An exterior route (redistributed from one other routing protocol, static route or related route) will likely be tagged as a Kind 5 LSA (E route). This LSA is circulated all through the OSPF area apart from Stub, Completely Stubby and Not-so-stubby areas.
Exterior routes are propagated by an OSPF space as a kind 5 from an ASBR, or kind 7 LSA from an ASBR in an NSSA. These routes from outdoors the OSPF area, can both be E1 or E2 routes and they’re handled in barely other ways. On this article we are going to talk about the distinction E1 vs E2.
E1 or Exterior Kind Routes –
The price of E1 routes is the price of the exterior metric with the addition of the interior price inside OSPF to achieve that community.
E2 or Exterior Type2 Routes –
The price of E2 routes will all the time be the exterior metric, the metric will takes no discover of the interior price to achieve that community.
If 2 exterior kind 2 routes exist with the identical metric to the identical vacation spot the route with the lowest metric to the ASBR will is used. Additionally if an E1 and E2 route exist to the identical vacation spot the E1 route will all the time be most popular no matter the metric.
Associated- OSPF N1 and N2 Routes
OSPF Exterior E1 vs E2
Mainly the distinction between E1 and E2 exterior routes is:
E1 consists of – the interior price to ASBR added to the exterior price,
E2 doesn’t embrace – inner price. it’s similar as exterior price.
Beneath Diagram will assist in understanding how OSPF E1 and E2 exterior routes are calculated exterior routes inside the OSPF area –
Associated – OSPF Price Calculation
Community 10.1.1.0/24 will likely be redistributed on R3 into OSPF area with seed metric (price) of 20. This holds true for each E1 and E2 routes.
Now, when R2 must calculate metric/price to community 10.1.1.0/24, E1 and E2 route price computation will likely be totally different as illustrated –
For E1 Route Price –
R2 will calculate the metric or price between R2 and R3 and add to the seed price marketed by R3. Therefore, on this case, E1 price for R2 shall be = Price from R2 to R3 + Seed price = 1 + 20 = 21.
For E2 Route Price –
R2 will calculate the metric or price to achieve community 10.1.1.0/24 by solely contemplating the seed price and won’t add R2-R3 path price. Therefore, on this case, E2 price will likely be = Seed price = 20.
In the identical approach, R1 will calculate E1 and E2 price for Community 10.1.1.0/24 as –
For E2 Route Price = 20
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