BT blames Cisco for Colossus crash

BT has apologised for last week's ADSL network outages, blaming a Cisco software bug for its troubles.

The crash took down the UK's entire ADSL network for two hours on Tuesday morning after a fault with the Colossus IP backbone, with further problems later the same day and on Friday. The week before, the network shut down for 10 hours.

BT said the fault lay with the software for its core network interface cards, causing them to reset and resulting in data traffic flowing only sporadically, if at all, for much of last Tuesday.

According to a BT spokeswoman, the telco followed Cisco's advice in upgrading the software on the network cards on Tuesday afternoon, only for the process to cause more outages.

"Working with our supplier, which as you know is Cisco, we upgraded the software. But the upgrade caused route reflection, so it was removed," she said.

BT reverted back to the previous version of the software late on Tuesday, temporarily solving the problem, but the network fell over again for 50 minutes on Friday afternoon. The telco says it is now "confident" that a workaround put in place on Friday will prevent further crashes.

But BT admitted that it is yet to upgrade the troublesome network cards. A week on from last Tuesday's failed upgrade, the firm is still testing the planned new version of the software. "We are more likely to be talking weeks than days [before the process is completed]," the spokeswoman said.

Previously, BT had refused to explain the crash, arguing that such information may be of use to its rivals.

The failures in the last fortnight have lead BT's top executives to question their ADSL service levels. Pierre Danon, BT group director and chief executive of BT Retail, admitted last Friday at a European conference on broadband held in Montpellier that BT's ADSL service levels were "mediocre".