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ATM Half-Bridge Overview

308611-14.00 Rev 00

1-9

Maintaining the AHB Bridge Table

AHB maintains a bridge table on each slot. The table contains a list of host entries

to or from which the router will forward traffic. These host entries map the IP

address of a CPE host to the following:

• ATM interface on which it is learned on the AHB router

• Virtual Path Identifier/Virtual Channel Identifier (VPI/VCI) number

• RFC 1483 encapsulation type

• Ethernet header information

Table 1-1

shows a sample AHB bridge table.

Adding Bridge Table Entries

In unsecure learning mode, AHB adds a new entry to the bridge table whenever it

receives an IP or ARP packet that is not already in the table.

In secure learning mode, AHB adds new entries to its table when it receives

certain incoming and outgoing DHCP messages. AHB adds new table entries

when the CPE host on the remote site sends a DHCPDISCOVER message (source

IP address equals 0.0.0.0). This new table entry identifies the incoming port,

VPI/VCI, and RFC 1483 encapsulation data (including source MAC address).

There is no IP address for the new table entry at this point.

AHB forwards only certain DHCP packets (ACK or NAK) to the CPE host using

this entry before an IP address is assigned. When AHB receives a DHCPACK

message, it updates the table entry to identify the correct IP address as provided by

the DHCP server. When AHB learns the first host entry on a network, it inserts a

route into the IP routing table for that network.

Table 1-1. Sample AHB Bridge Table

Host ID

Outgoing

Circuit VPI/VCI RFC 1483 Bridge Header

200.10.10.1 2 101/31 Bridged Ethernet frame:

src MAC addr= 010203040506

dest MAC adrr= 07080oaaboc

Ethertype= 0800 (IP)

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 93 94

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Avaya Configuring ATM Half-Bridge Services Manual de usuario Pagina 27