[c-nsp] asr9k dhcp relay + ipv4 verify unicast

[Phil Mayers]

On 23/05/16 15:45, Saku Ytti wrote:
> Hey Florian,
>
> Technically it is uRPF violation, you're getting packet from SADDR
> 0.0.0.0, which is clearly not routed to the interface. JunOS has this
> same behaviour and you need to create exception ACL for uRPF to fix
> it, I think it's fine, leveraging existing configuration infra,
> without introducing new hacks in the code, which invariably will cause
> bugs.
>
> However I don't think IOS-XR has this exception ACL support for uRPF.
> What you're seeing may be a bug, quick search for DDTS gave me this
> https://bst.cloudapps.cisco.com/bugsearch/bug/CSCuu01825
>
> I'm curious how '633892863' was solved. Perhaps 'not supported, use
> ACL instead of uRPF'.

I know nothing about -XR but surely if uRPF was eating packets with 
source of 0.0.0.0, the DISCOVER wouldn't make it to the server?

Seeing a DISCOVER at the server but no request sounds like the OFFER 
getting dropped, which can happen if the route back to the giaddr from 
the server hits an RPF failure (beyond tedious in ECMP-enabled HSRP 
setups as we recently discovered...)