[c-nsp] PBR v VRF for source-based routing

[Gert Doering]

Hi,

On Fri, Oct 23, 2009 at 11:34:05AM -0400, Philip Davis wrote:
>  From reading documentation, it appears that PBR and VRF-lite can both 
> be used to implement cases of source-based routing. I have only used PBR 
> for this, and most VRF documentation seems to be in the context of MPLS 
> or L3VPNs. What are the pros and cons of one vs the other? Am I all wet 
> that VRF can do this at all?

Well, what VRF gives you is completely de-coupled routing tables between
interfaces.  So for one ingress interface into the router, you use 
routing table A, and for another ingress interface, routing table B.

All interfaces belong to *one* VRF only, so if you want to share an
interface between traffic of "sort A" and "sort B", things with VRFs get
tricky.  You can do this with VRF select ("match an access-list, and 
depending on the result, go to VRF routing table A or B or C..."), but
that's a lot of configuration stuff if all you need to do is sort incoming 
traffic on one interface.

PBR will give you a lever to sort incoming traffic according to some
rules you define in a route-map, bypassing(!) normal routing tables.  PBR
is more powerful than VRFs, if the point is "sorting traffic coming in
on *one* interface", but if you need to scale this to dozens of routers,
and hundreds of interfaces, PBR will just be too complex to get right.


So it really depends what you need to achieve.  Tell us your goals, we
tell you why you want PBR or VRF :-)

gert
-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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