What is E1 and E2 routes in OSPF?
What is E1 and E2 routes in OSPF?
E1 routes indicate cumulative cost to reach the destination i.e. int indicates cost to reach ASBR + cost to destination from ASBR. E2 route reflects cost only from the ASBR to destination. This is the default used by ospf for redistribution.
What is OSPF E2 route?
OSPF External Routes (E2) are advertised into OSPF Autonomous System with a particular cost and the cost is not changed throughout the AS. The routes are learned via redistribution of other routing protocol or static route or a connected subnet. By default, all OSPF routes learned via redistribution are of E2 type.
Which route is preferred E1 or E2?
You can have ASBR 1 inject the external route as E1 and ASBR 2 inject the same external prefix as an E2 route. Due to the order of operations of OSPF, the E1 route will always be preferred regardless of the cost to the ASBR. But in case of single point of redistribution, it doesn’t matter what route type you use.
What are E1 routes in OSPF?
E1 routes will have internal area costs added to the seed metric. Use external type 1 (E1) routes when there are multiple Autonomous System Border Routers (ASBRs) advertising an external route to the same autonomous system to avoid suboptimal routing (see Figure 4-1).
What is the difference between OSPF external type 1 and type 2?
Type 1 external metrics are equivalent to the link-state metric, where the cost is equal to the sum of the internal costs plus the external cost. Type 2 external metrics use only the external cost to the destination and ignore the cost (metric) to reach the AS boundary router.
What is a Type 1 LSA?
Type 1 – Router LSA – the router announces its presence and lists the links to other routers or networks in the same area, together with the metrics to them. Type 1 LSAs are flooded across their own area only. The link-state ID of the type 1 LSA is the originating router ID.
What is OSPF external type1?
OSPF supports two types of external metrics: Type 1 and Type 2. The difference between the two metrics is how OSPF calculates the cost of the route. Type 1 external metrics are equivalent to the link-state metric, where the cost is equal to the sum of the internal costs plus the external cost.
How does OSPF choose best path?
If there are multiple routes to a network with the same route type, the OSPF metric calculated as cost based on the bandwidth is used for selecting the best route. The route with the lowest value for cost is chosen as the best route.
What is E1 route?
What is OSPF type1?
What are the E1 and E2 routes in OSPF?
E1/E2 routes in OSPF. In OSPF we have 2 types of external routes. E1 and E2. For example. R1#show ip route. Codes: C – connected, S – static, I – IGRP, R – RIP, M – mobile, B – BGP. D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area. N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2.
What’s the difference between E1 and E2 external routes?
E1 vs E2 external routes. External routes fall under two categories, external type 1 and external type 2. The difference between the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
Can a OSPF E2 be redistributed to an ASBR?
If you have an ASBR or two redistributing E2 routes into an OSPF autonomous system (not just an area, but the whole AS), every router that gets the route will see the route with whatever metric you configured for it on the ASBR.
Which is the default route type in OSPF?
E2 is the default route type for routes learned via redistribution. The key with E2 routes is that the cost of these routes reflects only the cost of the path from the ASBR to the final destination the cost of the path from R4 to R1 is not reflected in this cost. (Remember that OSPF’s metric for a path is referred to as “cost”.)