Hello packet, also called Type1 OSPF Packet, is a special packet/message that is sent out periodically from a router to establish and confirm network adjacency relationships. These packets are sent periodically on all interfaces in order to establish and maintain neighbor relationships.
Hello Packets contain different parameters including Network mask, Hello Interval and Router Dead Interval,…. These parameters are needed to form neighbor relationships. All routers connected to a common network (NBMA,…) must agree on certain parameters. Below is the detailed description of Hello Packet & its fields:
Below is description of fields in the OSPF Hello Packet:
Consider the simple below topology with two Routers:
As soon as we enable OSPF on the router interfaces, it starts exchanging Hello Packets.
It is obvious from the below detail, spend some time with it to understand it fully:
We can see from the above capture that OSPF Hello Packets are defined as Type1 in the header frame. Both Routers are exchanging the Hello Packets once the OSPF has been enabled & configured properly.
How does the OSPF router know the neighbor’s interface address in the LAN ?
Actually Hello packet is sourced from the router’s unicast address on that link, providing a unicast destination for the receiver. Other side receiving router knows to begin formation of a new adjacency by seeing itself in the header of Hello Packet. It sees its own router ID in the “Neighbor” field of the Hello Packet.
Visit this RFC for more information (Hello Protocol and Receiving Hello Packets): https://www.ietf.org/rfc/rfc2328.txth
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Thanks for detailed Thanks.
Nice one
Thank you for helping me in hello packets.
Is hello pack behave as same as IEGRP
No, please visit & revert back to me if still some concerns: https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html
Thank you for the awesome explanation.
Thanks for app
Thank you very much for starting this tutorial..I request to please continue it. Thanks.
Thanks!
First step of Levels? Good!
I’m also studying ospf type messages, its helps to understand behavior of a hello message in ospf.
Thanks!
Nice post
Thnx