[c-nsp] IP SLA tracking, static routes and OSPF announcements

[Gert Doering]

Hi,

On Fri, Apr 20, 2018 at 09:52:32AM -0500, Scott Harvanek wrote:
> ip route x.x.x.x 255.255.255.224 <MY DESTINATION> track 5
> ip route x.x.x.x 255.255.255.248 <MY DESTINATION> track 5

As a side note, and it might not be relevant to this at all.

We have a very strong policy to *NEVER* point a route towards just an
supposedly-connected IP address, always use an interface along with it.

As in:

ip route x.x.x.x 255.255.255.248 <interface> <MY DESTINATION> track 5

because when <interface> goes down, your construction has a high 
chance of creating routing loops.  If there is a path to <my destination>,
via whatever protocol, the router will see the route as valid and
keep announcing it via OSPF.

Intermediate routers on the path to <my destination> might see *this*
box as "best!", so -> routing loop.


If you have <interface> in the route statement, it will ensure that the
route will only ever take the local interface, or be gone for good.

gert
-- 
"If was one thing all people took for granted, was conviction that if you 
 feed honest figures into a computer, honest figures come out. Never doubted 
 it myself till I met a computer with a sense of humor."
                             Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany                             gert at greenie.muc.de
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