Re: [mif] Hybrid Access Problem

[Alexandru Petrescu <[e-mail]>]

Le 11/11/2014 05:08, Margaret Wasserman a écrit :
>
>
> Let me see if I can start a technical discussion here...
>
> If you have an ISP today that has two different access networks
> available, such as one 3GPP network and one DSL network, how do(es) the
> gateway box(es) (connected to both networks) decide where it should send
> each packet it receives?  I think there are several possible cases here;
>
> (1) There is one gateway attached to both outbound networks.  This has
> two sub-cases:
>
> (1.1) Hosts behind the single gateway have separate addresses on the two
> attached networks.  In that case, the gateway is constrained to send
> packets over the outgoing network that uses the address prefix that
> matches the source address, or the packets will be thrown away by
> ingress filters on the other side.  So, the network choice is made by
> the hosts.
>
> (1.2) Hosts behind the gateway have only one address each.  This has two
> sub-cases:
>
> (1.2.1) The gateway has separate addresses on the two networks, and does
> some sort of translation from internal to external addresses in the
> prefix of the "right" outgoing link.

I agree with most points above.

>
> (1.2.2) The gateway has only one IP address that is somehow shared
> across the two links.

I think this is hardly possible, in the context of this CPE scenario. 
Even though operators recently are able to control both cellular and DSL 
offerings to end users they really have distinct networks for each. 
'Distinct' in that they are very remote one from another in terms of IP 
hops - makes it hard to have a common IP address shared across two 
egress links of CPE.

Unless of course we speak tunnels.

> (2)  There are two gateways, each attached to a single outbound network.
>   In this case, hosts will always have separate addresses for the two
> networks, and will need to make a decision about which outbound network
> to use.

This is a difficult case as well but here I think we talk one single CPE 
with multiple egress interfaces.

I think we need to clarify this.

> Cases 1.1 and 2 are essentially the same from a host standpoint, in that
> the host needs to make a network choice.  This is a problem we have
> discussed in MIF -- What sort of information does/should the host need
> to make that choice, and how is that information communicated to the host?

And, alternatively, how does the host make such choices and communicate 
them to the network.

And, alt2, how does the CPE make choices and communicate them to its 
upper gateways.

>
> Case 1.2.1 is a typical case of how NAT (or NPTv6) can be used for
> multi-homing.  The IETF generally prefers to avoid recommending
> solutions that use NAT, but do we have a better answer?

Yes tunnelling.

Alex

>
> Case 1.2.2 becomes a layer 2 problem and is probably outside the scope
> of the IETF.
>
> Are there cases that I am missing here?
>
> Margaret
>
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