The MPLS WG Archive

[Keith McCloghrie <kzm@cisco.com>]

Yakov,

I don't know about OSPF, the protocol, but the OSPF MIB (RFC 1850)
uses different MIB objects to hold an IP address and an ifIndex value.
For example,

    ospfIfIpAddress OBJECT-TYPE
        SYNTAX   IpAddress
        MAX-ACCESS   read-only
        STATUS   current
        DESCRIPTION
           "The IP address of this OSPF interface."
       ::= { ospfIfEntry 1 }

    ospfAddressLessIf OBJECT-TYPE
        SYNTAX   Integer32
        MAX-ACCESS   read-only
        STATUS   current
        DESCRIPTION
           "For the purpose of easing  the  instancing  of
           addressed   and  addressless  interfaces;  This
           variable takes the value 0 on  interfaces  with
           IP  Addresses,  and  the corresponding value of
           ifIndex for interfaces having no IP Address."
       ::= { ospfIfEntry 2 }

ifIndex was originally defined (in RFC 1066) as INTEGER, which was
later refined (in RFC 1563) as:

   InterfaceIndex ::= TEXTUAL-CONVENTION
       DISPLAY-HINT "d"
       STATUS       current
       DESCRIPTION
               "A unique value, greater than zero, for each interface
               or interface sub-layer in the managed system.  It is
               recommended that values are assigned contiguously
               starting from 1.  The value for each interface sub-
               layer must remain constant at least from one re-
               initialization of the entity's network management
               system to the next re-initialization."
       SYNTAX       Integer32

and Integer32 is defined as:

   Integer32 ::=
           INTEGER (-2147483648..2147483647)

So, it's unlikely, but increasingly possible, that ifIndex values can
be as large as 2147483647.

Keith. 


> Keith,
> 
> > An SNMP ifIndex will not fit inside 3 bytes.
> 
> Taking this point of view, an SNMP ifIndex wouldn't fit in anything
> less than 4 bytes. Yet, in OSPF with unnumbered links ifIndex is
> carried in the same field as a plain IP address So, when this field
> carries the value 33620225, is that an IP address (2.1.1.1) or an
> ifIndex (33620225) ?
> 
> Yakov.
>