Section 4-5. Token Ring


4-5. Token Ring

  • Token Ring ports are capable of running at 4 or 16 mbps, and either half- or full-duplex.

  • Token Ring ports can operate as Token Ring concentrators or as end stations.

  • The following bridging modes are supported:

    - Source-route bridging (SRB) Routing Information Fields (RIFs) forward packets from rings to bridges, instead of learning MAC addresses. Both the IBM and IEEE STPs are supported.

    - Source-route transparent (SRT) SRB is combined with transparent bridging. Packets with a RIF are forwarded through SRB, whereas packets without a RIF are forwarded through transparent bridging. Only the IEEE STP is supported.

    - Source-route switching (SRS) Packets can be forwarded based on MAC addresses or RIFs.

Configuration

1.

(Optional) Assign a descriptive name to the port:

COS

 set port name mod/port [port-name] 

IOS

N/A


The description port-name (text string) is assigned to the port for human use. Usually, the description includes a reference to the location, function, or user of the port.

2.

Set the port speed:

COS

 set port speed mod/port {4 | 16 | auto} 

IOS

N/A


The port speed can be set to 4 or 16 mbps. If the auto (the default) keyword is used instead, the port automatically senses the speed of the connected ring. If the speed is changed on a port, the port leaves and reenters the ring at the new speed.

CAUTION

If the default autosensing speed is not used, be careful to choose the correct speed for the attached ring. If the port's transmission speed is different from the ring, the port sends beacon frameseffectively making the entire ring inoperable.

3.

Set the port mode:

COS

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 set tokenring portmode mod/port {auto | fdxcport |  hdxcport | fdxstation | hdxstation | riro} 

IOS

N/A


Depending on how the port is used, its mode can be set to one of auto (automatically detect the connection mode; the default), fdxcport (act as a full-duplex concentrator when connected to a single station), hdxcport (act as a half-duplex concentrator when connected to a single station), fdxstation (act as a full-duplex station when connected to another Token Ring switch), hdxstation (act as a half-duplex station when connected to a MSAU), or riro (act as a ring-in/ring-out when using a fiber connection).

4.

(Optional) Use early token release (ETR):

COS

 set tokenring etr mod/port {enable | disable} 

IOS

N/A


With ETR, the port is allowed to release its token onto the ring immediately after transmitting (enable; the default). Ordinarily, the port must wait to release the token until after the transmitted frame has returned around the ring (disable). ETR is only possible on ports participating in 16 mbps rings.

5.

(Optional) Control the use of explorer frames.

a. (Optional) Use All-Routes Explorer (ARE) reduction:

COS

 set tokenring reduction {enable | disable} 

IOS

N/A


When a Token Ring network has parallel paths, ARE frames are flooded onto all possible paths. The amount of ARE frames can be reduced (enable; the default) by discarding the identical explorers that have already been seen on the ring where the port is attached.

b. (Optional) Throttle the amount of incoming ARE frames:

COS

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 set tokenring explorer-throttle mod/port  maximum-explorers 

IOS

N/A


The number of ARE frames is limited to maximum-explorers (frames per second; default 0, or no throttling). After the throttle threshold has been reached during a 1-second interval, the additional ARE frames received on the port are dropped.

6.

(Optional) React to error conditions on a port.

a. (Optional) Use soft error monitoring:

COS

 set station softerror mod[/port] {disable | enable} 

IOS

N/A


By default, soft error monitoring is disabled. When enabled, soft error statistics are collected on the module or port. Soft errors normally occur on a ring, indicating noncritical errors.

b. (Optional) Set a soft error threshold:

COS

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 set station softerror mod[/port] threshold  thres-num interval int-num 

IOS

N/A


A threshold for the number of soft errors from a single station can be set to thres-num (1 to 255; default 100) errors per time interval int-num (0 to 65534 seconds; default 60 seconds). When the threshold is reached, the switch sends a "soft error exceeded" trap, unless the interval is set to 0 seconds.

c. (Optional) Remove an error-producing station from the ring:

COS

 clear station mod/port mac-addr 

IOS

N/A


If a station is seen to produce a large number of soft errors and is degrading the ring performance, it might be a candidate to be removed from the ring. Give the station's mac-addr in noncanonical format (00:11:22:33:44:55). Be aware that the switch will send a "Remove Station" MAC frame to the station, which will force it to remove itself from the ring.

d. (Optional) Automatically disable a port with configuration losses:

COS

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 set tokenring configloss mod/port [threshold  thresh-num] [interval int-num] 

IOS

N/A


A configuration loss occurs when a port enters the ring, passes data, and then closes or is removed from the ring for some reason. A threshold for the number of configuration losses can be set to thres-num (1 to 100; default 8) losses per time interval int-num (0 to 99 minutes; default 10 minutes). When the threshold is reached, the switch disables the port. To regain use of the port, you must reenable it with the set port enable command.

7.

(Optional) Use a filter to control MAC addresses or protocols entering a port:

COS

[View full width]

 set port filter mod/port {mac-addr | protocol-type } {permit | deny} 

IOS

N/A


You can permit or deny frames containing the MAC address mac-addr (either source or destination, entered in canonical format, 00-11-33-44-55, or noncanonical format, 00:11:22:33:44:55) or the protocol type given as protocol-type on a switch port.

The protocol-type can be a four-digit hex value (0x1234, for example) for the Ethernet type, as given in "Appendix B-5: Ethernet Type Codes", a four-digit hex value for a SNAP (0x1234, for example), or a two-digit hex value for a destination service access point (DSAP) (0x12ff, for example, always ending in ff).

Up to 16 MAC address filters and 16 protocol filters (8 SAP and 8 DSAP) can be defined per Token Ring port.

Token Ring Example

Token Ring switch port 2/5 is connected to a 3745 FEP in a data center, using a 16 mbps speed. The port is set to autodetect its role on the ring. Early token release is enabled. Port 2/5 is also set to be disabled if 5 or more configuration losses occur during a 15-minute interval.

Switch port 2/6 is connected to a multistation access unit (MSAU), which also connects to several other hosts. This port is set for hdxstation mode, to properly connect with the MSAU. Early token release is used on the 16 mbps ring. ARE reduction is enabled for the entire switch:

COS

 set port name 2/5 3745 FEP set port speed 2/5 16 set tokenring portmode 2/5 auto set tokenring etr 2/5 enable set tokenring configloss 2/5 threshold 5 interval 15 set port name 2/6 1st floor MSAU set port speed 2/6 16 set tokenring portmode 2/6 hdxstation set tokenring etr 2/5 enable set tokenring reduction enable 

IOS

N/A


Displaying Information About Token Ring

Table 4-4 lists some switch commands that you can use to display helpful information about Token Ring links.

Table 4-4. Switch Commands to Display Token Ring Link Information

Display Function

Switch OS

Command

Token Ring port status

COS

 show tokenring 

IOS

N/A

Status of stations on a ring

COS

 show station controltable [mod[/port]] 

IOS

N/A

Connection order of stations on a ring

COS

 show station ordertable [mod[/port]] 

IOS

N/A

Soft error configuration

COS

 show station softerror config [mod[/port]] 

IOS

N/A

Soft error statistics

COS

 show station softerror counters mod/port [mac-addr] 

IOS

N/A

Token Ring filters

COS

 show port filter [mod[/port]] [canonical] 

IOS

N/A




Cisco Field Manual. Catalyst Switch Configuration
Cisco Field Manual. Catalyst Switch Configuration
ISBN: 1587050439
EAN: N/A
Year: 2001
Pages: 150

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