Configuring Bridges
This chapter describes how to configure bridging for the ML-Series card. For more information about the Cisco IOS commands used in this chapter, refer to the Cisco IOS Command Reference publication.
This chapter includes the following major sections:
•Understanding Bridging
•Configuring Bridging
•Monitoring and Verifying Bridging
Caution
Cisco Inter-Switch Link (ISL) and Cisco Dynamic Trunking Protocol (DTP) are not supported by the ML-Series cards, but the ML-Series broadcast forwards these formats. Using ISL or DTP on connecting devices is not recommended. Some Cisco devices attempt to use ISL or DTP by default.
Understanding Bridging
The ML-Series card supports transparent bridging for Fast Ethernet, Gigabit Ethernet and POS ports. It supports a maximum of 255 active bridge groups. Transparent bridging combines the speed and protocol transparency of a spanning-tree bridge, along with the functionality, reliability, and security of a router.
To configure bridging, you must perform the following tasks in the modes indicated:
•In global configuration mode:
–Enable bridging of IP packets.
–Select the type of Spanning Tree Protocol (STP) (optional).
•In interface configuration mode:
–Determine which interfaces belong to the same bridge group.
The ML-Series card bridges all nonrouted traffic among the network interfaces comprising the bridge group. If spanning tree is enabled, the interfaces became part of the same spanning tree. Interfaces not participating in a bridge group cannot forward bridged traffic.
If the destination address of the packet is known in the bridge table, the packet is forwarded on a single interface in the bridge group. If the packet's destination is unknown in the bridge table, the packet is flooded on all forwarding interfaces in the bridge group. The bridge places source addresses in the bridge table as it learns them during the process of bridging.
Spanning tree is not mandatory for an ML-Series card bridge group. But if it is configured, a separate spanning-tree process runs for each configured bridge group. A bridge group establishes a spanning tree based on the bridge protocol data units (BPDUs) it receives on only its member interfaces. The ML-Series card has a 255 active bridge group maximum.
Configuring Bridging
Use the following steps to configure bridging:
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Step 1 |
Router(config)# no ip routing
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Enables bridging of IP packets. This command needs to be executed once per card, not once per bridge-group. This step is not done for integrated routing and bridging (IRB). |
Step 2 |
Router(config)# bridge
bridge-group-number [protocol
{drpi-rstp | rstp | ieee}]
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Assigns a bridge group number and defines the appropriate spanning-tree type: bridge-group-number can range from 1 to 4096. drpri-rstp is the protocol used to interconnect dual RPR to protect from node failure rstp is the IEEE 802.1W Rapid Spanning Tree. ieee is the IEEE 802.1D Spanning Tree Protocol . Note Spanning tree is not mandatory for an ML-Series card bridge group. But configuring spanning tree blocks network loops. |
Step 3 |
Router(config)# bridge
bridge-group-number priority
number
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(Optional) Assigns a specific priority to the bridge, to assist in the spanning-tree root definition. Lowering the priority of a bridge makes it more likely the bridge is selected as the root. |
Step 4 |
Router(config)# interface type
number
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Enters interface configuration mode to configure the interface of the ML-Series card. |
Step 5 |
Router(config-if)# bridge-group
bridge-group-number
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Assigns a network interface to a bridge group. |
Step 6 |
Router(config-if)# no shutdown
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Changes the shutdown state to up and enables the interface. |
Step 7 |
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Returns to privileged EXEC mode. |
Step 8 |
Router# copy running-config
startup-config
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(Optional) Saves your entries in the configuration file. |
Figure 6-1 shows a bridging example. Example 6-1 shows the code used to configure ML-Series A. Example 6-2 shows the code used to configure ML-Series B.
Figure 6-1 Bridging Example
Example 6-1 Router A Configuration
Example 6-2 Router B Configuration
Monitoring and Verifying Bridging
After you have set up the ML-Series card for bridging, you can monitor and verify its operation by performing the following procedure in privileged EXEC mode:
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Step 1 |
Router# clear bridge
bridge-group-number
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Removes any learned entries from the forwarding database of a particular bridge group, clears the transmit, and receives counts for any statically configured forwarding entries. |
Step 2 |
Router# show bridge
{bridge-group-number |
interface-address}
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Displays classes of entries in the bridge forwarding database. |
Step 3 |
Router# show bridge verbose
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Displays detailed information about configured bridge groups. |
Step 4 |
ML_Series# show spanning-tree
[bridge-group-number][brief]
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Displays detailed information about spanning tree. bridge-group-number restricts the spanning tree information to specific bridge groups. brief displays summary information about spanning tree. |
Example 6-3 shows an example of the monitoring and verifying bridging.
Example 6-3 Monitoring and Verifying Bridging
Total of 300 station blocks, 298 free
Codes: P - permanent, S - self
Maximum dynamic entries allowed: 1000
Current dynamic entry count: 2
0000.0001.6000 forward FastEthernet0
0000.0001.6100 forward POS0
ML-Series# show bridge verbose
Total of 300 station blocks, 298 free
Codes: P - permanent, S - self
Maximum dynamic entries allowed: 1000
Current dynamic entry count: 2
BG Hash Address Action Interface VC Age RX count TX co
1 60/0 0000.0001.6000 forward FastEthernet0 -
1 61/0 0000.0001.6100 forward POS0 -
ML-Series# show spanning-tree brief
Spanning tree enabled protocol ieee
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0 Desg FWD 19 128.3 P2p
PO0 Desg FWD 9 128.20 P2p