Note: If you are connected to the Internet through a wireless modem (usually a USB stick) which uses mobile phone wireless telecommunications technology (such as GPRS, EDGE, EVDO, HSPA, UMTS, etc.) most likely your Internet connection will be firewalled at the ISP site by default (so you basically get only half of an Internet connection, without the possibility of successful incoming connections). Short of contacting your ISP to ask if there is a possibility to get full Internet connections on the same device or changing your Internet subscription plan for one that has incoming connections unfirewalled by default (all xDSL, cable or FiOS providers usually offer unfirewalled connections), there is nothing you can do on your side to unblock incoming connections, therefore there is no point in following this guide or any other port-forwarding guide, for that matter, because you will still have incoming connections blocked on all your ports!
To get the best speeds, BitComet needs an open listening port, just as most other P2P applications do. But if you are behind a router or use Windows Internet Connection Sharing (ICS) or you are behind a firewall, you might need to make some adjustments before you get rid of the infamous yellow light and BitComet works as intended. Namely, you'll probably have to configure your router and/or firewall(s) in order to open the listening port of BitComet. In this topic we will discuss the configuration of the router (port forwarding) both automatic (through UPnP) and manual, to the end of opening a port in your router's firewall and forwarding it on the setup page of your router, for BitComet. Software firewall configuration (the one residing on your computer) is discussed in the next topic (Create Firewall Rules).
As with software personal firewalls, there are a wide variety of routers available, and because of the sheer number, it is impossible to include port forwarding instructions for each router model in this user guide. Fortunately many routers support Universal Plug and Play (UPnP), which simply allows BitComet to open and forward a port on the router automatically, without user intervention, then close the port when it is done being used. The problem with Universal Plug and Play is that it's not supported by all routers, and different/incompatible implementations of the UPnP protocol are included in many routers. By default, UPnP port mapping is enabled in BitComet.
Also you need to make sure that UPnP is enabled on your Windows OS or if it's not or you're not sure, you can configure/verify that at Windows UPnP panel as shown below in this guide. If after that you find that you are still in a firewalled state (i.e. yellow status light), then it likely means your router does not support UPnP, or it includes an implementation incompatible with the UPnP mapper used by BitComet.
If this is your case (i.e. you already tried UPnP port mapping and it didn't work), or if you simply do not wish to try/use UPnP forwarding then it is recommended that you disable UPnP in BitComet, set up a static IP, and forward your ports manually. Detailed steps on how to do all that can be found in the Manual Port Forwarding section on this page; also go to this section if you're trying to troubleshoot a manual port forwarding attempt.
However, you should understand that no matter which forwarding method you will be using on your router(s) you'll still have to make sure that the software firewalls installed on your computer are configured as well, to permit incoming connections on BitComet's listening port. For tips about software firewall configuration follow the link above, at the end of the first paragraph on this page.
So, to sum it up, there are two ways you can go about port forwarding, in order to open your listen port in your router:
They are both presented below (first Automatic then Manual), but make sure that you acknowledge them for what they are: two alternative methods towards the same end (materialized in the two independent parts of the guide: the first one about UPnP port mapping and the second one about Manual port mapping).
If you choose one or another is up to you, just make sure that you know which method you want to follow and that you read the appropriate part of the guide.
In BitComet Options → Connections. Check the box “Enable UPnP Port Mapping”. WAN users do not need port mapping, it's suggested for them to uncheck this box.
Note: UPnP is only supported in Windows XP or above, and your hardware router must support UPnP and have it enabled. By default, BitComet won't release the port-mapping when you exit, but you may configure it to do so in Options → Connections Dialogs.
How to check whether UPnP devices are successfully enabled: