Original message <199707110721.HAA01250@ice.genuity.net> From: Danny McPherson <danny@genuity.net> Date: Jul 11, 0:21 Subject: Re: weird BGP cisco-ism?

if the primary route becomes unavailable and routing falls over to the "nailed up" route, a bgp update is still sent. (if dampening is enabled) this update is recorded by ebgp peers as a "flap". i'd guess from your message below that when this occurs your router(s) are also changing the med attached to the prefix, which seems normal to me...

WHAT?!? This is ridiculous. There *must* be a way to have routes truly "nailed up" such that flaps do not occur. I have static routes in there precisely because I want to be friendly and reduce the number of routing announcements which occur when interfaces transition (I have dozens and dozens of people with class C networks attached via unreliable dialup lines)

i'd suggest you have a look at the stability of the interface to which the primary route is attached (?carrier transitions, interface resets, etc...?). you might also consider breaking the primary route (/20) into 2 /21 blocks internally and allowing the longer "nailed up" route to be the permanent source of the /20 advertisement. for example:

However, in this case, I don't have *anything* as the "primary route". In fact, the very first /24 of the route is currently unused and goes nowhere... and the rest of the block goes as /24's, /29's and the like to various people who connect and disconnect all the time... just like I have on several other CIDR blocks I've got. But *this* one, and *only* this one, insists on sending a readvertisement. So, to readdress my first paragraph, apparently these static routes as I have them configured do just the trick, since if they didn't, I'd see lots of other things flapping on my BGP monitor software I just wrote, but instead I only see this one. Sounds like a real bug of some sort. -matthew