Your server is advertising NETBIOS services (Port 137) to the network segment that the machine is connected to. This is a normal service for Windows computers, and is usually enabled by default. NETBIOS services are frequently used to advertise Windows Shared items, such as a network share, but can also be used for other services as well, including network printing.
I cannot understand why you would have NETBIOS enabled on a DHCP/DNS server, unless you are also using it as a WINS server. NETBIOS services are usually blocked by a router, especially in this situation, because the packets are being sent to the broadcast address of the local subnet, so the router ignores the packets because they are not required to go any further. In the meantime, these packets are being transmitted to every device on the 192.168.1.* segment, which would certainly slow your traffic down, if they are frequently transmitted.
Some things that you haven’t said is how often these packets are being blocked by the firewall and their size. You also haven’t said if you have logging enabled on the router, which could also assist in diagnosing this problem. The only other item that you haven’t mentioned is what version of Windows Server you are running (2000, 2003
You can disable NETBIOS service advertising, but before you do so, it would be very wise to check that you are NOT running any service that require the UDP packets. Once you find that out, then consult you Server Admin Manual to find the correct procedure to stop NETBIOS services on the segment.