On Thu, Jul 17, 2014 at 10:33 PM, Dino Farinacci <[email protected]> wrote:
> On Thu, Jul 17, 2014 at 10:03 PM, Dino Farinacci <[email protected]> > wrote: > > But when an EID is assigned to a node (either static or via DHCP) > > > > Is there a case in LISP that EID would be assigned to its interface > rather than to a node? > > That is independent of LISP. Yes, in principle. But if you'd maintain the assertion (if such an assertion has ever been made) that the network elements within a site doesn't change, it would automatically assumed that - nodes in a site maintains the IP address (already) assigned, and - the IP addresses would have been assigned to the interfaces. And a node can have multiple EIDs if one chooses to do that. In fact, a > dual-stack host will have two EIDs, one IPv4 and one IPv6. > This multiple EIDs for a node is not my immediate concern in this discussion. I'm try to confine myself to the most basic model of LISP, in order better to understand it. > > Somewhere, it is said that the behavior of network elements within a > site doesn't change, which is thought to be one of the major strong feature > of LISP. If that is the case, then the EID would be assigned to the > interface like with the current Internet. > > Right, there are no requirements how EIDs are assigned locally within a > system. Remember, the EID is on a unchanged host. From that host's point of > view, it is just an address. From the LISP site's point of view, that > address is reachable via local routing. > This means... (if an EID is assigned to an interface)... the e2e transport connection would break if a node move from one subnet to another within a site. LISP doesn't contribute to solving/improving the intra-site mobility. Right? > Assuming you really meant the node, not the interface, which existing > mechanism would allow the mobility? OSPF or ISIS? > > What I meant is the "IP address" is moving. Saying it that way means no > matter how it is assigned on the local device, what is moving is the IP > address. > I'm still in the same hole. Does this IP address change when a node moves from one subnet to another or not? > > If you meant, in fact, the interface but not the node in your discussion > of the EID assignment, do you mean a MIP like mechanism would provide the > mobility within a site? > > I didn't and don't need to make that distinction. > So, you don't care about the intra-site problems at all. You focus on the inter-site routing, don't you? The whole idea of LIS(locator/id separation) is to solve, among many things, the mobility problem. To ensure that, an ID would be kept constant at moving of a node while locator would be updated at every such moving. Am I correct? However, if behavior of the all network elements within a site doesn't have to change, as asserted somewhere in the main documents, (this would mean that ARP is also at work as usual), the ID (in fact, the IP address) would change at any such moving, which would not keep the EID constant. Such move would not only break a intra-site connection but also a connection between sites. So, you cannot just ignore the intra-site problems. If the EID(IP address) has to change at every node moving across subnets within a site, the whole purpose of ID (in LIS) would be questioned. Isn't this in contradiction to the whole idea of LIS? If the EID would be kept constant even at moving within a site, then some network elements within a site have to change their behavior, don't they? Even the host behavior might have to change like, for example, shutting off the ARP operation. Also, EIDs can be flat, as with other usual LIS proposals, and need not necessarily be out of a power-of-2 EID prefix. Correct? > So in the static case, that would mean a host route would need to be > injected into the IGP if the node's address stays the same > > > > I cannot catch what you exactly mean here by 'injection'. Sorry... > > When a host 10.1.1.1 moves off subnet 10.1.0.0/16 to subnet 11.1.0.0/16, > the routers attached to 11.1 need to advertise a 10.1.1.1/32 route into > the routing system. > Got it. This is exactly what ISIS is doing, right? > So, in short, what mobility solution is provided by LISP in addition to > the existing mobility mechanisms? > > There are different scopes of mobility. When you roam across LISP site, > you use LISP mobility. You mean the tunneling..? Tunneling implicitly provides some sort of mobility... like that? > When you roam within LISP sites you use IP-mobility or host routes. > So, no additional contribution by LISP as far as intra-site mobility is concerned. Right? -- DY
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