[Xorp-users] policy on static route

[Bruce Simpson]

Hi Andy,

Yes, static routes may have policies applied to them. Can you provide 
details of the error when you try to implement the next-hop rewrite?

Andy Yuen wrote:
>
> Suppose there is a node 10.2.2.2. I want to set up a policy such that 
> the next-hop to destination 10.1.1.0/24 is 10.2.5.5 when some metric 
> or tag value is 1 and the next-hop is 10.2.4.4 when the corresponding 
> metric  or value is 2. Is it possible to define policy statement for 
> static routes?

It is likely what you are attempting to do is not possible without 
additional support from the forwarding plane, as in XORP's RIB, routes 
are normally exclusively keyed by protocol addresses/network prefixes in 
the tries.


>
> Normally, I want to use 10.2.5.5, but occasionally I want to use 
> 10.2.4.4 based on the current value of metric as defined in the policy 
> statement. The reason behind doing this is making it possible to 
> modify the static route by modifying a metric value only, instead of 
> uploading the whole router configuration with new static route. This 
> try to emulate multi-topology routing, where the metric value 
> corresponds to the DSCP value.

XORP will not be able to see or rewrite the DSCP field without 
assistance from the kernel.

One workaround for this would be to implement an outgoing packet rewrite 
policy using your favorite OS's packet filtering facilities. Obviously 
because XORP attempts to drive several host OS layers, it is not 
guaranteed that this can be integrated within the configuration language 
/ framework.

Patches for this and other issues are very welcome.

thanks
BMS