Thursday, April 20, 2006

Adherence to standards

It would be really nice if networking equipment vendors would stop screwing around with accepted standards by either not supporting them fully, or by adding extended functionality.

Along with a colleague, I spent all day Tuesday and Wednesday at one of our customers. We installed a dual cable modem solution to provide a degree of redundancy. Most of our customers get an SMC 8013, which is an integrated unit, essentially a router with a DOCSIS 2.0 cable modem as the WAN interface. This customer is high profile and has a large number of users, so the 8013 wasn't up to the task. What we wanted to do was provide a failover in case the primary modem got overwhelmed by either the amount of traffic being passed or a DDOS attack.

The solution we tried to implement this week involved a Cisco 1811 dual-WAN port router connected to two Cisco uBR 905 cable modem routers. The 1811 has a static public subnet assigned to it, as do each of the 905s. The 1811 advertises its subnet to the 905s using RIP v2, and the 905s in turn advertise their own respective subnets and the 1811's subnet to our CMTS (Cable Modem Termination System, akin to a DSLAM in a DSL provider's network), again via RIP v2.

It worked great in the lab but failed quickly in the field. After a day and a half of scratching our heads I finally ran across the reason why: RIP (v1 or v2) does not support multiple paths to the same network, except in certain vendors' implementations. "Certain vendors" = Cisco.

The configuration was tested in our lab against a Cisco CMTS. Unfortunately, the customer is on an Arris CMTS, and Arris apparently adheres more closely to the RFCs than does Cisco. Sooooo, no workee.

Actually, IMO it was a good thing that this customer is on an Arris CMTS. Had they been on a Cisco CMTS we'd have continued down the primrose path that Cisco's proprietary extensions to RIP lead us down in the lab, and not realized the problem until we tried this configuration elsewhere.

If we used only Cisco CMTSes this would not have been a problem. But because we use other vendors' CMTSes as well, we cannot use the proposed configuration in much of our network. A hell of a lot of time would not have been wasted on a futile effort had Cisco adhered to the accepted industry standards.

1 comment:

Scott said...

So, what's your view on the 8013. Just had one installed here today...