Avaya Configuring ATM Half-Bridge Services Manual de usuario descargar pdf (Pagina 23)

ATM Half-Bridge Overview

308611-14.00 Rev 00

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Forwarding Outbound Packets to CPE Hosts

IP packets received from ISPs or corporate networks that are destined for CPE

hosts are sent to AHB based on the AHB route in the IP routing table. When AHB

receives IP packets, it searches its local bridge table for an associated bridge entry

based on the packet’s destination IP address. If AHB finds an associated bridge

entry, it adds the RFC 1483 encapsulation and Ethernet header information to the

packet. Then it forwards the packet on the correct outgoing interface and PVC to

reach the remote CPE host.

If AHB does not find an associated bridge entry for the packet in its bridge table, it

drops the packet.

Using DHCP to Dynamically Assign IP Addresses

CPE hosts can use DHCP to obtain their IP address and default gateway address.

When you boot the router, the CPE host sends a DHCP request packet, which is

relayed by the DSL modem to the AHB router. The AHB router acts as a DHCP/

BootP relay agent. When the BootP relay agent configured on the ATM service

record receives the DHCP request packet, it fills in the associated IP interface

address (the address you specified for the ATM interface) as the gateway address.

The BootP relay agent then forwards the packet to the DHCP server using either

the BootP forwarding interface method or the BootP preferred server method.

When the DHCP server receives the DHCP REQUEST packet, it checks to see

whether the gateway address is filled in. If this address is filled in, DHCP sends a

reply packet (DHCPACK) to the BootP relay agent on the AHB router. The AHB

router then forwards the DHCPACK reply to the CPE host using the associated IP

address of the unnumbered IP interface.

DHCP servers often use the gateway address in the DHCP request to determine

the address pool to use when assigning a client IP address.

The DHCP server may not respond if it receives a DHCP request where the

gateway address is on the same subnet as the DHCP server’s IP address.

Therefore, when selecting an associated IP address for the unnumbered ATM

circuit, choose an address other than the IP address of a directly connected DHCP

server.

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Avaya Configuring ATM Half-Bridge Services Manual de usuario Pagina 23