When using the BGP module in Free Range Routing, the 'network The draw back to advertising connected prefixes is that the prefix is advertised even a related interface is not 'up'. This could lead to a blackhole scenario.
A better way to handle the advertisements of connected prefixes is to use the 'redistribute connected' command.
Even with the use of this command, there may be scenarios (which I need to test at some point) where the prefix is advertised or withdrawn depending upon the link state. Free Range Routing has an additional command which could be used to ensure link state checking: 'bgp network import-check'.
There is more about the Linux state checking flags in the
Why Link-State Matters presentation from LinuxCon 2015.
In addition, the Free Range Routing developers have brought together some
relevant sysctl settings.
Monday, April 30. 2018
Linux Link State and Free Range Routing
Linux Drive Access
When a drive has lots of activity for seemingly no reason, what tools are available to troubleshoot? Here are a few possibilities.
Debian provides a tool called iotop, via the package iotop, which, by default, provides a 'top'-like experience. A different command line experience can be achieved through something like (which every 10secs prints a list of processes that read/wrote to disk and the amount of IO bandwidth used):
# iotop -o -b -d 10 Total DISK READ : 0.00 B/s | Total DISK WRITE : 0.00 B/s Actual DISK READ: 0.00 B/s | Actual DISK WRITE: 0.00 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND Total DISK READ : 0.00 B/s | Total DISK WRITE : 2041.86 B/s Actual DISK READ: 0.00 B/s | Actual DISK WRITE: 1837.68 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND 19967 be/4 root 0.00 B/s 2041.86 B/s 0.00 % 0.00 % conntrackd -C /etc/conntrackd/conntrackd.conf 14023 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % perl /usr/sbin/x2gocleansessions
More use cases are available at How to find which process is regularly writing to disk?
General statistics, which could be coupled with a 'wait', or in this case it refreshes itself with -k:
Continue reading "Linux Drive Access" »# iostat -xk 2 /dev/sdb Linux 4.14.0-0.bpo.3-amd64 (host01.ny1) 05/26/18 _x86_64_ (16 CPU) avg-cpu: %user %nice %system %iowait %steal %idle 0.31 0.00 0.66 0.09 0.00 98.94 Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util sdb 0.00 1.78 0.24 6.80 98.41 432.03 150.76 0.60 85.97 114.91 84.95 2.13 1.50
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