From: Mike Harrison (michael.h4@blueyonder.co.uk)
Date: Sat May 10 2008 - 07:22:54 ART
Geert
I see what you are asking - The default route that is generated by the ABR
for the stub area, is not a candidate to go into the ABRs routing table. I
believe this is because it is a self generated summary and these routes are
not eligible for inclusion in the route table. So the type 5 external
default route would always be selected.
sh ip ospf data summary self-originate
OSPF Router with ID (150.1.4.4) (Process ID 1)
Summary Net Link States (Area 45)
LS age: 1274
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 0.0.0.0 (summary Network Number)
Advertising Router: 150.1.4.4
LS Seq Number: 80000001
Checksum: 0x2A74
Length: 28
Network Mask: /0
TOS: 0 Metric: 1
Mike
----- Original Message -----
From: "Geert Nijs" <Geert.Nijs@simac.be>
To: "Mike Harrison" <michael.h4@blueyonder.co.uk>; <ccielab@groupstudy.com>
Sent: Friday, May 09, 2008 10:10 PM
Subject: RE: OSPF area question
Yes. I understand that in any router in the stub area there will only be the
type 3 lsa default.
But what about on the ABR itself ?
regards,
Geert
________________________________________
From: Mike Harrison [michael.h4@blueyonder.co.uk]
Sent: 09 May 2008 22:04
To: Geert Nijs; ccielab@groupstudy.com
Subject: Re: OSPF area question
Geert
Type 5 lsas wouldnt be allowed in a stub area ? The default route would be a
type 3 lsa and therefore always an inter area route.
Mike
----- Original Message -----
From: "Geert Nijs" <Geert.Nijs@simac.be>
To: <ccielab@groupstudy.com>
Sent: Friday, May 09, 2008 4:01 PM
Subject: OSPF area question
> Hi group,
>
> I was wondering how an OSPF router would react in the following case.
> Suppose you have an ABR router between area 0 and area 1100 (stub
> no-summary area).
> This router generates a default route into area 1100 as an intra-area
> route.
>
> Suppose this router also receives a default route from area 0 as an
> External route (LSA 5).
> What will be put in the routing table of this ABR ? The OSPF database
> would look like:
>
>
> Summary Net Link States (Area 1100)
>
> Link ID ADV Router Age Seq# Checksum
>
> 0.0.0.0 10.216.157.1 1334 0x80006654 0x0061A1
>
> 0.0.0.0 10.216.157.2 1336 0x800074D3 0x003242
>
>
>
> Type-5 AS External Link States
>
> Link ID ADV Router Age Seq# Checksum Tag
>
> 0.0.0.0 192.168.1.32 1238 0x80012829 0x0057F8 1
>
> 0.0.0.0 192.168.1.43 1513 0x80008D14 0x0013E2 1
>
>
>
> The router should put the external in its routing table (and probably
> will), but
>
> doesn't a summary (intra-area) take precedence over an external link
> (inter-area) ?
>
> Or will the router see that the summary intra-area route is generated by
> itself
>
> and therefore not put it in the routing table (avoiding blackholing) ?
>
> What if there is a redundant router present also advertising this default,
> maybe
>
> it will except this one over the external ones ?
>
>
>
> regards,
>
> Geert
>
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