OSPF LSA

[pate.miral]

how does lsa know's where to send the packet?

[acampbell]

Pate,

In OSPF the LSA packets are sent to the common OSPF multicast address 224.0.0.6

See this link - it has some nice pictures and descriptions:-

http://www.firewall.cx/networking-topics/routing/ospf-routing-protocol/1147-ospf-lsu-lsa-packet-structure-lsa-types-overview.html

Regards

Alex

[pate.miral]

Thank you and i appreciate for your answer. but if asbr will get the external route to reach the backbone area using lsa 5. how lsa 5 will transmit those packet to backbone area?

[acampbell]

Pate,

Have a look at this link.

Again the LSA5 from the ASBR is directed to the All OSPF routers multicast address 244.0.0.6

https://ccie20728.wordpress.com/2009/08/18/ospf-type-5-lsa/

Use sh ip ospf data exter

On an Area "0" router.

Regards

Alex

[Rolf Fischer]

Alex,

In OSPF the LSA packets are sent to the common OSPF multicast address 224.0.0.6

This is very often true but not always. Here some quotes from RFC 2328:

13.  The Flooding Procedure

Link State Update packets provide the mechanism for flooding LSAs. A Link State Update packet (...) floods each LSA one hop further [to the neighbors] from its point of origination. (...)

The flooding procedure starts when a Link State Update packet has been received. (...)

On broadcast networks, the Link State Update packets are multicast.  The destination IP address specified for the Link State Update Packet depends on the state of the interface.  If the interface state is DR or Backup, the address AllSPFRouters [224.0.0.5] should be used.  Otherwise, the address AllDRouters [224.0.0.6] should be used.

On non-broadcast networks, separate Link State Update packets must be sent, as unicasts, to each adjacent neighbor (i.e., those in state Exchange or greater).  The destination IP addresses for these packets are the neighbors' IP addresses.

Regards
Rolf