OSPF encapsulates directly into IP

Answered Question
Jul 17th, 2007
User Badges:

Hello,


I have a query regarding encapsulation of OSPF & EIGRP packets into IP packet.As we know that RIP use UDP and BGP use TCP so we call them application layer routing protocols. My question is that in which layer OSPF & EIGRP lies and what is the format of encapsulted OSPF & EIGRP packets ? What is the difference in encapsulation process of these protocols as compare to RIP & BGP.


Regards,


Mujeeb

Correct Answer by Richard Burts about 9 years 10 months ago

Mujeeb


Yes OSPF data (and EIGRP data) travel as the payload of their IP packets. And OSPF packets and EIGRP packets do not contain UDP or TCP.


There are a number of situations where IP packets going through the network do not have TCP or UDP transport layer. For example protocol 47 is for GRE packets which do not use either UDP or TCP. And protocol 50 is for ESP (part of IPSec) which does not use UDP or TCP.


These protocols (including OSPF) do not need the services provided by the traditional transports of UDP or TCP.


HTH


Rick

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4.5 (3 ratings)
Loading.
rais Tue, 07/17/2007 - 08:03
User Badges:
  • Silver, 250 points or more

RIP and BGP use already existing transport protocols UDP/TCP. e.g. BGP can rely on all the features already provided by TCP such as ACKed packets.


OSPF is a protocol on IP:protocol value = 89. Other values can be found at:

http://www.iana.org/assignments/protocol-numbers


OSPF packets are carried by IP without TCP/UDP headers. Packet formats can be found at: ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt


Thanks.


Richard Burts Tue, 07/17/2007 - 10:54
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Mujeeb


Rais gives a good answer in terms of OSPF and much the same thing can be said for EIGRP. The designers of RIP and of BGP decided to utilize existing transport protocols to carry their routing traffic. The developers of OSPF and of EIGRP decided that there were advantages in not using an existing transport layer protocol and just encapsulating their content directly in IP. Part of the advantage of this is that it simplifies the formatting of the packet and simplifies the processing of the packet when it is received (rather than passing the data from layer 3 IP to layer 4 UDP or TCP which will look at the data and determine that it needs to be sent to the routing protocol, the data goes directly from layer 3 IP to the routing protocol.


HTH


Rick

rmujeeb81 Wed, 07/18/2007 - 05:30
User Badges:


Hello Rick,


It means that OSPF packet travel in payload field of an IP packet and that IP packet does not contain UDP/TCP in it so where will be transport layer come into play.EIGRP use RTP as transport layer protocol , is there no need of transport layer function for OSPF ?


Regards,


Mujeeb

Correct Answer
Richard Burts Wed, 07/18/2007 - 05:42
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Mujeeb


Yes OSPF data (and EIGRP data) travel as the payload of their IP packets. And OSPF packets and EIGRP packets do not contain UDP or TCP.


There are a number of situations where IP packets going through the network do not have TCP or UDP transport layer. For example protocol 47 is for GRE packets which do not use either UDP or TCP. And protocol 50 is for ESP (part of IPSec) which does not use UDP or TCP.


These protocols (including OSPF) do not need the services provided by the traditional transports of UDP or TCP.


HTH


Rick

rmujeeb81 Wed, 07/18/2007 - 21:09
User Badges:


Hello Rick,


I got your point , thanks for the response.



Regards,


Mujeeb

Richard Burts Thu, 07/19/2007 - 10:41
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Mujeeb


I am glad that we were able to clarify that point. Thank you for using the rating system to indicate that your question was answered satisfactorily (and thanks for the rating). It helps make the forum more useful when people can read a question and can know that they will read a good answer to the question. I encourage you to continue your participation in the forum.


HTH


Rick

minumathur Tue, 07/17/2007 - 10:46
User Badges:
  • Bronze, 100 points or more

Hi


OSPF is relies on IP packet for delivery of routing information.OSPF information is carried inside IP packet .


it is using protocol number 89 .


-minu

Actions

This Discussion