From: Tarun Pahuja (pahujat@gmail.com)
Date: Thu May 24 2007 - 14:47:19 ART
Vince,
You are Absolutely right. A destination address of 0.0.0.0 would
never exist. An exercise performed in one of the previous threads confirms
your findings.
Case 1) No default route present
R1(config-if)#do ping 10.10.10.10 re 2
Type escape sequence to abort.
Sending 2, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
*May 24 13:27:17.991: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
unroutable.
*May 24 13:27:19.991: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
unroutable.
*Note: Destination was unroutable.*
Case 2) A static 0.0.0.0/32 route was addred.
R1(config-if)#ip route 0.0.0.0 255.255.255.255 140.101.35.5
R1(config)#do ping 10.10.10.10 re 2
Type escape sequence to abort.
Sending 2, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
*May 24 13:27:42.655: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
unroutable.
*May 24 13:27:44.655: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
unroutable.
*Note: Still unroutable as no default route existed.*
Case 3) A Default route was added to the config in addition to the
previously created /32 static route and the interface through which default
route was going to send packets out was probably shutdown.
Gateway of last resort is 140.101.35.2 to network 0.0.0.0
S 0.0.0.0/32 [1/0] via 140.101.35.5
S* 0.0.0.0/0 [1/0] via 140.101.35.2
R1(config)#do ping 10.10.10.10 re 2
Type escape sequence to abort.
Sending 2, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
*May 24 13:28:16.719: IP: tableid=0, s=140.101.35.1 (local), d=10.10.10.10
(FastEthernet0/0), routed via RIB
*May 24 13:28:16.719: IP: s=140.101.35.1 (local), d=10.10.10.10
(FastEthernet0/0), len 100, sending
*Note: Encapsulation Failed message is a way for Layer 3 to tell that their
is a problem with Layer 2 transport.*
Hope this Helps.
Thanks,
Tarun Pahuja
CCIE#7707(R&S,Security,SP,Voice,Storage)
On 5/24/07, Vince Mashburn <cciegroupstudy@gmail.com> wrote:
>
> a /32 does not make any since for a quad 0 entry. It means that the
> router
> would be looking for an exact match for a destination address 0.0.0.0, not
> a
> default route.
>
> On 5/24/07, Scott Morris <swm@emanon.com> wrote:
> >
> > I think the effect would be COMPLETELY different:
> >
> > R1(config-if)#do sh ip ro
> > 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
> >
> > 140.101.0.0/24 is subnetted, 3 subnets
> > C 140.101.35.0 is directly connected, FastEthernet0/0
> > C 140.101.36.0 is directly connected, FastEthernet0/1
> > C 140.101.1.0 is directly connected, Loopback0
> > R1(config-if)#do ping 10.10.10.10
> >
> > Type escape sequence to abort.
> > Sending 5, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
> > .....
> > Success rate is 0 percent (0/5)
> > R1(config-if)#do debug ip pack
> > IP packet debugging is on
> > R1(config-if)#do ping 10.10.10.10 re 2
> >
> > Type escape sequence to abort.
> > Sending 2, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
> >
> > *May 24 13:27:17.991: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
> > unroutable.
> > *May 24 13:27:19.991: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
> > unroutable.
> > Success rate is 0 percent (0/2)
> > R1(config-if)#ip route 0.0.0.0 255.255.255.255 140.101.35.5
> > R1(config)#do ping 10.10.10.10 re 2
> >
> > Type escape sequence to abort.
> > Sending 2, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
> >
> > *May 24 13:27:42.655: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
> > unroutable.
> > *May 24 13:27:44.655: IP: s=140.101.1.1 (local), d=10.10.10.10, len 100,
> > unroutable.
> > Success rate is 0 percent (0/2)
> > R1(config)#do sh ip ro | in 0.0.0.0
> > S 0.0.0.0/32 [1/0] via 140.101.35.5
> > R1(config)#ip route 0.0.0.0 0.0.0.0 140.101.35.2
> > R1(config)#do sh ip ro | in 0.0.0.0
> > Gateway of last resort is 140.101.35.2 to network 0.0.0.0
> > S 0.0.0.0/32 [1/0] via 140.101.35.5
> > S* 0.0.0.0/0 [1/0] via 140.101.35.2
> > R1(config)#do ping 10.10.10.10 re 2
> >
> > Type escape sequence to abort.
> > Sending 2, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
> >
> > *May 24 13:28:16.719: IP: tableid=0, s=140.101.35.1 (local), d=
> 10.10.10.10
> > (FastEthernet0/0), routed via RIB
> > *May 24 13:28:16.719: IP: s=140.101.35.1 (local), d=10.10.10.10
> > (FastEthernet0/0), len 100, sending
> > *May 24 13:28:16.719: IP: s=140.101.35.1 (local), d=10.10.10.10
> > (FastEthernet0/0), len 100, encapsulation failed.
> > *May 24 13:28:18.719: IP: tableid=0, s=140.101.35.1 (local), d=
> 10.10.10.10
> > (FastEthernet0/0), routed via RIB
> > *May 24 13:28:18.719: IP: s=140.101.35.1 (local), d=10.10.10.10
> > (FastEthernet0/0), len 100, sending
> > *May 24 13:28:18.719: IP: s=140.101.35.1 (local), d=10.10.10.10
> > (FastEthernet0/0), len 100, encapsulation failed.
> > Success rate is 0 percent (0/2)
> > R1(config)#
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > Salau,Olayemi
> > Sent: Thursday, May 24, 2007 5:08 AM
> > To: Radioactive Frog; ccielab@groupstudy.com
> > Subject: RE: IP route 0.0.0.0 vs 255.255.255
> >
> > Hello Frog,
> >
> > 0.0.0.0 0.0.0.0 means default route out thru 2.2.2.2 0.0.0.0
> > 255.255.255.255
> > means any destination route out thru 2.2.2.2
> >
> > The first is like generating or originating default route towards the
> > destination while the second is just matching any destination route not
> > included in the RIB.
> >
> > The router will prefer to use the default route (/0 over /32) if you
> have
> > both in the RIB. This behaviour is reverse of the longest prefix match
> for
> > dynamic routing.
> >
> > In the case the interface using the /0 is down, then it uses the route
> via
> > the interface through /32
> >
> > Many Thanks
> > _________________________________________________
> > Olayemi Salau
> > Network Analyst
> > I.T. Solutions Division
> > Southampton City Council
> > ( 023 8083 4070 7 077 8811 2036 3 079 5825 7509
> > * olayemi.salau@southampton.gov.uk
> > _________________________________________________
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> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > Radioactive Frog
> > Sent: 24 May 2007 07:35
> > To: Cisco certification
> > Subject: IP route 0.0.0.0 vs 255.255.255
> >
> > Hi Group,
> > What and where is the scenario when we should use:
> >
> > ip route 0.0.0.0 0.0.0.0 <next hop ip>
> > Vs.
> > ip route 0.0.0.0 255.255.255.255 <next hop ip>
> >
> > What if I do on a router both route? For example:
> >
> > ip route 0.0.0.0 0.0.0.0 2.2.2.2
> > ip route 0.0.0.0 255.255.255.255 2.2.2.2
> >
> > Frog
> >
> > _______________________________________________________________________
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> >
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