The MPLS WG Archive

[Kireeti Kompella <kireeti@juniper.net>]

Hi,

>	In draft-kompella-mpls-unnum-02.txt, the interface ID field is shown
> to be 16 bits.  Previous e-mails have suggested that the size be increased
> to 32 bits to match the SNMP ifIndex size.  Can this be increased?

16 bits should be enough to number all interfaces on a box.  If
it isn't, you have other much more serious problems (IS-IS and OSPF
cannot even carry the information (this is not even going into the
scaling issues)).  If you do get to the point where you have more
than a few thousand interfaces on a box, you probably really should
be considering bundling; this will reduce the number of interfaces
from the routing protocols point-of-view to as few as the number of
adjacent nodes.  Then number the bundles, not the actual interfaces.

> We could have ifIndex values that are larger than 16 bits.

We hereby resolve to remove all text that suggests using the SNMP
ifIndex for interface indices :-)  The only requirement for interface
indices is that indices generated by a node are unique, and that the
routing and signalling modules use the same number for an interface.
If your ifIndexes are larger than 16 bits, don't use them, generate
new indices.

Note that the requirements for SNMP indices are much stronger than
for interface indices: they need to remain stable, reusing them can
be an issue, etc., which is why ifIndexes tend to grow beyond 2^16.

Note too that the interface index cannot be made bigger than 2^24;
this is so that the distinction between IP addresses and interface
indices is clear.  Given that, and given the fact the SNMP ifIndexes
can be 32 bits, ifIndexes are ruled out as potential interface
indices.

Kireeti.