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glyle
Beginner

GRE tunnel issue

I am experiencing a strange problem with GRE tunnels we are using to connect a remote site. There are two routers, RT1 & RT2, using HSRP & each router has its own GRE tunnel connected over the internet to a router in our network hub. I am running EIGRP over the tunnels. The problem occurs when the tunnels go down due to an internet outage, when it comes back up everything is ok except i cannot ping an NMS server at our hub, i can ping devices in the same subnet as the server but not the server. I then need to shut down the inside interfaces to switch HSRP over to router 2, which can ping the server. If the tunnels go down again then router 2 cannot ping the server as with router 1. I have noticed that after roughly 4 hours the routers are able to ping the server again. I have checked the routing tables after each outage & all the correct routes are there. The only traffic going over the active tunnel when it goes down is to & from the server so i am not sure if this has anything to do with it.

I am puzzled as to why this is happening, has anyone out there seen this issue before?

33 REPLIES 33
andrew.prince
Advocate

1) - what is the delay/bm metrics for the tunnels used?

2) - try reducing ther EIGRP hello and dead timers on the tunnels to say 1 hello 3 dead

3) - which is the primary and which is the secondary?

4) - you may have an EIGRP mis-match and asymentric route.

5) - have you tried using tunnel keepalives?

HTH>

Hi Andrew

Firstly, thanks for the quick reply.

1, I set the delay on the tunnel interface connecting to RT2 at our hub to 500050 so the tunnel to RT1 is prefered at 500000, i think thats what you are asking?

2, I'll look at that & give it a try but to be honest EIGRP seems to be working well with fast convergence when the tunnels come back up.

3, Rt1 is primary & RT2 secondary.

4, I have looked at the routing tables & all looks ok.

5, The tunnels are using keepalives.

Graeme

Graeme,

OK - have you made sure the delay is the SAME at both ends of the tunnel?

Can you supply the output from both devices:-

show ip eigrp int

show ip eigrp nei

show ip eigrp top

show ip route eigrp

?

The delay was only changed at the hub side, RT2 is still using the default.

I have attached the output you asked for so a short explanation of what is what is required:

Hub

Tunnel 2 to RT1 172.20.20.13

Tunnel 3 to RT2 172.20.20.17

RT1

Tunnel 0 to Hub 172.20.20.14

int Vlan 12 to RT2 10.10.9.2

int Vlan 190 to RT2 192.168.10.34

The server is in subnet 192.168.0.16/29

Graeme

Graeme,

From rt1 the route to 192.168.0.16 is via tunnel 0?

I would have thought that you would want a direct path back to the hub?

Hi Andrew

We are using a dedicated router inside our hub to terminate multiple VPN's & route the traffic from there.

Graeme

OK - so from rt1 I see no feasible sucessor for the route to 192.168.0.16 from anywhere else other than tunnel0 that goes to the hub.

Can you supply the same outputs from rt2 ??

Andrew

I have attached the RT2 configs.

Graeme

Graeme,

From looking at what you have sent I see 2 issues:-

1) Both router 1 and router 2 have the same cost to 192.168.0.16 in the eigrp table

2) Router 2 does not see the route from router 1 as a feasbile sucessor - as I am assuming that router 1 is the hsrp master, and router 2 is the standby.

what bandwidth have you configured for tun0 on rt1 and tun0 on rt2? what delay is configured on these tunnels

Ideally what you want is for tunnel 0 on rt1 to be the primary. The tunnel 0 on rt2 as the secondary with a feasbile sucessor seen from rt1. Rt1 is the hsrp master - with rt2 as the standby, so if the tunnel 0 in rt1 goes down, rt2 will distribute the route from tunnel 0 into rt1 as rt1 is the hsrp master. If rt1 goes down completly - all routes a valid.

Hi Andrew

Yes, RT1 is active & RT2 is the standby. I haven't configured the bandwidth on the tunnels for routers 1 & 2 only increased the delay on tunnel 3 at the hub which points to RT2 thus traffic prefers the route to RT1. I had though that load balancing traffic from the hub may have caused this issue but it still remains.

I will be back at my desk on Monday, as i am on a trip for the next 3 days so i will increase the delay at the tunnel interface on RT2 then & see what happens. If you have any other ideas to try i will have a look at these also.

Thanks for the replies.

Graeme

Graeme,

OK - in the hub tunnel 3 configure:-

delay 1000000

on rt2 tunnel 0

delay 1000000

HTH>

Hi Andrew

I have added the config on both ends of the tunnel & now i can ping the server when the tunnel comes back up. When the tunnel is down on router 1 i still cannot ping the server even though there are routes via router 2. I had increased the delay on one of the vlan interfaces on both routers but still i cannot ping the server. This is not a problem though as router 2 has taken over but i wuold like to understand why this config change worked a far as the tunnel interface is concerned.

OK cool, we have one issue fixed. Can you post the output of:-

show ip route

show ip route static

show ip eigrp int

show ip eigrp top

from all 3 devices?

Hi Andrew

The issue still remains, when i arrived this morning the tunnel had come back up 1 hour previously, can ping everything else but not the server. When i tested yesterday i shut the tunnel interface, in reality when the tunnel goes down, for what ever reason, the tunnel interface will always be up so this was probably not an accurate test. I have attached the configs you requested.

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