[ net-snmp-Bugs-3440752 ] eth-tool speed detection fails for flexible speed envs.

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Bugs item #3440752, was opened at 2011-11-21 07:21
Message generated for change (Comment added) made by iamasmith
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Category: agent
Group: linux
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Andrew Smith (iamasmith)
Assigned to: Nobody/Anonymous (nobody)
Summary: eth-tool speed detection fails for flexible speed envs.

Initial Comment:
eth-tool speed detection for interfaces fails for speeds that aren't one of the predefined heather values from linux/ethtool.h and falls back to MII detectionn which reports the interface speed incorrectly

net-snmp-5.7.1/agent/mibgroup/if-mib/data_access/interface_linux.c

    if (edata.speed != SPEED_10 && edata.speed != SPEED_100
#ifdef SPEED_10000
        && edata.speed != SPEED_10000
#endif
#ifdef SPEED_2500
        && edata.speed != SPEED_2500
#endif
        && edata.speed != SPEED_1000 ) {
        DEBUGMSGTL(("mibII/interfaces", "fallback to mii for %s\n",
                    ifr.ifr_name));
        /* try MII */
        return netsnmp_linux_interface_get_if_speed_mii(fd,name,defaultspeed);
    }



alternative mechanism actually used by ethtool (from ethtool-copy.h)

static __inline__ __u32 ethtool_cmd_speed(struct ethtool_cmd *ep)
{
        return (ep->speed_hi << 16) | ep->speed;
}

Note that the speed is simply read directly from the structure and either shifted for a high speed value or reported directly for the standard value.


Example of system effected..

[root@zzzzzz ~]# ethtool eth0
Settings for eth0:
	Supported ports: [ AUI ]
	Supported link modes:   10000baseT/Full 
	Supports auto-negotiation: No
	Advertised link modes:  Not reported
	Advertised auto-negotiation: No
	Speed: 5000Mb/s
	Duplex: Full
	Port: AUI
	PHYAD: 0
	Transceiver: internal
	Auto-negotiation: off
	Supports Wake-on: g
	Wake-on: d
	Link detected: no
	
Note the 5Gb/s speed available on this blade enclosure using the.. 	

Ethernet controller: ServerEngines Corp. Emulex OneConnect 10Gb NIC (rev 02)

..controller.

snmpwalk of this host reports this NIC as follows..

IF-MIB::ifName.2 = STRING: eth0
IF-MIB::ifSpeed.2 = Gauge32: 10000000
IF-MIB::ifHighSpeed.2 = Gauge32: 10

Whereas another one of our (identical SW revision) hosts with an uncapped speed (10Gb) reports the correct values.

This host initially manifest with 290% NIC utilisation in Zenoss and the problem was tracked down as follows.

The problem is clearly related to the use of fixed constant matches from linux/ethtool.h which have no meaning in a gigabit network environment with variable speed allocation. Examining the fixed constants from linux/ethtool.h we find..

/* The following are all involved in forcing a particular link
 * mode for the device for setting things.  When getting the
 * devices settings, these indicate the current mode and whether
 * it was foced up into this mode or autonegotiated.
 */

/* The forced speed, 10Mb, 100Mb, gigabit, 2.5Gb, 10GbE. */
#define SPEED_10                10
#define SPEED_100               100
#define SPEED_1000              1000
#define SPEED_2500              2500
#define SPEED_10000             10000

It seems these speeds are useful as arbitrary increments only when attempting to select rather than retrieve the interface speed from the host.

It would seem to make more sense on the face of it to simply read and utilise the value when retrieving speed rather than confine the selections to the values present in the header.


----------------------------------------------------------------------

>Comment By: Andrew Smith (iamasmith)
Date: 2011-11-22 07:21

Message:
Patch tested... snmpwalk results

snmpwalk results... before...

IF-MIB::ifDescr.2 = STRING: eth0
IF-MIB::ifSpeed.2 = Gauge32: 10000000
IF-MIB::ifHighSpeed.2 = Gauge32: 10

and with patched version of SNMP module..

IF-MIB::ifDescr.2 = STRING: eth0
IF-MIB::ifSpeed.2 = Gauge32: 4294967295
IF-MIB::ifHighSpeed.2 = Gauge32: 5000

This correctly reports the 5GBit/s allocated via the blade enclosure.


----------------------------------------------------------------------

Comment By: Andrew Smith (iamasmith)
Date: 2011-11-22 06:36

Message:
Have patch, will upload following tests for comment. 
Just awaiting approval to test on one of the problem hosts.

----------------------------------------------------------------------

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