The Roles Of The OSPF ASBR Cisco CCNP / BSCI Tutorial
To pass the BSCI exam & earn your CCNP certification, you've got to master the (many) details of OSPF. You might have thought there were a few OSPF details in your CCNA studies, but you'll now build on that foundation on the way to earning your CCNP.
seven such detail is the role of the Autonomous System Border Router (ASBR) in OSPF. The name itself raises some eyebrows, since you learned in your CCNA studies that OSPF doesn't use autonomous systems! as an OSPF Area Border Router borders multiple OSPF areas, the ASBR borders the entire OSPF domain & another source of routes. This can be another dynamic routing protocol, or directly connected networks that are not being advertised into OSPF by the network command.
Let's say they have a router running both OSPF & RIP version 2. By default, the RIP process won't contain any OSPF-discovered routes, & vice versa. The one separate routing processes are that - separate. If they need the other OSPF routers to know about the RIP routes, route redistribution must be configured. When the RIP routes are redistributed into OSPF, that router is then an ASBR.
In the below example, RIP subnets have been redistributed into OSPF. A seed metric is not necessary when redistributing routes into OSPF. The command "show ip ospf" confirms that this router is now an ASBR.
R1(config-router)#redistribute rip subnets
R1(config)#router ospf 1
Routing Process "ospf 1" with ID 1.1.1.1
R1#show ip ospf
Supports opaque LSA
Supports only single TOS(TOS0) routes
The ASBR can also perform route summarization on the routes being injected into OSPF with the summary-address command. (To configure OSPF inter-area summarization, use the area range command.) By mastering route summarization & route redistribution, you are well on your way to passing the BSCI exam & earning your CCNP certification!
it is an autonomous system boundary router
To pass the BSCI exam & earn your CCNP certification, you've got to master the (many) details of OSPF. You might have thought there were a few OSPF details in your CCNA studies, but you'll now build on that foundation on the way to earning your CCNP.
seven such detail is the role of the Autonomous System Border Router (ASBR) in OSPF. The name itself raises some eyebrows, since you learned in your CCNA studies that OSPF doesn't use autonomous systems! as an OSPF Area Border Router borders multiple OSPF areas, the ASBR borders the entire OSPF domain & another source of routes. This can be another dynamic routing protocol, or directly connected networks that are not being advertised into OSPF by the network command.
Let's say they have a router running both OSPF & RIP version 2. By default, the RIP process won't contain any OSPF-discovered routes, & vice versa. The one separate routing processes are that - separate. If they need the other OSPF routers to know about the RIP routes, route redistribution must be configured. When the RIP routes are redistributed into OSPF, that router is then an ASBR.
In the below example, RIP subnets have been redistributed into OSPF. A seed metric is not necessary when redistributing routes into OSPF. The command "show ip ospf" confirms that this router is now an ASBR.
R1(config-router)#redistribute rip subnets
R1(config)#router ospf 1
Routing Process "ospf 1" with ID 1.1.1.1
R1#show ip ospf
Supports opaque LSA
Supports only single TOS(TOS0) routes
The ASBR can also perform route summarization on the routes being injected into OSPF with the summary-address command. (To configure OSPF inter-area summarization, use the area range command.) By mastering route summarization & route redistribution, you are well on your way to passing the BSCI exam & earning your CCNP certification!
it is an autonomous system boundary router
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