Avaya Configuring ATM Half-Bridge Services Manual do Utilizador descarregar pdf (Página 22)

Configuring ATM Half-Bridge Services

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308611-14.00 Rev 00

The ATM network, located at the central office, switches the ATM cells and

forwards them over PVCs to the ATM interface on the AHB (BLN/BCN)

router.

How the AHB Router Works

AHB combines bridging and IP routing on the router platform. On the DSL access

side, the router receives RFC 1483 encapsulated bridged Ethernet frames

containing IP packets from CPE hosts. On the WAN side, ISP’s and corporate

networks receive routed IP frames. AHB dynamically learns the association

between IP addresses assigned to CPE hosts and the correct RFC 1483 bridged

Ethernet header data for the host.

Forwarding Inbound Packets from CPE Hosts

AHB decapsulates and then routes IP packets it receives from a remote CPE host

to an ISP or corporate network. When AHB receives the incoming packets on its

ATM interface, it checks its local bridge table to determine whether the packet’s

source IP address corresponds to the host IP address in the associated AHB table

entry. If the bridge table contains the bridge entry, and the entry matches the

bridge information (the correct circuit and VCID), then AHB strips off the RFC

1483 bridged Ethernet header information and forwards the packet using IP

routing to the appropriate ISP’s and corporate networks.

If AHB does not find the bridge entry in its local bridge table, and you selected

unsecure learning mode, AHB creates a new bridge entry using the packet header

data from the incoming packet. If you selected secure learning mode, AHB

creates a new bridge entry only if this is a new DHCP request (for information

about using unsecure and secure learning mode, see “Dynamically Learning New

Bridge Table Entries”). The AHB router cannot use this bridge entry until it

receives a DHCP reply on a non-AHB interface that matches the destination MAC

address in the bridge entry. The IP address is assigned at this time. If no matching

bridge entry is found for an incoming packet on an AHB interface, the packet may

still be forwarded if either it is a DHCP packet or if you have disabled inbound

packet filtering.

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Avaya Configuring ATM Half-Bridge Services Manual do Utilizador Página 22