WAN and FDDI RMON Implementation

WAN Implementation

This section describes SwitchProbe Systems implementation guidelines for monitoring WAN traffic using RMON RFC 1757. The agent uses the Ethernet MIB with some modifications to account for WAN-specific conditions, as shown in Table C-1.

Table C-1: WAN MIB Extensions

Ethernet MIB Counter	WAN	WAN Frame Relay	WAN Frame Relay (DLCI)
CRCAlignErrors	CRC Errors	CRCErrors	CRC Errors
Undersize	Aborts	Aborts	DLCI Down Time
Oversize	Pkts > 1518	Pkts > 1518	Pkts > 1518
Fragments	N/A (not used)	Discard Eligible	Discard Eligible
Jabbers	N/A (not used)	BECN	BECN
Collisions	N/A (not used)	FECN	FECN
Pkts = 64	<=64	<=64	<=64

The agent converts all WAN traffic to Ethernet traffic before processing and supports multiple WAN encapsulation techniques, including those of the most popularly used routers. The process is as follows:

• The WAN header and trailer are removed.

• When the MAC header is missing, it is rebuilt using the DTE address of 0x7ee1000000 and DCE address of 0x7ee2000000 (pseudo MAC header).

• The inOctets counter and the Utilization calculations use actual frame size, including the WAN header and trailer.

• The following formula calculates utilization, given the octets and link_speed in bits per second:

utilization = ((octets*8 per second)/link_speed)*100

• In protocol decode displays, the adjusted frame size is displayed. This is the size of the Ethernet frame, formed after the WAN header and trailer are removed.

• In the protocol decode summary mode, a right arrow (->) indicates a packet transmitted from DTE to DCE. A left arrow (<-) indicates a packet transmitted from DCE to DTE. In the 32 bit RMON-MIB status word, the MSB is clear for DTE to DCE frames, and set for DCE to DTE frames.

CDDI and FDDI Implementation

Table C-2 describes Cisco's implementation guidelines for monitoring CDDI and FDDI traffic using RMON RFC 1757. The agent uses the Ethernet MIB without modification, except for "UnderSize," "Oversize," "Collisions," "Fragments," and "Jabbers," which are redefined slightly to account for FDDI-specific conditions.

Table C-2: Ethernet and FDDI MIB Comparison

Ethernet MIB Variables	FDDI MIB Variables	Explanations
Fragments	SMT Pkts	Number of SMT packets
Collisions	Token Pkts	Number of Token packets
Oversize	Pkt > 1518	Packets greater than 1518 bytes in length
Undersize	Pkt < 64	Packet lengths less than 64 bytes
Jabbers	Not Used	Reserved

In addition, the agent also monitors average Token Rotation Time (TRT) for FDDI and CDDI segments. TRT is the average time (in microseconds) it takes a token on the segment to complete a ring rotation. The agent calculates three separate TRTs based on the following:

• Segment Zoom sample interval

• Short-Term History interval

• Long-Term History interval

The agent applies the following formula to calculate each TRT:

x / y = TRT

where x is the number of times the token completes a ring rotation during the interval (secs) specified for Segment Zoom, Short-Term History, or Long-term History.

where y is the interval (secs) specified for Segment Zoom, Short-Term History, or Long-term History.

However unlike Ethernet, FDDI is based on a ring topology similar to Token Ring. To implement the FDDI Ring Monitor application, the agent uses Token Ring RMON MIB (RFC 1513) groups as follows:

• The agent uses the Token Ring Ring Station Order Group without modification.

• In Table C-2, the agent uses the Token Ring Ring Station Group with some modifications. The agent does not use all of the MIB variables, in Table C-4, but does use the rest of the MIB variables without modification.

The agent does not use the remaining groups in the Token Ring MIB extensions.

Table C-3: Ring Station Group (Changed Variables)

Token Ring MIB Variable Name	FDDI NIB Variable Name	Change
ringStationDuplicateAddresses	Node Class	Indicates FDDI node type: 0 : Station 1 : Concentrator
ringStationInLineErrors	Mac Count	Gives a count of MACs within the node.
ringStationOutLineErrors	Non-Master Count	Indicates number of Non-Master ports in a concentrator-type FDDI node. Valid only if "Node Class" is 1 (Concentrator).
ringStationInternalErrors	Master Count	Indicates number of Master ports in a concentrator-type FDDI node. Valid only if "Node Class" is 1 (Concentrator).
ringStationInBurstErrors	StationState	Bit-encoded variable that indicates state of the FDDI node. The following bits are used: Bit 0=1, station state is "Wrap" Bit 1=1, station state is "Attached-Concentrator". Valid only if "Node Class" is 1. Bit 2=1, station state is "Twisted-ring AA" Bit 3=1, station state is "Twisted-ring BB" Bit 4=1, station state is "Rooted-Station" Note: Bit 0 is the Least Significant Bit.
ringStationOutBurstErrors	DuplicateAddressTest	Indicates status of Duplicate Address test the FDDI Node's SMT performs. 0 indicates node passed the Duplicate Address test. 1 or 2 indicates node failed the Duplicate Address test.

Table  C-4: Ring Station Group (Unused Variables)

MIB Variable Name	Change
ringStationACEErrors	Unused
ringStationLostFrameErrors	Unused
ringStationCongestionErrors	Unused
ringStationFrameCopiedErrors	Unused
ringStationFrequencyErrors	Unused
ringStationTokenErrors	Unused
ringStationInBeaconErrors	Unused
ringStationTokenOutBeaconErrors	Unused