Title: DECbrouter90 V10 partially meshed OSPF over X.25 example 

Product:  DECbrouter90 V10.x

Question: How do I configure OSPF to run over X.25 without requiring a Fully
Meshed Frame-Relay topology?

Solution:

        The following is an example of creating a non fully-meshed OSPF 
topology over an X.25 PSN. Normally, OSPF requires that all routers connected
to the same NBMA (Non Broadcast Multi Access) network be fully meshed. In the
below topology, this would require that BRUTA, B, and C all have VC's
established to each other. As more and more routers are added, each router is
required to have a VC to every other router, which may be cost-prohibitive.

        With DECbrouter90 V10.x, subinterfaces in different IP networks may be 
created which allow partially-meshed OSPF networks to be created over X.25 and 
Frame Relay PSN's, as in the example. This is particularly applicable to sites 
where most of the communication from the leaf sites is to a central site, 
BRUTA's ethernet LAN in this case. 




                __________________________________
                                |
                                | 172.16.1.122
                                | E0
                        ------------------
                        |                |
                        |                |
                        |                |
                        |                |
                        |     BRUTA      |
                        |                |
                        ------------------
                                | X.121 address 111111111111
                                | S0    172.16.254.1
                                | S0.1  172.16.253.1
                                |


                            X.25 CLOUD



                           /         \
                          /           \
                         /             \
        172.16.254.26  /               \  172.16.253.27 
                   S0  /                 \  S0 
   X.121 222222222222 /                   \ X.121 333333333333
                ---------               ---------
                |       |               |       |
                | BRUTB |               | BRUTC |
                |       |               |       |
                ---------               ---------
    172.16.99.126 |                         | 172.16.105.254
                E0 |                        | E0
        -------------------------       ---------




                                BRUTA's CONFIG:


BRUTA#sho conf
Using 985 out of 32762 bytes
!
version 10.2
!
hostname BRUTA
!
enable password xxxx
!
!
interface Ethernet0
description BRUTA Ethernet
ip address 172.16.1.122 255.255.255.128
no mop enabled
!
interface Serial0
ip address 172.16.254.1 255.255.255.128
encapsulation x25
bandwidth 56
x25 address 111111111111
x25 map ip 172.16.254.26 222222222222 broadcast
!
interface Serial0.1 multipoint
ip address 172.16.253.1 255.255.255.128
ip ospf retransmit-interval 8
bandwidth 56
x25 map ip 172.16.253.27 333333333333 broadcast
!
interface Serial1
no ip address
shutdown
!
router ospf 100
passive-interface Ethernet0
network 172.16.0.0 0.0.255.255 area 0.0.0.0
neighbor 172.16.253.27
neighbor 172.16.254.26
!
!
!
line con 0
line vty 0 4
login
!
end


                                BRUTB's CONFIG:



BRUTB#sho conf
Using 805 out of 32762 bytes
!
version 10.0
!
hostname BRUTB
!
enable password xxxx
!
!
interface Ethernet0
description BRUTB ethernet
ip address 172.16.99.126 255.255.255.128
!
interface Serial0
ip address 172.16.254.26 255.255.255.128
ip ospf retransmit-interval 8
encapsulation x25
bandwidth 56
x25 address 222222222222
x25 map IP 172.16.254.1 111111111111 BROADCAST
!
interface Serial1
no ip address
shutdown
!
router ospf 100
network 172.16.0.0 0.0.255.255 area 0.0.0.0
passive-interface Ethernet0
!
!
!
line con 0
line vty 0 4
login
!
end



                                BRUTC's CONFIG:



BRUTC#sho conf
Using 792 out of 32762 bytes
!
version 10.2
!
hostname BRUTC
!
enable password xxxx
!
!
interface Ethernet0
description BRUTC ethernet
ip address 172.16.105.254 255.255.255.128
!
interface Serial0
ip address 172.16.253.27 255.255.255.128
ip ospf priority 0
ip ospf retransmit-interval 8
encapsulation x25
bandwidth 56
x25 address 333333333333
x25 map ip 172.16.253.1 111111111111 broadcast
!
interface Serial1
no ip address
shutdown
!
router ospf 100
passive-interface Ethernet0
network 172.16.0.0 0.0.255.255 area 0.0.0.0
!
!
!
line con 0
line vty 0 4
login
!
end