[FS#1184] Gateway bug when using multiple network IPs (VLANs)

[LEDE Bugs]

The following task has a new comment added:

FS#1184 - Gateway bug when using multiple network IPs (VLANs)
User who did this - Jo-Philipp Wich (jow-)

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There may only be one "option gateway" on the system which denotes the default route to use for non-subnet traffic.

If the gateway is within the interface subnet, ARP resolution is used to find peer hosts and an explicity gateway must not be provided.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=1184#comment3900