OSPF Default-originate question/issue

[mwilson]

Ok, I have another question.  I don't know if my interpretation of the documentation is incorrect or this doesn't work as advertised. 

My interpretation is that default-originate will send out a Type 5 LSA IF it has a default route installed in the route table

default-originate always will send out the LSA regardless if it has a default route in the table. 

Is that correct?

What I am seeing in real life is that the default-originate will send out the Type 5 when it sees a default route in the OSPF database.  Even if the route is not installed in the RIB. 

Is this normal behavior?  Any thoughts would be greatly appreciated. 

[Georg Pauwen]

Hello,

how do you see the default route in the routing table and NOT in the OSPF database ?

ip route 0.0.0.0 0.0.0.0 x.x.x.x

will show up as a type 5 LSA with a link id 0f 0.0.0.0. 

This is assuming that you are using normal areas. Can you post the configs of both your routers ?

[mwilson]

George,

  It is just the opposite.  The FW has the route in the OSPF database but NOT in the RIB.  Yet it still advertises it.  The ultimate goal is that BGP router tells FW the default route.  FW tells other routers it is default route IF it has one from BGP.  If it does not have a default route from BGP it should NOT advertise it downstream.  Thanks!

router ospf 10

router-id x.x.x.x

redistribute bgp xxxxx

network xxxxx 0.0.x.x area 0.0.0.0

default-information originate

distribute-list prefix Block_DefaultOSPF in  ( I don't want the default route learned from OSPF but by BGP)

router bgp xxxxx

bgp redistribute-internal

neighbot x.x.x.x

no auto-summary

[Georg Pauwen]

What is the link id of the default route in the OSPF database ? In theory, as you originally said it yourself, without the 'always' keyword, it shouldn't be there if there is no default route in the routing table.

Can you post the output of 'show ip ospf database' ?

[mwilson]

Here is the Type 5

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
0.0.0.0         X.X.X.X           598         0x8000000A 0x00C12B 10

 OSPF Router with ID (X.X.X.X) (Process ID 10)

                Type-5 AS External Link States

  Routing Bit Set on this LSA
  LS age: 644
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 0.0.0.0 (External Network Number )
  Advertising Router: X.X.X.X
  LS Seq Number: 8000000A
  Checksum: 0xC12B
  Length: 36
  Network Mask: /0
        Metric Type: 2 (Larger than any link state path)
        TOS: 0
        Metric: 1
        Forward Address: 0.0.0.0
        External Route Tag: 10

[Georg Pauwen]

Hello,

you x-ed out the advertising router, that is actually what I am after. Is that the local router ?

[Georg Pauwen]

Also, what does the prefix list look like ?

distribute-list prefix Block_DefaultOSPF in

Post the full configs of both OSPF neighbors, otherwise it is just guesswork...

[mwilson]

Here is the full config and the ospf database.  I have tested now with 2 seperate vendors equipment and it appears that this is by design.  

R3#sh run
Building configuration...

Current configuration : 1554 bytes
!
! Last configuration change at 13:18:34 UTC Thu Aug 3 2017
!
version 15.2
service timestamps debug datetime msec
service timestamps log datetime msec
!
hostname R3
!
boot-start-marker
boot-end-marker
!
!
!
no aaa new-model
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
!
!
no ip domain lookup
no ipv6 cef
!
!
multilink bundle-name authenticated
!
!
!
!
!
!
!
!
!
ip tcp synwait-time 5
!
!
!
!
!
!
!
!
!
!
!
!
interface Loopback1
ip address 3.3.3.3 255.255.255.0
!
interface FastEthernet0/0
description UPLINK to R1
ip address 100.100.100.3 255.255.255.0
duplex full
!
interface FastEthernet1/0
description "To R5"
ip address 10.10.10.3 255.255.255.0
speed auto
duplex auto
!
interface FastEthernet1/1
no ip address
shutdown
speed auto
duplex auto
!
router ospf 10
router-id 3.3.3.3
redistribute bgp 11111 metric 50
network 3.3.3.0 0.0.0.255 area 0.0.0.0
network 10.10.10.0 0.0.0.255 area 0.0.0.0
default-information originate
distribute-list prefix Block_DefaultOSPF in
!
router bgp 11111
bgp router-id 100.100.100.3
bgp log-neighbor-changes
bgp redistribute-internal
neighbor 100.100.100.1 remote-as 11111
neighbor 100.100.100.1 timers 10 30
distance 90 100.100.100.1 0.0.0.0
!
ip forward-protocol nd
!
!
no ip http server
no ip http secure-server
!
!
ip prefix-list Block_DefaultOSPF seq 5 deny 0.0.0.0/0
!
!
!
control-plane
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line vty 0 4
login
!
!
end

R3#sh ip ospf database

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

Router Link States (Area 0.0.0.0)

Link ID ADV Router Age Seq# Checksum Link count
3.3.3.3 3.3.3.3 1889 0x80000026 0x00682C 2
4.4.4.4 4.4.4.4 1949 0x80000023 0x00A1AB 2
5.5.5.5 5.5.5.5 1872 0x80000027 0x009813 3
6.6.6.6 6.6.6.6 1359 0x80000024 0x00D68C 3

Net Link States (Area 0.0.0.0)

Link ID ADV Router Age Seq# Checksum
10.10.10.3 3.3.3.3 1889 0x80000002 0x001DCE
20.20.20.4 4.4.4.4 1698 0x80000021 0x00A1FF
30.30.30.6 6.6.6.6 1359 0x80000021 0x00F97B

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 4.4.4.4 1440 0x80000002 0x006335 10

[paul driver]

Hello
No it wont - Ospf will only install  default route via the Default-Originate command if it has a valid default route to install, by a static or other routing protocol it can see.

As for the LSA, Ospf distribute-lists will filter the desired prefix from the rib but NOT from the Database, that isnt filtered

res

Paul

[Georg Pauwen]

Hello,

from the output it appears that the default route comes from a router with id 4.4.4.4. Is that router originating a default route ?

[paul driver]

Hello

@Georg

I dont think the OP is asking that, I think they are querying why the exteranl LSA  is still getting populated in the OSPF database even when they have filted the default route from the RIB-  that my understanding anyway.

res
Paul

[mwilson]

Here is the topology.  R1,3,5 are Site A.  R2,4,6 are Site B.  Both in Area 0.  R1 adn R2 are internet routers.  They give Default Route to R3 and 5 respectively via BGP.  It is then Redistributed to R 5,6 via OSPF.  Ultimately R5 should default to R3 and R6 to R4.  If internet goes down at one site the default route would disappear and the other sites default route would install.  However, that is not the case.  

THanks!

[Georg Pauwen · Accepted solution]

Hello,

the default route you are seeing in the OSPF database on R3 has nothing to do with the 'default-information originate' command on R3. The default route is coming from R4.

It will be in the OSPF database even if you do not configure 'default-information originate' on R3.