Eric Stewart: Running Off At The Mouth

So we powered on our first to arrive Nexus 7706s (two of them). Here’s some notes so far.

As is not unusual, I run into an edge case that might be specific to us. While attempting to monitor IPv6 reachability of an NTP server I had just upgraded, I ran into an interesting case where NTP was responding via IPv4, but not IPv6, and they appeared to be identically configured.

It’s been a while since I’ve done more than just update the Unified Trees post for new versions, and I stumbled across an issue that Linux administrators that make use of iptables should be aware of. The case is actually true for any “client initiated connection” when it comes to iptables – not just MySQL slaves. That’s just where I stumbled across the issue.

Got multiple Cacti installs? Want the Tree view of your graphs to show all of your trees mashed together? Then this is the plugin for you.

I wrote a Cacti plugin I called DPDiscover – Discovery Protocol Discover, which uses LLDP, CDP, and FDP information pulled from SNMP to ‘spider’ a network and attempt to automatically add equipment to Cacti. It is heavily based off of the original “Auto Discovery” plugin that would sweep IP ranges.

An attempt to communicate an issue (and the solution) I ran into with Perl’s Net::SNMP function “get_table”, that would result in a “The message size exceeded the buffer maxMsgSize of 1452” error. It took a couple of packet captures and Googling to figure out why this problem was occurring and implement a fix.

A fellow engineer attempting to debug a jumbo frames issue was seeing what should have been a bunch of fragmented frames as a single 13,000 byte frame. Once he figured out why, I was told to fix it. Here’s my solution.

Just a quickie, probably subject to some editing later on, about how to use the “bind” option multiple times with a given service – mainly, to have a TFTP server operate from behind a virtual IP as the virtual IP (instead of becoming its real IP in the middle of the transfer).

While my home setup is unlikely to change any time soon, I recently started pondering switching my main workstation at work from Windows 7 to XUbuntu, and making my secondary machine my Windows 7 system. But if Windows 7 is no longer the Synergy server, but a Synergy client, how do you keep the connection secure through SSH? Easy! Keep the Windows box as the SSH server, just change the tunnel direction. Read on for additional details.

Just a quickie post about something that was requested of me by the other engineers. You can rename your interfaces (which usually start as something like “eth0”, “em1”, or “p1p1” depending on hardware and CentOS version) to something a little more useful. Here’s how.