Configuring Bridging
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:
•Bridging
•Configuring Bridging Example
•Monitoring and Verifying Bridging
Caution
Cisco Inter-Switch Link (ISL) and Cisco Dynamic Trunking Protocol (DTP) are not supported by the ML-Series, 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.
Bridging
The ML-Series card can be configured to serve as an IP router and a bridge. Cisco IOS software supports transparent bridging for Fast Ethernet, Gigabit Ethernet, and POS. Cisco IOS software functionality combines the advantages of a spanning-tree bridge and a router. This combination provides 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.
•In interface configuration mode:
–Determine which interfaces belong to the same bridge group.
These interfaces become part of the same spanning tree, allowing the ML-Series card to bridge all nonrouted traffic among the network interfaces comprising the bridge group. 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.
A separate spanning-tree process runs for each configured bridge group. Each bridge group participates in a separate spanning tree. A bridge group establishes a spanning tree based on the bridge protocol data units (BPDUs) it receives on only its member interfaces.
Configuring Bridging
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Step 1 |
Router(config)# no ip routing
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Enables bridging of IP packets.1 2 |
Step 2 |
Router(config)# bridge
bridge-group-number protocol
{rstp | ieee}
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Assigns a bridge group number and defines the appropriate spanning-tree type: either IEEE 802.1D Spanning Tree Protocol or IEEE 802.1W Rapid Spanning Tree. |
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. The lower the priority, the more likely the bridge is selected as the root. |
Step 4 |
Router(config)# interface
interface type interface 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. |
Configuring Bridging Example
Figure 5-1 illustrates an example of bridging.
Figure 5-1 Bridging Example
Router A Configuration
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 |
Router# show spanning-tree
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Displays the spanning tree topology known to the ML-Series card. |
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
Router# 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 -
Router# show spanning-tree
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