UsdIpAddrLessIf
Compressed index representation to identify both numbered and unnumbered ('address-less') IP subnetworks. One approach is to identify such interfaces with a 2-tuple consisting of <IpAddress, ifIndex>, where only one of the pair is nonzero for a valid interface (IpAddress is nonzero for numbered interfaces, ifIndex is nonzero for unnumbered interfaces). As an alternative, this textual convention compresses the 2-tuple information into an IpAddress (32-bit) format a.b.c.d having the following interpretation: Format Interpretation IP Interface Type ------------------------------------------------------------------ 0.0.0.0 'null' value 'none' or 'wildcard', etc. a.b.c.d, a != 0 IP Address Numbered 0.b.c.d ifIndex Unnumbered For the unnumbered case, the value of the ifIndex is given by (b * 65536) + (c * 256) + (d) A side-effect of this approach is that ifIndex values for IP network interfaces must fall in the range 1..16777215 (i.e. 24 bits).