Shim6, was: Re: filtering /48 is going to be necessary

Iljitsch van Beijnum iljitsch at
Sun Mar 11 17:15:38 CDT 2012

On 11 Mar 2012, at 20:15 , Joel jaeggli wrote:

>> The IETF and IRTF have looked at the routing scalability issue for a
>> long time. The IETF came up with shim6, which allows multihoming
>> without BGP. Unfortunately, ARIN started to allow IPv6 PI just in
>> time so nobody bothered to adopt shim6.

> That's a fairly simplistic version of why shim6 failed. A better reason
> (appart from the fact the building an upper layer overlay of the whole
> internet on an ip protocol that's largely unedeployed was hard) is that
> it leaves the destination unable to perform traffic engineering.

I'm not saying that shim6 would have otherwise ruled the world by now, it was always an uphill battle because it requires support on both sides of a communication session/association.

But ARIN's action meant it never had a chance. I really don't get why they felt the need to start allowing IPv6 PI after a decade, just when the multi6/shim6 effort started to get going but before the work was complete enough to judge whether it would be good enough.

> That fundementaly is the business we're in when advertising prefixes to more
> than one provider, ingress path selection.

That's the business network operators are in. That's not the business end users who don't want to depend on a single ISP are in. Remember, shim6 was always meant as a solution that addresses the needs of a potential 1 billion "basement multihomers" with maybe ADSL + cable. The current 25k or so multihomers are irrelevant from the perspective of routing scalability. It's the other 999,975,000 that will kill the routing tables if multihoming becomes mainstream.

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