CCDA IP Packet Headers

nkillgore

So, I need to get the CCDA for work. Is there any reason for me to memorize IP packet header fields and what they do? I know Cisco is known for random questions, but, the actual packet headers and what bits they are on don't seem to have much to do with design.

azaghul

I did the previous exam, and think it would be safe to say without breaking the NDA, that going that deep would be over-kill.

Brakarific

About the only thing they might ask about header fields is in relation to QoS, which is only one field in both Layer 2 and 3 headers (ToS or DiffServ/DSCP). Without going into too much detail (NDA), the material doesn't go super deep into switching/routing decisions made by individual network nodes. Everything is talked about at a pretty high level as in what Module does what (Distribution handles ACLs/Policies etc). The only time you have to worry about individual header fields in when you get into traffic flow manipulation. In my experience, knowing what is in each header is very useful if you get into either granular QoS, Content Switching, or you are going for your CCIE My day to day job deals a lot with Content Switching so I have to know, but in all my other networking Jobs all I ever cared about were QoS tags, Vlan Tags, and source/destination MAC and IPs.

nkillgore

Thanks. I appreciate the help.

amsic

Are you specifically referring to IPv4, IPv6 or both? You definitely need to know the difference between an IPv4 and IPv6 header. You should probably also know what some of the fields are such as source, destination, DSCP, flags, etc. Why is the flags field important to network design? Ask yourself why each header and its respective fields are important to design and you'll have an easier time than merely memorizing each header and its fields.