From: Scott M Vermillion (scott_ccie_list@it-ag.com)
Date: Tue Nov 18 2008 - 23:46:44 ARST
Hey Pavel,
I gotta run just now so I won't be around to carry the conversation on for
at least several hours, if not until tomorrow, but I've read and re-read
your final statement below:
> This refers to RIP and EIGRP protocols which do redistribute default route
automatically, if "ip default-network" command is present.
Trying to figure out if I'm misreading you or if I disagree with what you've
said. The whole *default-network* thing tends to get slightly convoluted if
you're not somewhat careful about the use of the terms "redistribute,"
"propagate," "generate," "default-network," and "0.0.0.0/0." The original
question, as I understood it, had to do with *redistribution* of RIP into
OSPF, and the subsequent *generation* and *propagation* (or lack thereof) of
*0.0.0.0/0* into OSPF - not anything to do with a *default-network*, per se.
Example lab I just threw up (and, in retrospect, I confess that a better lab
would have had an additional router Rd out to the right of Rc for a couple
of different reasons, but I'm in a bit of a rush this afternoon and this was
something I had handy):
Ra <-> 192.168.1.0 <->Rb<->192.168.2.0<->Rc
I run RIP on 192.168.1.0/24 between Ra and Rb. I run OSPF on 192.168.2.0/24
between Rb and Rc. On Rc I issue the following under OSPF config:
'default-inf orig always'
On Rb I see the following:
Rb(config-router)#do sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static
route
o - ODR, P - periodic downloaded static route
Gateway of last resort is 192.168.2.2 to network 0.0.0.0
C 192.168.1.0 is directly connected, Serial0/0
192.168.2.0/30 is subnetted, 1 subnets
C 192.168.2.0 is directly connected, Serial0/1
O*E2 0.0.0.0/0 [110/1] via 192.168.2.2, 00:00:10, Serial0/1
On Ra, thus far, I see:
Ra#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static
route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.1.0/30 is subnetted, 1 subnets
C 192.168.1.0 is directly connected, Serial1/0
Now on Rb I issue the following under RIP config:
Rb(config-router)#redist ospf 100 met 8
Now on Ra I see:
Ra#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static
route
o - ODR, P - periodic downloaded static route
Gateway of last resort is 192.168.1.2 to network 0.0.0.0
192.168.1.0/30 is subnetted, 1 subnets
C 192.168.1.0 is directly connected, Serial1/0
R 192.168.2.0/24 [120/8] via 192.168.1.2, 00:00:01, Serial1/0
R* 0.0.0.0/0 [120/8] via 192.168.1.2, 00:00:01, Serial1/0
Note the following on Ra and Rb:
Ra#sh run | inc default-network
(no output)
Rb#sh run | inc default-network
(no output)
Now, just to round things out (and wind up back where the OP was), if I flip
the whole thing around, eliminate the 'default-inf orig always' on Rc, do an
'ip route 0.0.0.0 0.0.0.0 nul0' on Ra, redistribute static into RIP on Ra,
then redistribute RIP into OSPF on Rb, I see no default route on Rc until I
issue the 'default-inf orig' on Rb. Also note that my static *0.0.0.0/0*
route to nul0 *redistributed* at Ra is *propagated* via RIP to Rb,
regardless of any *default-network* configuration.
So *redistribution* and *propagation* of *0.0.0.0/0* routes into RIP (and,
IIRC, EIGRP as well) is no problem and does not require any specific
additional configuration (as does OSPF, hence the excerpt earlier posted).
This is a reasonably good document that I refer back to whenever I forget
the nuances of *default-networks* and use/applicability of the 'ip
default-network' command in various contexts:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094374
.shtml
Regards,
Scott
From: Pavel Bykov [mailto:slidersv@gmail.com]
Sent: Tuesday, November 18, 2008 4:07 PM
To: Scott M Vermillion
Cc: Sachin D; Cisco certification
Subject: Re: Redistributing Default route
Just FYI, in Scott's excerpt it is mentioned that "By default, in normal
areas OSPF routers don't generate default routes into
their routing domains, even if one exists."
This refers to RIP and EIGRP protocols which do redistribute default route
automatically, if "ip default-network" command is present.
On Tue, Nov 18, 2008 at 11:06 PM, Scott M Vermillion
<scott_ccie_list@it-ag.com> wrote:
From:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a74
<http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a7
4.shtml>
.shtml
"Normal Areas
By default, in normal areas OSPF routers don't generate default routes into
their routing domains, even if one exists. To have an OSPF router generate a
default route, use the default-information originate [always] [metric
metric-value] [metric-type type-value] [route-map map-name] command in the
OSPF router configuration mode. This generates an external Type-2 link with
link-state ID 0.0.0.0 and network mask 0.0.0.0, which makes the router an
ASBR."
Cheers,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Sachin D
Sent: Tuesday, November 18, 2008 9:35 AM
To: Cisco certification
Subject: Redistributing Default route
Hi
Need help on the below redistribution problem
_ _ _ _ _ _ _ _ _ _ _ _ _
| | |
| RIP | OSPF |
| | |
R1<------------>R|2<----------->R3
| | |
| | |
| _ _ _ _ _ _ _ | _ _ _ _ _ _ _ |
In the above topology
R2 is connected to R1 and R3.
R1 and R2 are running RIP,
R2 and R3 are running OSPF
R1 is sending only default route to R2 via RIP
Hence R2 has only 1 route for RIP subnets
R* 0.0.0.0/0 [120/1] via x.x.x.x, 00:00:03,
But when I am redistributing RIP into OSPF this default route is not getting
redistributed into OSPF i.e R3 is not learning this default route.
On the vice versa if default is generated in OSPF i.e by R3 and
redistributed in RIP on R2 default route is passed to R1 i.e R1 learns the
default route.
Is there any concept I am missing here ?
Why the default route is not getting redistributed into OSPF from RIP ?
Regards
Blogs and organic groups at http://www.ccie.net
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