Re: [Dime] [RFC3588bis-34] - Host-IP-Address AVP

Ralph Loader <suckfish@ihug.co.nz> Mon, 24 September 2012 19:31 UTC

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Date: Tue, 25 Sep 2012 07:31:50 +1200
From: Ralph Loader <suckfish@ihug.co.nz>
To: Glen Zorn <glenzorn@gmail.com>
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Subject: Re: [Dime] [RFC3588bis-34] - Host-IP-Address AVP
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> The draft says:
> 
>     The Host-IP-Address AVP (AVP Code 257) is of type Address and is used
>     to inform a Diameter peer of the sender's IP address.
> 
> Suppose that I send, instead of one address, three (assuming the use of 
> TCP).  Which one do you use?  What if the list doesn't contain the 
> address from which the CEr/CEA command was sent?

There are other problems with using the AVP to obtain IP addresses:

1.  The set of IP addresses assigned to a machine can change.  Unlike proper protocols for distributing IP addresses, the capabilities exchange has no mechanism for handling that.

2.  There is no guarentee that a particular IP address of a machine is accessable from a peer (address scoping, firewalling, NAT...).

I don't see any reason for Diameter to reinvent the wheel in distributing IP addresses.

Just leave the field as advisory for logging / debugging purposes (ditto all the other underspecified fields in the capabilities exchange, for that matter).

Cheers,
Ralph.


>  If my solution to 
> transport failure is to send you three addresses assuming that you'll 
> try them sequentially and you don't understand that, my scheme fails and 
> since you only have one registered address for me, this could cause a 
> much longer outage than if my network admins just did their job and 
> registered all the available addresses in the DNS.
> 
> >>
>  >
>  > I don't have a specific error in mind. My intent was to point out
>  > that while there may be interesting things you can do with
>  > Host-IP-Address (like the example you gave), anything that requires a
>  > mutual understanding between the client and server aren't going to
>  > work unless the understanding exists. In you example, using
>  > Host-IP-Address to tell the peer about other available addresses to
>  > be used for load balancing and/or failover won't work across
>  > implementations unless it's documented somewhere.
>  >
>  > The original poster pointed out that they were seeing real IOT issues
>  > because different implementors interpreted the spec differently in
>  > regards to Host-IP-Address. Assuming that these differences were due
>  > to reasonable interpretations of the spec, rather than simple
>  > misunderstandings, that's a pretty big indicator that there's a
>  > problem.
> 
> I would be inclined to write a short draft clarifying that, in the case 
> of TCP, exactly one instance of the Host-IP-Address MUST be included in 
> the CER/CEA messages.
> 
> ...
> 
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