ROUTE Notes - IGP Redistribution

As always, feel free to correct.

Study Questions

• When you redistribute OSPF into EIGRP, what are you really redistributing?

Routes knows via OSPF
Networks of OSPF-enabled interfaces

• What’s the default cost of an EIGRP route redistributed into OSPF?

20

• What’s the default metric of an OSPF route redistributed into EIGRP?

There is none since EIGRP has all those nifty k-values that have to be processed.  Routes actually won’t redistribute without them.

• How do you set the metrics of a route redistributed into EIGRP?

Set the default metric with the default-metric subcommand
Set the metric in the redistribute … metric subcommand
Set the metric with a route-map in the redistribute … route-map subcommand

• If you have a default metric set under EIGRP and a metric set on a redistribution of OSPF, which does the router use?

The router uses the metric for the redistribution.

• What’s special about the metric when redistributing one EIGRP AS into another?

The metric is copied from one AS to the other.

• What is I redistribute one OSPF domain into another?

The same thing happens – the metric is copied from the originating domain.

• What’s the difference in AD between an EIGRP and an external EIGRP route?

EIGRP: 90
External EIGRP: 170  [Didn’t I do a blog post about this last month?]

• What’s the difference between an external type 1 and  an external type 2 OSPF route?

External 2 routes, only the external cost is used; no router increments the cost.  For external 1 routes, the external cost is incremented by each route with the internal cost.

• Which of O E1 and O E2 routes is more preferred and why?

E1s are preferred because they’re considered more accurate.  [Didn’t I blog on this last month, too?]

• I have redistribute eigrp 1 configured in my OSPF config, but 10.0.0.0/24 isn’t showing up in OSPF.  What gives?

OSPF only redistributes classful routes unless you add the subnets option to the redistribution command.

• What are the options in the redistribute directive when redistributing OSPF into EIGRP?

redistribute ospf process-id [ metric bandwidth delay reliabilityload  mtu ] [ match { internal | nssa-external | external 1 | external 2 } ] [ tag tag-value ] [ route-map route-map ]

• What are the options in the redistribute directive when redistributing EIGRP into OSPF?

redistribute ospf process-id [ metric metric ] [ metric-type metric-type ] [ match { internal |nssa-external | external 1 | external 2 } ] [ tag tag-value ] [ route-map route-map ] [ subnets ]

• What do type-4 LSAs do?

If an external route comes from another area, the ABR uses type-4 LSAs to advertise the cost of the route from the ABR to the ASBR.  Routes use this cost as a tie breaker if the internal cost is the same from two ABRs.

• What type of LSA are used to flood routing advertisements from an external NSSA area into area 0?

The NSSA ASBR uses type-7s to flood into the NSSA, but the ABR to area 0 converts those to type-5s.

What Command Was That

What command…

• …show all the EIGRP routes that originated from other routing protocols?

show ip route eigrp | inc ^D EX

• …shows all the OSPF routes that originated from other routing protocols?

show ip route ospf | incl ^O E[12]

• …show all the type-4 LSAs floating around in an OSPF area?

show ip ospf database asbr-summary

• …show the cost to get from a router to an ASBR?

show ip ospf border-routers