Beware CARP !! (or, very similarly, HSRP or VRRP).
In essence, there are a number of routers, which share a single MAC
address - and it is passed between them (so there is always one active
router and only it responds to the shared MAC address). Meanwhile they
each use their own MAC address to run their routing protocols, and the HSRP.
Gives fast, easy and transparent fail-over (but with some pitfalls), so
AFAIK not very widely used.
Alex.
P.S. within Cisco, the engineering name for this was CRAP - but
pressure form the marketing guys changed it, initally to CARP, and then
to HSRP before it was released.
On 22/10/2019 19:05, Bob Sneidar via use-livecode wrote:
Hi all.
MacOS only for now.
I think I put together a way to tell if the default network has changed since
the last time an internet connection took place. It's no good of course, just
getting the IP address, as given an identical subnet, you have a 1 in 254
change of getting the same IP address on a different network. We want to be
absolutely certain.
Similarly, the gateway, subnet mask and DNS might also be identical. Finally,
the only adapter we care about is the one that is being used as the default
route to the internet or local resources. (there may be more than one active
adapter, as in the Ethernet and Wireless adapters).
The trick is to get the MAC address of the router, then store it and compare it
each time you attempt to communicate. Here's what I came up with. Feel free to
chide me if I am overthinking this:
on mouseUp
put "route get default" into tShellCommand
put shell(tShellCommand) into tDefaultAdapter
put lineOffset("Interface: ", tDefaultAdapter) into tInterfaceLine
if tInterfaceLine = 0 then
answer info "No default interface found!" as sheet
exit mouseUp
end if
put word 2 of line tInterfaceLine of tDefaultAdapter into tDefaultInterface
put "ipconfig getpacket " & tDefaultInterface into tShellCommand
put shell(tShellCommand) into tInterfaceDetail
put lineOffset("router (ip_mult): ", tInterfaceDetail) into tRouterLine
put word 3 of line tRouterLine of tInterfaceDetail into tRouterAddress
put char 2 to -2 of tRouterAddress into tRouterAddress
put tRouterAddress
put "arp " & tRouterAddress into tShellCommand
put shell(tShellCommand) into tArpReply
put word 4 of tArpReply into tDefaultMACAddress
end mouseUp
Bob S
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