Howard, Chuck et al,
Even more strange is if you configure the loopback interface
as a point-to-point network -
e.g.
int lo0
ip address 172.16.1.1 255.255.255.0
ip osdpf network-type point-to-point
router ospf 10
network 172.16.1.1 0.0.0.0 area 0
In this configuration, the OSPF process won't use this loopback
address as the router id.
(See Advanced IP Network Design - ISBN 1-57870-097-3, Retana,
SLice and White - Cisco Press p108 for more info)
Hope this adds some to the party - I'll have a go at Howard's
challenge later when I can get onto my lab, but I suspect the
output from "debug ip ospf adjency" might help here. I have included
Howard's OSPF router ID selection table as a pointer to why I
think this will help.
Regards
Pete S.
>>SNIPed some stuff, this is HCB's bit>>
>Unless there have been recent IOS changes (I'm really most >current
in
>11-something), it's even more unpredictable than just the >highest
IP
>address:
>At the time of OSPF initialization, the router ID is:
>
> if there are multiple loopback interfaces, the highest >IP
address on any
> loopback (i.e., not highest loopback interface >number)
> if there is a single loopback interface, use its >address
> if there are no loopback interfaces, use the highest >IP
address on any
> active interface (i.e., if all interfaces are in >shutdown,
OSPF
> can't initialize. Using loopbacks avoids this >because
a loopback
> cannot be down.)
>A fiendish troubleshooting scenario:
>
>R1 comes up first, then R2. They share an Ethernet. >Neither
has
>any loopbacks.
>
>Scenario 1 (R1 is initially misconfigured)
>R1 E0: 10.6.0.1 DOWN R2 E0: 10.1.0.1 UP/UP
>E1: 10.5.0.2 UP/UP E1: 10.5.0.2 UP/UP
>E2: 10.2.0.1 UP/UP E2: 10.2.0.2 UP/UP
>
>Admin discovers that R1 E1 is misconfigured and should >have
been 10.5.0.1.
>Our Heroine corrects that interface to 10.5.0.1.
>
>Assuming both routers had OSPF configured with
>network 10.0.0.0 0.255.255.255 area 0.0.0.1
>
>Will a device on R1 E2 be able to ping a host on R2 E2?
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