LSM - Link Status Monitor

LSM is a Link Status Monitor which can be used to monitor for example a Linux router/firewall connectivity and if you happen to have multiple connections it can change routing when an up/down event happens by utilizing external script.

When a SIGUSR1 is received current connection states are syslogged.

This package is highly influenced by fping and iputils arping. Many thanks for their efforts.

LICENSE

GPLv2, you should be able to find GNU Public License 2.0 from www.gnu.org.

TODO

• Add "odd" icmp packet handling (may not be necessary)
• You can't set source ip for ping packets. It's always autodiscovered.
• Could the arping connection targets use only one socket ...
• IPv6 support.
• Should be able to check ENODEV somehow before first sendto. Now exits with error code 2 after daemon which init-script can't handle.
  • This is now changed so that ENODEV causes LOG_ERR with each ping but no exit and behave just as the packet was sent. So for ENODEV you should get a down -event just as if there was packet loss.
• The source is kind of ugly ...

DECISION MAKING

As of lsm v0.27, the detection algorithm works like this:

LSM keeps track of

1) the result of the most recent pings (up to 100)

2) the number of consecutive lost pings.

3) the number of consecutive received pings.

Let A == the number of recently lost pings

Let B == the number of consecutive lost pings

Let C == the number of consecutive returned pings

If connection (or group) is UP

AND ( (A >= max_packet_loss) OR (B >= max_successive_pkts_lost) then change the connection (or group) to down.

Else If connection (or group) is DOWN

AND ( (A <= min_packet_loss) AND (C > min_successive_pkts_rcved) ) then change the connection (or group) to up.

Note: LSM assumes each connection starts UP.

AUTHORS

Mika Ilmaranta <ilmis at nullnet.fi>

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