Abr
The routers are sending different type 7 routes, but first the router R1 is redistributing static in configuration. This is used to summarize the single-attached routers. Routers with singleattachment to R1 would be learned vi a RIP. R1 will not redistribute any of the RIP-learned routes into OSPF.
R1 will only redistribute the static null route into OSPF. This way, a single PVC flap does not cause flooding of external link states. Only those RIP routes that are coming from dual-attached sites would be redistributed into OSPF because routers that are connected to the same remote sites should share specific routes. For these specific routes to be leaked between the two hub routers via OSPF, the administrative distance for RIP should be lower than that of OSPF. Otherwise, one of the routers will install the OSPF-learned route rather than the RIP routes from the remote sites.
Another method is to insert a PVC between the two hub routers, and then allow them to leak specific routes via RIP on that PVC.
In case MKS decides to run RIP on the PVC be tween the two routers, the configuration is as follows:
interface Serial 2/0 no ip address encapsulation frame-relay interface Serial 2/0.1 point-to-point ip address 10.1.252.1 255.255.255.252 interface Serial 2/0.2 multipoint ip address 10.1.252.3 255.255.254.0 router rip network 0.0.0.0
distribute-list 2 out serial 2/0.1 distribute-list 1 out serial 2/0.2 access-list 1 permit 0.0.0.0 0.0.0.0 access-list 2 permit 10.1.96.0 0.0.31.255
You can see from the configuration that both routers R1 and R2 are sending information about specific routes to RIP only on the point-to-point PVC between them. The routers are still sending default RIP routes to all the remote routers on the multipoint subinterface.
The configuration of the ABRs would be as follows:
router ospf 1
summary-address 10.1.0.0 255.255.0.0 network 10.1.254.0 0.0.0.255 area 11 network 10.4.255.0 0.0.0.255 area 0 area 11 nssa
Assume that you decided not to insert the PVC between R1 and R2 and that you will use the leak-specific routes in OSPF via type 7 LSA. ABR1 would summarize all the external LSA type 7s of the remote sites it has received from R1 and R2. For this case, R1 would send summaries 10.1.0.0/18, and 10.1.64.0/19 for dual-attached routers. R2 is sending all these external type 7s for dual-attached remote sites to 10.1.128.0/18 and 10.1.192.0/19.
With dual-attached sites, if MKS is not sharing specific routes via RIP, all the /24 from 10.1.96.0/24 to 10.1.127.0/24 would be leaked as specifics via type 7 LSA. At the ABR, type 7 could be summarized into one update for area 0. This is done by the summary-address command for OSPF at the ABR. This only could be performed by NSSA because you have the option to summarize external type 7, not only at the ASBR (where the LSA originated), but also at ABR (where the LSA changed from type 7 to type 5).
The process is simpler if the core routing protocol for MKS is Enhanced IGRP. R1 and R2 can send specific routes on the PVC, and then summarize them on the Ethernet. For the hub-and-spoke setup with dual-attached remote sites, Enhanced IGRP is much more flexible because it does not require a hierarchy. Also, filtering of information is not tied to any particular points such as ABR or ASBR.
Therefore, if MKS is running Enhanced IGRP as the core routing protocol, the configuration of R1 would be the following:
interface FastEthernet 0/0
ip address 10.1.254.0 255.255.255.0
ip summary-address eigrp 1 10.1.96.0 255.255.224.0
interface Serial 2/0
no ip address encapsulation frame-relay interface Serial 2/0.1 point-to-point ip address 10.1.252.1 255.255.255.252
interface Serial 2/0.2 multipoint ip address 10.1.252.3 255.255.254.0
passive-interface FastEthernet 0/0
passive-interface Ethernet 3/0
passive-interface Ethernet 3/1
passive-interface Ethernet 3/2
passive-interface Ethernet 3/3
network 10.0.0.0
distribute-list 1 out rip router eigrp 1
network 10.0.0.0
passive-interface Serial 2/0
redistribute static redistribute rip route-map Spoke default-metric 1 1 1 1 1
ip route 10.1.0.0 255.255.192.0 null0
ip route 10.1.64.0 255.255.224.0 null0
access-list 2 permit 10.1.96.0 0.0.31.255
route-map Spoke match ip address 2
In this configuration, R1 has redistributed the single-attached sites via the static route, and then has redistributed the dual-attached sites into Enhanced IGRP via route-map Spoke. Ethernet R1 is sending an Enhanced IGRP summary. Note that the distance command from RIP is missing because Enhanced IGRP redistributes routes with an administrative distance of 170, which is higher than RIP's.
Continue reading here: On Demand Routing
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