Redistribution Overview

- Redistribution rules and guidelines:
 -- Redistributed routes cannot be redistributed again on the same router (RIP > OSPF > EIGRP)
 -- Manual Split-Horizon - Never redistribute a prefix injected from domain-A into domain-B back to  domain-A.

-- You cannot change the EIGRP external AD (170) per-route. It can only be done for all prefixes or none.
--  Sub-optimal routing in the lab is not a problem unless specified, as long as there is full reachability.
-- The redistribute command redistributes only routes which are in the router’s current IP routing table (RIB).
-- Before enabling any redistribution, make sure each protocol have full reachability within itself.
-- The metric assigned using the "redistribute metric" command takes precedence over metrics assigned with the "default-metric" command.

- When redistributing into RIP and EIGRP:
-- The metrics must be set via configuration as RIP and EIGRP have no default values.
-- RIP cannot use a 0 metric, the hop count must be between 1 and 16.
-- The 0 metric is also incompatible with the EIGRP multi-metric format.

- When redistributing into OSPF:
-- By default, routes are redistributed into OSPF as external type-2 (E2) routes, with a metric of 20.

- These logical steps happen when redistribution is enabled:
-- The router ONLY looks at the routing table to get the routes that are to be redistributed.
-- Not all the routes that the redistributed protocol sends to the routing table, will be redistributed.
-- Verify what routes, with "sh ip route " before redistribution is enabled.
-- The router takes all connected subnets matched by that routing protocol’s network commands.
-- Verify these interfaces, by looking at the redistributed protocol's network statements OR look at the individual routes with "sh ip route x.x.x.x" as listed with "advertised by".
-- Passive-interfaces for the redistributed protocol ARE included when redistributing.
-- This hidden step is the equivalent of the following: (Hidden: H>)
#router ospf 1
#redistribute rip subnets
    >redistribute connected subnets route-map NAME
    >route-map NAME permit
    >match interface fa0/0 s0/1 <--- All the RIP enabled interfaces
-- If ever asked to redistribute specific interfaces, ALWAYS INCLUDE the interfaces that the redistributed
protocol runs on.
- Mutual Router Redistribution
-- Redistributing from a low AD protocol(eg OSPF) to a higher AD protocol(eg RIP) won’t cause feedback as the lower AD is always preferred.
-- But redistributing from a high AD protocol to a low AD protocol could create problems, because the high AD protocol routes might prefer the redistributed low AD routes to a destination.