07-10-2020 08:39 PM
Hi!
I can't find the ‘network type’ field in the OSPF Hello packet, How can received router determine which network type interface of his neighbor are? Can someone please tell me?
Thanks!
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07-10-2020 11:23 PM - edited 07-11-2020 09:58 AM
no, there are no fields for that in Hello packets but OSPF does have several LSA packet types (or codes); we care mostly about Router LSA type 1, Network LSA is 2, Network Summary is 3, 4 , external 5 and 7.
Hello Packets have necessary info to discover OSPF routers such Router and Area IDs, hello and dead timers, DR/BDR, network mask, and others but no ‘network type’. Timers and DR election (or not) are based on link media type and encapsulation.
After Hellos are exchange, LSA headers are exchanged before each router exchanges all LSA types he knows.
Regards, ML
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07-10-2020 11:23 PM - edited 07-11-2020 09:58 AM
no, there are no fields for that in Hello packets but OSPF does have several LSA packet types (or codes); we care mostly about Router LSA type 1, Network LSA is 2, Network Summary is 3, 4 , external 5 and 7.
Hello Packets have necessary info to discover OSPF routers such Router and Area IDs, hello and dead timers, DR/BDR, network mask, and others but no ‘network type’. Timers and DR election (or not) are based on link media type and encapsulation.
After Hellos are exchange, LSA headers are exchanged before each router exchanges all LSA types he knows.
Regards, ML
**Please Rate All Helpful Responses **
07-11-2020 10:28 AM
07-11-2020 12:30 AM
Network type is determined from the physical interface type .. e.g. ethernet = broadcast, serial = non-broadcast
ospf behaviour changes when physical interface type changes e.g. ospf will advertise subnet configured on loopback interface as /32 by default we change that by changing the interface type to point-to-point ..
07-11-2020 02:36 AM
If I understand correctly you looking network types - like p2p or p2m scenario. if so here some of the Wireshark capture for your reference, you can view for reference.
here is a good explanation :
https://ccieblog.co.uk/ospf/ospf-hello-protocol
Wireshark samples.
https://packetlife.net/captures/protocol/ospf/
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