Re: Difference between 0.0.0.0/0 and 0.0.0.0/32

0.0.0.0/0 le 32 <--- This matches ANY route. Basically the logic here is "0
bits must match AND the subnet mask can be anything <= 32 bits (anything

0.0.0.0/0 <--- This matches ONLY the default route. The logic here is that
we are matching EXACTLY 0.0.0.0 with a mask of 0.0.0.0. Nothing more,
nothing less.

0.0.0.0/32 <--- Logically, this would match EXACTLY 0.0.0.0 with a mask of
255.255.255.255. From my testing (see below) this does *NOT* match every
route. You will have to excuse the fact that tonight I have been playing
with VRFs...

*BEFORE applying the prefix-list called from a distribute-list in OSPF...
*
R1(config-router)#do sh ip route vrf VRF1 ospf

Routing Table: VRF1

     2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/2] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
     100.0.0.0/8 is variably subnetted, 6 subnets, 2 masks
O 100.100.56.0/24
           [110/66] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
O 100.100.200.2/32
           [110/1] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
O 100.100.200.4/32
           [110/65] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
O 100.100.200.5/32
           [110/65] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
O 100.100.200.6/32
           [110/65] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
     4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/66] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
     5.0.0.0/32 is subnetted, 1 subnets
O 5.5.5.5 [110/66] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
     6.0.0.0/32 is subnetted, 1 subnets
O 6.6.6.6 [110/66] via 100.100.12.2, 00:01:39, FastEthernet0/0.12
     7.0.0.0/32 is subnetted, 1 subnets
O 7.7.7.7 [110/67] via 100.100.12.2, 00:01:42, FastEthernet0/0.12

*Now, we create and apply the prefix-list...*

ip prefix-list foo seq 5 permit 0.0.0.0/32

*Apply to the OSPF process and check the routing table...*

R1(config)#router ospf 1
R1(config-router)#distribute-list prefix foo in
R1(config-router)#do sh ip route vrf VRF1 ospf

Routing Table: VRF1

*You see we have NO OSPF learned routes...and that below the entire routing
table shows only connected routes...*

R1(config-router)#do sh ip route vrf VRF1

Routing Table: VRF1
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

     1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback1
     100.0.0.0/24 is subnetted, 1 subnets
C 100.100.12.0 is directly connected, FastEthernet0/0.12

On Mon, Sep 14, 2009 at 1:02 AM, Anantha Subramanian Natarajan <
anantha.natarajan_at_gravitant.com> wrote:

> Hi Khurram,
>
> Thank you for clarifying .....So 0.0.0.0/0 le 32 is equal to 0.0.0.0/32 ?
>
> Thank You
>
> Regards
> Anantha Subramanian Natarajan
>
> On Sun, Sep 13, 2009 at 11:59 PM, Khurram Noor <
> engr.khurramnoor_at_googlemail.com> wrote:
>
> > 0.0.0.0/0 means (0.0.0.0 0.0.0.0) only default route where as
> 0.0.0.0/32means (0.0.0.0 255.255.255.255) all routes.
> >
> >
> > --
> > Khurram Noor
> > CCIE # 24419
> >
> > http://www.linkedin.com/in/khurramnoor
>
>
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-- 
Regards,
Joe Astorino - CCIE #24347 R&S
Technical Instructor - IPexpert, Inc.
Cell: +1.586.212.6107
Fax: +1.810.454.0130
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