Tag Archives: 3.6a

3.6.a Describe packet types

3.6.a [ii] Route types [N1, N2, E1, E2]

cloudshark is my new best friend… i can  upload caps and they can be analyzed from the link… below is an example of the e-bit (external bit) set to 1 for a type E2…

R3(config-router)#do sh ip route | i E2
E1 – OSPF external type 1, E2 – OSPF external type 2
O E2     2.2.2.0 [110/20] via 192.168.13.1, 00:04:45, FastEthernet1/0
R3(config-router)#

cloudshark_e-bit

click on this damn thing…

down arrow smaller

https://www.cloudshark.org/captures/c7a3e400bc58?filter=ospf

 

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

3.6.a Describe packet types

3.6.a [i] LSA types [1, 2, 3, 4, 5, 7, 9]

below is the link i posted yesterday about the lsdb tutorial by plumbis from cln:

the link is busted…

download this:

down arrow smaller

cisco_support_community_-_reading_and_understanding_the_ospf_database_-_2013-04-15

i’m reposting it as i have built a gns3 topology to accompany it. it is completely addressed. feel free to download it and take a shot following along with the tutorial as i will. it should be a great exercise.

i am b.osgood2011@gmail.com… below you’ll find the rar:

this is the topology i came up with: (tip; makes sure to use router-id’s on all routers, they should be 10.0.0.x, replace x with the router number as in the diagram.)

lsdb_tutorial_w_r`112

 

down arrow smaller

special_ lsdb_tutorial

good luck.

and thank plumbis over on cln.