From: Bit Gossip (bit.gossip@chello.nl)
Date: Wed Jul 25 2007 - 15:27:36 ART
Hi Ben,
this is really very interesting: I have re-labbed it and I have same result.
I think at this point that there is a difference in behaviour between IOS
versions. On R1, which is the one that matters here, I am running:
c2600-advipservicesk9-mz.124-12.bin.
The behaviour seems to be inline with:
http://cisco.com/en/US/partner/tech/tk365/technologies_tech_note09186a008009405a.shtml
Thanks,
Bit
r2#show ip route
<...>
10.0.0.0/24 is subnetted, 2 subnets
O E2 10.1.3.0 [110/20] via 10.1.1.3, 06:25:42, FastEthernet0/0
C 10.1.1.0 is directly connected, FastEthernet0/0
r2#show ip route 10.1.3.0
Routing entry for 10.1.3.0/24
Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric
1
Last update from 10.1.1.3 on FastEthernet0/0, 06:25:55 ago
Routing Descriptor Blocks:
* 10.1.1.3, from 10.1.1.1, 06:25:55 ago, via FastEthernet0/0
Route metric is 20, traffic share count is 1
Here are the configs:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ R1
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
speed 100
full-duplex
!
router ospf 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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ R2
interface FastEthernet0/0
ip address 10.1.1.2 255.255.255.0
duplex full
!
router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ R3
interface Loopback0
ip address 10.1.3.3 255.255.255.0
!
interface FastEthernet1/0
ip address 10.1.1.3 255.255.255.0
duplex full
!
router rip
version 2
network 10.0.0.0
no auto-summary
!
----- Original Message -----
From: "Ben" <bmunyao@gmail.com>
To: "Bit Gossip" <bit.gossip@chello.nl>
Cc: "Cisco certification" <ccielab@groupstudy.com>
Sent: Wednesday, July 25, 2007 10:56 AM
Subject: Re: IP redirect with OSPF IGP
> 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
> > >
> > >
This archive was generated by hypermail 2.1.4 : Sat Aug 18 2007 - 08:17:42 ART