why do people use GRE tunnels

[carl_townshend]

HI all

Why do people mainly use GRE tunnels ?

do they support broadcast and Multicast ?

cheers

[mvsheik123]

Hi Carl,

Yes..it does support Multicast & broadcast support compared to traditional IPsec tunnels. Search in your favourite browser to gather more information on GRE tunnels and the purpose. Below is link from Cisco website for OSPF (Multicast) across GRE .

http://www.cisco.com/en/US/tech/tk583/tk372/technologies_configuration_example09186a00800a43f6.shtml

hth

MS

[Kishore Chennupati]

GRE Tunnels enable you to run routing protocols over the tunnels which makes it attractive.and routing protocols like ospf, eigrp, rip need multicast capability which the GRE tunnels provide.

However, gre tunnels add some over head of 24 bytes to your over all MTU.

There is something called "VTI" which is like GRE but not GRE. its a ipsec tunnel but you can run ur routing protocols on it. below is the link

http://www.cisco.com/en/US/technologies/tk583/tk372/technologies_white_paper0900aecd8029d629_ps6635_Products_White_Paper.html

HTH

Kishore

[david.tran]

"However, gre tunnels add some over head of 24 bytes to your over all MTU."

28 bytes if you use "tunnel key"

[carl_townshend]

hi there

So is a VTI not using GRE? Does it just use IPsec Tunnel mode ?

also is it not the same as a GRE over IPsec tunnel ?

cheers