[c-nsp] GRE Tunnels and vrfs

[Gert Doering]

Hi,

On Sun, Sep 12, 2004 at 09:51:25AM +0300, Mihai CHELARU wrote:
> Gert Doering wrote:
> 
> >>Question 2: Why is this setup working after I disable CEF ?
> >
> >How exactly is this "not working" with CEF?
> tcpdump shows that nothing is routed through this tunnel so packets are 
> just black-holed. I checked the routes in RIB and they appear to be OK. 
> A simple 'no ip cef' solves it. I think I'll update IOS these days and 
> see how it does ;/

OK, this is certainly not the way it should be.

I can't say which bug this is, but I can say for sure that it works
the way you intended it on 3640 with 12.3(6a)...  (modulo CEF TTL bug).

> >There are lots of funny bugs in GRE tunneling with CEF regarding TTL 
> >decrementation (TTL not being decrement -> router not visible in 
> >traceroute, and worse, if you have a loop, the packet will loop forever, 
> >burning CPU like mad).
> 
> Yes, I saw this too on other tunnels that I use but it's not so disturbing.

If you can make sure that packets won't loop, it's just a nuisance.

We managed to build a setup where certain packets would loop (aggregate
routed statically into the tunnel, but not all individual routes were
known on the B end, so the packets came back via the tunnel due to a
default route inside the VRF), and that drove CPU to 90% for hours...

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de