Today I learned about IGMP, which stands for Internet Group Message Protocol. There are three different ways packets are sent out to other devices. There’s unicast, which just sends a packet to one specific device. Then there’s broadcast, which sends packets to all the devices that is in the network. Lastly, there’s multicast. Multicast sends packets to more than one device but not all the devices.

If a device wants to be part of a multicast group, it sends out an IGMP packet, or more specifically, an IGMP join packet. The join packet expresses the device’s desire to subscribe to the multicast feed.

Usually, a switch is the receiving end of this join request. If IGMP snooping is enabled on the switch, it will listen for requests and add the device to the group.


TIL: Adding Policies in Cisco Firewalls

Identify traffic with an access-list

access-list acl-name permit ip source destination dscp dscp-value

Apply the access-list with the dscp value to an interfact

class-map match-all interface
match ip dscp dscp-value

Apply the policy

policy-map map-name
    class class-name
        [bandwidth bandwidth-value]
        [priority priority-level]
        set ip dscp dscp-value

Today at work I was going over firewalls. We want to check the configuration of the firewalls and compare them to our QoS standards. I’m not too familiar with how policies and QoS are implemented on Cisco devices so it was pretty interesting to learn.