Multihome

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SeeCwriter
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Multihome

Post by SeeCwriter » Thu Apr 29, 2021 3:20 pm

Is there any documentation about what multihome is and how to use it, beyond what is said in example program MultiHome?

Also, what is the difference between Multihome and AutoIP?

I'm using v2.9.5, with the MOD5441X.

SeeCwriter
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Joined: Mon May 12, 2008 10:55 am

Re: Multihome

Post by SeeCwriter » Fri Apr 30, 2021 11:44 am

I found some information on MultiHome in the Programmers Guide. That helped. But it didn't explain the difference between MultiHome and AutoIP. Why would I want to use one over the other?

In any case, I built the MultiHome example and ran it on a MOD5441X. The terminal printout shows the DHCP address and the MultiHome address, but it has 0.0.0.0 for an AutoIP address, which I would expect since the example doesn't set it as far as I can see. When I open the webpage via the DHCP address, it displays the same IP addresses but it shows a AutoIP address of 169.254.125.23. Where did that come from? I can open the webpage using the AutoIP address but not the multihome address. My initial thought was that was normal because the multihome address is not compatible with my network. But then neither is the AutoIP address. So is there something special about the AutoIP address? I searched all the netburn include files and can find nothing about a default AutoIP address.

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pbreed
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Re: Multihome

Post by pbreed » Mon May 03, 2021 5:29 am

Autoip and Multihome are conceptually differnt...

Autoip is for automatically assigning an IP address when none is set and no DHCP server existis....
Think Laptop to board with direct cable...

MultiHome is for when you need the board to have more than one IP Address...
IE you want it to have whatever DHCP assigns, and you want an additional static IP that never changes...(probably on a totally different subnet.)

SeeCwriter
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Re: Multihome

Post by SeeCwriter » Mon May 03, 2021 7:21 am

That makes sense. In the example program, where did the AutoIP address come from? The module was connected to a DHCP server and received an IP address, and AutoIP also got an IP address from somewhere.

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pbreed
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Re: Multihome

Post by pbreed » Mon May 03, 2021 7:32 am

They way autoip works, is the module picks one...
the asks the network (using arp) if anyone has that address...
Does this twice and waits for a response...
If this times out with no one saying they already claim the address it marks it as good...
If someone else says they are using that address, it picks another and tries again...

SeeCwriter
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Re: Multihome

Post by SeeCwriter » Mon May 03, 2021 8:10 am

Is that the way AutoIP is suppose to work or is that just the way Netburner implemented it? I only ask because in searching online for AutoIP some were saying that it only comes into play if there is no DHCP server, in which case AutoIP would then assign an address.

Also, it appears as if AutoIP is enabled by default, and that my program has been getting AutoIP addresses all along even though MULTIHOME was undefined. Is that correct?

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pbreed
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Re: Multihome

Post by pbreed » Mon May 03, 2021 12:54 pm

Most PC's don't start the autoip dance unless they find no DHCP server.
This is not a requirement of the autoip specification, so if AutoIP is enabled we just always select one.

Yes you get an autoip address...is autoip is enabled even if multihome is not..

SeeCwriter
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Re: Multihome

Post by SeeCwriter » Tue May 04, 2021 9:02 am

Sorry to keep peppering you with questions. But I have what I hope is the last one.

When I disconnect the module from the network and rebooted it, it still has the same AutoIP address of 169.254.125.23. I thought maybe it would be 169.254.0.0. Is that because the previous address was saved, or does it start testing addresses at that address?

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pbreed
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Re: Multihome

Post by pbreed » Tue May 04, 2021 6:10 pm

It uses its MAC address (which is supposed to be unique) to seed the Autoip value...
So if a herd of NetBurners all come up they will each,most likely, pick different non-conflicting autoip values.

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