From: Saad Adam (subjectvsobject@yahoo.com)
Date: Sat Feb 11 2006 - 04:14:22 GMT-3
Hi,
Virtual link and GRE are both tunnels, the difference is Virtual link is what I would say the recomended way of ospf to do overcome the area 0 limitation, but has its own limitations, like it can not pass over stub areas.
On the other hand GRE as the name says is a routing protocol Generic tunnel my personal opinion is use virtual links whenever possible and go for GRE only when you have the stuf limitation, or when the ques tells you to use GRE which might be in the form of.
1) Configure ospf neighbors as if they are directly connected.
2) or Do not use Virtual links.
Another place where you will have to use gre is when you don't have ospf running between your router and area 0, like in the case below.
------------------------ ------------- --------------------
| OSPF Area 0 | ------| EIGRP | -----------| Ospf Area 1 |
------------------------ ------------- --------------------
R1 R2 R3
In the above senario R3 running ospf area 1 does not have a direct connection to area 0 and neighter does it have a transit ospf area to link it to area 0, in this case the only option you have is to run a gre tunnel from R3 to R1 making them look as if they are directly connected.
I hope this answers the question.
Best regards,
Saad.
Regards,
Saad.
Venkatesh Palani <kvpalani@gmail.com> wrote:
HI all,
This might be a basic one, but I am just trying to understand given a chance
which is best to use GRE tunnel or Virtual links in OSPF. Also under which
circumstance GRE is preffered or the only solution over Virtual link.
to start with ..
1. GRE is used when there is a Stub area between the disjoint area
could any one add more to this ?
Thank you,
Venkatesh
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