OSPF default interface

[Steph1963]

Hello to All

I have found the following info this link http://www.cisco.com/en/US/docs/ios/12_0t/12_0t2/feature/guide/defint.html

Network managers may not always be able summarize type-5 link-state advertisements (LSAs) at the router level where redistribution occurs, as in the first possibility. Thus, a large number of type-5 LSAs can be flooded over the domain.

Question 1): Does that means that OSPF would redistributed connected interface as type 5 LSA and this type cannot be summarized while going through another area (I think that type 5 in area 1 will remain type 5 in area 0)

In the second possibility, large type-1 link-state LSAs might be flooded into the area. The area border router (ABR) creates type-3 LSAs, one for each type-1 LSAs, and floods them to the backbone. It is possible, however, to have unique summarization at the ABR level, which will inject just one summary route into the backbone, thereby reducing processing overhead.

Question 2) Doest that means using OSPF passive interface that will used type 1 LSA ant that type 1 LSA can be summarized at the Area Border Router

In the following network, does somebody knows why the OSPF database does not show any LSA entry for the 172.31.129.0 network on R3 router while LSA entry are present on R1 router.

R3#show ip ospf database

            OSPF Router with ID (3.3.3.3) (Process ID 10)

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count

1.1.1.1         1.1.1.1         476         0x80000002 0x00D732 1

3.3.3.3         3.3.3.3         475         0x80000002 0x0054CD 4

                Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum

10.0.0.6        3.3.3.3         475         0x80000001 0x000D04

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum

1.1.1.1         1.1.1.1         516         0x80000001 0x0047EC

2.2.2.2         1.1.1.1         467         0x80000001 0x00230C

11.0.0.0        1.1.1.1         267         0x80000004 0x00DF4A

R1#show ip ospf database

OSPF Router with ID (1.1.1.1) (Process ID 10)

                Router Link States (Area 0)

Link ID         ADV Router      Age        

1.1.1.1         1.1.1.1         446       

2.2.2.2         2.2.2.2         446        

                Net Link States (Area 0)

Link ID         ADV Router      Age        

11.0.0.2        2.2.2.2         447        

                Summary Net Link States (Area 0)

Link ID         ADV Router      Age        

3.3.3.3         1.1.1.1         431        

10.0.0.4        1.1.1.1         426        

172.31.129.0    1.1.1.1         431        

                Router Link States (Area 1)

Link ID         ADV Router      Age        

1.1.1.1         1.1.1.1         441        

3.3.3.3         3.3.3.3         442        

                Net Link States (Area 1)

Link ID         ADV Router      Age        

10.0.0.6        3.3.3.3         443       

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age        

1.1.1.1         1.1.1.1         482        

2.2.2.2         1.1.1.1         432        

11.0.0.0        1.1.1.1         232

Router 3 configuration:

R3 Configuration

interface Loopback0

ip address 3.3.3.3 255.255.255.255

!

interface FastEthernet0/0

ip address 10.0.0.6 255.255.255.252

duplex auto

speed auto

!

interface FastEthernet1/0

ip address 172.31.129.1 255.255.255.252

duplex auto

speed auto

!

interface FastEthernet2/0

ip address 172.31.129.5 255.255.255.252

duplex auto

speed auto

!

router ospf 10

log-adjacency-changes

passive-interface FastEthernet1/0

passive-interface FastEthernet2/0

network 3.3.3.3 0.0.0.0 area 1

network 10.0.0.4 0.0.0.3 area 1

network 172.31.129.0 0.0.0.255 area 1

Router 1 Configuration

R1 Configuration

interface Loopback0

ip address 1.1.1.1 255.255.255.255

!

interface FastEthernet0/0

ip address 10.0.0.5 255.255.255.252

duplex auto

speed auto

!

interface FastEthernet1/0

ip address 11.0.0.1 255.255.255.252

duplex auto

speed auto

!

router ospf 10

router-id 1.1.1.1

log-adjacency-changes

area 0 range 11.0.0.0 255.0.0.0

area 1 range 172.31.129.0 255.255.255.0

network 1.1.1.1 0.0.0.0 area 0

network 10.0.0.4 0.0.0.3 area 1

network 11.0.0.0 0.0.0.3 area 0

Thanks for your help

Stéphane

[cadet alain]

Hi,

Question  1): Does that means that OSPF would redistributed connected interface  as type 5 LSA and this type cannot be summarized while going through  another area (I think that type 5 in area 1 will remain type 5 in area 0)

In  the second possibility, large type-1 link-state LSAs might be flooded  into the area. The area border router (ABR) creates type-3 LSAs, one for  each type-1 LSAs, and floods them to the backbone. It is possible,  however, to have unique summarization at the ABR level, which will  inject just one summary route into the backbone, thereby reducing  processing overhead.

You can summarize at the ASBR or ABR, these are the only 2 points in the network where you can do it  with OSPF and all redistributed routes

are E2 routes by default.

Question
 2) Doest that means using OSPF passive interface that will used type 1 
LSA ant that type 1 LSA can be summarized at the Area Border  Router

Passive interface in OSPF breaks the neighbour relationship

 the following network, does somebody knows why the OSPF database does 
not show any LSA entry for the 172.31.129.0 network on R3 router while 
LSA entry are present on R1 router.

on R1 you summarized at ABR and that's what appears but are you sure your 2 interfaces on R3 going to hosts are in the OSPF process?

---> sh ip ospf interface brief or sh ip ospf interface f1/0 and sh ip cospf interface f2/0 will tell you

Regards.

Alain.

[Steph1963]

Hi Alain,

Thanks for your response,

1) I was under the impression that E2 routes (Type 5 LSA) could not be summarized at the ABR or ASBR based on the following paragraph:

Network managers may not always be able summarize type-5 link-state advertisements (LSAs) at the router level where redistribution occurs, as in the first possibility. Thus, a large number of type-5 LSAs can be flooded over the domain.

I am not too sure how OSPF can summarized redistributed rip (or any other routing protocol) directly at the ASBR. Is there a way of summarizing RIP or EIGRP redistributed route into OSPF across another area with the area range XX command or with any other command.

2) Using passive-interface or redistribute connected seems to generate same LSA-type 1 (Router) and these ones seems to summarizable with the OSPF area range XX comand. I do not know what is the difference between using passive-interface and redistribute connected.

3) I was able to found that 172.31.129.0 and 172.31.129.4 are defined as LSA-type 1 stub network and are shown under show ip ospf database router but not under show ip ospf database, do not know why.

Thanks for your help

Stephane

[cadet alain · Accepted solution]

1)

Is there a way of summarizing RIP or EIGRP redistributed route into OSPF
 across another area with the area range XX command or with any other 
command.

The command to summarize at ASBR is summary- address (under router ospf config)

2)

I do not know what is the difference between using passive-interface and redistribute connected

Passive-interface in OSPF(as in EIGRP) means no neighbour relationship anymore

redistribute connected means to redistribute into OSPF process the directly connected routes already in the rib.

So these 2 features have no relationship whatsoever.

3)

as far as I know lsa type1 is router lsa and so sh ip ospf database router will only show this lsa type but if you see them here then

   you'll see them in the output of sh ip ospf database as well

Regards.

Alain.

[Steph1963]

Hi,

Makes a lot of sense.

Thanks for your help
Stephane