Route Redistribution in EIGRP

Redistribution is technique using which the boundary routers connecting different routing domains can exchange and advertise routing information. In this article we will learn how to redistribute any routing protocol into EIGRP. Below syntax is followed. The command has to be configured in router configuration mode.

redistribute protocol [process-id] [metric metric-value] [match route-type] [route-map name]

Description:
  • protocol: For example the protocol you want to redistribute into EIGRP (i.e. OSPF, RIP, or BGP etc.)
  • process-id: This field is specifically used while redistributing the protocols OSPF and BGP into EIGRP. The value of this field is AS number in case of BGP and  process-id in case of OSPF. This field is not required for RIP and ISIS.
  • metric: This is an optional field  that specifies the EIGRP seed metric, in the fixed order of bandwidth, delay, reliability, load, and maximum transmission unit (MTU), for the route going to be redistributed. When redistributing other protocol routes into EIGRP (other than ISIS), if this metric value is not specified and  also if no value is specified using the 'default-metric' router configuration command, the default metric is 0. The routes will not be redistributed because like RIP, EIGRP also considers the 0 metric as infinity. In EIGRP, the metric is calculated based only on bandwidth and delay by default.
  • match/route-type: This is an optional field and specifically used while redistributing OSPF into RIP. Three types of routes exist in OSPF namely Internal (that are internal to an OSPF domain), External type-1, External type 2, or NSSA-External.
  • route-map: This is again an optional field and used when when we have to do any route filtering while redistribution.
Imp Point: When redistributing routes from other routing protocols into EIRGP, the routes are denoted by D EX and the Administrative Distance (AD) of the redistributed routes 170 compared to internal EIGRP routes that are denoted by D and have AD value of 90. Because of their higher AD, EIGRP external routes are less preferred than EIGRP internal routes.


R2(config)#router eigrp 10
R2(config-router)#redistribute ospf 1 metric 10000  100  255  1  1500 route-map FILTER

Imp Point: Kindly also note that you have to configure the the route-map 'FILTER'. An empty route-map or wrong route-map configured will not allow redistribution of routes.

Below is description of EIGRP metric fields:


Using above topology given in beginning of the this article, let's try a simple redistribution of OSPF into EIGRP.

R2(config)#router eigrp 10
R2(config-router)#redistribute ospf 1 metric 10000  100  255  1  1500

Or if you don't want to specify metric specifically while redistributing OSPF but a general reference value for all protocols, we can explicitly use 'default-metric' router configuration command to specify the metric.

R2(config)#router eigrp 10
R2(config-router)#redistribute ospf 1 
R2(config-router)#default-metric 10000  100  255  1  1500


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