Partial vs Full tables

Thu Jun 11 15:36:23 UTC 2020

On 6/10/20 6:01 PM, Baldur Norddahl wrote:
> Am I correct in assuming loose mode RPF only drops packets from
> unannounced address space in the global routing table? And the downside
> of doing so is that sometimes we do receive packets from that address
> space, usually back scatter from traceroute or other ICMP messages.
> 
> Currently about 25% of the routable address space is not advertised in
> the DFZ. Loose mode RPF could filter this. Is there any data on how much
> traffic actually arrives from this space?
> 

Loose mode RPF will essentially drop traffic received on the interface
if the router does not have any route for. (will not match a default or
a discard route, at least in IOS-XR)

As Bill has pointed out, this may drop traffic from some peering
networks that are not in the global routing table. Though one could
argue that if a packet needs to be fragged it's typically closer to the
edges rather than the transit/peering links.

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