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funny new firewall rule

I'm just starting to learn Linux firewalling and iptables --- unfortunately almost all of the information that is on an introductory level is years out of date and mainly for other *NIX versions. This is true for both online resources and what's at the local library. Can anyone point me towards a good online resource for this?
Am I supposed to have this line in my firewall rules (this is from an "iptables -L" command):
ACCEPT udp -- anywhere 224.0.0.251 udp dpt:5353
I don't think it was there yesterday, but I'm not sure. I haven't doner any modifications and this is a fresh install.

Traffic on udp/5353 is multicast DNS, and IP addresses 224.0.0.0 and above are used for multicasting. If you're not using multicasting, you can remove it but it won't be doing any harm so there's no real need to get rid of it.

Try

Code:

man iptables

as a good place to start for iptables info.