Hi guys,

So i´ve been wrapping my head around this configuration task 12.6 in Volume 1. 
Seen here that other have been in the same situation so decided to throw in my 
2 cents.

My solution was to create a tunnel from R2 to R7 and running OSPF over that, 
which worked fine, however when i checked back to the DSG it mentioned 
switching the secondary address around.

Which makes sense since OSPF won´t advertise through secondary unless it is 
already advertising through the primary address, so making it primary and 
having the RIP run on secondary on R2 instead. Now even though we can sidetrack 
the secondary issue in the already established RIP between R2 and R1 with the 
"no validate-source" there is still a problem. And here is where validation of 
our work comes into play. If you follow the DSG you will see that R1 is not 
receiving RIP updates any more. R2 say's it is sending them out :

RIP: sending v2 flash update to 150.100.36.1 via FastEthernet0/0 (150.100.36.2) 
- suppressing null update

But R1 doesn´t receive anything. Now "debug ip packet" on R2 revels that even 
though RIP says it is sending the update, no packet is leaving the interface. 
So what is happening ? Well, ip split horizon is happening, cause apparently if 
ip split horizon is on, it will not necessarily send update through secondary 
addresses.

"If an interface is configured with secondary IP addresses and split horizon is 
enabled, updates might not be sourced by every secondary address. One routing 
update is sourced per network number unless split horizon is disabled." 
-http://www.cisco.com/en/US/docs/ios/12_0/np1/configuration/guide/1crip.html

Just my two cents, if anyone encounters this issue :).

My question is though,  as long as i´m following the rules and don´t brake any 
others, is something against just setting up the tunnel and sourcing from the 
secondary interface, and running the OSPF over the tunnel ? Skipping the whole 
changing the interface and validate etc....???

Kær Kveðja / Best Regards,
Gustav H. Haraldsson
Netsérfræðingur / Network Specialist
- M.Sc. Communication Network Engineer
- CCNP, CCIP, DCUCI, DCUCD
- RSA Certified Systems Engineer (RSA-CSE)
DDI - +354 414 1420
Mob - +354 842 1920
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