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Routing for GRE tunnel Destination

We have two links from ISP and both are terminated on Same Backbone /Core Router

One on Giga Ethernet Gi0/0 -- and another on Gi0/1

One is primary Link and other is used as backup

We have created GRE for both the Links to destination with address as 10.10.2.100

GRE Tunnel Configurations are something like

Tunnel 1

Ip address 192.168.0.1 255.255.255.252

tunnel source Gi0/0

Tunnel destination 10.10.2 100

keepalive 5 2

ip tcp-adjust mss 1436

Tunnel 2

Ip address 192.168.0.9 255.255.255.252

tunnel  source Gi0/1

Tunnel destination 10.10.2 100

keepalive 5 2

ip  tcp-adjust mss 1436

Since tunnel destination is same for both Links but Tunnel 1 is made for Primary link terminated on Gi0/0 and Tunnel2 made for backup link terminated on Gi0/1

we have put a specific route like

ip route 10.10.2.100 255.255.255.255 192.168.0.2

and whenever primary link goes down we have to change the specific route

ip route 10.10.2.100 255.255.255.255 192.168.0.10

since this requires manual intervention , is there some way we can keep the second route as floating and should come in picture only when primary goes down because incase primary link goes down , router still is able to reach next hop 192.168.0.2

Both links provided by ISP come from two MUX ports placed in our premises

4 REPLIES
Cisco Employee

Re: Routing for GRE tunnel Destination

You can automatically issue the commands onto CLI by using the EEM, take a look at http://www.cisco.com/en/US/docs/ios/12_4t/12_4t2/ht_eem.html

That said, the next hop values that you have specified are probably not that you use, because this configuration would not work due to recursive routing:

Router(config)#ip route 10.10.2.100 255.255.255.255 192.168.0.2

Router(config)#^Z

Router#

00:07:44: %SYS-5-CONFIG_I: Configured from console by console

00:07:53: %TUN-5-RECURDOWN: Tunnel0 temporarily disabled due to recursive routing

00:07:54: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state to down

Re: Routing for GRE tunnel Destination

snice you have keepalive configured on the tunnel interface, then any issue with the links connectivity on the first lin kwill take the tunnel interface to down state

in this case you can use the following routing config:

ip route 10.10.2.100 255.255.255.255 192.168.0.2

ip route 10.10.2.100 255.255.255.255 192.168.0.10  5

when the tunnel 1 gose down the second route with higher AD will be used, once the tunnel comes back to up state the original static route will be used as it has lower AD

good luck

if helpful Rate

New Member

Re: Routing for GRE tunnel Destination

Hi Marwanshawi

AD will not come in picture in this case because Gi0/0 is directly connected to MUX Port Say X and Gi0/1 is directly connected to MUX Port Say Y

What i mean is that the route 10.10.2.100 will not flush when first link goes down because the exit interface for this route is 192.168.0.2 , which is always reachable from Gi0/0 ( 192.168.0.1) irrespective of whether MPLS link beyond MUX Port is UP or Down

Ofcourse tunnel 1 will go down but Tunnel 2 will not come up because the route for its destination still remains via same MUX port ( ip route 10.10.2 100 255.255.255.255 192.168.0.2

Try to understand the destination of Both GRE Tunnels is same 10.10.2.100

Hall of Fame Super Silver

Re: Routing for GRE tunnel Destination

Perhaps I do not understand your environment or your post very well. You indicate that you have configured this static route:

ip route 10.10.2.100 255.255.255.255 192.168.0.2

But this should not work. It specifies that you should get to the destination of the tunnel by gong through the tunnel.  And that results in recursive routing. For the tunnel to work you need to specify a route to the tunnel destination that does not involve the tunnel.

Perhaps if you provide more information about the environment, especially the configuration of Gi0/0 and Gi0/1 we might understand better and be able to provide better answers to your issue.

HTH

Rick

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