Avaya Media Gateway G250, Administration Manual

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Configuring WAN interfaces
294 Administration for the Avaya G250 and Avaya G350 Media Gateways
Typical installations
The Avaya G250 and Avaya G350 Media Gateways were designed for small branch offices of a
larger enterprise. Consequently, the same RAS may serve many branch offices, and, therefore,
many G250/G350s. A reasonable assumption is that not all branch offices would need modem
dial backup at the same time. Therefore, the ratio of modem channels at the RAS to
G250/G350s at branch offices can be less than 1:1. There are several practical ways to
configure the RAS server for use with modem dial backup Dialer interfaces:
●
The RAS can assign an IP address to the calling G250/G350. This requires the RAS to
identify the call gateway using the PAP/CHAP username, and install an appropriate static
route to the branch office subnets accordingly. The username, password, and static route
can be configured in an external RADIUS/ server.
●
The RAS server can use OSPF to learn the branch office subnets. This is much simpler to
configure as all branch offices can share the same username and password. The
G250/G350 is configured to advertise the branch office subnets with OSPF. This feature
requires the use of unnumbered IP addresses at the G250/G350 and the RAS. Since the
Dialer and the primary interfaces are not expected to be up at the same time, the RAS
server can use passive-OSPF-interface and the G250/G350 can use static via routes.
●
The G250/G350 can call an ISP RAS (which is likely to assign it a dynamic IP address)
and open an IPSec VPN tunnel to an enterprise-owned VPN gateway.
While using OSPF and calling an ISP RAS are expected to be the most common scenarios,
they involve complex interaction with IP routing and the remote RAS server. For more detailed
configuration examples, see
Application Note - VoIP Network Resiliency .
Prerequisites for configuring modem dial backup
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At least one dialer string, which determines the phone number(s) of the remote modem(s)
dialed by the Dialer interface
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A configured interface to be backed up
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Read/write or admin access level
●
A Multitech MultiModem ZBA (MT5634ZBA) or MultimodemUSB (MT5634ZBA-USB)
modem
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RAS properties:
- A dialer string
- Authentication parameters (username, password, PAP/CHAP)
- IP addressing (static, dynamic, or unnumbered)
- Routing (static, RIP, or OSPF)
- IPSec VPN, with all necessary parameters configured