# Multiple mutual redistribution points

• posted

I admit that I'm purposely trying to create broken and/or unnecessarily complex examples (to try to understand how things work), but this one I really can't understand.

Topology: +----+ | R0 +--------LAN0-- +-+--+ | +---------LAN1------------+ | |

+-+--+ +--+-+ | R1 | | R2 | +-+--+ +-+--+ | | r1r3 r2r4 | | +-+--+ +-+--+ | R3 +----- r3r4 -------+ R4 | +----+ +----+

LAN0: 192.168.0.0/24 LAN1: 172.31.3.0/24 (R1 is .1, R2 is .2, R0 is .3) r1r3: 10.3.1.0/24 (R1 is .1, R3 is .3) r2r4: 10.3.2.0/24 (R2 is .2, R4 is .4) r3r4: 10.3.3.0/24 (R3 is .3, R4 is .4)

ospf is running on R0, R1 and R2 for LAN0 and LAN1 (the upper half of the figure); RIP (v2, no auto-summary) is running on R1, R2, R3, R4 for links r1r3, r2r4, and r3r4 (the lower half of the figure).

At R1, I do mutual redistribution between RIP and ospf, with these commands:

router rip redistribute ospf 1 metric 5 router ospf 1 redistribute rip metric 10000 metric-type 1 subnets

The metrics are high to avoid route feedback. At this point, R1 advertises RIP routes into ospf on LAN1, R2 learns these redistributed routes and prefers them to the old RIP ones:

R2#sh ip route [snip] 172.31.0.0/24 is subnetted, 1 subnets C 172.31.3.0 is directly connected, Ethernet2/0 10.0.0.0/24 is subnetted, 3 subnets O E1 10.3.1.0 [110/10064] via 172.31.3.1, 00:00:13, Ethernet2/0 O E1 10.3.3.0 [110/10064] via 172.31.3.1, 00:00:13, Ethernet2/0 C 10.3.2.0 is directly connected, FastEthernet0/0 O 192.168.0.0/24 [110/65] via 172.31.3.3, 00:00:13, Ethernet2/0

Of course, R1 routing table does not change:

R1#sh ip route [snip] 172.31.0.0/24 is subnetted, 1 subnets C 172.31.3.0 is directly connected, Ethernet2/0 10.0.0.0/24 is subnetted, 3 subnets C 10.3.1.0 is directly connected, FastEthernet0/0 R 10.3.3.0 [120/1] via 10.3.1.3, 00:00:19, FastEthernet0/0 R 10.3.2.0 [120/2] via 10.3.1.3, 00:00:19, FastEthernet0/0 O 192.168.0.0/24 [110/65] via 172.31.3.3, 00:01:56, Ethernet2/0

No surprises up to this point. Now, I do mutual redistribution also on R2, with the same commands used on R1. My understanding here is that R2 should redistribute ospf routes into RIP, with a metric of 5. Thus, R1 ignores those routes since it has already ospf, or connected, or better RIP routes to the destinations advertised into RIP by R2. But, in the reverse direction, R2 should NOT redistribute any RIP route into ospf, since it has no RIP routes in its routing table (they were all discarded in favor of ospf routes). Contrary to what I thought, an ospf E1 route appears at R1:

R1#sh ip route [snip] 172.31.0.0/24 is subnetted, 1 subnets C 172.31.3.0 is directly connected, Ethernet2/0 10.0.0.0/24 is subnetted, 3 subnets C 10.3.1.0 is directly connected, FastEthernet0/0 R 10.3.3.0 [120/1] via 10.3.1.3, 00:00:18, FastEthernet0/0 O E1 10.3.2.0 [110/10064] via 172.31.3.2, 00:00:14, Ethernet2/0 O 192.168.0.0/24 [110/65] via 172.31.3.3, 00:00:14, Ethernet2/0

That is, R1 changes its route to 10.3.2.0/24 (the network directly connected to R2). The same happens if I make routes redistributed into ospf E2 (the default). The only explanation I can imagine for this is that somehow the redistribution makes R2 advertise the 10.3.2.0/24 route into ospf. But how can it do that, if it has no RIP routes? Does redistributing RIP routes into ospf imply redistributing connected networks? Or is there some other explanation?

Thanks

• posted

"pk" ha scritto nel messaggio news:f800ii\$ukf\$ snipped-for-privacy@aioe.org...

Hi,

Redistribution is done for installed routes received by RIP or connected routes advertised by RIP.... since 10.3.2.0 is advertised by RIP (network

10.0.0.0) it is redistributed also.

Regards, Gabriele

• posted

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Ah, this is the bit I was missing (although it makes perfect sense now that you told me)!

Many thanks!

Cabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.