This is a great discussion! By building on IP addresses in the base protocol, PIDs can serve as either locators or identifiers, which I think is at the core of the discussion.
My intuitive visualization of PIDs is that they represent the ports (PoPs) of a giant, abstract switch. Without multihoming (connecting to multi ports) or dynamics (e.g., mobility), it is obvious that each endhost (I mean an interface, and a host with multiple interfaces are multiple endhosts) connects to only one port of the switch. Next consider multihoming, and assume two homing only for simplicity. It just means that the same endhost connects to two ports. If it is physical multihoming, the endhost should use two interface cards each with its own address (assume each interface should have a unique address) and we have no problem. But in BGP style multihoming, the same address can be announced on both ports. One clean definition is that we do not consider control-plane multihoming and assume that the routing system will pick only a single active port to reach the address (using src address is trickier, and I prefer to forget it for now). Hence, we still have the semantics of unique PID (port). This seems to be good as a first base design. One can think of a PID represent an identifier in some settings. The discussion is for a different time. Richard On Oct 28, 2013 11:08 AM, "Reinaldo Penno (repenno)" <[email protected]> wrote: > [RP] And endpoint is an application, not an IP. So, an endpoint can be > in many PIDs. > > More inline.. > > From: Wendy Roome <[email protected]> > Date: Monday, October 28, 2013 7:57 AM > To: Cisco Employee <[email protected]>, "Y. Yang" <[email protected]> > Cc: Sebastian Kiesel <[email protected]>, IETF ALTO <[email protected]> > Subject: Re: [alto] Problem with "longest prefix" rule for mapping > endpoints to PIDs > > I agree with #1 & #3. But those just move an endpoint between PIDs. > That's fine. At any given time, the endpoint is only in one PID. > > But I disagree with #2. The endpoints in a multi-homed network may have > two different routes, but they are in one PID, not two PIDs. Here's how I > look at it: if I want to send a packet to 10.0.0.1, I just tell the network > to send the packet. I do *not* tell the network the route or which gateway > to use. > > [RP] The interface and source selection address determines to a great > extend the path the packet will take through a network. Both are possible > today and with IPv6 will be much more pervasive. > > > That's the network's job. And the network does its best to hide that > from users. Similarly, an ALTO client just wants the cost from endpoint A > to B. The client doesn't want to guess the best route. That's the ALTO > server's job. > > - Wendy > > > From: "Reinaldo Penno (repenno)" <[email protected]> > Date: Mon, October 28, 2013 10:37 > To: Wendy Roome <[email protected]>, "Y. Richard Yang" < > [email protected]> > Cc: Sebastian Kiesel <[email protected]>, IETF ALTO <[email protected]> > Subject: Re: [alto] Problem with "longest prefix" rule for mapping > endpoints to PIDs > > A few points to consider. > > Yes, an endpoint can move from one PID to another in case of Mobile IP > > Yes, and endpoint can be found in multiple PIDs if it is in a > multi-homed network, I.e., a network where the gateway is connected to > multiple networks. > > Yes, and endpoint can move from one PID to another if the Gateway is > down since a host interface can be withdraw and the endpoint will move. > > Thanks, > > Reinaldo > >
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