Followup British Telecom outage reason

Jesper Skriver jesper at
Tue Nov 27 20:03:25 UTC 2001

On Mon, Nov 26, 2001 at 11:51:08AM -0500, Daniel Golding wrote:
> This used to be the cc train, then later the S train. However, the S train
> has never been as stable as cc, and it has become increasingly less stable
> over time, with too many new features rolling in.
> I'd be curious as to exactly which CEF bugs bit them. The introduction of
> greater MPLS functionality seems to have given CEF a nasty bit of
> destabilization.

Tell me about it, 12000's disabling CEF on LineCards due to various bugs
has probably been the biggest problem I've seen over the past year or

Especially since our IGP (ISIS) doesn't use IP as transport, and thus
keep it's adjacencies, and blackhole all traffic recieved on such a
LineCard until a human acts :-(

But it seems that Cisco has a undocumented, and little know command,
that will disable ISIS on interfaces residing on LineCards with CEF
disabled, and trigger a reroute around the affected LineCard.

router isis
 external overload signalling

Note: We've configured it recently, and hasn't been in a situation
      where we've seen it in action yet, but Cisco claim that atleast
	  one significant carrier has been using it for months.


Jesper Skriver, jesper(at)skriver(dot)dk  -  CCIE #5456
Work:    Network manager   @ AS3292 (Tele Danmark DataNetworks)
Private: FreeBSD committer @ AS2109 (A much smaller network ;-)

One Unix to rule them all, One Resolver to find them,
One IP to bring them all and in the zone to bind them.

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