„src/change-default-gw.md“ hinzufügen

Signed-off-by: Theenoro <theenoro@noreply.git.dev-c.at>

src/change-default-gw.md

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+# Change default GW 
+
+## Preparing
+
+- `MAINGW` is your main route where all traffic goes
+- `DSL` is default route to your DSL router, set the distance there to 2, and set the comment `DSL`
+- `LTE` is default route to your LTE router, set the distance there to 2, and set the comment `LTE`
+- set one route to 1.1.1.1 to your DSL router 
+
+The script will set the `DSL` GW IP on the `MAINGW` if 1.1.1.1 is reachable, if not it will change to LTE 
+
+
+```perl
+:local PingTargetOne 1.1.1.1
+:local FailThreshholdOne 3
+
+:global PingFailCountOne
+
+
+:local maingw [/ip route get [find comment="MAINGW"] gateway ];
+:local dslgw [/ip route get [find comment="DSL"] gateway ];
+:local ltegw [/ip route get [find comment="LTE"] gateway ];
+
+:set $PingResult [ping 1.1.1.1 count=1]
+:put $PingResult
+
+:if ($PingResult = 0) do={
+    :if ($PingFailCountONE < ($FailTresholdOne+2)) do={
+        :set $PingFailCountOne ($PingFailCountOne + 1)
+        :log warning "HMM Ping to $PingTargetONE failed."
+        
+        :if ( PingFailCountOne >= $FailTreshold) do={
+            :log warning "Ping Failed."
+            /ip route set [find comment="MAINGW"] gateway=$ltegw;
+        }
+    }
+}
+:if ($PingResult = 1) do={
+    :if ($PingFailCountOne > 0) do={
+        :set PingFailCountOne 0
+        :log info "Reset route to DSL"
+        /ip route set [find comment="MAINGW"] gateway=$dslgw;
+    }
+}
+```