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Posts in Networking
Getting the Linux NetworkManager process to respect custom DNS server settings
I recently switched my work Desktop from Ubuntu to Fedora 11, and noticed that there are some new configuration options now that network intefaces are managed by the NetworkManager process. Two useful options are the ability to specify the DNS servers and search domains in the network-scripts files, and have those applied when a DHCP lease is acquired (this assumes you override the values provided by your DHCP server). To override the DNS servers and search domains, you can set the DNS1, DNS2 and DOMAIN variables in your favorite ifcfg-eth[0-9]+ script: Hopefully the NetworkManager is all it's cracked up to be. Only time will tell of course…
$ read more →Monitoring traffic across a Solaris 802.3ad link aggregation
I manage a number of Solaris hosts that push a fair amount of data each day. These servers utilize Solaris 802.3ad link aggregations, which contain anywhere from 4 to 8 physical NICs. Monitoring the bandwidth across the links in an aggregation is a snap with Solaris, since most of the dladm subcommands support the "-s" (show statistics) option: In the example above, dladm printed the number of bytes and packets received for each link in the aggregation that was created with key number 1. While not quite as awesome as nicstat, the statistics option is handy for getting a quick overview of the number of packets and bytes traversing each link.
$ read more →Great resource for managing djbdns servers
I am in the process of setting up a couple of caching DNS servers, and decided to test out djbdns (we used it at my last job with great success). While perusing the web, I came across the life with djbdns site. This site provides a thorough explanation of djbdns, and also covers configuration in detail. If you are interested in learning how djbdns works, this site is for you!
$ read more →Enabling IPv4 forwarding on Centos and Fedora Linux servers
When I was playing around with KeepAlived, I managed to create a few HA scenarios that mirrored actual production uses. One scenario was creating a highly available router, which would forward IPv4 traffic between interfaces. To configure a CentOS or Fedora Linux host to forward IPv4 traffic, you can set the "net.ipv4.ip_forward" sysctl to 1 in /etc/sysctl.conf: net.ipv4.ip_forward = 1 Once the sysctl is added to /etc/sysctl.conf, you can enable it by running sysctl with the "-w" (change a specific sysctl value) option: If routing is configured correctly on the router, packets should start flowing between the interfaces on the server. Nice!
$ read more →Measuring TCP and UDP throughput between Linux and Solaris hosts
I have been assisting a friend with tuning his Netbackup installation. While debugging the source of his issues, I noticed that several jobs were reporting low throughput numbers. In each case the client was backing up a number of large files, which should have been streamed at gigabit Ethernet speeds. To see how much bandwidth was available between the client and server, I installed the iperf utility to test TCP and UDP network throughput…
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