSX

  - by Mike A

  I'm trying to determine the difference between capturing 802.11 frames in the following ways on OSX (10.8.5). It's a bit esoteric, but I use "Option 2" to capture frames for later analysis, and am wondering if I'm missing something. Option 1: use "airportd": $sudo /usr/libexec/airportd en0 sniff Option 2: use "airport" followed by tcpdump: sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport --channel= sudo tcpdump -I -P -i en0 -w /tmp/capture.pcap (or alternatvely eliminate the -w and watch packets real-time). From what I can tell: Both commands, according to the wifi icon on OSX, put the interface into 'monitor' mode. Both commands output a pcap file that is readable in both wireshark/tcpdump & Eye PA. Both commands appear to capture management, control and data frames. The rub: Option 1 disconnects you from the network. This is expected, when putting an interface into 'monitor' mode. Option 2 does NOT disconnect you, provided you've set the channel to the same channel your currently connected to. This has a distinct advantage of keeping your connection up while capturing in monitor mode. My question: Option 2 does not seem like it should work, or more specifically, it does not seem like I should be able to remain connected while also capturing frames in monitor mode. On a wired NIC, you can be 'promiscuous' and still send frames, though I didn't think the same was true for wireless NIC. I'm questioning the validity of capturing frames w/ Option 2?

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• Nagios check_host_alive and check_ping not showing host as down

  - by Kyle

  I am using the check_host_alive command to send 5 packets every minute to all my routers at remote locations. I noticed today I received a notification from The AT&T Global Client Support Center that a router was down (which can take 5-30 minutes to send these notices out) and never received a notice from Nagios. I went onto Nagios and it is was showing the host as alive with a latency of 0ms. This tells me it is seeing the automated response from my router in the data center that, "TTL expired in transit" as a reply from the remote router. Is there anyway for me to tell nagios to check where the reply is comming from? I feel like other people have to of had this issue... I tested it with the check_ping command and it produced the same results. I have the command defined has %hostname% and the proper IP in the host definition, and it works fine for telling me the latency is high. Any ideas are welcome, I have already exercised my Google skills with no results. EDIT: root@IM-UBTU:/# /usr/local/nagios/libexec/check_ping -H 192.168.250.1 -w 100.0,10% -c 200.0,20% -vvv CMD: /bin/ping -n -U -w 10 -c 5 192.168.250.1 Output: PING 192.168.250.1 (192.168.250.1) 56(84) bytes of data. Output: From 10.69.10.2 icmp_seq=1 Time to live exceeded It knows something is wrong why doesn't it give me a warning?

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• Debian Stable: Can't update kernel, libc won't update.

  - by pascal

  I use Debian Stable (squeeze) on a virtual host where I can't touch the kernel, it's stuck (and will be for some time as support told me) at Linux 2.6.18-028stab070.3 #1 SMP Wed Jul 21 18:33:27 MSD 2010 x86_64 So when I try to update, several packages fail with FATAL: kernel too old for example Preparing to replace libgcc1 1:4.6.0-11 (using .../libgcc1_1%3a4.6.1-1_amd64.deb) ... Unpacking replacement libgcc1 ... Setting up libgcc1 (1:4.6.1-1) ... FATAL: kernel too old Segmentation fault dpkg: error processing libgcc1 (--configure): subprocess installed post-installation script returned error exit status 139 and some version chaos ensued: The following packages have unmet dependencies: libc-dev-bin : Depends: libc6 (> 2.13) but 2.11.2-13 is installed libc6 : Depends: libc-bin (= 2.11.2-13) but 2.13-5 is installed libc6-dev : Depends: libc6 (= 2.13-5) but 2.11.2-13 is installed libquadmath0 : Depends: gcc-4.6-base (= 4.6.0-2) but 4.6.0-11 is installed libstdc++6 : Depends: gcc-4.6-base (= 4.6.0-2) but 4.6.0-11 is installed locales : Depends: glibc-2.13-1 What should I do? I want to keep the system up-to-date, so I want to pin as few packets as possible, but I also don't want to have to compile anything manually. Trying to pin the status quo and figured out where the error came from: ldconfig segfaults. -v doesn't print anything more so I can't tell what's the actual problem. # ldconfig FATAL: kernel too old

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• Routing table on Linux not respected

  - by MRHaarmann

  I have a very specific problem, building a Linux VPN endpoint (with external VPN Gateway), which should route certain networks over the tunnel, others via default gateway. The Linux VPN should do a NAT on the outgoing connections for the VPN peers. Setup is as following: Internet gateway LAN 192.168.25.1/24 VPN Gateway LAN 10.45.99.2/24 (VPN tunnel 10.45.99.1 to net 87.115.17.40/29, separate connection to Internet) Linux VPN Router eth0 192.168.25.71/24 eth0:503 10.45.99.1/24 Default 192.168.25.1 route to 87.115.17.40/29 via 10.45.99.2 (send_redirects disabled, ip_forward enabled) Linux clients (multiple): eth0 192.168.25.x/24 Default 192.168.25.1 route to 87.115.17.40/29 via 192.168.25.71 Ping to the machines via tunnel from the VPN Router is working. Now I want to establish a routing from my clients over the VPN gateway and the client packet gets routed to 192.168.25.1 ! traceroute output shows the packets get routed to 192.168.25.71, but then to 192.168.25.1. So the route is not respected in forward ! IPTables and Routing: ip route show 87.115.17.40/29 via 10.45.99.2 dev eth0 10.45.99.0/24 dev eth0 proto kernel scope link src 10.45.99.1 192.168.25.0/24 dev eth0 proto kernel scope link src 192.168.25.71 default via 192.168.25.1 dev eth0 iptables -A INPUT -i eth0:503 -j REJECT iptables -t nat -A POSTROUTING -o eth0:503 -j MASQUERADE iptables -A FORWARD -i eth0:503 -m state --state RELATED,ESTABLISHED -j ACCEPT iptables -A FORWARD -s 192.168.25.0/24 -o eth0:503 -j ACCEPT So what is wrong with my setup ? The route is chosen correctly from localhost, but all the clients get forwarded to the Internet GW. thanks for helping, Marcus

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• Can't display RSSI values in Wireshark

  - by Giovanni Soldi

  I am trying to analyze the up-link Wireless traffic generated by my Sony Ericsson phone and captured by my D-Link router, on which I installed the DD-WRT firmware. To do this, first I log in the router and enable the prism0 interface by typing the command: wl -i eth1 monitor 1 and then I start to capture the packets by typing: tcpdump -i prism0 ether src xx:xx:xx:xx:xx:xx -s0 -w /tmp/smbshare/sony_ericsson_test.pcap where xx:xx:xx:xx:xx:xx is the MAC address of my Sony Ericsson phone. After a while I transfer the sony_ericsson_test.pcap file to my computer and open it with Wireshark program. In order to display the RSSI values I follow this procedure: Edit - Preferences... - Columns - Press "Add" button - As "Field type" I choose "IEEE 802.11 RSSI" and finally I choose name "Power" and click on "Apply" button. The problem is that the column "Power" is empty with no RSSI values. Does Anyone has a clue on why are RSSI values not displayed? Maybe I am missing a passage. Looking forward to hearing from anyone of you! Thanks in advance for your help!

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• Virtualizing an Inline network appliance with VirtualBox (or VMWare)

  - by Tzury Bar Yochay

  My device, which is a Linux based IP in-liner is transparent to the network peripherals, that is, no IP address assigned to any of its interfaces. For the sake of the conversation, let's use ADSL connection as an example, while the device is inspecting the bi-directional traffic, the network is behaving same as if device was not there, attached to the wire (see Physical setup at the attached diagram). I wonder if I can enclosed that "device" within a Windows machine and have it operated virtually so it still seats inline between the ADSL router and the Windows netwroking interface by using virtual NICs, (or whatever their name is in windows), and inspecting the traffic, same as if it was on a separate physical device, the drawing under "Virtual Setup" in the attached diagram show what I am trying to achieve. Reading a bit on the VirtualBox docs, seems like binding the right side is relatively simple, perhaps I should have one network adapter set as Bridge Networking and VirtualBox will connect it to the physical NIC on the host machine, and network packets are exchanged directly, circumventing the host operating system's network stack (WinXP in my case). However, I have no idea how to achieve the left side of my diagram, which requires adding virtual NICs to windows and configure them correctly in a way to make that pipeline possible. I would appreciate any help. by the way, if that is not possible with VirtualBox but with other virtualization solution (e.g. VMWare), I would accept the other as well.

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• Flow of packet in network

  - by user58859

  I can't visualize in my mind the network traffic flow. eg. If there are 15 pc's in a LAN. When packet goes from router to local LAN, do it passes all the computers? Means did it goes to ehernet card of every computer and those computers accept the packet based on their physical address. To which pc the packet will go first? To the nearest to the router? What happen if that first pc captures that packet(though it is not for it)? What happens when a pc broadcast a message? Do it have to generate 14 packets for all the pc's or only one packet reach to all pc's? If it is one packet and captured by first pc, how other pc's can get that? I can't imagine how this traffic is exactly flows? May be my analogy is completely wrong. Can anybody explain me this? Thanks in advance.

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• Cisco BVI: Claiming IP addresses

  - by cjavapro

  I would like to make sure I understand this correctly. Given a Cisco ISO router that is set up with a BVI (a variation of a bridge route).. and the following layout "ISP router" \ "Network switch" # nothing special here. | \ | \ | \ | \ "Router 1 with NAT" "Router 2 with BVI" If I understand correctly.. the outside of a BVI will only respond to IP addresses that have already been claimed on the inside of the BVI... example subnet is 123.123.123.??? and servers inside the BVI on 123.123.123.10 and 123.123.123.11, and the NAT router is holding a public IP address of 123.123.123.50. If a connection comes in to 123.123.123.10 it will be received by router 2 but if it is received on 123.123.123.50, it will be received by router 1 and not received by router 2. and if a connection comes in to 123.123.123.90 (does not exist) it will not be received by either router. Am I correct? Is it true that the BVI router will not even receive packets to IP addresses that it does not see as existing on the inside?

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• Ubuntu 12.04 open port 80 inside WLAN

  - by Eduard

  I have an nginx server running on ubuntu 12.04 that serves http through port 80 and https through port 443. Everything works fine if I access it from the same computer via localhost, 127.0.0.1 or the local IP 192.168.0.11. If I try to access the server from another computer in the same VLAN it does not work for http; it works for https. I have changed my nginx configuration to also listen to port 8000 for http; I can then access http from the other computer in the same VLAN via "http://192.168.0.11:8000". I also have a web server running on port 80 on a windows machine and can access it from another device in the same VLAN, therefore the router is not blocking incoming http traffic. The nginx process is run by root. I have used tcpdump and I see that packets are arriving to Ubuntu: 192.168.0.16.49735 192.168.0.11.80 and that some response is being given 192.168.0.11.80 192.168.0.16.49735 (I do not know what the response is though). There is no request arriving at the nginx web server (I have checked the access log). I have iptables empty. I have unsuccessfully tried to find a solution for a long time to this, it has now become a matter of happiness or bitterness :).

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• VLAN ACLs and when to go Layer 3

  - by wuckachucka

  I want to: a) segment several departments into VLANs with the hopes of restricting access between them completely (Sales never needs to talk to Support's workstations or printers and vice-versa) or b) certain IP addresses and TCP/UDP ports across VLANS -- i.e. permitting the Sales VLAN to access the CRM Web Server in the Server VLAN on port 443 only. Port-wise, I'll need a 48-port switch and another 24-port switch to go with the two existing 24-port Layer 2 switches (Linksys); I'm looking at going with D-Links or HP Procurves as Cisco is out of our price range. Question #1: From what I understand (and please correct me if I'm wrong), if the Servers (VLAN10) and Sales (VLAN20) are all on the same 48-port switch (or two stacked 24-port switches), afaik, the switch "knows" what VLANs and ports each device belongs to and will switch packets between them; I can also apply ACLs to restrict access between VLANs at this point. Is this correct? Question #2: Now lets say that Support (VLAN30) is on a different switch (one of the Linksys) switches. I'm assuming I'll need to trunk (tag) switch #2's VLANs across to switch #1, so switch #1 sees switch #2's VLAN30 (and vice-versa). Once Switch #1 can "see" VLAN30, I'm assuming I can then apply ACLs as stated in Question #1. Is this correct? Question #3: Once Switch #1 can see all the VLANs, can I achieve the seemingly "Layer 3" ACL filtering of restricting access to Server VLAN on only certain TCP/UDP ports and IP addresses (say, only permitting 3389 to the Terminal Server, 192.168.10.4/32). I say "seemingly" because some of the Layer 2 switches mention the ability to restrict ports and IP addresses through the ACLs; I (perhaps mistakenly) thought that in order to have Layer 3 ACLs (packet filtering), I'd need to have at least one Layer 3 switch acting as a core router. If my assumptions are incorrect, at which point do you need a Layer 3 switch for inter-VLAN routing vs. inter-VLAN switching? Is it generally only when you need that higher-level packet filtering ability between your departments?

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• Manual NAT on Checkpoint (Redirect all http requests to a local web server)

  - by B. Kulakli

  We have a proxy server in our internal network and I want to redirect all internet http requests to a web server in local network. It'll be like a Network Billboard that says "No direct connection is available. Set up your proxy etc." For example: A user starts the computer Opens the browser Tries to open www.google.com Should see web server output on local network Tries another web site on internet Should see web server output on local network Sets up proxy Tries to connect to a web site Web site should be loaded I have added a simple manual NAT rule to address translation in Checkpoint firewall but it simply does not work. Here is my address translation rule Source Destination Service T.Source T.Destination T.Service MY_PC A_GOOGLE_IP ALL ORIGINAL INT_WEB_SRV ORIGINAL Then when I ping A_GOOGLE_IP, replies come from INT_WEB_SRV, as I expected. However, when I try to connect A_GOOGLE_IP from browser (http://A_GOOGLE_IP), no replies come from SYN_SENT and falls into timeout. When I look at the firewall log of INT_WEB_SRV, I can see the incoming connection requests from MY_PC is accepted and NO denies. By the way, there is no problem to see INT_WEB_SRV (http://INT_WEB_SRV) from browser. My understanding is, my NAT rule at checkpoint NGX R60 does not include return packets. I definitely need some help.

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• Should I expect ICMP transit traffic to show up when using debug ip packet with a mask on a Cisco IOS router?

  - by David Bullock

  So I am trying to trace an ICMP conversation between 192.168.100.230/32 an EZVPN interface (Virtual-Access 3) and 192.168.100.20 on BVI4. # sh ip access-lists 199 10 permit icmp 192.168.100.0 0.0.0.255 host 192.168.100.20 20 permit icmp host 192.168.100.20 192.168.100.0 0.0.0.255 # sh debug Generic IP: IP packet debugging is on for access list 199 # sh ip route | incl 192.168.100 192.168.100.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.100.0/24 is directly connected, BVI4 S 192.168.100.230/32 [1/0] via x.x.x.x, Virtual-Access3 # sh log | inc Buff Buffer logging: level debugging, 2145 messages logged, xml disabled, Log Buffer (16384 bytes): OK, so from my EZVPN client with IP address 192.168.100.230, I ping 192.168.100.20. I know the packet reaches the router across the VPN tunnel, because: policy exists on zp vpn-to-in Zone-pair: vpn-to-in Service-policy inspect : acl-based-policy Class-map: desired-traffic (match-all) Match: access-group name my-acl Inspect Number of Half-open Sessions = 1 Half-open Sessions Session 84DB9D60 (192.168.100.230:8)=>(192.168.100.20:0) icmp SIS_OPENING Created 00:00:05, Last heard 00:00:00 ECHO request Bytes sent (initiator:responder) [64:0] Class-map: class-default (match-any) Match: any Drop 176 packets, 12961 bytes But I get no debug log, and the debugging ACL hasn't matched: # sh log | inc IP: # # sh ip access-lists 198 Extended IP access list 198 10 permit icmp 192.168.100.0 0.0.0.255 host 192.168.100.20 20 permit icmp host 192.168.100.20 192.168.100.0 0.0.0.255 Am I going crazy, or should I not expect to see this debug log? Thanks!

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• Looking for a small, portable, port-mirroring ethernet switch.

  - by user37244

  I recently had a mac go haywire, taking half a minute or more to get www.google.com loaded. Getting its owner to give up the machine for repair was like pulling teeth - they were insisting that it must be something to do with the network, since so much had changed with the local configuration at about the same time their box went haywire. I eventually set up a port mirror to a box that I could remote to so I could show that the mac was only irregularly getting packets onto the network. Demonstrating this faced an additional challenge: the latency of the remote desktop software I was using meant that I had to point to timestamps instead of just the moment the packet flashed up on the screen as my evidence. This particular user was the reason this was so challenging this time around, but I would like to have a box that I can cart from desk to desk to use wireshark on my laptop at any station where I need it. 3com, cisco, netgear, etc. (ad nauseum), all make switches that can be configured for port mirroring, but in my case, the smaller, the better. For the sake of my sanity, I'll probably end up running it off a battery anyway. If my laptop had two ethernet ports, this would be easy. So, whaddya recommand for a device that requires 0 configuration at each powerup (though I'm fine with poking at it for a while to set it up initially.) Small, light, and cheap enough to get it past purchasing? Thanks,

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• Alfa AWUSO36H 1W dysfunctional driver

  - by BrainStorm

  I recently purchased an Alfa AWUSO36H 1W wireless USB adapter for my notebook, in order to improve signal strength and quality. I'm currently using Linux Mint 11, and the it uses the RTL8187 driver for this adapter, I'm also using a 4dbi antenna, though I have others. The problem is that this adapter does exactly the opposite of what it should, actually my internal Broadcom BCM4313 adapter works way better than the alfa. Browsing is slow, some network applications don't even work, pings against Google.com on the internal adapter runs smooth, while in the alfa it gets like 25% packets lost or more! I'm less them 50 feet from my AP, the internal adapter gets 44/70 link quality, and the alfa gets around 60/70 (iwconfig output). Also the system always sets alfa power to 20dbm(100mw), then I have to do sudo iw set reg B0 to make it 30dbm(1000mw), but apparently no significant change. I've installed wireless-compat drivers, no change either. And worst of all, in Windows 7 it works way more smoothly for browsing, though I couldn't test it properly there. I hope its a driver problem, even if it's a pain to find/compile Linux drivers for a starter, I prefer it to a hardware problem where I would need to buy another adapter, since I have no money left (except for the cantenna pieces).

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• how to setup a bridge with 2 NICs and few virtual machines

  - by Bond

  Here is my situation. I have a server with 2 NICs. I have installed virtual box and I have created a few Guest Operating Systems on it. I want these Virtual Machines to be using a bridge.NIC2 would be used to setup this bridge and NIC1 would be connected to corporate network.I am not clear with how should I go on doing this. /etc/network/interfaces is the file which I am trying to modify etc. My approach is following 1) Define a configuration file /etc/network/interfaces 2) Create IPTABLES as how NIC1 will forward the packets to Bridge on NIC2 Now comes the problem I do not understand what is the meaning of following lines in the configuration file auto lo iface lo inet loopback # The primary network interface auto eth2 iface eth2 inet manual auto br0 iface br0 inet static address 192.168.1.14 netmask 255.255.255.0 network 192.168.1.0 broadcast 192.168.1.255 gateway 192.168.1.10 # dns-* options are implemented by the resolvconf package, if installed dns-nameservers 192.168.13.2 dns-search myserver.net bridge_ports eth2 bridge_fd 9 bridge_hello 2 bridge_maxage 12 bridge_stp off So any pointers to what should be the entries of /etc/network/interfaces file. So that I understand which parameter is to be used when and where that would help me.

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• server dosnt produce syn-ack

  - by steve

  I have a small program that take packets from the nfqueue . change the ip.dst to my server dst (and ttl), recalc checksum and return the packet to the nfqueue. The server and the client are linux and apache web server is run on the server and listen on port 80. i open telnet in the client to fake ip on port 80 . the packet is changed by my program and sent to the server, but the target server (the new dst ip) get the syn , but dosnt generate syn-ack (the server also belong to me , so i can see that it get the syn with checksum correct , but dosnt generate syn-ack). if i do the same , but with the real server ip as the dest, the tcp handshake is done correct (in this case i just change the ttl and checksum. The change that i did to the ttl is just a test to see that my checksum calc is ok). i compare the sys's , but didnt find and difference. Any idea? Ps. i saw this topic : Server not sending a SYN/ACK packet in response to a SYN packet and i set all flags the same , but this didnt help. Thank you

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• Manual NAT on Checkpoint (Redirect all http requests to a local web server)

  - by kulakli

  Hi, We have a proxy server in internal network and I want to redirect all internet http requests to a web server in local network. It'll be like a Network Billboard that say "No direct connection is available. Set up your proxy etc." For example: A user starts the computer Opens the browser Trys to open www.google.com Should see web server output on local network Trys another web site on internet Should see web server output on local network Sets up proxy Trys to connect to a web site Web site should be loaded I have added a simple manual NAT rule to address translation in Checkpoint firewall but it simply does not work. Here is my address translation rule Source Destination Service T.Source T.Destination T.Service MY_PC A_GOOGLE_IP ALL ORIGINAL INT_WEB_SRV ORIGINAL Then when I ping A_GOOGLE_IP, replies come from INT_WEB_SRV, as I expected. However, when I try to connect A_GOOGLE_IP from browser (http://A_GOOGLE_IP), No replies come from SYN_SENT and falls into timeout. When I look at the firewall log of INT_WEB_SRV, I can see the incoming connection requests from MY_PC is accepted and NO denies. By the way, there is no problem to see INT_WEB_SRV (http://INT_WEB_SRV) from browser. My understanding is, my nat rule at checkpoint NGX R60 does not include return packets. I definitely need some help. Regards, Burak

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• TCPDump and IPTables DROP by string

  - by Tiffany Walker

  by using tcpdump -nlASX -s 0 -vvv port 80 I get something like: 14:58:55.121160 IP (tos 0x0, ttl 64, id 49764, offset 0, flags [DF], proto TCP (6), length 1480) 206.72.206.58.http > 2.187.196.7.4624: Flags [.], cksum 0x6900 (incorrect -> 0xcd18), seq 1672149449:1672150889, ack 4202197968, win 15340, length 1440 0x0000: 4500 05c8 c264 4000 4006 0f86 ce48 ce3a E....d@[email protected].: 0x0010: 02bb c407 0050 1210 63aa f9c9 fa78 73d0 .....P..c....xs. 0x0020: 5010 3bec 6900 0000 0f29 95cc fac4 2854 P.;.i....)....(T 0x0030: c0e7 3384 e89a 74fa 8d8c a069 f93f fc40 ..3...t....i.?.@ 0x0040: 1561 af61 1cf3 0d9c 3460 aa23 0b54 aac0 .a.a....4`.#.T.. 0x0050: 5090 ced1 b7bf 8857 c476 e1c0 8814 81ed P......W.v...... 0x0060: 9e85 87e8 d693 b637 bd3a 56ef c5fa 77e8 .......7.:V...w. 0x0070: 3035 743a 283e 89c7 ced8 c7c1 cff9 6ca3 05t:(>........l. 0x0080: 5f3f 0162 ebf1 419e c410 7180 7cd0 29e1 _?.b..A...q.|.). 0x0090: fec9 c708 0f01 9b2f a96b 20fe b95a 31cf ......./.k...Z1. 0x00a0: 8166 3612 bac9 4e8d 7087 4974 0063 1270 .f6...N.p.It.c.p What do I pull to use IPTables to block via string. Or is there a better way to block attacks that have something in common? Question is: Can I pick any piece from that IP packet and call it a string? iptables -A INPUT -m string --alog bm --string attack_string -j DROP In other words: In some cases I can ban with TTL=xxx and use that should an attack have the same TTL. Sure it will block some legit packets but if it means keeping the box up it works till the attack goes away but I would like to LEARN how to FIND other common things in a packet to block with IPTables

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• CentOS 6.3 Virtual under OpenVZ cannot ping, host lookups, outbound connections while postfix running

  - by Paul Cravey

  My best theory is that some kernel limit is being hit preventing outbound connections. We have tried basically everything from tcpdumps to provisioning an entirely new virtual server (we do not have this problem on any other virtuals), however the problem somehow carried over, even with new postfix build (working). Emails work, and outbound connections work, so long as postfix does not have too much going on. /proc/user_beancounters shows no limits being hit (show below). Nevertheless, pings fail even to IP addresses. TCP stack appears healthy. Load is low. No iowait. Flushed iptables already. Has anyone experienced anything like this? uid resource held maxheld barrier limit failcnt 3: kmemsize 166216365 170262528 9223372036854775807 9223372036854775807 0 lockedpages 0 0 9223372036854775807 9223372036854775807 0 privvmpages 285727 351885 9223372036854775807 9223372036854775807 0 shmpages 16933 17605 9223372036854775807 9223372036854775807 0 dummy 0 0 0 0 0 numproc 150 303 9223372036854775807 9223372036854775807 0 physpages 314156 326191 0 1280000 0 vmguarpages 0 0 9223372036854775807 9223372036854775807 0 oomguarpages 165355 165355 9223372036854775807 9223372036854775807 0 numtcpsock 89 172 9223372036854775807 9223372036854775807 0 numflock 22 76 9223372036854775807 9223372036854775807 0 numpty 1 2 9223372036854775807 9223372036854775807 0 numsiginfo 0 75 9223372036854775807 9223372036854775807 0 tcpsndbuf 2733472 4371752 9223372036854775807 9223372036854775807 0 tcprcvbuf 1798336 5427296 9223372036854775807 9223372036854775807 0 othersockbuf 491120 1000760 9223372036854775807 9223372036854775807 0 dgramrcvbuf 0 238728 9223372036854775807 9223372036854775807 0 numothersock 361 505 9223372036854775807 9223372036854775807 0 dcachesize 135941831 136114679 9223372036854775807 9223372036854775807 0 numfile 2905 4990 9223372036854775807 9223372036854775807 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 numiptent 8 9 9223372036854775807 9223372036854775807 0 [root@bni /]# ping 4.2.2.1 PING 4.2.2.1 (4.2.2.1) 56(84) bytes of data. --- 4.2.2.1 ping statistics --- 9 packets transmitted, 0 received, 100% packet loss, time 8493ms [root@bni /]# service postfix stop [root@bni /]# ping 4.2.2.1 PING 4.2.2.1 (4.2.2.1) 56(84) bytes of data. 64 bytes from 4.2.2.1: icmp_seq=1 ttl=53 time=8.63 ms 64 bytes from 4.2.2.1: icmp_seq=2 ttl=53 time=8.62 ms 64 bytes from 4.2.2.1: icmp_seq=3 ttl=53 time=8.63 ms 64 bytes from 4.2.2.1: icmp_seq=4 ttl=53 time=8.66 ms Outbound connections of all sorts fail when postfix is running.

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• Linux: prevent outgoing TCP flood

  - by Willem

  I run several hundred webservers behind loadbalancers, hosting many different sites with a plethora of applications (of which I have no control). About once every month, one of the sites gets hacked and a flood script is uploaded to attack some bank or political institution. In the past, these were always UDP floods which were effectively resolved by blocking outgoing UDP traffic on the individual webserver. Yesterday they started flooding a large US bank from our servers using many TCP connections to port 80. As these type of connections are perfectly valid for our applications, just blocking them is not an acceptable solution. I am considering the following alternatives. Which one would you recommend? Have you implemented these, and how? Limit on the webserver (iptables) outgoing TCP packets with source port != 80 Same but with queueing (tc) Rate limit outgoing traffic per user per server. Quite an administrative burden, as there are potentially 1000's of different users per application server. Maybe this: how can I limit per user bandwidth? Anything else? Naturally, I'm also looking into ways to minimize the chance of hackers getting into one of our hosted sites, but as that mechanism will never be 100% waterproof, I want to severely limit the impact of an intrusion. Cheers!

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• Juniper router dropping pings to external interface

  - by Alexander Garden

  My organization has a Juniper SSG20-WLAN that routes our traffic to the outside world. We've been having intermittent problems with our internet connection so I wrote up a Python script to ping the internal interface of the router, the external interface, a couple of our internal servers, the ISP router our router talks to, their upstream provider, and Google and Yahoo for good measure. It does that about every minute. What I have found is that when our internet goes out, our Juniper router ceases responding to pings on the external interface. Everything past that is, of course, unreachable. The internal interface and our internal servers continue to echo back without interruption. None of the counters indicate dropped packets of any type. They all look normal. The logs complain about VIP servers being unavailable but otherwise nothing indicative of network issues. My questions are these: Does this exonerate our ISP? Or, contrawise, might a problem with the connection be causing the external interface to go down? Is there somewhere else in the SSG20, beside the system log and counters, that might help me track down info on the problem? UPDATE: Turned out that one of the switches between my monitoring box and the router was a router itself, and occasionally diverting from the gateway to itself. Kudos to those who made suggestions along those lines. Not really sure which answer to mark as accepted, as it was really stuff in the comments that turned out to be right. Thanks for the suggestions.

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