3.6.a Describe packet types

wanted to make room for hello’s, dbd’s, lsr, lsu, lsa (acknowledgment

HELLO PACKET

OSPF HELLO

arrow rightospf hello

arrow up

notice the bottom part of wireshark that’s highlighted. if you can interpret hex you’ll see the fields in the body correspond to the raw data below, ie, the mask field is 255.255.255.0 and is represented in hex by ff ff ff 00. the hello interval is ten seconds, or 0a, etc.

DBD

ospf dbdospf ws dbd

note mtu is highlighted.

remember with hex

multiples of 16 place|the 16’s place|units place

since there are 3 places you have left to right (the fourth on the left = 0):

05 dc

0 + 5* 256 +  d=13 *16 + c = 12

total 1500

each corresponding place holder is multiplied by 16.

so the fourth place holder is 4096 or 16 times 256

4096|256|16|units

more than that, get a calculator…

LSR

lsr internet diaospf lsr

note here that three lsa types are represented, 1) router 3) summary and 4) asbr summary

LSU

this is a response to an LSR. it may contain multiple LSA’s as in the output.

ospf_lsu_ws

LSA (acknowledgment)

multiple lsa’s may be acknowledged witjh a single ack

ospf lsa ack