OSPF Path Selection With Default Information Originate - How You Gonna Fix It ? - Part 2

As OSPF recent design issue discussed here can possibly turn into obnoxious CCIEv5 R&S troubleshooting scenario, I got one email from another friend who also ran into interesting OSPF design issue recently around OSPF default information originate too.

Here is a quick topology of his network design:

At high level the design looks pretty simple. R1 & R2 are peering with WAN cloud using E-BGP. Between R1-R2-R3-R4-R5 we are running OSPF Area 0. To ensure R3-R4-R5 have reachability to external prefixes (Since it's always good to avoid BGP to IGP Redistribution), R1 & R2 are injecting default route into the network using "default-information originate always metric-type 1" option.

Also R1 & R2 are connected to each other over a link running OSPF.

Now let's talk about problem...which is the fun part :)

If R1's WAN connection goes down, R4 can't reach any external prefixes using default route any longer. Whereas at the same time both R3 & R5 don't lose their connectivity to same external prefixes.

Now ideally once R1 find it's WAN interface down, it should get default route from R2 and should be able to route R4's traffic in that direction.

Let me show you same behaviour using CLI :

Before R1's WAN Link goes down

After R1's WAN Link goes down 

No ICMP Packets Received Any Longer on R6

R1 is not installing default route from R2

See if you can figure out " WHY " behind this and offer different ways we can fix this design issue. Feel Free to post you solution, recommendation and findings under comments section. I'll update the post around next weekend with my findings and solutions to the design.

HTH...

Deepak Arora

Evil CCIE



Update

 In SPF Debug

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As I am currently in middle of my JNCIA-JUNOS prep I thought to take a look on my progress by taking the pre-assessment exam. 

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Here is the URL in case you are interested to earn discount voucher as well :)

https://learningportal.juniper.net/

But in the mean while Jan 2015 First week seems to be good time to go for exam and start the new year with a small bang.

HTH....
Deepak Arora
Evil CCIE