ospf hello...

hellllllllllllllllllllllllllllllooooo...

the ospf hello packet contains

the router id of the originator

the area id

address mask

authentication, type and information

hello interval

RouterDeadInterval

router priority

dr and bdr

five flag bits of optional capabilities

router id's of it's neighbors



When a router receives a Hello from a neighbor, it will verify that the Area
ID, Authentication, Network Mask, HelloInterval, RouterDeadInterval, and Options values match the values configured on the receiving interface. If they do not, the packet is dropped and no adjacency is established.

If everything matches, the Hello packet is declared valid.

spanning tree very pretty...

STP summary

1.  all bridge (switch ports) stabilize at forwarding or blocking.  Forwarding ports are considered part of the spanning tree.

2.  one switch is elected root, and its ports will all move to forwarding state.

3.  each switch receives hellos from the root, directly or through another switch. The port that receives the least cost BPDU is placed in forwarding and becomes that switch’s root port

4.  for each segment one switch forwards the BPDU with the lowest cost.  That switch becomes that segment’s designated bridge.

5.  the other interfaces are placed in blocking

6.  the root sends BPDU’s every 2 seconds. This time interval can be modified and will be noted in the BPDU.

7.  if max-age elapses (20 seconds, default) and no BPDU, panic ensues and the spanning tree changes.

8.  forward delay (default 15 seconds) is the time it takes for a port to transition through the dumbass states to forwarding. (listening, 15 seconds, learning 15 seconds)

9.  when a switch goes into listening, it sends a TCN BPDU (topology change notification) through the new path to the root. Other switches will refresh their tables with the new entry.

10. spanning tree creates these delays to prevent transitional loops because…

spanning tree, very pretty and the bpdu’s are sweet,

but the root of the poor spanning, is impossible to eat…

say hello ospf

don't forget to issue un all first, then:

r2620_01#debug ip ospf hello

OSPF hello events debugging is on
r2620_01#
1d08h: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0 11.0.0.3
1d08h: OSPF: End of hello processing
1d08h: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.0.0.2
1d08h: OSPF: End of hello processing
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 192.168.1.50
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/0 from 11.0.0.1
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/1 from 10.0.0.1
1d08h: OSPF: Rcv hello from 100.0.0.1 area 0 from FastEthernet0/0 192.168.1.100
1d08h: OSPF: End of hello processing
1d08h: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0 11.0.0.3
1d08h: OSPF: End of hello processing
1d08h: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.0.0.2
1d08h: OSPF: End of hello processing
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 192.168.1.50
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/0 from 11.0.0.1
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/1 from 10.0.0.1
1d08h: OSPF: Rcv hello from 100.0.0.1 area 0 from FastEthernet0/0 192.168.1.100
1d08h: OSPF: End of hello processing
1d08h: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0 11.0.0.3
1d08h: OSPF: End of hello processing
1d08h: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.0.0.2
1d08h: OSPF: End of hello processing
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 192.168.1.50
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/0 from 11.0.0.1
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on Serial0/1 from 10.0.0.1
1d08h: OSPF: Rcv hello from 100.0.0.1 area 0 from FastEthernet0/0 192.168.1.100
1d08h: OSPF: End of hello processing
1d08h: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0 11.0.0.3
1d08h: OSPF: End of hello processing
1d08h: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.0.0.2
1d08h: OSPF: End of hello processing
1d08h: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 192.168.1.50
all possible debugging has been turned off
r2620_01#

it's a whole new world out there...