From: Ben (bmunyao@gmail.com)
Date: Wed Jul 25 2007 - 05:56:22 ART
Hi Bit
Thank you for responding.
I had not tried it before, but after your post, I did and here is what I
got.
When I used "net 10.1.1.1 0.0.0.0 area 0" on R1, R2 forwards to the external
network 192.168.2.0 via R1, as shown below.
R1#sh run
Building configuration...
...
!
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
speed auto
half-duplex
!
...
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
redistribute rip subnets
network 10.1.1.1 0.0.0.0 area 0
!
router rip
version 2
network 10.0.0.0
no auto-summary
!
ip classless
!
...
R1#sh ip route
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, FastEthernet0/0
R 192.168.2.0/24 [120/1] via 10.1.1.3, 00:00:03, FastEthernet0/0
150.4.0.0/16 is variably subnetted, 3 subnets, 2 masks
R1#
R2#
R2#sh run
...
!
interface Ethernet0
ip address 10.1.1.2 255.255.255.0
no ip directed-broadcast
!
...
!
router ospf 1
router-id 2.2.2.2
network 10.1.1.2 0.0.0.0 area 0
!
ip classless
!
R2#
R2#sh ip route
!
...
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, Ethernet0
O E2 192.168.2.0/24 [110/20] via 10.1.1.1, 00:12:27, Ethernet0
150.4.0.0/16 is variably subnetted, 2 subnets, 2 masks
R2#
R2#sh ip route 192.168.2.0
Routing entry for 192.168.2.0/24
Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric
10
Redistributing via ospf 1
Last update from 10.1.1.1 on Ethernet0, 00:14:00 ago
Routing Descriptor Blocks:
* 10.1.1.1, from 1.1.1.1, 00:14:00 ago, via Ethernet0
Route metric is 20, traffic share count is 1
R2#
R3#
R3#sh run
...
!
interface Loopback10
ip address 192.168.2.1 255.255.255.0
!
...
!
interface Ethernet0
ip address 10.1.1.3 255.255.255.0
!
...
!
router rip
version 2
network 10.0.0.0
network 192.168.2.0
no auto-summary
!
I then changed the network statement on R1 to include the whole subnet, and
indeed the next hop on R2 changed as indicated below.
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#no network 10.1.1.1 0.0.0.0 area 0
R1(config-router)#net
00:25:29: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from
FULL to DOWN, Neighbor Down: Interface down or detached
R1(config-router)#net 10.1.1.0 0.0.0.255 area 0
R1(config-router)#^Z
R1#
00:25:45: %SYS-5-CONFIG_I: Configured from console by cisco on console
R1#
00:25:53: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from
LOADING to FULL, Loading Done
R2#
R2#sh ip route
...
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, Ethernet0
O E2 192.168.2.0/24 [110/20] via 10.1.1.3, 00:05:25, Ethernet0
R2#
R2#
R2#sh ip route 192.168.2.0
Routing entry for 192.168.2.0/24
Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric
10
Redistributing via ospf 1
Last update from 10.1.1.3 on Ethernet0, 00:06:08 ago
Routing Descriptor Blocks:
* 10.1.1.3, from 1.1.1.1, 00:06:08 ago, via Ethernet0
Route metric is 20, traffic share count is 1
R2#
Remember R3 is not running ospf.
Ben
PS: The source I got this information from was NMC.
On 7/24/07, Bit Gossip <bit.gossip@chello.nl> wrote:
>
> I have labbed your setup and in both cases I have R2 sending directly to
> R3
> because R1 set R3 as forward-address in its update to R2.
> So no intervention of ICMP in any case.
>
> r2#show ip ospf database external
>
> OSPF Router with ID (10.10.4.2) (Process ID 1)
>
> Type-5 AS External Link States
>
> Routing Bit Set on this LSA
> LS age: 57
> Options: (No TOS-capability, DC)
> LS Type: AS External Link
> Link State ID: 10.1.3.0 (External Network Number )
> Advertising Router: 10.1.1.1
> LS Seq Number: 80000001
> Checksum: 0x7AFB
> Length: 36
> Network Mask: /24
> Metric Type: 2 (Larger than any link state path)
> TOS: 0
> Metric: 20
> Forward Address: 10.1.1.3
> External Route Tag: 0
>
> The only way I can think to force R1 not to set the forward address is to
> change the OSPF network type to P2P or P2M on R1 and R2
>
> r2#show ip route ospf
> 10.0.0.0/24 is subnetted, 2 subnets
> O E2 10.1.3.0 [110/20] via 10.1.1.1, 00:00:13, FastEthernet0/0
>
> r2#show ip ospf database external
>
> OSPF Router with ID (10.10.4.2) (Process ID 1)
>
> Type-5 AS External Link States
>
> Routing Bit Set on this LSA
> LS age: 54
> Options: (No TOS-capability, DC)
> LS Type: AS External Link
> Link State ID: 10.1.3.0 (External Network Number )
> Advertising Router: 10.1.1.1
> LS Seq Number: 80000002
> Checksum: 0xC6BD
> Length: 36
> Network Mask: /24
> Metric Type: 2 (Larger than any link state path)
> TOS: 0
> Metric: 20
> Forward Address: 0.0.0.0
> External Route Tag: 0
>
> In this case indeed ICMP comes into play
>
> r2#ping 10.1.3.3
>
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 10.1.3.3, timeout is 2 seconds:
> !!!!!
> Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
> r2#
> *Jul 24 14:33:38.271: ICMP: redirect rcvd from 10.1.1.1- for 10.1.3.3 use
> gw
> 10.1.1.3
> *Jul 24 14:33:38.275: ICMP: echo reply rcvd, src 10.1.3.3, dst 10.1.1.2
>
> ----- Original Message -----
> From: "Ben" <bmunyao@gmail.com>
> To: "Cisco certification" <ccielab@groupstudy.com>
> Sent: Saturday, July 21, 2007 3:16 PM
> Subject: IP redirect with OSPF IGP
>
>
> > Hi
> >
> > Sometime back, I came across this interesting piece of information on
> the
> > use of OSPF on a multiaccess segment (Ethernet):
> >
> > R2
> > |
> > | 10.1.1.0/24
> > ---------------------------------------------
> > | |
> > | |
> > R1 R3
> > |
> > --------------
> > 10.1.3.0/24
> >
> > R1,R2 running OSPF, R1,R3 running RIP. if you use "net 10.1.1.1 0.0.0.0
> > area
> > 0" to enable ospf on R1, then R2 will forward traffic for 10.1.3.0/24 to
> > R1,
> > R1 will send an icmp redirect to R2, informing it that R3 is metrically
> > closer to the destination.
> >
> > What I didn't know was that if instead you use "net 10.1.1.0 0.0.0.255
> > area
> > 0" on R1, R2 will no longer send traffic to 10.1.3.0 via R1, and will
> > instead learn dynamically the metrically closer next-hop of 10.1.1.3
> > through
> > OSPF, thus saving one hop.
> >
> > Does anyone have variations of this scenario I could try out, to test
> this
> > concept.
> >
> > TIA
> > Ben
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sat Aug 18 2007 - 08:17:41 ART