From: Peter Phaal (peter.phaal@inmon.com)
Date: 07/01/03
I wasn't thinking of any particular situation. It just seems prudent to
define an unknown value for address so that the condition is well defined.
It makes the address definition more useful for future extensions and in
vendor specific structures where a undefined value may be more applicable.
As far as the current set of sFlow structures is concerned, address is
currently used to encode nexthop values in the extended_router,
extended_gateway, extended_mpls structures and in the extended_nat
structure.
In the case of a directly connected subnet, the IP address of the next hop
should probably be consistent with the MIB-2 definition of ipRouteNextHop:
"The IP address of the next hop of this route.
(In the case of a route bound to an interface
which is realized via a broadcast media, the value
of this field is the agent's IP address on that
interface.)"
The only case I can think of where the nexthop might not be known would be a
statically defined route to an unnumbered interface.
RFC 2096 (IP Forwarding Table MIB) anticipates that the nexthop might not be
known, and defines an unknown ipCidrRouteNextHop as 0.0.0.0. However, RFC
2046 uses the IpAddress type from SNMPv2-SMI and so only deals with IPv4
addresses. Since the sFlow address type supports IPv6 it seems more
appropriate to explicitly encode the unkown value, rather than return an
IPv4 address where an IPv6 address was expected.
Peter
> -----Original Message-----
> From: owner-sflow@inmon.com [mailto:owner-sflow@inmon.com]On Behalf Of
> Marc Lavine
> Sent: Monday, June 30, 2003 4:59 PM
> To: peter.phaal@inmon.com; sflow@sflow.org
> Subject: Re: [sFlow] Encoding unknown addresses in sFlow datagrams
>
>
> Peter,
>
> Is this for directly connected subnets, or is there some
> other case you have
> in mind?
>
> Marc
>
> ----- Original Message -----
> From: "Peter Phaal" <peter.phaal@inmon.com>
> To: <sflow@sflow.org>
> Sent: Thursday, June 26, 2003 11:25 AM
> Subject: [sFlow] Encoding unknown addresses in sFlow datagrams
>
>
> > Currently there is no specified way to encode an unknown
> address (for
> > example, the next_hop address may not be known for a static route).
> >
> > One could specify that an IPv4 address of 0.0.0.0 means
> unknown, although
> > this may be a little obscure, especially if returned by an
> IPv6 router. An
> > explicit unknown value is preferable and can easily be
> defined as follows:
> >
> > /* Address types */
> >
> > typedef opaque ip_v4[4];
> > typedef opaque ip_v6[16];
> >
> > enum address_type {
> > UNKNOWN = 0,
> > IP_V4 = 1,
> > IP_V6 = 2
> > }
> >
> > union address (address_type type) {
> > case UNKNOWN:
> > void;
> > case IP_V4:
> > ip_v4;
> > case IP_V6:
> > ip_v6;
> > }
> >
> > Comments?
> >
> > Peter
>
This archive was generated by hypermail 2.1.4 : 07/01/03 PDT