show cef drop command

[sarahr202]

Hi every body!

Let me quote from my Cisco pres book:

"Drop adjacency:

Used to switch packets that can not be forwarded normally. in effect, these packets are dropped without being forwarded. Packets can be dropped because of an encapsulation failure, an resolved address, an unsupported protocol,no valid route present,no valid adjacency or checksum error. you can gauge drop adjacency activity with the following command:

show cef drop"

The output shows slot, encap-fail,unresolved,unsupported, no route,

no-adja, chksum-err

Under slot, i find " RP'

I thought we are dealing with packets that cef drops for above mentioned reasons. But " RP" makes me feel these are the packets dropped by "RP" not by cef(layer 3 forwarding engine).

There is another question

My understanding is if there is no valid adjacency, packet is punted to "RP" not drop. But as I quoted above under drop adjacency, one of the reasons for drop adjacency is no-adj,My question is what would happen if there is no valid adjacency , will the packet be dropped because it satisfies drop adjacency condition i.e no-adj or the packet will be punted to"RP" because it satisfies punt adjacency condition 1.e no-adj?

thanks a lot!

[Giuseppe Larosa · Accepted solution]

Hello Sarah,

to protect the main cpu RP from excessive requests the CEF punted process has a built-in rate limiter.

Suppose that suddenly a lot of packets for a flow that has no valid adjacency are received

(for example a unicast streaming).

The first packet of the flow is sent the RP so that a valid adjacency can be built or rebuilt.

There's no reason to send to the RP the subsequent packets for the same destination.

So until the RP completes the creation of the CEF adj entry these packets have to be dropped to protect the cpu and because they cannot be fowarded.

These should be the meaning dropped on the path to RP because they are the first packets of the flow and waiting for CEF entry creation.

Hope to help

Giuseppe

[sarahr202]

Thanks a lot Giuseppe!