Resolving Reachability Be ...
    26 March 08

    Resolving Reachability Between Spokes in a Hub and Spoke Frame-Relay Network

    Posted byINE

    A common question that I get from students in class is what are the options to resolve spoke to spoke reachability in a Frame-Relay network. Below are your "standard" choices in order of preference:

    1) Use point-to-point subinterfaces on the spokes.  This option is preferred as all IP addresses on the subnet will automatically be mapped to the DLCI that is bound to the subinterface.
    2) Multipoint interfaces (physical or multipoint subinterfaces) on the spokes with Frame-Relay mappings pointing to the hub's DLCI to reach the other spokes.
    3) Multipoint interfaces on the spokes along with using the OSPF point-to-multipoint network type on all routers on the subnet. Each end point will advertise out a /32 and this advertisement will be relayed to the other spokes by the hub. This is exactly what the OSPF point-to-multipoint network type was designed for (full layer 3 reachability in a network that doesn't have full layer 2 connectivity.
    4) Use PPP over Frame-Relay (PPPoFR). By using PPPoFR IP will now be running over PPP and not directly over Frame-Relay. This means that IP sees everything as point-to-point links and no layer 3 to layer 2 mappings are needed.
    5) Static /32 routes on the spokes point to the hub to reach the other spokes. Not a pretty solution but it will resolve the reachability issue.

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