[j-nsp] OSPF next hop

[Aaron Dewell]

On Jul 24, 2012, at 4:56 AM, Wayne Tucker wrote:

> On Mon, Jul 23, 2012 at 11:02 PM, Aaron Dewell <aaron.dewell at gmail.com> wrote:
>> I ran into an odd behavior here tonight, I'm hoping someone has some ideas.  We have 8 routers on a broadcast OSPF segment.  All are advertising their loopback addresses (amongst other things).  I'll call this R1 to R8 for now.  Their IP addresses on this shared segment are 192.168.0.16X/28 (X corresponding to RX).
>> 
>> R2 is the current DR and R6 is the BDR.  All the priorities are the same, not that it matters.
>> 
>> From R7, all routes to the other routers' loopback address cross R2!  I'm not sure if it's because it happens to be the DR or what.
>> 
>> acd at R7> show route <R6's loopback>
>> 
>> inet.0: xxxx destinations, xxxx routes (xxxx active, 0 holddown, 4 hidden)
>> + = Active Route, - = Last Active, * = Both
>> 
>> <R6's loopback>/32  *[OSPF/10] 23:57:02, metric 40045
>>> to 192.168.0.162 via ge-0/0/3.200
>> 
>> The metric indicates that the path is: R7->R2->R1->R6, which is proven by the traceroute.  The metric for this broadcast segment is 20000 on all routers.  The 45 is a 10G interface directly connecting R2 and R1.  The metric of the correct path is exactly 20k (directly connected over this shared segment).
>> 
>> The example is typical, all of the other router's loopback's look the same (except R8 which is it's buddy and directly connected).
>> 
>> Any ideas on what else to look at?  The OSPF database looks reasonable.  Our other shared segments act normal.  All routers are on 11.4R2.
> 
> That is odd.  Do all of the routers have a full adjacency with the DR and BDR?
> 
> Does each router LSA show a transit link to the ID if the type 2 LSA
> for that network (it should show that address in the "data" field)?
> 
> :w

Yes, Type Transit (2).  However, the Network LSA only includes 3 attached routers (should be 6 currently).  There are two Network LSAs in R7.  One has the interface IP of R1 (non-DR/BDR) with 3 attached routers (R1, R5, R6).  The other has the interface IP of R2 and shows 3 attached routers (R2, R7, and R8).  The interfaces on R3 and R4 are currently shut down.

Further looking into it, there is disagreement all across this network about who is the DR and BDR.  Half the routers show one set, and half show the other.  I think that might produce some issues!

Aaron