Routing

Hi,

I have a following topology,

loopback(10.0.3.5)

   |

R5(ethernet0) --> R6(ethernet0)

When i give show ospf database on R6, then it shows me loopback address as Router LSA

run show ospf database lsa-id 10.0.3.5    
    OSPF link state database, Area 0.0.0.1 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len Router   10.0.3.5         10.0.3.5         0x80000009     5  0x22 0x5259  48

I understand that i didn't enable OSPF on loopback and it is also in understanding that Router LSA always has information about all directly connected interfaces. But isn't it ambiguous that why OSPF would care for such interface on which OSPF isn't enable(loopback in this case). Because when any body sees it in OSPF database then he might expect to have reachability to it as well. Looking forward for some input on it.

Regards,

Khurram

Dear Khurrum,

Here is the rule of the JUNOS software that it obtain Router ID from the first interface that is detected and Lo0 is the First interface that is detected with a non-Martian address.Because lo0 is always examined when rpd(routing protocol demon) start, except if manual Router ID is configured in routing-option.

JUNOS software automatically advertises a stub route to the interface from which the RID is obtained; therefore it is not actually necessary to explicitly configure lo0 as an OSPF interface to meet the lo0 connectivity requirements.Omitting the lo0 interface from your OSPF configuration results in the lo0 address being advertised as a stub network in the router LSAs (type 1 LSAs) that are generated and flooded into all areas to which a given router attaches.

(from
Juniper® Networks Certified Internet Professional Study Guide by Harry Reynolds)

If this worked for you please flag my post as an "Accepted Solution" so others can benefit.
A kudos would be cool if you think I earned it.

Thanks

Farooq

---

@marwat wrote:

 

JUNOS software automatically advertises a stub route to the interface from which the RID is obtained;

 

---

This is no longer the case since JUNOS 8.5

http://www.juniper.net/techpubs/software/junos/junos90/rn-sw-90/changes-in-default-behavior-and-syntax.html#default-and-syntax-changes

Beginning with JUNOS Release 8.5, OSPF no longer advertises a router identifier interface that is not configured to run OSPF as a stub network in its link-state advertisements. [Routing Protocols]

@khurram,

What you are seeing is the router LSA with id == router-id indeed exists in Your OSPF LSDB. You haven't actually showed us the contents of this LSA.

Could You please run the command "show ospf database lsa-id <id> extensive" (to verify if Your loopback is actually included in this LSA as stub network) and post the printout to this thread.

HTH

Regards

Alex

Dear Alex,

You are right as router identifier is no more as stub in advertisements,

root@OLIVE-R6# run show ospf database lsa-id 10.0.3.5 extensive    
    OSPF link state database, Area 0.0.0.1 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len Router   10.0.3.5         10.0.3.5         0x80000009    17  0x22 0xb8d6  48  bits 0x1, link count 2  id 10.0.8.5, data 10.0.8.6, Type Transit (2)  TOS count 0, TOS 0 metric 1  id 10.0.8.10, data 10.0.8.9, Type Transit (2)  TOS count 0, TOS 0 metric 1  Aging timer 00:59:42  Installed 00:00:14 ago, expires in 00:59:43, sent 00:00:14 ago  Last changed 00:30:11 ago, Change count: 3

Regards,

Khurram

Well, I guess there is no ambiguity in lo0.0 status anymore 

If primary nonmartian IPv4 address on lo0.0 exists, OSPF is not enabled on lo0.0 and primary nonmartian IPv4 address on lo0.0 is _not_ present in OSPF router LSA as "stub network" then this is correct behaviour from JUNOS 8.5 onwards.

HTH

Regards

Alex