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C
HAPTER
 6: B
ASIC
 C
ONFIGURATION
 
OF
 P
ORTS
 
AND
 P
ATHS
Virtual Ports over Frame Relay and X.25
Frame Relay and X.25 are peer-to-peer protocols that connect two nodes 
on the network. Boundary Routing and bridging, Internet Protocol-Open 
Shortest Path First (IP-OSPF), DECnet IV, VINES, and Xerox Network 
Systems (XNS) require virtual ports because they do not provide a method 
for dealing with Frame Relay or X.25 topologies where bridge/routers are 
not directly connected to all others (full mesh). With Boundary Routing 
system architecture, when you create a virtual port over a particular path, 
each remote network attached to the Frame Relay or X.25 cloud is 
treated as a separate network.
Internet Protocol-Routing Information Protocol (IP-RIP), Internetwork 
Packet Exchange (IPX), DECnet V, and AppleTalk can operate over partially 
meshed or nonmeshed Frame Relay or X.25 topologies without the use of 
virtual ports.
The next-hop split horizon feature in IP-RIP, IPX, and AppleTalk RTMP 
allows communication between bridge/routers that are not directly 
connected to one another. To configure next-hop split horizon for these 
routing protocols, you must have a list of neighbors, which can be 
dynamically generated or manually configured in IP-RIP. Next-hop split 
horizon is configured by adding static mappings to the address mapping 
table.
You can configure dynamic neighbor learning for IPX using the CONTrol 
parameter in the NRIP, SAP, and NLSP Services.
Although it is not necessary to define virtual ports on IP-RIP, IPX, or 
AppleTalk routers in partially meshed or nonmeshed Frame Relay or X.25 
topologies, virtual ports do provide the following additional benefits:
A virtual port can be defined for each configured neighbor, which 
allows you to set up such features as filters and routing policies on a 
per-neighbor basis. 
Virtual ports provide easier control over your network, turning your 
network into several point-to-point lines.
If you want your SuperStack II bridge/router to act as an Open System 
Interconnection (OSI) router in a Frame Relay or X.25 topology, you do 
not need to create virtual ports.