Click here to learn how to use the trace route command.

This might help identify where things are going wrong.

From the Second Life Knowledge Base:

    How do I configure my hardware firewall (such as a router)?

    Hardware firewalls need to allow access on certain network ports. Second Life needs to connect to ports 443/TCP, 12035/UDP, 12036/UDP, 12043/TCP, and 13000-13050/UDP. You should configure your firewall to allow outbound traffic on those ports, and related inbound traffic. You’ll need to consult your firewall’s documentation, or the manufacturer’s website, for instructions on how to make these changes to your firewall. As of Version 1.13.2, released Jan. 10th, 2007, you may need to enable UDP/TCP in order to access Second Life.

    Cisco

    If your hardware firewall is a Cisco router/switch that uses reflexive access lists (IOS 11.0 or later), add these lines to your outbound access list:
    permit tcp any any eq 443
    permit udp any any eq 12035 reflect outbound-SL
    permit udp any any eq 12036 reflect outbound-SL
    permit udp any any range 13000 13050 reflect outbound-SL

    Then, on your inbound access list, add:
    permit tcp any any established
    evaluate outbound-SL

    Then, apply these access lists. SL should now be able to communicate through this router.

    Linux Killerwall

    If your hardware firewall is a Linux box that uses Killerwall, add these lines to your /etc/killerwall.acl:
    IN IFACE <your lan interface> FROM 0.0.0.0/0 TO 0.0.0.0/0 tcp TOPORT 443 ACCEPT
    IN IFACE <your lan interface> FROM 0.0.0.0/0 TO 0.0.0.0/0 udp TOPORT 12035 ACCEPT
    IN IFACE <your lan interface> FROM 0.0.0.0/0 TO 0.0.0.0/0 udp TOPORT 12036 ACCEPT
    IN IFACE <your lan interface> FROM 0.0.0.0/0 TO 0.0.0.0/0 udp TOPORT 13000-13050 ACCEPT

    Then, restart Killerwall. Killerwall automatically tracks related reply packets, so SL should now work correctly.

    Linux Firewall

    If your hardware firewall is a Linux box that uses IPF (Linux Firewall)
    pass out quick on rl0 proto tcp from any to any port = 443 flags S keep state
    pass out quick on rl0 proto udp from any to any port = 12035
    pass out quick on rl0 proto udp from any to any port = 12036
    pass out quick on rl0 proto tcp from any to any port = 12043 flags S keep state
    pass out quick on rl0 proto udp from any to any port 12999 <> 13051
    pass in quick on rl0 proto tcp from any to any port = 443 flags S keep state
    pass in quick on rl0 proto udp from any to any port = 12035
    pass in quick on rl0 proto udp from any to any port = 12036
    pass in quick on rl0 proto udp from any to any port 12999 <> 13051

    Can I use voice from behind a firewall?

    Voice, like Second Life itself, is designed to work with “zero configuration” and should work with most firewalls. Your firewall sofware may request permission to let “SLVoice.exe” and “SLVoiceAgent.exe” access the internet on their first execution; you should allow this access.

    The following ports need to be reachable through any firewall infrastructure:

    Port 21002 – TCP – for voice control signals
    Ports 12000-13000 – UDP – for voice media
    Port 80/443 – TCP – for Web server
    Ports 5060 or 5062 – UDP – for voice control signals

    Second Life also has voice servers at the following IPs (this list will grow over time):

    64.127.123.194 to 64.127.123.254
    64.147.180.130 to 64.147.180.142
    69.80.215.226
    64.127.112.106
    70.42.62.21-25

    It’s also true that if the SIP connection on port 5060 fails (as it might if the router is designed to provide VoIP services of its own) our software will automatically retry on port 5062. This means that port 5062 may need to be opened on some restrictive firewalls in rare instances.

    You can verify if your firewall is configured for voice by visiting this website to identify common problems.

The information above is copied from the Second Life Knowledge Base produced by Linden Research, Inc.