Allworx 24X Manual do Utilizador descarregar pdf (Página 26)

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Revised: February 8, 2007

Page 23

14 Common Problems and Tips

This section explores some commonly observed problems and possible causes not specifically addressed by

the previous sections. This section also provides some general troubleshooting tips.

14.1 One-way audio

Having audio flow in one direction only after placing or receiving calls, or even having NO audio flowing at all is

a common problem with SIP and RTP, especially when NAT/Firewalls are on the path. As described in

previous sections, Allworx products implement several mechanisms to automatically deal with the majority of

configuration complexities required to get SIP and RTP to work with NAT firewalls. Still, it is possible for

specific routing asymmetries or packet filtering rules to interfere with one or more protocol mechanisms.

The most common configuration problem in this regard is in complex setups, where the Allworx server is

connected to the WAN and another firewall on the LAN is used for normal data traffic. The user-level symptom

is that a LAN phone will not get good audio either inbound or outbound to a remote phone located at another

site. While one might conclude this is a remote site configuration issue (since the LAN phone works normally

when talking to other LAN phones), this is not the case. Generally, the LAN gateway is set in the phones so

that Internet traffic traverses through the non-Allworx server firewall that is not SIP/NAT aware. In these cases,

it is important to configure the LAN IP phones so that they use the Allworx server LAN IP address as their

gateway to the Internet. This allows the Allworx to correctly orchestrate firewall filtering to pass the remote

phone audio traffic to the LAN properly.

Note: As of Allworx Server Release 5.2 and later, Allworx IP phones will automatically detect this

configuration concern and adapt automatically without having to manually set a unique gateway setting

in the phone. However, 3rd party phones may not have this capability, so one should still be aware of

this potential concern.

14.2 Intermittent connectivity or devices dropping off the network

In cases where connectivity between devices on the network or between IP phones and the Allworx server is

spotty or random, some sort of configuration or network topology problem usually exists. The primary things to

look for are duplicate IP addresses on the network, multiple DHCP servers enabled on the LAN, or more

fundamental QoS issues (including bad cables or improperly configured VLANs). It is normally best to start the

investigation at the point of recent changes to network topology or on the newest configuration settings.

Connectivity problems, especially when intermittent, can be very subtle and sometimes difficult to track down.

A network packet sniffer or protocol analyzer is a great companion to analyze packet flow and look for

problems. If all else fails, generally the best thing to do is isolate as many things as possible from the network

and start adding things back one-by-one (over time) to discover which added device is interacting with the

already existing devices on the LAN. Just because a specific device starts the trouble doesn’t necessarily

mean that it is at fault, only that it is a necessary accomplice. A careful review of packet data on the analyzer

and/or configuration settings is always justified.

14.3 Common MAC address on LAN and WAN ports of a router or firewall

Most dual Ethernet interface firewall products (including Allworx) use the same MAC address for both or all

interfaces of the device. This is perfectly legal, however there is one specific instance where this can cause

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