Redistribution External Routes

[Tiago Eduardo Zacarias]

Good evening gentlemen,

I have a small doubt, perhaps so obvious but I could not see logic. Regarding Redistribution of OSPF Routes in the process. When I perform the redistribution of static routes conectdas and if I give the command show ip ospf it reports the following message:

Redistributing External Routes from,

     connected, includes subnets in redistribution

     static, includes subnets in redistribution

From what I understand he will do with the redistribution metric type E2, but if I give the show ip route on a neighbor some routes announced announced the same origin are marked only with E2 and other The. which the logic he used to redistribute some routes as E2 and other metric as the internal?

From already thank.

[Peter Paluch]

Hi,

I believe that all routes that are static on the router performing the redistribution are recognized as External type 2 on the neighboring routers.

However, regarding the connected routes that are redistributed, those directly connected networks that are covered by network commands in OSPF configuration or whose interfaces are added to OSPF using ip ospf process-id area area-id command will be always advertised as internal. Only those directly connected networks which are not added to OSPF via the network or the ip ospf command will be advertised as external.

Would this explanation match your observations?

Best regards,

Peter

[Tiago Eduardo Zacarias]

Peter,

Thank you for reminding me of this theory's of redistribution via network command and redistribute via connected interfaces. Was studied in the book about issu CCPN Routing of cisco press and had forgotten. I appreciate the help.

[Richard Burts]

I am having some difficulty in understanding parts of the question. But I will make this suggestion. On the other router check a route that is reported as internal and see what is the next hop for that route. Check and see if that next hop is the same router as the one that does redistribution. It is possible that while the router you look at is doing redistribution it is possible that some other router has that route with a network statement which will produce an internal route. If OSPF has a choice of an internal route and an external route then OSPF will always prefer the internal route.

HTH

Rick

[Tiago Eduardo Zacarias]

Good evening gentlemen ,

Thanks for the help , I'll post part of tebela routing for the purpose of understanding .

18x.x.0.0/16 is variably subnetted, 4 subnets, 2 masks                                                                                                                                   

O E2    18x.x.1xx.14/32 [110/7] via 18x.x.18x.1, 01:37:27, FastEthernet0.10                                                                                                                   

O E2    18x.1.18x.8/29 [110/7] via 18x.1.18x.1, 01:37:27, FastEthernet0.10                                                                                                                    

O       18x.1.18x.4/32 [110/11] via 18x.1.18x.1, 01:37:27, FastEthernet0.10                                                                                                                   

C       18x.1.18x.0/29 is directly connected, FastEthernet0.10                                                                                                                                

     172.17.0.0/32 is subnetted, 1 subnets

C       172.17.0.1 is directly connected, Loopback0

     10.0.0.0/8 is variably subnetted, 4 subnets, 3 masks

C       10.255.253.0/30 is directly connected, Loopback1

O E2    10.0.2.0/29 [110/20] via 18x.1.18x.2, 01:37:27, FastEthernet0.10

C       10.255.255.0/28 is directly connected, FastEthernet0.100

O E2    10.0.1.0/29 [110/7] via 18x.1.1x3.1, 01:37:27, FastEthernet0.10

     192.168.0.0/30 is subnetted, 1 subnets

O       192.168.0.0 [110/11] via 18x.1.18x.1, 01:37:27, FastEthernet0.10

     20x.1xx.11.0/27 is subnetted, 1 subnets

C       20x.1xx.11.224 is directly connected, FastEthernet0.9

S*   0.0.0.0/0 [1/0] via 2xx.1xx.1x.254

According to the table , there are several routes whose origin 18x.1.18x.1 neighbor , and all routes advertised by him station directly connected to it . so that some shows as internal route and others like E2 .

[Richard Burts · Accepted solution]

Thanks for the additional information. Here is what I am seeing in the output and what I think that it means.

First let us notice that  18x.1.18x.0/29 is directly connected, FastEthernet0.10     

So this is a local subnet of this router.

Then let us look at this route O       18x.1.18x.4/32 [110/11] via 18x.1.18x.1

we see that this is a host address within the connected subnet and is reported as OSPF internal by the neighbor router which is 18x.1.18x.1. It makes sense to believe that there is an OSPF network statement for this interface on that router and it produces the internal route.

Then let us look at this route O E2    18x.1.18x.8/29 [110/7] via 18x.1.18x.1

and the related route O E2    18x.x.1xx.14/32 [110/7] via 18x.x.18x.1

So we have a remote subnet and a host address within that subnet which are both reported by the neighbor and are OSPF external. It would make sense to believe that the neighbor has a redistribute command that gets these routes into the routing table as external rather than using a network statement to match the subnet.

To verify whether my theory is correct it would be helpful to have information from the neighbor router, especially how its OSPF is configured (what network statements, is there a redistribute connected).

HTH

Rick

[Tiago Eduardo Zacarias]

Good Morning Richard

Below is the configuration of the neighbor to conclude this theory:

router ospf

  ospf router-id 18x.1.18x.1

  redistribute connected

  passive-interface eth1.31

  passive-interface eth1.200

  passive-interface tap0

  18x.1.18x.0/29 area network 0.0.0.0

  network 192.168.0.0/30 area 0.0.0.0

  default-metric 7

  distribute-list out 1 connected

Note: the Neighbor and a linux server with the zebra.

[Richard Burts]

Good Morning

Thank you for the additional information. I believe that it does support my suggestions. Note that it does seem to have a network statement for 18x.1.18x.0/29 (though the word network is not in the right location) so this network will be advertised as an internal route. Note also redistribute connected which explains why O E2    18x.1.18x.8/29 is advertised as external.

I do not understand your mention about the Neighbor. I do not see anything in this output about a neighbor. And I do not see anything about a linux server with zebra (and am not sure that it would change anything in what we have discussed).

HTH

Rick