[kv85s]

No, the router still forwards the traffic, but in software rather than hardware. Read the section entitled "Background Information" inside the Cisco document linked at the bottom of the article.

In particular, the telling error message is:

%MLSCEF-DFC4-7-FIB_EXCEPTION: FIB TCAM exception, Some entries will be software switched

[mprovost]

On something like a Sup720 that's a 600MHz MIPS processor, so it's not going to break any speed records. And forwarding traffic is considered lower priority than essential things like routing protocols so once you start hitting the CPU you'll see packet loss and high latency.

[yusyusyus]

a few things...

1) there is a 1 gig inband channel to CPU. the traffic prioritization referred to (selective packet discard) really doesn't matter at the point in which the inband channel is saturated. when you start punting large amounts of traffic to CPU, it will take down your routing protocols, kill ARP, etc, even with selective packet discard, due to this saturation. the only way to prevent this is CoPP in the fast path.

2) inband traffic is interrupt driven on this platform. high inband traffic, by itself, will cause the CPU to spike and drop protocols (missed hellos, etc).

the result will be, without a doubt, an outage. packet loss and high latency would be the best case scenario, but only on a box that doesn't carry much traffic (typically not the case for anything taking full tables).

as a side note, these boxes should have started alarming well before overrunning the TCAM (iirc, it begins at 97% utilization), so operators should have had notice to implement the necessary TCAM carving changes.

[kosinus]

3% of 512,000 is 15,360. So if the table truly spiked up in the 15k, that notice may have been very short.