This is an annotated version of the Lua device control script that was shown in last week's PowerHour about Restorepoint automation.
The objective was to connect to a Cisco IOS device, identify any GigabitEthernet interfaces whose current MTU was >1500, and then configure those interfaces to use an MTU of 1500. We can do this by running the "show interfaces" command and processing the output. Here is the script I described during the PowerHour:
timeout (10)
-- Run the "show interfaces" command, collect the output, and store that output
-- as a list of text lines.
sendget("show interfaces","#")
output = before()
lines=splitlines(output)
-- Start looping through the output lines.
for i,line in pairs(lines) do
-- Look for lines like "InterfaceName is up|down, line protocol is up|down".
if line:match(".* is [a-z]+, line protocol is [a-z]+") then
-- When we find one, save the interface name as intf.
intf=line:match("^(.*) is [a-z]+, line protocol is [a-z]+")
mtu=nil
end
-- If we find a line with MTU data, convert the MTU to a numeric value and save it.
if line:match("MTU") then
mtu = tonumber(line:match("MTU ([0-9]+) bytes"))
-- Check if the interface meets our criteria of being a GigabitEthernet interface
-- with a current MTU above 1500.
if intf:match("GigabitEthernet") and mtu > 1500 then
-- If it is, execute the Cisco IOS commands to change the configuration. We use a local
-- variable 'in_config_mode' to avoid going in/out of config mode multiple times.
if not in_config_mode then
sendget("conf terminal","#")
in_config_mode = true
end
sendget("int "..intf,"#")
sendget("mtu 1500","#")
sendget("exit","#")
print("Changed MTU on "..intf.." from "..mtu.." to 1500 bytes")
end
end
end
-- Finally, exit from config mode if needed.
if in_config_mode then
sendget("exit","#")
end
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