Jorge Martinez de Salinas

Opera has introduced a new feature called Opera Unite in its browser. Opera Unite allows service sharing from the web browser. These services include File Sharing, Fridge, Media Player, Photo Sharing, The Lounge and Web Server.

Since it looked promising, I decided to try it out. Setting up the File Sharing service just took a few minutes and everything worked fine. Which made me think … how does it really work? I’m behind a NAT connection and haven’t configured my router which, by the way, doesn’t support UPnP. Perhaps magic? … don’t think so.

To test how it worked I started a file download and fired up Wireshark to examine the packets. They were coming from an Opera server. This happened on the client’s side. On the server’s side Opera had opened a connection to another Opera’s server. So it seems that the service works the same way as a Reverse SSH Tunnel:

1. The browser establishes a connection to an Opera server (tunnel A).
2. When the clients access the service they’re really establishing a connection to an Opera Server (tunnel B).
3. Tunnel A and Tunnel B get connected and the data flows.

The question that comes up is … Does the service always operate this way? Is the connection direct when the user is not behind a NAT or supports automatic port forwarding?

In general the service looks good to me, being its main advantage the ease of use. On the other hand, the information exchange is not strictly between the server and the client (shared files go through the Opera’s network), which can be a deterrent for some users.

This article highlights the most important concepts regarding Public Key Infrastructure (PKI). It also includes a practical step-by-step guide explaining how to set up a PKI on Linux using the OpenSSL package.

In a previous post we talked about RIP. Today I’m going to show you how to configure OSPF. OSPF is a dynamic link-state routing protocol used in IP networks. OSPF is perhaps the most widely used interior gateway protocol (IGP) in large enterprise networks. OSPF exceeds RIP in many aspects:

• It has very low convergence times.
• When no topology changes occur, OSPF is very quiet.
• OSPF enables network subdivision into areas.
• Supports authentication.
• Uses multicast.
• Only routing changes are propagated, not the full routing table like in the RIP case.
• …

To configure OSPF in your cisco router you should follow these steps:

fry> enable 
fry# configure terminal 
fry(config)#router ospf 1 
fry(config-router)#network 192.168.2.0 0.0.0.255 area 0 
fry(config-router)#network 192.168.3.0 0.0.0.255 area 0
fry(config-router)#network 192.168.4.0 0.0.0.255 area 0

You have to specify all the interfaces in which you want to run OSPF with network commands. 0.0.0.255 is a wildcard and means that OSPF will run in any interface with an IP address belonging to the 192.168.2.0/24 network. You can also indicate a specific IP address. If the interface’s IP address changes (e.g. from 192.168.4.1 to 192.168.4.2), OSPF will stop running. The configuration is as follows:

fry(config-router)#network 192.168.4.1 0.0.0.0 area 0

To propagate a default route you can execute this command:

fry(config-router)#default-information originate always

One OSPF drawback could be the configuration complexity. However, if the network topology is point-to-point and we only have one area (like in this case) configuration is pretty straightforward.

Routing Information Protocol (RIP) is an Interior gateway protocol that uses the distance-vector routing algorithm. The original specification of RIP, defined in RFC 1058, uses classful routing. The periodic routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). RIPv2 introduces VLSM support, multicast and authentication capabilities. Although RIP has important limitations (slow convergence times, 15 hop limit, full routing updates periodically…) it’s very easy to configure and can come in handy for some networks. To configure RIP in your cisco router you should follow these steps:

router> enable 
router# configure terminal 
router(config)#router rip 
router(config-router)#network 192.168.2.0 
router(config-router)#network 192.168.3.0 
router(config-router)#network 192.168.4.0 
router(config-router)#version 2

You have to specify all the interfaces in which you want to run RIP with network commands. And that’s all. You have RIP running on your router. Note: In most current networking environments, RIP is not the preferred choice for routing as its capabilities are poor compared to EIGRP, OSPF, or IS-IS.