OSPF DR- DROTHER exchange
setup in GNS3
BDR .1/25---SWITCH--- .2/25 DR
|
|.3/25
DROTHER
3 routers share a common subnet 10.0.0.0/25 subnet
Lo0 DR: 192.168.254.84
Lo0 BDR: 192.168.254.83
Lo0 DROTHER: 192.168.254.82
Situation:
I configured first the DR and BDR (interface,loopback and ospf config)
example of DR config
interface Loopback0
ip address 192.168.254.84 255.255.255.0
!
interface FastEthernet0/0
ip address 10.0.0.2 255.255.255.128
duplex auto
speed auto
router ospf 100
log-adjacency-changes
network 10.0.0.0 0.0.0.127 area 0
network 192.168.254.0 0.0.0.255 area 0
Ok so far so good
problem:
I started Wireshark on DRother to see what happens when I configure DRother
what happens:
DRother sends a mcast to 224.0.0.5 with BDR/DR 0.0.0.0
BDR's hello timer expires and send a hello to 224.0.0.5, has DR and DRother in it's neighbo list
DR's hello timer expires and send a hello to 224.0.0.5, has BDR and DRother in it's neighbo list
=>biderectional communication is established with his neighbors
I expected that now and exchange would follow with the DR (DBD,LSR,LSU)
DROTHER --> DR via 224.0.0.6
DR --> DROTHER unicast to DR
and finally DR via 224.0.0.5 to all routers
but this is not the case.
I see unicast(in both directions) exchanges(DBD, LSupdate) with both DR and the BDR(???) in both directions?? even unicast exchanges(DBD/LSupdate,...) between DR and BDR (while stable)
(30 messages in 2 seconds)??
In this stream I see only 2 messages to 224.0.06?? While the same message is also sent from DROTHER has been sent to 224.0.0.5
Is this due to GNS3 and wireshark or do I really don't understand how the sync works
BDR .1/25---SWITCH--- .2/25 DR
|
|.3/25
DROTHER
3 routers share a common subnet 10.0.0.0/25 subnet
Lo0 DR: 192.168.254.84
Lo0 BDR: 192.168.254.83
Lo0 DROTHER: 192.168.254.82
Situation:
I configured first the DR and BDR (interface,loopback and ospf config)
example of DR config
interface Loopback0
ip address 192.168.254.84 255.255.255.0
!
interface FastEthernet0/0
ip address 10.0.0.2 255.255.255.128
duplex auto
speed auto
router ospf 100
log-adjacency-changes
network 10.0.0.0 0.0.0.127 area 0
network 192.168.254.0 0.0.0.255 area 0
Ok so far so good
problem:
I started Wireshark on DRother to see what happens when I configure DRother
what happens:
DRother sends a mcast to 224.0.0.5 with BDR/DR 0.0.0.0
BDR's hello timer expires and send a hello to 224.0.0.5, has DR and DRother in it's neighbo list
DR's hello timer expires and send a hello to 224.0.0.5, has BDR and DRother in it's neighbo list
=>biderectional communication is established with his neighbors
I expected that now and exchange would follow with the DR (DBD,LSR,LSU)
DROTHER --> DR via 224.0.0.6
DR --> DROTHER unicast to DR
and finally DR via 224.0.0.5 to all routers
but this is not the case.
I see unicast(in both directions) exchanges(DBD, LSupdate) with both DR and the BDR(???) in both directions?? even unicast exchanges(DBD/LSupdate,...) between DR and BDR (while stable)
(30 messages in 2 seconds)??
In this stream I see only 2 messages to 224.0.06?? While the same message is also sent from DROTHER has been sent to 224.0.0.5
Is this due to GNS3 and wireshark or do I really don't understand how the sync works
Comments
when situation of above is stable (synced)
I add new loopback to DROTHER and add the loopback to the OSPF routing process, same area as the rest
DROTHER --> 224.0.0.6 LSupdate (included: updated LSA1 with 3 links instead of 2)
DR -->224.0.0.5 LS update (included: LSA 1 of DROTHER)
so far so good
but then
BDR --> 224.0.0.5 LS update(old LSA type 1 of BDR)* [DROTHER knows this network long time]
DROTHER --> BDR LS update (included: updated LSA1 of DROTHER with 3 links instead of 2) WTF?(**)
BDR--> DROTHER LS ack (Ack for **)
BDR --> 224.0.0.5 LS Ack (Ack for **)
DROTHER-->224.0.0.6 (LS Ack)(Ack for *)
DR --> 224.0.0.5 LS Ack(Ack for *)
I understand that you won't understand this
But I'm just trying to follow the DBD, Update messages etc via Wireshark
Like the sequence
BDR --> 224.0.0.5 LS update(old LSA type 1 of BDR)*
DROTHER-->224.0.0.6 (LS Ack)(Ack for *)
DR --> 224.0.0.5 LS Ack(Ack for *)
While the network is stable:s
Route is not aged out,
why does the BDR send it to 224.0.05
...
new router exchanges hello packets (neighbor discovery)
all other neighbors reply with the new neighbor's router ID in their neighbor list
==> bidirectional communication + new router has learnt about DR/BDR via the hello's of the neighbors
then
new router communicates with DR via 224.0.0.6 and DR unicast with the new router
>Exstart, Exchange Loading Full
and then DR sends a LSA type 2 out to 224.0.0.5
or how is it actually going?
Or does the DR sends out the new LSA 1 out to 224.0.0.5. But of what use is LSA type 2 then.
I'm confused
the LSA 2 seems to be useless as it lists only the attached networks without any further detail.