Title: DECbrouter90 - DECnis interop: Frame Relay mulitpoint .vs. pt-to-pt.

Product: DECbrouter90 V9.14/V10.x

Question:

        I'm trying to route OSI using IS-IS across frame relay between a
DECbrouter90 and a DECnis. Are there Frame Relay interoperability issues I 
should be aware of?

Solution:
       
      On the DECbrouter90, unless you use subinterfaces which are explicitly 
    designated as "point-to-point" (see other Tech Tips for configuration
    examples), the DECbrouter treats the frame-relay serial port as a
    "LAN" or "multipoint" interface, for the purposes of routing protocols.
    Unfortunately, the Frame-Relay specifications did not specify how to treat
    a Frame-relay circuit, and different vendors implemented their Frame Relay
    products differently.
  
      If the frame-relay circuit is multipoint, or "LAN" encapsulated, then 
    protocols such as IS-IS or OSPF which discriminate between
    WAN and LAN interfaces (i.e., they use different message types for
    handshaking, adjacency monitoring, etc., depending on whether the circuit
    is a point-to-point "WAN" or multipoint "LAN" circuit) will not 
    work between the DECbrouter90 and the DECnis, which has always treated 
    the FR circuits as point-to-point "WAN" circuits. Protocols which do *not* 
    discriminate between WAN and LAN circuits (such as IP-RIP or Spanning-tree,
    either DEC or 802.1d) should interoperate between the BRUT and the DECnis 
    even if the circuit is not designated as point-to-point on the
    DECbrouter90.
    
       Beginning in 10.0 (actually, IOS 9.21, but that was never released for
    the DECbrouter) cisco IOS supports subinterfaces, and these can be
    designated "point-to-point". On point-to-point subinterfaces, the
    DECbrouter will use the same WAN message types as the DECnis for ISIS
    circuit initialization, and they should become adjacent without requiring 
    static routes. DECbrouter V9.14 only supports multipoint, or "LAN" 
    encapsulation, and static routes must be used.
    
        Another consideration is the data encapsulation chosen for the
    circuits. The DECnis will run either CHDLC or PPP encapsulation on FR
    circuits; the DECbrouter only supports CHDLC or ietf (rfc1294/1490,
    depending on version). To interoperate, you must configure the DECnis
    to support CHDLC encapsulation, which is the default for the DECbrouter. 
    You also need to be sure that your lmi type matches your FR provider's 
    (ansi annexD, cisco (default), or Q933a), and that your keepalive interval 
    matches the provider's.

        If you are using the DECnis and DECbrouter in a mixed DECnet
    PhaseIV/PhaseV environment, see the Tech Tip which discusses DECnet
    PhaseIV/V interoperability issues.