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• DHCP Server on local machine

  - by EralpB

  Hello I am trying to setup a dhcp3-server on Ubuntu. But my question is more generic, if dhcp server is in a blockbox and all clients are connected to it I think I get what is going on but when dhcp server is installed on one of the "clients" that confuses me. When I send a dhcp packet from that client to the dhcp server, will my ethernet card read and write at the same time? Or will it handle it internally without writing any data to ethernet cable. It's the first time I am encountering these network things so I am a little bit confused. Also I wonder If I am in a big network with lan IP let's say 192.168.0.100 and I install a dhcp server to my computer, can any other computers accidentally get IP from my dhcp server? Every computer has one ethernet card (if that matters?). And every computer is connected to one router. I guess the answer is no because the broadcast message won't reach to my computer since when router receives a dhcp search packet it will answer and it won't let other computers know about it because they don't need to. And without router sending that packet one by one, it cannot travel further. I'd be glad if someone enlightens me. Thank you very much.

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• VMware ARP/Mac Networking

  - by Ross Wilson

  Hi Guys, I am very interested in how VMware networking works. I have scoured the VMware website and read their data sheets, this has given me some basic knowledge. I now have some questions. Lets assume that we have a physical server running the VMware hypervisor. The physical server is running a Virtual Machine. The physical box has one physical NIC. The NIC is connected to a switch, as so is a desktop client. Now, this is where my first question lies. The VM has an IP address: 192.168.1.1. How do desktop clients on the network communicate with this VM? So, the client pings 192.168.1.1. The ping packet is sent to the switch. The switch checks its MAC address table and sees that 192.168.1.1 is associated with the MAC address of the physical NIC. Correct? I then assume that the ping packet is sent to the server's physical NIC, where the hypervisor routes the packet to the VM thats using 192.168.1.1? Please could you give me a run down as to how VM networking works? Many thanks, Ross

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• Only one domains not resolving via Windows DNS server at multiple locations, but is at others

  - by Brett G

  I'm having quite a weird issue. Had mail delivery issues to a specific domain. After looking closer, I realized that the DNS for that domain isn't resolving via the in-house Windows 2003 SP2 DNS server. C:\>nslookup foodmix.net Server: DC.DOMAIN.com Address: 10.1.1.1 DNS request timed out. timeout was 2 seconds. DNS request timed out. timeout was 2 seconds. *** Request to DC.DOMAIN.com timed-out (DC.DOMAIN.com and 10.1.1.1 are generic values to replace the actual ones) Even if I run this nslookup from the DC.DOMAIN.com server, I get the same result. However, all other requests are working as they should. I tried it on severs at completely separate organizations on different networks(Windows 2003 AD servers). The weird thing is some of these were having the same exact issue. However using public DNS servers work. I have tried clearing the DNS cache, restarting the server, restarting the services, etc. Nothing has worked. One weird event I noticed in the DNS Server Event Logs that might be related is an event ID of 5504 with the following description: The DNS server encountered an invalid domain name in a packet from 192.33.4.12. The packet will be rejected. The event data contains the DNS packet. For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp. In the data section below, I can see the following mentioned: ns2.webhostingstar.com Which happens to be the nameserver for the domain in question. Several discussion threads and a MS KB have pointed to disabling EDNS. I have done this via "dnscmd /config /enableednsprobes 0" and it has not fixed the issue.

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• Make isolinux 4.0.3 chainload itself in VMWare

  - by chainloader

  I have a bootable iso which boots into isolinux 4.0.3 and I want to make it chainload itself (my actual goal is to chainload isolinux.bin v4.0.1-debian, which should start up the Ubuntu10.10 Live CD, but for now I just want to make it chainload itself). I can't get isolinux to chainload any isolinux.bin, no matter what version. It either freezes or shows a "checksum error" message. I'm using VMWare to test the iso. Things I have tried: .com32 /boot/isolinux/chain.c32 /boot/isolinux/isolinux-debug.bin (chainload self) this shows Loading the boot file... Booting... ISOLINUX 4.03 2010-10-22 Copyright (C) 1994-2010 H. Peter Anvin et al isolinux: Starting up, DL = 9F isolinux: Loaded spec packet OK, drive = 9F isolinux: Main image LBA = 53F00100 ...and the machine freezes. Then I've tried this (chainload GRUB4DOS 0.4.5b) chainloader /boot/isolinux/isolinux-debug.bin Result: Error 13: Invalid or unsupported executable format Next try: (chainload GRUB4DOS 0.4.5b) chainloader --force /boot/isolinux/isolinux-debug.bin boot Result: ISOLINUX 4.03 2010-10-22 Copyright (C) 1994-2010 H. Peter Anvin et al isolinux: Starting up, DL = 9F isolinux: Loaded spec packet OK, drive = 9F isolinux: No boot info table, assuming single session disk... isolinux: Spec packet missing LBA information, trying to wing it... isolinux: Main image LBA = 00000686 isolinux: Image checksum error, sorry... Boot failed: press a key to retry... I have tried other things, but all of them failed miserably. Any suggestions?

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• Do all routers really must know all routes to every router?

  - by Philipili

  This is my complicated and long question. First let's talk about the context. Network topology: PC A --- RT A --- RT C --- RT B --- PC B (RT C has a WAN NIC connected to "the cloud") With this situation : PC A must send a packet to PC B Default routes direct packets to the cloud We haven't access to RT C's configuration RT C only knows how to join network A, not network B RT A knows about network B RT B knows about network A RT C's routing table: Destination NIC Gateway 0.0.0.0 WAN Cloud Network A LAN A RT A's WAN RT A's routing table: Destination NIC Gateway 0.0.0.0 WAN LAN A Network B WAN LAN A RT B's routing table: Destination NIC Gateway 0.0.0.0 WAN LAN B Network A WAN LAN B I would like to permit PC A and PC B to communicate, but I don't have access to RT C. Networks B and BC are new. Can PC A send a packet to RT B's WAN NIC (which is possible) and "ask RT B to direct the packet to PC B" ? I believe replacing RT B with a VPN server should do the trick, but I would like to know if it is possible to make it without establishing a new connection.

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• Make isolinux 4.0.3 chainload itself

  - by chainloader

  I have a bootable iso which boots into isolinux 4.0.3 and I want to make it chainload itself (my actual goal is to chainload isolinux.bin v4.0.1-debian, which should start up the Ubuntu10.10 Live CD, but for now I just want to make it chainload itself). I can't get isolinux to chainload any isolinux.bin, no matter what version. It either freezes or shows a "checksum error" message. I'm using VMWare to test the iso. Things I have tried: .com32 /boot/isolinux/chain.c32 /boot/isolinux/isolinux-debug.bin (chainload self) this shows Loading the boot file... Booting... ISOLINUX 4.03 2010-10-22 Copyright (C) 1994-2010 H. Peter Anvin et al isolinux: Starting up, DL = 9F isolinux: Loaded spec packet OK, drive = 9F isolinux: Main image LBA = 53F00100 ...and the machine freezes. Then I've tried this (chainload GRUB4DOS 0.4.5b) chainloader /boot/isolinux/isolinux-debug.bin Result: Error 13: Invalid or unsupported executable format Next try: (chainload GRUB4DOS 0.4.5b) chainloader --force /boot/isolinux/isolinux-debug.bin boot Result: ISOLINUX 4.03 2010-10-22 Copyright (C) 1994-2010 H. Peter Anvin et al isolinux: Starting up, DL = 9F isolinux: Loaded spec packet OK, drive = 9F isolinux: No boot info table, assuming single session disk... isolinux: Spec packet missing LBA information, trying to wing it... isolinux: Main image LBA = 00000686 isolinux: Image checksum error, sorry... Boot failed: press a key to retry... I have tried other things, but all of them failed miserably. Any suggestions?

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• Prevent outgoing traffic unless OpenVPN connection is active using pf.conf on Mac OS X

  - by Nick

  I've been able to deny all connections to external networks unless my OpenVPN connection is active using pf.conf. However, I lose Wi-Fi connectivity if the connection is broken by closing and opening the laptop lid or toggling Wi-Fi off and on again. I'm on Mac OS 10.8.1. I connect to the Web via Wi-Fi (from varying locations, including Internet cafés). The OpenVPN connection is set up with Viscosity. I have the following packet filter rules set up in /etc/pf.conf # Deny all packets unless they pass through the OpenVPN connection wifi=en1 vpn=tun0 block all set skip on lo pass on $wifi proto udp to [OpenVPN server IP address] port 443 pass on $vpn I start the packet filter service with sudo pfctl -e and load the new rules with sudo pfctl -f /etc/pf.conf. I have also edited /System/Library/LaunchDaemons/com.apple.pfctl.plist and changed the line <string>-f</string> to read <string>-ef</string> so that the packet filter launches at system startup. This all seems to works great at first: applications can only connect to the web if the OpenVPN connection is active, so I'm never leaking data over an insecure connection. But, if I close and reopen my laptop lid or turn Wi-Fi off and on again, the Wi-Fi connection is lost, and I see an exclamation mark in the Wi-Fi icon in the status bar. Clicking the Wi-Fi icon shows an "Alert: No Internet connection" message: To regain the connection, I have to disconnect and reconnect Wi-Fi, sometimes five or six times, before the "Alert: No Internet connection" message disappears and I'm able to open the VPN connection again. Other times, the Wi-Fi alert disappears of its own accord, the exclamation mark clears, and I'm able to connect again. Either way, it can take five minutes or more to get a connection again, which can be frustrating. Why does Wi-Fi report "No internet connection" after losing connectivity, and how can I diagnose this issue and fix it?

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• Server 2012, Jumbo Frames - should I expect problems?

  - by TomTom

  Ok, this sound might stupid - but is there any negative on just enabling jumbo frames in practice? From what I understand: Any switch or ethernet adapter that sees a jumbo frame it can not handle will just drop it. TCP is not a problem as max frame size is negotiated in the setinuo phase. UCP is a theoretical problem as a server may just send a LARGE UDP packet that gets dropped on the way. Practically though, as UDP is packet based, I do not really think any software WOULD send a UDP packet larger than 1500 bytes net without app level configuration changes - at least this is how I do my programming, as it is quite hard to get a decent MTU size for that without testing yourself, so you fall back in programming to max 1500 packets. The network in question is a standard small business network - we upgraded now from a non managed 24 port switch to a 52 port switch with 4 10g ports (netgear - quite cheap) and will mov a file server to 10g for also ISCSI serving. All my equipment on the Ethernet level can handle minimum 9000 bytes and due to local firewalls I really want to get packets larger (less firewall processing), but the network is also NAT'ed to the internet. On top, different machines move around (download) large files (multi gigabyte area) quite often for processing. The question is - can I expect problems when I just enable jumbo frames? Again, this is not totally ignorance - I just don't see programs sending more than 1500 byte UDP packets (if that is a practical problem please tell me) and for TCP the MTU is negotiated anyway. if there is a problem I can move to a dedicated VLAN, but this has it's own shares of problems as basically most workstations must then be on both VLAN's.

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• Why Wireshark does not recognize this HTTP response?

  - by Alois Mahdal

  I have a trivial CGI script that outputs simple text content. It's written in Perl and using CGI module and it specifies only the most basic headers: print $q->header( -type => 'text/plain', -Content_length => $length, ); print $stuff; There's no apparent issue with functionality, but I'm confused about the fact that Wireshark does not recognize the HTTP response as HTTP--it's marked as TCP. Here is request and response: GET /cgi-bin/memfile/memfile.pl?mbytes=1 HTTP/1.1 Host: 10.6.130.38 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20100101 Firefox/11.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: cs,en-us;q=0.7,en;q=0.3 Accept-Encoding: gzip, deflate Connection: keep-alive HTTP/1.1 200 OK Date: Thu, 05 Apr 2012 18:52:23 GMT Server: Apache/2.2.15 (Win32) mod_ssl/2.2.15 OpenSSL/0.9.8m Content-length: 1048616 Keep-Alive: timeout=5, max=100 Connection: Keep-Alive Content-Type: text/plain; charset=ISO-8859-1 XXXXXXXX... And here is the packet overview (Full packet is here on pastebin) No. Time Source srcp Destination dstp Protocol Info tcp.stream abstime 5 0.112749 10.6.130.38 80 10.6.130.53 48072 TCP [TCP segment of a reassembled PDU] 0 20:52:23.228063 Frame 5: 1514 bytes on wire (12112 bits), 1514 bytes captured (12112 bits) Ethernet II, Src: Dell_97:29:ac (00:1e:4f:97:29:ac), Dst: Dell_3b:fe:70 (00:24:e8:3b:fe:70) Internet Protocol Version 4, Src: 10.6.130.38 (10.6.130.38), Dst: 10.6.130.53 (10.6.130.53) Transmission Control Protocol, Src Port: http (80), Dst Port: 48072 (48072), Seq: 1, Ack: 330, Len: 1460 Now when I see this in Wireshark: there's usual TCP handshake then the GET request shown as HTTP with preview then the next packet contains the response, but is not marked as an HTTP response--just a generic "[TCP segment of a reassembled PDU]", and is not caught by "http.response" filter. Can somebody explain why Wireshark does not recognize it? Is there something wrong with the response?

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• Router vs switch in a LAN [closed]

  - by servernewbie

  If I have a LAN and and connect it with a switch, I understand it uses a CAM table to route packets in layer 2 (by saving mac to port relations). So far all good. However, when using a router for a LAN (ONLY for a LAN, not to connect it to "the outside" WAN/internet/etc) I get a bit confused as to how it internally processes packets. I would first split this into two router scenarios: Router with buit-in switch In this scenario, I would expect that it will act exactly as a switch with a CAM table internally. This would probably benefit a bit in speed (guessing here?) compared to the next option. Router without built-in switch Here is where I get confused. If hostA wants to send a packet to hostB, it will ARP to find hostB's MAC address and send it there. Now, if we had a switch (above scenario) this would be easy. But how does it work now in a router WITHOUT a switch? If I would guess, hostA would send an Ethernet frame with hostB's MAC address to the line. The router would fetch the packet (even though the router has another MAC address, it would still fetch this packet even if it only contains hostB's MAC address). It would strip the Ethernet frame header and check the IP, and then check its own internal ARP table again for the MAC address. Now, this would seem like a waste of resources compared to a router with a built-in switch. But maybe it does not work like that at all. Does it also contain a CAM table? If that would be true, what would then the difference between these two routers really be?

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• How to prevent asymmetric routing with multiple eBGP routers?

  - by Andy Shinn

  I have 2 routers announcing a /22 subnet to different providers (one providers connects to each of the 2 routers). I have split the /22 in two /23 to announce one /23 on each of the routers plus the /22 (the providers will take the more specific route). This allows me to fail over and keep traffic inside the /23 in and out the same provider. What are other ways in which I could announce just the /22 with both routers and have packets from servers on the network behind the routers go back out the same router in which they came in from? EDIT: The main problem I come across, which end users and clients complain about the most, is that the least hop route is sometimes not the "optimal" route. In my case, I know that Provider B may have better latency to X nation. But when packets come in from provider B, they may go out Provider A or provider B. The reverse is also true. If I send a packet to X nation out provider A, even though it may have more hops back, the packet will likely come in from Provider B (which may have higher latency, packet loss, etc. to this nation)

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• NAT and P2P router crash

  - by returnFromException

  So..i had this argument with my networks teacher. He said that some people complains about router crashes due to many entrys on NAT tables on a router. I didnt understand and i asked: "If the application uses the same port, why does the router crash?. It should have only one entry (pc-ip,pcport;public-ip,public-port)". And he said: "it doesnt matter its using the same port". I got the idea that NAT creates an entry for every packet that passes trought it. Iam assuming NAT with overloading as you might have guessed. So the questions are: 1-How does nat entrys are created? On a packet basis or connection basis? I mean: suppose i send a udp packet..does the router create an entry? 2-When i start a TCP connection, does the router create a persistant nat entry until the connection closes? 3-Was my teacher right? The NAT table can overload assuming an aplication on the same port sending packets? Thanks in advance.

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• Wireshark WPA 4-way handshake

  - by cYrus

  From this wiki page: WPA and WPA2 use keys derived from an EAPOL handshake to encrypt traffic. Unless all four handshake packets are present for the session you're trying to decrypt, Wireshark won't be able to decrypt the traffic. You can use the display filter eapol to locate EAPOL packets in your capture. I've noticed that the decryption works with (1, 2, 4) too, but not with (1, 2, 3). As far as I know the first two packets are enough, at least for what concern unicast traffic. Can someone please explain exactly how does Wireshark deal with that, in other words why does only the former sequence work, given that the fourth packet is just an acknowledgement? Also, is it guaranteed that the (1, 2, 4) will always work when (1, 2, 3, 4) works? Test case This is the gzipped handshake (1, 2, 4) and an ecrypted ARP packet (SSID: SSID, password: password) in base64 encoding: H4sICEarjU8AA2hhbmRzaGFrZS5jYXAAu3J400ImBhYGGPj/n4GhHkhfXNHr37KQgWEqAwQzMAgx 6HkAKbFWzgUMhxgZGDiYrjIwKGUqcW5g4Ldd3rcFQn5IXbWKGaiso4+RmSH+H0MngwLUZMarj4Rn S8vInf5yfO7mgrMyr9g/Jpa9XVbRdaxH58v1fO3vDCQDkCNv7mFgWMsAwXBHMoEceQ3kSMZbDFDn ITk1gBnJkeX/GDkRjmyccfus4BKl75HC2cnW1eXrjExNf66uYz+VGLl+snrF7j2EnHQy3JjDKPb9 3fOd9zT0TmofYZC4K8YQ8IkR6JaAT0zIJMjxtWaMmCEMdvwNnI5PYEYJYSTHM5EegqhggYbFhgsJ 9gJXy42PMx9JzYKEcFkcG0MJULYE2ZEGrZwHIMnASwc1GSw4mmH1JCCNQYEF7C7tjasVT+0/J3LP gie59HFL+5RDIdmZ8rGMEldN5s668eb/tp8vQ+7OrT9jPj/B7425QIGJI3Pft72dLxav8BefvcGU 7+kfABxJX+SjAgAA Decode with: $ base64 -d | gunzip > handshake.cap Run tshark to see if it correctly decrypt the ARP packet: $ tshark -r handshake.cap -o wlan.enable_decryption:TRUE -o wlan.wep_key1:wpa-pwd:password:SSID It should print: 1 0.000000 D-Link_a7:8e:b4 - HonHaiPr_22:09:b0 EAPOL Key 2 0.006997 HonHaiPr_22:09:b0 - D-Link_a7:8e:b4 EAPOL Key 3 0.038137 HonHaiPr_22:09:b0 - D-Link_a7:8e:b4 EAPOL Key 4 0.376050 ZyxelCom_68:3a:e4 - HonHaiPr_22:09:b0 ARP 192.168.1.1 is at 00:a0:c5:68:3a:e4

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• Openvpn - stuck on Connecting

  - by user224277

  I've got a problem with openvpn server... every time when I trying to connect to the VPN , I am getting a window with login and password box, so I typed my login and password (login = Common Name (user1) and password is from a challenge password from the client certificate. Logs : Jun 7 17:03:05 test ovpn-openvpn[5618]: Authenticate/Decrypt packet error: packet HMAC authentication failed Jun 7 17:03:05 test ovpn-openvpn[5618]: TLS Error: incoming packet authentication failed from [AF_INET]80.**.**.***:54179 Client.ovpn : client #dev tap dev tun #proto tcp proto udp remote [Server IP] 1194 resolv-retry infinite nobind persist-key persist-tun ca ca.crt cert user1.crt key user1.key <tls-auth> -----BEGIN OpenVPN Static key V1----- d1e0... -----END OpenVPN Static key V1----- </tls-auth> ns-cert-type server cipher AES-256-CBC comp-lzo yes verb 0 mute 20 My openvpn.conf : port 1194 #proto tcp proto udp #dev tap dev tun #dev-node MyTap ca /etc/openvpn/keys/ca.crt cert /etc/openvpn/keys/VPN.crt key /etc/openvpn/keys/VPN.key dh /etc/openvpn/keys/dh2048.pem server 10.8.0.0 255.255.255.0 ifconfig-pool-persist ipp.txt #push „route 192.168.5.0 255.255.255.0? #push „route 192.168.10.0 255.255.255.0? keepalive 10 120 tls-auth /etc/openvpn/keys/ta.key 0 #cipher BF-CBC # Blowfish #cipher AES-128-CBC # AES #cipher DES-EDE3-CBC # Triple-DES comp-lzo #max-clients 100 #user nobody #group nogroup persist-key persist-tun status openvpn-status.log #log openvpn.log #log-append openvpn.log verb 3 sysctl : net.ipv4.ip_forward=1

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• IPv6 works only after ping to routing box

  - by Ficik

  Situation: There is ipv4 only router in network and every computer is connected to it (wifi or cable). Server with ipv4 and ipv6 is connected to this router as well. Server has configured tunnelbrokers 6to4 tunnel and radvd. Clients in network has right prefix and can ping each other. But they can't ping to internet until they ping Server (the one with tunnel). I found somewhere that it's icmp problem, but I couldn't find solution. Is it problem that there is ipv4 only router? server and client runs linux router runs dd-wrt without ipv6 support :( Ping try: standa@standa-laptop:~$ ping6 ipv6.google.com PING ipv6.google.com(2a00:1450:8007::69) 56 data bytes ^C --- ipv6.google.com ping statistics --- 29 packets transmitted, 0 received, 100% packet loss, time 28223ms standa@standa-laptop:~$ ping6 2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478 PING 2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478(2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478) 56 data bytes 64 bytes from 2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478: icmp_seq=1 ttl=64 time=3.55 ms 64 bytes from 2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478: icmp_seq=2 ttl=64 time=0.311 ms 64 bytes from 2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478: icmp_seq=3 ttl=64 time=0.269 ms 64 bytes from 2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478: icmp_seq=4 ttl=64 time=0.292 ms ^C --- 2001:470:XXXX:XXXX:21c:c0ff:fe2b:6478 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3000ms rtt min/avg/max/mdev = 0.269/1.107/3.559/1.415 ms standa@standa-laptop:~$ ping6 ipv6.google.com PING ipv6.google.com(2a00:1450:8007::69) 56 data bytes 64 bytes from 2a00:1450:8007::69: icmp_seq=1 ttl=57 time=20.7 ms 64 bytes from 2a00:1450:8007::69: icmp_seq=2 ttl=57 time=20.2 ms 64 bytes from 2a00:1450:8007::69: icmp_seq=3 ttl=57 time=23.4 ms ^C --- ipv6.google.com ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2001ms rtt min/avg/max/mdev = 20.267/21.479/23.413/1.392 ms

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• Only one domain is not resolving via Windows DNS server at multiple locations, but is at others

  - by Brett G

  I'm having quite a weird issue. Had mail delivery issues to a specific domain. After looking closer, I realized that the DNS for that domain isn't resolving via the in-house Windows 2003 SP2 DNS server. C:\>nslookup foodmix.net Server: DC.DOMAIN.com Address: 10.1.1.1 DNS request timed out. timeout was 2 seconds. DNS request timed out. timeout was 2 seconds. *** Request to DC.DOMAIN.com timed-out (DC.DOMAIN.com and 10.1.1.1 are generic values to replace the actual ones) Even if I run this nslookup from the DC.DOMAIN.com server, I get the same result. However, all other requests are working as they should. I had a sysadmin friend try this DNS lookup on servers at several companies that he consults for (which are also Windows 2003 AD servers). The weird thing is some of these were having the same exact issue. However using public DNS servers work. I have tried clearing the DNS cache, restarting the server, restarting the services, etc. Nothing has worked. One weird event I noticed in the DNS Server Event Logs that might be related is an event ID of 5504 with the following description: The DNS server encountered an invalid domain name in a packet from 192.33.4.12. The packet will be rejected. The event data contains the DNS packet. For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp. In the data section below, I can see the following mentioned: ns2.webhostingstar.com Which happens to be the nameserver for the domain in question. Several discussion threads and a MS KB have pointed to disabling EDNS. I have done this via "dnscmd /config /enableednsprobes 0" and it has not fixed the issue.

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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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• certificate SSH login does not work on 22 but other port

  - by Hugo

  On my Red Hat server, the sshd will not accept my correct certificate login. However, If i start another sshd on another port, it works! (I assume the second sshd loads the same configruation files.) second sshd started with: sudo /usr/sbin/sshd -p 54321 -d #-d is optional and prints debug output ssh strange-host -p 22 -vvv prints: debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password debug1: Offering public key: /home/me/.ssh/id_dsa debug3: send_pubkey_test debug2: we sent a publickey packet, wait for reply debug3: Wrote 528 bytes for a total of 2389 debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password debug2: we did not send a packet, disable method debug3: authmethod_lookup password ssh strange-host -p 54321 -vvv prints: debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password debug1: Offering public key: /home/me/.ssh/id_dsa debug3: send_pubkey_test debug2: we sent a publickey packet, wait for reply debug3: Wrote 528 bytes for a total of 2389 debug1: Server accepts key: pkalg ssh-dss blen 433 debug2: input_userauth_pk_ok: SHA1 fp 0f:1c:df:27:f7:86:49:a8:47:7e:7f:f3:32:1c:7d:04:a3:73:a5:72 So the question is why the difference? I have thought of no way to get any helpful logging from the "standard" sshd to troubleshoot the problem.

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• Cisco FWSM -> ASA upgrade broke our mail server

  - by Mike Pennington

  We send mail with unicode asian characters to our mail server on the other side of our WAN... immediately after upgrading from a FWSM running 2.3(2) to an ASA5550 running 8.2(5), we saw failures on mail jobs that contained unicode. The symptoms are pretty clear... using the ASA's packet capture utility, we snagged the traffic before and after it left the ASA... access-list PCAP line 1 extended permit tcp any host 192.0.2.25 eq 25 capture pcap_inside type raw-data access-list PCAP buffer 1500000 packet-length 9216 interface inside capture pcap_outside type raw-data access-list PCAP buffer 1500000 packet-length 9216 interface WAN I downloaded the pcaps from the ASA by going to https://<fw_addr>/pcap_inside/pcap and https://<fw_addr>/pcap_outside/pcap... when I looked at them with Wireshark Follow TCP Stream, the inside traffic going into the ASA looks like this EHLO metabike AUTH LOGIN YzFwbUlciXNlck== cZUplCVyXzRw But the same mail leaving the ASA on the outside interface looks like this... EHLO metabike AUTH LOGIN YzFwbUlciXNlck== XXXXXXXXXXXX The XXXX characters are concerning... I fixed the issue by disabling ESMTP inspection: wan-fw1(config)# policy-map global_policy wan-fw1(config-pmap)# class inspection_default wan-fw1(config-pmap-c)# no inspect esmtp wan-fw1(config-pmap-c)# end The $5 question... our old FWSM used SMTP fixup without issues... mail went down at the exact moment that we brought the new ASAs online... what specifically is different about the ASA that it is now breaking this mail? Note: usernames / passwords / app names were changed... don't bother trying to Base64-decode this text.

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• How to send raw data over a network?

  - by youllknow

  Hi everyone! I've same data stored in a byte-array. The data contains a IPv4 packet (which contains a udp-packet). I want to send these array raw over the network using C# (preferred) or C++. I don't want to use C#'s udp-client for example. Does anyone know how to perform this? Sorry for my bad English and thanks for your help in advance!!!

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• Examples for Winsock?

  - by bobber205

  What do you guys recommend for a resource for winsock? I have an assignment that we have only have a few days to do that needs to send a simple packet using UDP (and receive the same type of packet). I am fairly familiar with C# sockets but nothing with C++. Any tips or resources?

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• What does it mean whether network device is Loopback?

  - by Gtker

  Does it mean that the Loopback device handles the request like ping localhost ? If so, there should be at least one device that's loopback,but seems none of my two network device is Loopback: rpcap://\Device\NPF_{45D5ADA0-095E-49F3-BEA1-E8754390F2D4} Description: Network adapter 'Intel(R) PRO/Wireless 2200BG Network Conne ction (Microsoft's Packet Scheduler) ' on local host Loopback: no rpcap://\Device\NPF_{783C5467-4026-473C-86A0-5E5A3708C624} Description: Network adapter 'Realtek RTL8169/8110 Family Gigabit Ethern et NIC (Microsoft's Packet Scheduler) ' on local host Loopback: no Can someone clarify all this?

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• What happens with TCP packets between 2 Socket.BeginReceive Call??

  - by Rodrigo

  Hi, i have a doubt about Socket Programming, i am developing a TCP packets Sniffer, i am using Socket.BeginAccept, Socket.BeginReceive to capture every packet, but when a packet is received i have to process something, it is a fast operation, but would take some milliseconds, and then call the BeginReceive again. My question is, what would happen if some packets are sent while i am processing, and havent called BeginReceive??...are lost?...are buffered internally?...is there a limit?... Thanks in advance.

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• Hibernate Communications Link Failure in Hibernate Based Java Servlet application powered by MySQL

  - by Vatsala

  Let me describe my question - I have a Java application - Hibernate as the DB interfacing layer over MySQL. I get the communications link failure error in my application. The occurence of this error is a very specific case. I get this error , When I leave mysql server unattended for more than approximately 6 hours (i.e. when there are no queries issued to MySQL for more than approximately 6 hours). I am pasting a top 'exception' level description below, and adding a pastebin link for a detailed stacktrace description. javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Cannot open connection - Caused by: org.hibernate.exception.JDBCConnectionException: Cannot open connection - Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure - The last packet successfully received from the server was 1,274,868,181,212 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago. - Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure - The last packet successfully received from the server was 1,274,868,181,212 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago. - Caused by: java.net.ConnectException: Connection refused: connect the link to the pastebin for further investigation - http://pastebin.com/4KujAmgD What I understand from these exception statements is that MySQL is refusing to take in any connections after a period of idle/nil activity. I have been reading up a bit about this via google search, and came to know that one of the possible ways to overcome this is to set values for c3p0 properties as c3p0 comes bundled with Hibernate. Specifically, I read from here http://www.mchange.com/projects/c3p0/index.html that setting two properties idleConnectionTestPeriod and preferredTestQuery will solve this for me. But these values dont seem to have had an effect. Is this the correct approach to fixing this? If not, what is the right way to get over this? The following are related Communications Link Failure questions at stackoverflow.com, but I've not found a satisfactory answer in their answers. http://stackoverflow.com/questions/2121829/java-db-communications-link-failure http://stackoverflow.com/questions/298988/how-to-handle-communication-link-failure Note 1 - i dont get this error when I am using my application continuosly. Note 2 - I use JPA with Hibernate and hence my hibernate.dialect,etc hibernate properties reside within the persistence.xml in the META-INF folder (does that prevent the c3p0 properties from working?) edit - Here are the c3p0 parameters I tried out - select 1; 2

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• change attributes of SVG graph without refresh

  - by Mike Hudak

  Hello, I have a simple SVG graph generated by GraphViz: <?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> <!-- Generated by graphviz version 2.26.3 (20100126.1600) --> <!-- Title: G Pages: 1 --> <svg width="138pt" height="168pt" viewBox="0.00 0.00 138.00 168.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> <g id="graph1" class="graph" transform="scale(1 1) rotate(0) translate(4 164)"> <title>G</title> <polygon fill="white" stroke="white" points="-4,5 -4,-164 135,-164 135,5 -4,5"/> <!-- Node1 --> <g id="node1" class="node"><title>Node1</title> <a xlink:href="http://localhost/viz/applet.php" xlink:title="Internet"> <image xlink:href="images/cloud.png" width="130px" height="77px" preserveAspectRatio="xMinYMin meet" x="0" y="-159.5"/> <text text-anchor="middle" x="65" y="-116.4" font-family="Times New Roman,serif" font-size="14.00">&#39;.$Internet.&#39;</text> </a> </g> <!-- Node2 --> <g id="node2" class="node"><title>Node2</title> <a xlink:href="http://localhost/viz/applet.php"> <image xlink:href="images/file server.png" width="44px" height="45px" preserveAspectRatio="xMinYMin meet" x="43" y="-45.5"/> </a> </g> <!-- Node1&#45;&gt;Node2 --> <g id="edge2" class="edge"><title>Node1&#45;&gt;Node2</title> <a xlink:title="Bandwidth: 1544kbps&#10;Using link: 12%&#10;VOIP calls: 4&#10;Packet rate: 10000&#10;Packet loss: 2"> <path fill="none" stroke="black" d="M65,-82.2678C65,-73.5404 65,-64.358 65,-55.8964"/> <polygon fill="black" stroke="black" points="68.5001,-55.6524 65,-45.6524 61.5001,-55.6525 68.5001,-55.6524"/> </a> </g> </g> </svg> I want to change some atributes: for example " VOIP calls: 4 " -changing "4" to value from Database(LDAP) without refreshing whole SVG graph <a xlink:title="Bandwidth: 1544kbps&#10;Using link: 12%&#10;VOIP calls: 4&#10;Packet rate: 10000&#10;Packet loss: 2"> Thank you for your answers

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