[j-nsp] 8.2R2.4 -> 8.4R2.4 route installation delay

[Kevin Day]

Tonight we upgraded from 8.2R2.4 to 8.4R2.4 on a production M20.  
Everything seemed to go well except for one problem that I'm not sure  
I can explain. I did a full reboot of the router after the upgrade.  
BGP sessions started coming up fine, but the router was sending  
"network unreachable" messages for routes that "show route" was  
displaying. Doing a "show route extensive" showed that many routes  
were in the state "<Record Pending>". The header of "show bgp sum"  
said that there were 150,000+ routes stuck in the "pending" column.

While it was like this, it seemed to route traffic normally for the  
routes that weren't stuck pending. After 10-15 minutes of being stuck  
like this, suddenly the backlog disappeared(the pending count dropped  
to zero) and everything was normal.

Just to be safe, I did a full reboot again, and the problem happened a  
second time exactly the same way. When the traffic suddenly spiked  
back up from everything starting to work properly, the routes had an  
age listed of approx 15 minutes. I looked through the official  
documentation for any clues as to what a high count of pending routes  
means, but I didn't come up with much. Our import policy is extremely  
simple, and nothing like this happened before upgrading to 8.4.

Has anyone seen anything similar before? Is there something new that  
tries to throttle updates to the pfe?

-- Kevin