Re: OSPF conditional default route injection

Narbik,

You know you are too good.. :)

On Wed, Jun 9, 2010 at 9:18 AM, Narbik Kocharians <narbikk_at_gmail.com> wrote:

> *Here you go my friend:*
> **
> *Let s say you have the following topology:*
>
>
>
> *R1 (F0/0)---------- (F0/0) R2 (F0/1)-------------(F0/1) R3*
>
> * *
>
> *IP addressing:*
>
> *R1 s F0/0 = 10.1.12.1 /24*
>
> *R2 s F0/0 = 10.1.12.2 /24*
>
> *R2 s F0/1 = 10.1.23.2 /24*
>
> *R3 s F0/1 = 10.1.23.3 /24*
>
> *R3 s Loopback0 = 3.3.3.3 /24*
>
> * *
>
> *Routing protocols:*
>
> *R1 and R2 are running OSPF in area 0*
>
> * *
>
> *R2 and R3 are running Eigrp As 100, R3 s Loopback0 interface is advertised
> in this routing protocol.*
>
>
>
> *Policy:*
>
> *R2 should inject a default route ONLY if it does NOT see network 3.3.3.0
> /24 in its routing table:*
>
>
>
> *On R2*
>
>
>
> *router ospf 1*
>
> *network 10.1.12.2 0.0.0.0 area 0*
>
> *default-information originate*
>
>
>
> *We know that default-information originate on its own will NOT inject a
> default route, and we need a default route in order to originate one. Let s
> configure one:*
>
>
>
> R2(config)#*ip route 0.0.0.0 0.0.0.0 Null0*
>
>
>
> *We should see a default route injected in R1 s routing table:*
>
>
>
> *R1#Show ip route ospf | Inc O*
>
> * *
>
> *O*E2 0.0.0.0/0 [110/1] via 10.1.12.2, **00:08:09**, FastEthernet0/0*
>
>
>
> *Now let s implement the policy:*
>
>
>
> *The state of the following Boolean will ONLY be UP, if object 1 is NOT up
> (Specified by the NOT keyword in the second line of the following
> configuration):*
>
>
>
> R2(config)#*track 3 list boolean and*
>
> R2(config -track)#*object 1 NOT*
>
>
>
> *But the question is, what is object 1? So let s define object 1:*
>
>
>
> R2(config)#*track 1 ip route 3.3.3.0 255.255.255.0 reachability*
>
>
>
> *Now let s test:*
>
>
>
> *On R1*
>
>
>
> R1#Show ip route ospf | Inc O
>
> R1#
>
>
>
> *Note R1 does NOT have a default route anymore because R2 can see network
> 3.3.3.0 /24 in its routing table, here is the proof:*
>
>
>
> *On R2*
>
>
>
> *R2#Show ip route | B Gate*
>
> Gateway of last resort is not set
>
>
>
> 3.0.0.0/24 is subnetted, 1 subnets
>
> *D 3.3.3.0 [90/156160] via 10.1.23.3, **00:01:56**, FastEthernet0/1*
>
> 10.0.0.0/24 is subnetted, 2 subnets
>
> C 10.1.12.0 is directly connected, FastEthernet0/0
>
> C 10.1.23.0 is directly connected, FastEthernet0/1
>
>
>
> *So let s shutdown the loopback0 interface on R3 and see the result:*
>
>
>
> *On R3*
>
>
>
> R3(config)#*Int lo0*
>
> R3(config-if)#*Shut*
>
>
>
> *Let s check the routing table on R1:*
>
>
>
> *On R1*
>
>
>
> *BB1#Show ip route ospf*
>
> * *
>
> *O*E2 0.0.0.0/0 [110/1] via 10.1.12.2, **00:01:07**, FastEthernet0/0*
>
>
> On Wed, Jun 9, 2010 at 8:03 AM, Sorin Platon <sorin.platon_at_gmail.com>
> wrote:
>
> > So i tried tested and labed the OSPF conditional default route injection,
> > all the scenarios i did were to inject a default route based on the
> > presence
> > of a subnet in the routing table
> >
> > This was done trough route-maps or reliable static routes
> >
> > I'm trying to do the reverse, inject a default route in case a subnet is
> > NOT
> > present in the routing table
> >
> > I did tried the obvious and did a deny on the ACL or a deny in the
> routing
> > map but didn't got the desired result
> >
> > is it feasible ?
> >
> > regards
> > Sorin
> >
> >
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> >
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> >
> >
> >
> >
> >
> >
>
>
> --
> Narbik Kocharians
> CCSI#30832, CCIE# 12410 (R&S, SP, Security)
> www.MicronicsTraining.com
> Sr. Technical Instructor
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-- 
Warm Regards
Raghav
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