[Ospf-manet] Regarding MPR-OSPF
Richard Ogier <rich.ogier@earthlink.net> Mon, 19 February 2007 17:36 UTC
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Date: Mon, 19 Feb 2007 09:36:17 -0800
From: Richard Ogier <rich.ogier@earthlink.net>
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To: Philippe Jacquet <philippe.jacquet@inria.fr>
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Cc: ospf-manet@ietf.org
Subject: [Ospf-manet] Regarding MPR-OSPF
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Philippe, I noticed two possible problems with your GTNetS code for MPR-OSPF. The first one regards the following code in need_adjacency(): #ifdef OSPF6_MANET_MPR_ADJ_REDUC_OSPF_MPR if (on->ospf6_if->synchNode) return 1; if (ospf6_lookup_relay_selector(on->ospf6_if, on->router_id)) return 1; else return 0; #endif //OSPF6_MANET_MPR_ADJ_REDUC_OSPF_MPR The above code code says that the router forms an adjacency with a neighbor only if the router is a synch node or the neighbor is an MPR selector. This can cause unidirectional adjacencies, as explained below. (A similar problem with the OSPF-MDR code was discovered and corrected over a year ago.) Suppose node i forms an adjacency with node j either because node i is a synch node or node j is an MPR selector. Suppose that node j later misses a few Hellos from node i, so that node j changes the state of neighbor i to Down and then to 2-Way, without sending a Hello that indicates neighbor i is Down (or perhaps node j sends one such Hello that is not received by i). Node j does not consider node i adjacent, since j is not a synch node and i is not an MPR selector. (The need_adjacency() condition is not symmetric.) Also suppose that node i never misses any Hellos from node j (or misses only one Hello from j). Then node i will still think node j is fully adjacent, even though node j does not consider node i adjacent. Thus, a unidirectional adjacency can exist. Therefore, it is necessary for the need_adjacency condition to be symmetric. I.e., node i should consider node j adjacent if and only if node j considers node i adjacent. More specifically, need_adjacency() should also return true if the neighbor is a synch node or an MPR. (Notice that the need_adjacency condition is symmetric in RFC 2328.) The other problem I noticed regards the selection of synch routers. Your GTNetS code does not agree with your draft. In your code, only one router in the entire network (area) is selected as a synch node, i.e., the one with the largest RID. This does not agree with your draft, which says: > A router decides it is a synch router if and only if: > o the router is a wireless router that has the highest willingness > in its neighborhood (in case of ties, the router that also has the > greatest ID is elected). Also, what if the router with the largest (willingness, RID) is not a MANET router? And what if you have multiple MANET interfaces, in addition to non-MANET interfaces? I think you are safer if you consider only MANET neighbors on a given interface when deciding whether a router is a synch router (as in your draft). I realize that this would result in more adjacencies and more overhead, but it may also improve robustness. Also, if you select only a single synch router (as in your code), it is not clear how to extend this to multiple interfaces or networks that include non-MANET interfaces. Please let us know which rule you plan to use for selecting synch routers. Richard _______________________________________________ Ospf-manet mailing list Ospf-manet@ietf.org https://www1.ietf.org/mailman/listinfo/ospf-manet
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Emmanuel Baccelli
- [Ospf-manet] MPR-OSPF GTNetS simulations report Emmanuel Baccelli
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Emmanuel Baccelli
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Emmanuel Baccelli
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Emmanuel Baccelli
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Aniket Desai
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Philippe Jacquet
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- Re: [Ospf-manet] MPR-OSPF GTNetS simulations repo… Richard Ogier
- [Ospf-manet] Regarding OSPF MDR Philippe Jacquet
- [Ospf-manet] Re: Regarding OSPF MDR Richard Ogier
- [Ospf-manet] Re: Regarding OSPF MDR Richard Ogier
- [Ospf-manet] Re: Regarding OSPF MDR Philippe Jacquet
- [Ospf-manet] Re: Regarding OSPF MDR Richard Ogier
- [Ospf-manet] Regarding MPR-OSPF Richard Ogier