Scalability issues in the Internet routing system

Thu Oct 27 05:48:08 UTC 2005

> One interesting note though is Pekka Savola's RFC3627:
> "Even though having prefix length longer than /64 is forbidden by
>    [ADDRARCH] section 2.4 for non-000/3 unicast prefixes, using /127
>    prefix length has gained a lot of operational popularity;"
> 
> Are you arguing in the popularity sense ? Is RFC 3513 that apart from
> reality ? An October 2005(this month) article I
> found(http://www.usipv6.com/6sense/2005/oct/05.htm) says "Just as a
> reminder, IPv6 uses a 128-bit address, and current IPv6 unicast
> addressing uses the first 64 bits of this to actually describe the
> location of a node, with the remaining 64 bits being used as an
> endpoint identifier, not used for routing.", same as RFC 3513.

I'd have to say that RFC 3513 is out of touch with reality here, yes.
As far as I know current routers with hardware based forwarding look
at the full 128 bits - certainly our Juniper routers do.

> Limiting prefix length to 64 bits is a good thing; it would be even
> better to guarantee that prefixes are always 32 bits or longer, in
> order to use exact match search on the first 32 bits of the address,
> and longest prefix match only on the remaining 32 bits of the prefix
> identifier.

Longer prefixes than 64 bits are already in use today (as an example,
we use /124 for point to point links). It would be rather hard for a
router vendor to introduce a new family of routers which completely
broke backwards compatibility here, just in order to be "RFC 3513
compliant".

Steinar Haug, Nethelp consulting, sthaug at nethelp.no