Landfill of Wisdom

Writing down the username and password for the vivacom ADSL router, in case I need it again. user: root pass: warmWLspot Useful to telnet 192.168.1.1 and then reboot . Originally found at Neo2SHYAlien blog . And here I found passwords for other models, just in case. ZTE ZXDSL 832 username: root password: GSrootaccess ZTE ZXDSL 831 username: root password: GSrootaccess ZTE username: root password: 831access Huawei SmartAX MT882 username: root password: MT882rootaccess ZTE ZXDSL-531b username: root password: rootWLaccess Pirelli – DRG – A124G username: root password: warmWLspot Comtrend CT-5367 username: root password: warmWLspot HG530 Home Gateway username: root password: warmWLspot

I struggled for a week having udev (on CentOS 6.3) do all kinds of silly things with the interfaces names on a server with 4 onboard 1G interfaces, an 2 dual port Mellanox ConnectX-3 cards. The short story is that udev was trying to preserve the names of the interfaces to be consistently numbered starting from eth0 and ending with eth7. The problem: the modules for the network cards do not always get probed/loaded in the same order. Udev does the module loading automatically and considering how heavily parallel it is, if the Mellanox driver gets loaded first and the onboard tg3 driver second, udev tries to swap eth eth0-eth3 interfaces with eth4-eth7. Most of the time this leaves a huge mess behind. I followed RedHat's advice to stop using the "eth" names but even then udev failed to rename one or two of the eth interfaces most of the time. Here comes the solution. Modify the 70-persistent-net.rules that udev generates, and add an extra rule for each matching interface w...

I've been struggling with a wireless SBG900 for a couple of hours now. The interface looks fine (as far as wireless router interfaces go) and I had the simple setting up WPA security on this router. The higher security setting was supposed to replace the current no password + MAC restriction setup. The bottom line is that after removing the registered MAC addresses the router simply refused connections from all clients. And the best part is that nowhere in the interface I could find a clicky button to enable it. [caption id="attachment_145" align="aligncenter" width="595" caption="There is no place to disable the MAC filter"] [/caption] Tamper Data to the rescue. Click "Apply" and just change the value of the Wireless.EnableAllowAccess.enableAllowAccess parameter to 0. Works fine now.

I have a pretty simple mythtv box. It boots over PXE and the root partition is read-only exported over NFS. After bumping the kernel on the server that hosts the NFS to 2.6.34 my mythbox no longer wanted to boot. It was hanging right after managing to look up the mountd port on the NFS server with RPC. After enabling NFS_DEBUG the output looks like this: Looking up port of RPC 100003/2 on 10.0.0.19 Root-NFS: Portmapper on server returned 2049 as nfsd port Looking up port of RPC 100005/1 on 10.0.0.19 Root-NFS: mountd port is 45731 tcpdump on the server didn't reveal much either. Everything was fine until the point of hanging, where the client sent a couple of retransmission requests for the last UDP packet. In wireshark, these packets look like: 5127 4.366527 10.0.0.42 10.0.0.19 NFS V2 NULL Call 5128 4.366638 10.0.0.19 10.0.0.42 NFS V2 NULL Reply (Call In 5127) 5129 5.463390 10.0.0.42 10.0.0.19 NFS [RPC retransmission of #5127]V2 NULL Cal...

A few common problems when setting up a stateful firewall to allow FTP traffic. FTP needs a separate data connection for transferring files or file listings. It has two modes of operation passive The clients request the server to listen for a connection. The server responds with the address and port where it is listening for the data connection. The client connects. active The client listens on a port for the data connection. The client notifies the server about the address and port. The server connects to the client Stateful firewalls only allow specific traffic or already established/related traffic. Since the data connection uses a separate port it cannot easily be distinguished as being related to the legitimate FTP connection. This is where the helpers come in play. ip_conntrack_ftp is a module that monitors ftp traffic and marks a data connection as RELATED to the control connection of a FTP session. When using the module, make sure you pass the option ports=21, or it will monito...

After trying to use jumbo frames on my newly upgraded network and realizing that one adapter is not enough, I simply left things as they were. Come today, my NFS mounted directories on the server were unaccessible and none of restarting the NFS server (just the NFS server process, not the machine itself) unmounting the directories or trying to mount them again helped. Eventually a little playing around with tcpdump on both the server and client tcpdump -i any port 2049 revealed that the client was sending requests and the server the appropriate responses, but for some reason the responses were not reaching the client. Quickly disabling the jumbo frames on the server ip link set mtu 1500 dev lan and everything was back in order. Conclusion: Jumbo frames are evil. Update: The Gentoo Linux Wiki has a nice tip about jumbo frames and NFS and why it is not good to mix jumbo with standard frames.

I got a new Intel Pro/1000 XT server adapter, a so-so switching hub ( NetGear GS105 ) and I immediately upgraded my network. Since both the Intel adapter and the switch were jumbo frame compatible, I decided to try that feature out. Ran the following commands on the server (with the Intel adapter): ip link set mtu 9000 dev lan and after a small delay everything seemed to be OK. Ran the same command on my workstation -- an Asus K8V SE Deluxe motherboard with an onboard Marvell Gigabit adapter. The screen froze and after a few seconds the computer rebooted. That's with a vanilla 2.6.18.5 kernel. Gotta be more careful.