There are good reasons for layer 3 addresses to be network interface specific.
In fact, that is how layer 3 is supposed to work. After all, each interface is potentially connected to acdifferent network. Hence, routing to those interfaces is different, and layer 3 is about routing.
The mistake instead is that TCP is not fully layer 4. They are entangled with layer 3. Specifically, a TCP socket is defined by an (IP, port) pair. Where the IP is layer 3. As such, it is fundamentally impossible to persist a TCP connection accross multiple IPs.
There is no reason for this. If instead a socket were identified as (uuid, port) then after I change my ip address, I can continue receiving packets sent to (uuid, port). And the other side will still recognize packets from me, because only my IP changed, not the connection uuid.
You'd maybe need to add some spoofing defenses, but we need those in current TCP too.
Watching people try to teach John Nagle how to do networking is half the reason why I like reading the HN forums :-).
I'm not one to defer to authority too easily, but it's my experience that, when someone with enough experience says something that sounds out of this world, it's a good idea to think about it for a bit.
Certainly, I'm convinced that neither you, nor the fine folks at BSD were/are clueless about these things. I think it's important to know why these decisions were made, and what trade-offs were involved, so that I don't get dogmatic about them.
I had no idea. This kind of stuff is why I like HN. I have no idea who the real 'celebrities' are. It feels like most of the discussion is on a pretty even ground.
Do note that SCTP is heavily used in telecom. Every network element in that world needs to be redundant, along with the multiple routes to get to each of those redundant elements. SCTP helps hide some of that from the application layers.
Yes, I think that SS7 architecture was used as some design criteria when it came SCTP. Just about everything in the telco world has (at least) an A- and a B-side for HA.
Sorry, my response was rather cryptic. I was more referring to the interface having both an L2 and L3 address. From an academic perspective, I agree with OP that assigning the L3 address to the interface probably causes more problems than it solves. MPTCP provides workaround over L4 to what is essentially an L3 problem. But it would take a huge architectural change to go back to assigning addresses to L3 hosts.
Just to provide my 2 cents on the issue:
There are a lot of things at play... Rekhter's law ("Addressing can follow topology or topology can follow addressing. Choose one.") doesn't combine well with the fact that it's not desirable to have end-hosts participate in routing updates. When these two are taken together, they have implications on scalability of any routing solution, especially in the cases of end-host mobility and multihoming.
When the "topology follows addressing" (like TCP/IP), the constraint of not wanting to advertise the end-host address (as someone mentioned, no ISP will accept your /32 on BGP) assigning the end-host a different address per attached network is the simplest solution. This indeed boils down to the assigning L3 addresses to the interface. The TCP connection problem can be handled by tunnels (as is the case in Mobile IP or LISP) but tunnels are rather expensive since the tunnel endpoint in the network has to maintain al lot of state.
In the case of "addressing follows topology", changes in topology, when taking the constraint of not advertising end-hosts via routing, requires address renumbering of the network elements.
So, when taken as a pure L3 problem, it boils down to choosing which problem to solve: constantly tracking the end-hosts, or constantly renumbering the network.
The latter, when used in combination with recursive network layering, shows quite some promise. It requires less addresses, but I know from experience that it's not the easiest idea to sell.
MPTCP provides a pragmatic workaround on top of L4 that doesn't require tunnels. It's a shame that it's not completely transparent to the applications (it requires explicit code changes to enable).I agree with a lot of the concerns of getting this upstream in the kernel. I tried to play around with it a couple of times, but the distribution as a full kernel was a bit of a roadblock. Would be easier if it was distributed as a kernel patch. And it seems perfectly doable to implement it in user space, that might further speed up adoption.
Ah, that is an interesting point. I think I see what you mean.
In my mind, L2 addresses are not for routing across organizations, and L3 addresses are. So the L2 address identifies an interface, and a L3 address identifies a routable entity. The weird thing is that there is an almost one-to-one mapping between these.
It might make sense for the same host on e.g. a WiFi and Ethernet interface off the same organization to have the same L3 address. After all, the organization responsible for routing to that host can know those interfaces belong to the same host.
However, once you get into multiple interfaces at disparate organizations things change. Take for example, a phone with LTE from some provider and WiFi from some how ISP. There are two separate organizations who are responsible for routing to those interfaces. Hence, the decisions needed to route to those interfaces differ. This makes routing based on the same address a lot harder.
I think my argument boils down to "topology follows addressing" being highly beneficial in our federated world of routing on the internet. It allows every autonomous network to handle internal routing however they want.
You are basically adding an address to TCP (the UUID) that names the host... Moreover, what happens if the connection fails during setup? A lot of edge cases here.
I am also removing the remote ip address from a socket. Hence, if you change your ip, you can just send from your new ip, include the same connection uuid, and I will still receive. You'd also need to know how to send data back. This could be done in many ways.
Biggest thing is to deal with really easy hijacks where you tell a server that your victim 's data should instead be sent to you. This is harder with the current TCP.
The mistake instead is that TCP is not fully layer 4. They are entangled with layer 3. Specifically, a TCP socket is defined by an (IP, port) pair. Where the IP is layer 3. As such, it is fundamentally impossible to persist a TCP connection accross multiple IPs.
There is no reason for this. If instead a socket were identified as (uuid, port) then after I change my ip address, I can continue receiving packets sent to (uuid, port). And the other side will still recognize packets from me, because only my IP changed, not the connection uuid.
You'd maybe need to add some spoofing defenses, but we need those in current TCP too.