ABR & ASBR

sumon_ahsan  Diamond  (1)
6 years 10 months ago  View: 2295  Reply: 3

Backbone router —The design rules for OSPF require that all the areas be connected through a single area, known as the backbone area, Area 0, or 0.0.0.0. A router within this area is

referred to as a backbone router. It can also be an internal router, an ASBR, or an Area Border Router (ABR). 

ABR? —This router is responsible for connecting two or more areas. It holds a full topological database for each area to which it is connected and sends LSA updates between the areas. These LSA updates are summary updates of the subnets within an area. Summarization should be configured for OSPF at the area border because this is where the LSAs make use of the reduced routing updates to minimize the routing overhead on both the network and the routers. 

? ASBR—To connect to the outside world or to any other routing protocol, you need to leave the OSPF domain. OSPF is an interior routing protocol or Interior Gateway Protocol (IGP);

gateway is an older term for a router. The router configured for this duty is the ASBR. If any routing protocols are being redistributed to OSPF on a router, the router will become an ASBR because the other routing protocols are outside the OSPF autonomous systems. Although you can place this router anywhere in the OSPF hierarchical design, it should reside in the backbone area. Because any traffic leaving the OSPF domain is also likely to leave the router’s area, it makes sense to place the ASBR in a central location that all traffic leaving its area must traverse.

This router could be configured within a single OSPF area, pointing to the outside world.

Armetta  Diamond 
6 years 10 months ago
documentation very useful for my job

gokibria  Diamond 
6 years 10 months ago
very good post..
user_2837311  Diamond 
2 years 11 months ago
useful document, thanks