From: Kinton Connelly (kinton@xxxxxxxxxxxx)
Date: Sat Apr 29 2000 - 20:43:13 GMT-3
Thanks for the explanation, Bob. Just to check my own sanity, I went back
to the routers and changed the wildcard bits on that ospf config entry to
see if anything would change. Here's what I found:
"network 137.20.25.0 0.0.0.255 area 2" gave me this in another router's
route table:
O IA 137.20.25.0/24 [110/128] via 137.20.100.34, 00:33:12, Serial0
and
"network 137.20.25.2 0.0.0.0 area 2" gave me this in another router's route
table:
O IA 137.20.25.0/24 [110/128] via 137.20.100.34, 00:00:05, Serial0
I can see how that works now - the route goes in the table based on the
subnet mask of the interface - not based on your ospf config entry.
But now I have to ask - why would you ever specify anything but 0.0.0.0 for
wildcard bits? In the same example I mentioned previously, why didn't they
just use 0.0.0.0 for all the following entries?:
> > router ospf 1
> > network 137.20.25.2 0.0.0.0 area 2
> > network 137.20.64.0 0.0.15.255 area 0
> > network 137.20.100.32 0.0.0.31 area 1
> > network 137.20.224.5 0.0.0.0 area 0
> > network 137.20.240.1 0.0.0.0 area 0
Ok, I just finished reading a little in Doyle's TCP/IP book and he cleared
it up for me some more. But I still have the question: what's the best
practice to use - when I'm in the lab, should I just use 0.0.0.0 for
everything?
Thanks,
Kinton
At 4/29/00, you wrote:
>The format "network ip-address wildmask" is used to specify which interfaces
>are in which areas. This is different from RIP, IGRP, EIGRP which use the
>network statement to say which addresses they are routing.
>
>By using the /32 format, there is no question of which interface you
>specify. Remember that the order of the network statements can affect the
>outcome when you are using the masks as other than /32. This is because for
>each interface, the network statements are scanned until a match is found,
>or there are no more.
>
>If you had an interface address of 132.10.100.1 and used the following,
>
>network 132.10.100.0 0.0.0.255 area 3
>network 132.10.100.1 0.0.0.0 area 0
>
>the interface would be in area 3, not 0.
>
>Bob Reed
>
>
>----- Original Message -----
>From: Kinton Connelly <kinton@oldmedia.com>
>To: <ccielab@groupstudy.com>
>Sent: Saturday, April 29, 2000 5:23 PM
>Subject: OSPF and wild card bits confusion
>
>
> > I've been going through the CCIE Boot Camp practice labs and just ran into
> > something that has me confused. On lab 8a, I don't understand where
>they're
> > getting the wild card bits for the OSPF areas. I've included a bit of
> > sample code from router 5 below.
> >
> > Here's what I don't understand: normally, if you give me an interface like
> > Serial1 below and tell me to put it in OSPF Area 2, I'll take the
>interface
> > address:
> >
> > 137.20.25.2/24
> >
> > and turn it into this OSPF statement:
> >
> > network 137.20.25.0 0.0.0.255 area 2
> >
> > But as you can see below, sometimes they do it this way and sometimes they
> > don't. Why? Why put it in there as "network 137.20.25.2 0.0.0.0 area 2" -
> > that would be the entry for a /32 network.
> >
> > Thanks for any help,
> >
> > Kinton
> >
> >
> > R5
> > --
> > interface Loopback0
> > ip address 137.20.240.1 255.255.240.0
> > !
> > interface Ethernet0
> > ip address 137.20.64.5 255.255.240.0
> > !
> > interface Serial0.1 multipoint
> > ip address 137.20.100.34 255.255.255.224
> > !
> > interface Serial0.2 point-to-point
> > ip address 137.20.200.17 255.255.255.240
> > !
> > interface Serial1
> > ip address 137.20.25.2 255.255.255.0
> > !
> > interface BRI0
> > ip address 137.20.224.5 255.255.240.0
> > !
> > router ospf 1
> > network 137.20.25.2 0.0.0.0 area 2
> > network 137.20.64.0 0.0.15.255 area 0
> > network 137.20.100.32 0.0.0.31 area 1
> > network 137.20.224.5 0.0.0.0 area 0
> > network 137.20.240.1 0.0.0.0 area 0
> >
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