GRE tunnel problem

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Sep 15th, 2008
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I have applied the below confgs on two remote cisco routers connected to internet,the tunnel status is up up but I cant ping the tunnel ip address,what might be the problem??


int tunnel 1

tunnel source s0/0

tunnel destination x.x.x.x (f0/0 of R2)


int tunnel 1

tunnel source f0/0 (real ip)

tunnel dest x.x.x.x (s0/0 of R1)


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Marwan ALshawi Mon, 09/15/2008 - 05:20
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do u have routing protocol configured?

have u included the tunel interfaces in ur routing

also put the tunnel mode

god luck

mohammady Mon, 09/15/2008 - 19:05
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I dont have routing protocol also I use the default tunnel mode

mohammady Tue, 09/16/2008 - 04:13
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the tunnel stat is up up but I cant ping the other end??for the route I have a default route on both routers.....

mohammady Tue, 09/16/2008 - 04:20
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the two routers connected to service provider routers (internet connection)

mohammady Tue, 09/16/2008 - 04:24
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really I dont know ,it is the service provider network>>>how can I make sure that the tunnel is working properly....???

To be honest - you need to know this.

As you will be using RFC1918 internal IP addresses. So you will NAT or your provider might NAT for you - you need a routable source and destination for the tunnel to work. You also need to know if there any devices in between the connection between the 2 sites that could be blocking the runnel. What is the connection to the internet?? MPLS? Frame-Relay? ADSL ??

Right now you don't have enought information - you need to do some digging.


mohammady Wed, 09/17/2008 - 06:52
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one of them has dedicated E1 connection and the other one connected to a second router in possession of our service provider and then to internet...


R2--->service provider Router --->internet

mohammady Wed, 09/17/2008 - 12:07
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the tunnel stat is up up >>>what this implies??

it implies nothing really, only the interface that is the source is know and up/up and that the router has a valid "live" route in it's routing table for the destination.

Just for you - configure your end with the following:-

int tun1

keepalive 1 3

Then close the tunnel and re-open it....does it come back up/up ????

At the end of the day you can trick a tunnel into being up/up if you have the time and a spare router with 1 ethernet interface do this:-

do not connect any cables to the ethernet interface.

Give the interface an ip address of

create a tunnel 1

tunnel source <>

tunnel destination

ip route <>

and here is the magic - in the ethernet interface configure "no keepalive" this tricks the interface to come up/up - the there wiull be a connected interface in the routing table of

As you have a configured static route out of the ethernet interface - there will be a static route in the routing table. As the tunnel can see a valid route - without keepalives, it will bring the tunnel up!

Try it out - great fun.

Your issue is still the path from 1 site to the other site and going over the internet I presume, you have nat issues, blocking issues or just plain connectivity/routing issues.



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