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New Member

Advertise route as OSPF, but I see it as "EIGRP" ?

Sorry if this is a stupid question but I don't understand well why I am able to see route

D 152.1.1.4/30 on RouterD.

Basically the network 152.1.1.4/30 has been advertised via OSPF on RouterC interface. However, that was not advertised there as an EIGRP route...

How come I am able to see it on RouterD as EIGRP ?

Please find attached complete run config.

Please note I am doing one-way redistribution EIGRP->OSPF. Therefore in my view that doesn't justify the EIGRP route for 152.1.1.4/30 on RouterD.

RouterB so]===[s0 RouterC s01]===[s0 RouterD]

RouterB s0=152.1.1.5/30

RouterB S1=152.1.1.6/30

RouterD S0=152.1.2.2/24

From RouterD:

Gateway of last resort is not set

152.1.0.0/16 is variably subnetted, 3 subnets, 2 masks

C 152.1.3.0/24 is directly connected, Loopback0

C 152.1.2.0/24 is directly connected, Serial0/0

D 152.1.1.4/30 [90/2681856] via 152.1.2.1, 00:01:58, Serial0/0

6 REPLIES

Re: Advertise route as OSPF, but I see it as "EIGRP" ?

Hi,

You are inadvertently advertising network 152.1.1.4/30 via EIGRP. The network statement you have under EIGRP, 152.1.0.0/16, includes 152.1.1.4/30 and hence, the route shows up as an EIGRP route on RouterD.

You are well advised to be as specific as possible when configuring the network statements under the protocol to avoid this type of problem.

Try this config.

router eigrp 100

no network 152.1.0.0

network 152.1.2.0 0.0.0.255

You can even configure the network statement as 152.1.2.1 0.0.0.0 and that's even better.

Hope this helps!

Sundar

New Member

Re: Advertise route as OSPF, but I see it as "EIGRP" ?

Ah, Sundar. I goofed on this.

Although I had the intention to advertise it as a specific route 'network 152.1.2.0 0.0.0.255' I forgot to enter the inverse mask. That explains.

Thank you for your speedy response !!

New Member

Re: Advertise route as OSPF, but I see it as "EIGRP" ?

hi

I think it's because you are summarising the 152 network which covers your 152.1.1.4/30 subnet and since EIGRP admin distance (90) is preferred over OSPFs (110) the router is placing it in the routing table as an EIGRP learned route.

Try no auto-summary in EIGRP....and OSPF for that matter. Also your network statement in OSPF technically are incorrect...for example for the serial links which have a /30 mask they should read for example 152.1.1.0 0.0.0.3 area 0.... unless of course you want to advertise the /32 host only

New Member

Re: Advertise route as OSPF, but I see it as "EIGRP" ?

This is important:

Are you saying that the ospf advertisements

as '152.1.1.5 0.0.0.0 area 0' are incorrect then ?

If I do 'show ip route', the route learned appears as '152.1.1.4/30', which is the correct network. Doesn't it mean that for the router, it is actually optional if I do '152.1.1.4 0.0.0.3' or '152.1.1.5 0.0.0.0' ? I thought it was optional and it would give same results.

New Member

Re: Advertise route as OSPF, but I see it as "EIGRP" ?

no Im not saying it's incorrect. If you are trying to advertise 152.1.1.4/30 then yes it is incorrect.Most people would advertise the network instead of the host. Generally when you advertise a /32 host it's a loopback.

Re: Advertise route as OSPF, but I see it as "EIGRP" ?

Just one correction here.

network 152.1.1.5 0.0.0.0 area 0 is CORRECT, if the interface IP is 152.1.1.5.

The main misunderstanding encountered is: the network statement and especially the wildcard mask determine the routing updates sent. Wrong.

The only purpose the network statement serves in OSPF is to identify the IP interfaces where to send hellos and include the networks with configured mask into routing updates (LSAs).

So f.e.

router ospf 10

network 0.0.0.0 0.0.0.0 area 0

has nothing to do with a default route. it just means: "Include any active IP interface into OSPF and send hellos." Still configured network/mask would be announced correctly.

Writing this I would even recommend instead of 0.0.0.0 0.0.0.0 to use

network 152.1.1.1 0.0.0.0 area 0

because you will not unintentionally enable OSPF on an interface, where it should not start (f.e. towards ISP).

Hope this helps! Please rate all posts.

Regards, Martin

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