The 2.4.x Kernel, ECN And Problem Websites

mitd writes: "Enterprise Linux Today is running an article about how some network devices i.e. routers, do not support ECN (Explicit Congestion Notification), causing WWW sites to be unavailable to 2.4.x kernel based hosts." The article does show you an easy workaround, though. (Read more below.)

"Nice quote: 'The answer is that Linux is once again on the cutting edge of networking technology ...' The article points out some major sites that have not updated their routers to handle ECN packets."

Anything that helps destroy congestion at least has my attention. (And in a parallel universe, legions of Windows users are howling that the Linux hegemonists have again chosen to implement new standards in order to drag them into the fold ;) )

Comments

ECN is *not* enabled by default!

[Frater 219]

Contrary to the article's implications, ECN is not enabled by default in the 2.4.x kernels as Linus shipped them. In order to enable ECN, you must reconfigure and recompile the kernel. The configuration documentation for the ECN option explicitly states that turning it on will cause some routers and firewalls to drop your connections, and suggests that you leave it off unless you know you need ECN.

If you find ECN enabled in your distributor's 2.4.x kernel package by default, please consider this a severe mistake on your distributor's part. Please do not consider it a bug in "the 2.4.x kernel". The author of the Enterprise Linux Today article owes Linus and the kernel developers a retraction and correction.

Odd.

[mindstrm]

I find it strange. In moving to 2.4 kernels, the first thing I did was, of course, run through the configuration.

For each option that I didn't recognize, I hit the help button. The help button for ECN (which defaults to off) specifically states that ECN is not supported by some routers, and currently may cause problems with reaching websites on the Internet, so I left it off.

So my question is: Why would you turn on a new network option without knowing what it was?

Before any more strange comments show up...

[Cerlyn]

Let me just say that it is the systems that do *not* handle ECN that are at fault, not the systems that *do* support it. Read the RFC specification here here, or from your nearest RFC mirror (#2481). Note how bits marked as "presently unused" and "reserved for future use" are used for explicit congestion notification.

Any protocol implementation with a bit of sanity would know to leave reserved bits it did not how handle unchanged. Unfortunately, many systems do not do this. Some firewalls see reserved bits being used as a threat, and reset connections. Other systems have no clue how to react if a reserved bit is not the default value.

A partial list of sites I know have trouble with ECN enabled (thank goodness they are the minority of web sites out there) is below. But this is like the Y2K bug; it never really should have existed.

Sites with known ECN problems (that I've seen, anyway)

• www.zdnet.com
• www.theregister.co.uk
• www.returnbuy.com
• www.uscourts.gov (the entire tree, more or less)
• www.burstnet.net (at least I don't see their ads!)
• www.time.com
• www.latimes.com
• www.e3expo.com

(These are only sites I visit rarely, thank goodness; I typically surf another 20+ websites daily without incident)