Re: [mpls] New Version Notification for draft-kompella-mpls-larp-02.txt
Bhupesh Kothari <bhupesh@gainspeed.com> Mon, 03 November 2014 19:29 UTC
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Date: Mon, 03 Nov 2014 11:28:46 -0800
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From: Bhupesh Kothari <bhupesh@gainspeed.com>
To: Kireeti Kompella <kireeti.kompella@gmail.com>
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Subject: Re: [mpls] New Version Notification for draft-kompella-mpls-larp-02.txt
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Hi Kireeti, > > Hi Bhupesh, > > > On Oct 30, 2014, at 14:02 , Bhupesh Kothari <bhupesh@anvaya.net> wrote: > > Hi Kireeti, > > Can you describe how L-ARP can be used between a DSLAM and its upstream > router to form bi-directional tunnels? I want to understand what, if any, > assumptions are made. > > > L-ARP is for the DSLAM (or server, or whatever) to talk to a BNG (or remote > server). For the reverse direction, one possibility is “labeled DHCP”. A > quick overview is that when a DSLAM X asks for an IP address, it also says, > allocate a label for me. The upstream node (switch/BNG/CMTS) Y then allocates > a label, which it advertises to reach X. That would establish bidirectional > connectivity. If you have X and Y to begin, the solution works. But that is not always the case. Take a L2 CMTS for example. It has an IP address but only for management, and is either connected on a separate physical network for management or the management traffic is in-band on a management VLAN. For customer data traffic, which is what I want to tunnel, it does not have visibility into what (and how many) upstream routers are and is just a bridge in the data path. In other words, for label exchange is such a scenario, ARP semantics does not fit well, especially in the reverse direction. > > To establish hierarchical tunnels, I would recommend L-BGP (RFC 3107). Two > possibilities: The X announces this label (with next hop Y); or Y announces > this label with itself as next hop. In the former case, the L-DHCP reply needs > to have a label for X to advertise. > > If this makes sense (and interests you), I’d be happy to collaborate with you > on the L-DHCP draft. Interested. Let me give you my general comments on the whole draft, and see if I am on the same page. Agree on the need for a simpler label distribution protocol in certain scenarios. Modeling the protocol as stateless with simple semantics is highly desirable in such cases. There are two key functions: endpoint discovery and label exchange (including service labels). The L-ARP message format though is biased for host use case. For example, a host knows (either static, DHCP or NDP as in v6) what its default gateways are. It also understands what subnets imply. But in the label exchange process for L2 topologies where nodes are connected over an Ethernet fabric, such semantics might not be applicable. Traffic entering into the tunnel could be based on some identifier other than IP destination such as a DOCSIS channel. In such a case, I am not looking to "resolve" an IP address. You might say that in this case for all traffic, I am looking to resolve the default gateway. Re-using (hijacking ;-)) ARP Ether type does not buy you much. Intermediate nodes on an Ethernet fabric does not care for Ether Type. The end nodes that consume ARP anyway needs the new functionality. I agree that re-using a Ether type saves some changes relatively, but hardware type in ARP, IMHO, is still intended for resolution and not for a new need. Label exchange sounds like a new protocol. One common use case I have is creating bi-directional tunnels between access nodes and all routers. In addition, there is a need to create multiple tunnels (PWs is more appropriate) between a pair of access node and its upstream routers for different traffic types. The topology fits your applicability. > > Kireeti. Bhupesh
- [mpls] Fwd: New Version Notification for draft-ko… Kireeti Kompella
- Re: [mpls] Fwd: New Version Notification for draf… Bhupesh Kothari
- Re: [mpls] New Version Notification for draft-kom… Kireeti Kompella
- Re: [mpls] New Version Notification for draft-kom… Bhupesh Kothari