[Devmon] New template for collision detection on Cisco 3550

[W.J.M. N. <ne...@nl...>]

Hello,

we've been using Hobbit / Devmon for a few months now. One problem we found is that often high 
collision (red) rates were reported on back-up trunks. It was found that this is caused by using the 
variable ifOutPktsSec, the average number of packets per second. However, if the number of packets 
per 5-minute interval is less than 300, this variable will have the value zero. This causes the 
value of the collision rate to become 1.0. On a back-up trunk, the packet-rate often is less than 
1.0 packet per second.

We've modified the templates of cisco_3550/if_col in the following way:

[hobbit if_col]$ cat oids.old
ifName          : .1.3.6.1.2.1.31.1.1.1.1       : branch
ifAlias         : .1.3.6.1.2.1.31.1.1.1.18      : branch
ifBps           : .1.3.6.1.2.1.2.2.1.5          : branch
ifOutCollisions : .1.3.6.1.4.1.9.2.2.1.1.25     : branch
ifOutPktsSec    : .1.3.6.1.4.1.9.2.2.1.1.9      : branch
[hobbit if_col]$ cat oids
ifName                  : .1.3.6.1.2.1.31.1.1.1.1       : branch
ifHCOutUcastPkts        : .1.3.6.1.2.1.31.1.1.1.11      : branch
ifHCOutMcastPkts        : .1.3.6.1.2.1.31.1.1.1.12      : branch
ifHCOutBcastPkts        : .1.3.6.1.2.1.31.1.1.1.13      : branch
ifAlias                 : .1.3.6.1.2.1.31.1.1.1.18      : branch
ifOutCollisions         : .1.3.6.1.4.1.9.2.2.1.1.25     : branch

[hobbit if_col]$ cat transforms.old
# Convert our total ifc octets(bytes) into bits
ifOutCps        : DELTA         : {ifOutCollisions}

# Create our REAL packets per second
ifOutPps        : MATH          : {ifOutCps} + {ifOutPktsSec}

# Determine percentage of packets that are collisions
ifOutColPct     : MATH          : ({ifOutCps} / {ifOutPps}) x 100

# Create an alias in a bracketed box, or nothing if alias is blank
ifAliasBox      : REGSUB        : {ifAlias} /(\S+.*)/ [$1]/

[hobbit if_col]$ cat transforms
# Fetch output packet rates and the collision rate
ifOutUP         : DELTA         : {ifHCOutUcastPkts}
ifOutMP         : DELTA         : {ifHCOutMcastPkts}
ifOutBP         : DELTA         : {ifHCOutBcastPkts}
ifOutC          : DELTA         : {ifOutCollisions}

# Compute the total output packet rate, such that the collision ratio
# is at most 1.00
ifOutPkts       : MATH          : {ifOutUP} + {ifOutMP} + {ifOutBP} + {ifOutC}

# Determine number of collisions per 100 packets
ifOutColPct     : MATH          : ({ifOutC} / {ifOutPkts}) x 100

# Create an alias in a bracketed box, or nothing if alias is blank
ifAliasBox      : REGSUB        : {ifAlias} /(\S+.*)/ [$1]/


Since this modification, we haven't had a single false red on collision-rate.

   Wim Nelis.