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-externalexternal 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

Aaron Conaway

I shake my head around sometimes and see what falls out. That's what lands on these pages. If you have any questions, the best way to contact me is through Twitter at @aconaway.

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3 comments for “ROUTE Notes – IGP Redistribution

  1. Thomas Bridge
    June 21, 2010 at 9:50 pm

    Surely for OSPF the command is:

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

  2. June 21, 2010 at 11:04 pm

    hey dude,
    looks like you’re stepping it up, when do you plan on taking the exam?
    hope you enjoy the ride 🙂

  3. June 22, 2010 at 8:00 am

    Yes, it is, Thomas. Thanks for the correction.

    I’m trying, Rofi. The deadline is looming, so I’m trying to get it out of the way so I can move on to other things on my time. I’m thinking of an attempt the first full week of July. Maybe next week, though. 🙂

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