Suggestions - GRE Tunnels

Unanswered Question
Mar 29th, 2010

Hi Guyz

Here it's my question. Is it possible to configure GRE tunnel with loadbalancing while terminating two ISP link on one router at one end.
Other end with Two Router terminating one isp link.Bandwidth of each ISP is different.

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Marwan ALshawi Mon, 03/29/2010 - 02:38

if the Tunnel running between the two switches then yes

but you need to have two default routes in the router with the two links using same metric each one point to one of the ISPs

in the switch connected to two routers there you need your default route to be created and each default route point to one of the routers

but this may lead to asymmetrical routing ( traffic come thorough one ISP and go back through another ISP !!)

good luck

if helpful Rate

tomfree_leo Mon, 03/29/2010 - 06:50

Hi

What other workable options I got keeping load balancing of bandwidth and link redundancy in mind.

asymmetrical routing will cause serious problem in terms of response time

Richard Burts Mon, 03/29/2010 - 12:57

Tom

Traditional GRE builds a point to point tunnel. So a single traditional GRE tunnel will not work for you in the enviroinment shown in your diagram. There are 2 options I can suggest:

- there is an option to configure multipoint GRE tunnels. This would create a single tunnel on each router and connect a single router at one end and 2 routers at the other end. But this is more complicated to configure and I do not believe that it would facilitate load balancing.

- you could configure 2 GRE tunnels. The single router end would have 2 tunnels on the router and the other end would have a single tunnel on each router. With 2 tunnels it is possible to get load balancing. To get the load balancing to reflect unequal bandwidth can get a bit complex but it is possible.

HTH

Rick

[edit]

Andrew

If you configure different bandwidths on the tunnels then PERHAPS EIGRP would load balance and reflect the variation in bandwidth. Running OSPF on tunnels with different bandwidth would generate routes with different costs and OSPF would provide redundancy but not load sharing.

tomfree_leo Mon, 03/29/2010 - 23:00

thanks rburts

2nd suggestion of yours is our preferred option. Whats your opinion on

               1.     running Eigrp on tunnels

               2.     running ospf on lan segment ( currently running on production with single area )

               3.     route-map to control the traffic flow

Bandwidth on tunnels are unequal, I am not aware of which parameter to adjust to get loadsharing and redundancy working.

Rick,

Agreed - however I must admit I jumped in before reading and comprehending the whole requirement.  EIGRP & OSPF will load balance across the GRE tunnels at the HUB end.  Yes you can mess with the Bandwith on the GRE tunnels - as by default they are virtual and have a BW of 9Kb, I personally tinker with the delay to get equal cost LB in EIGRP, another way would be to adjust the variance.  OSPF - agreed is just BW.

From seeing the diagram - did not see it before, I would create the 2 GRE tunnels on either end of the Layer 3 switches (not the routers - that way it would LB @ both ends.

JMTPW

tomfree_leo Tue, 03/30/2010 - 03:48

Hello

Can I get config help on variance and tuning of cost for load balancing. I am ok with configuring GRE tunnels, EIGRP basic, OSPF basic, redistribution basic

Variance should only be used - when you are traversing links of different speeds/bandwidth - and you want to multiply the best metric to encompass slower link speeds.

The default BW of a GRE tunnel is 9Kb - unless you have changed this, EIGRP/OSPF will calc the metrics for both tunnels as the same.  You should not need to change anything - unless you have changed the defaults?

tomfree_leo Tue, 03/30/2010 - 05:19

thanks prince

I am still not clear how loadbalancing will work as bandwidth are unequal and tunnels will terminate on different routers for redundancy,

I add more details to get more input from you

Location A
ISP_1 terminates on R1 with Bandwidth 6MB
ISP_2 terminates on R2 with Bandwidth 1MB

Location B
ISP_1 terminates on R1 with Bandwidth 2MB
ISP_2 terminates on R1 with Bandwidth 1MB

On Location_A
R1=  GRE_Tunnel 1 will be configured on ISP_1 with Location_B ISP_1
R2 = GRE_Tunnel 2 will be configured on ISP_2 with location_B ISP_2

can you input plz

tomfree_leo Tue, 03/30/2010 - 06:03

Prince,

the diagram is without IP but rest is the same.

My apology if it misguided.

Tom my first name is Andrew.

From your earlier post......

Location A
ISP_1 terminates on R1 with Bandwidth 6MB
ISP_2 terminates on R2 with Bandwidth 1MB

Location B
ISP_1 terminates on R1 with Bandwidth 2MB
ISP_2 terminates on R1 with Bandwidth 1MB

Your diagram does not show:-

1) Location A

2) Location B

3) Location A R1

4) Location A R2

5) Location B R1

Which site is the hub/core site?

Have you actually configured any of the tunnels?

Have you got a routing protocol running over the 2 sites?

What protocol are you using?

tomfree_leo Tue, 03/30/2010 - 07:27

Thank you Andrew,

Which site is the hub/core site?

* Location_A  ( Hub with 2 Routers )

Note sure if its call Dual Head VPN on Same Site

Have you actually configured any of the tunnels?

* tested in labs

Have you got a routing protocol running over the 2 sites?

* on LAN its already OSPF

What protocol are you using?

* for Tunnels planning for EIGRP

For Lan its already OSPF

Tom,

To answer one that you asked a couple opf postings ago:-

I am still not clear how loadbalancing will work as bandwidth are unequal and tunnels will terminate on different routers for redundancy.  The interface bandwdith on GRE tunnels does NOT refelct the actual bandwidth of the physical circuits.  The bandwidth is ONLY used in dynamic routing route metric calculations.  As previsouly stated a default bandwidth on a GRE tunnel is 9Kb, this does not reflect the physical circuit speed.  The dynamic routing protoclcol will use the 9Kb value in route path metric calculation.

OSPF will only use this - so OSPF will see both tunnels and cost them the same.

EIGRP K values (Metric calculation) by default are Bandwidth and Delay - a default delay of a GRE tunnel is 500000 milli sec.

So with regards to your diagram, if you configure a Tunnel on RT1 @ location A and a Tunnel on RT2 @ location, A both routers will get the route from location B.  If you configure 2 x Tunnels on RT1 @ location B - it will get the same both route from both tunnels - this router will auto load balance between the tunnels.  Location A routers will not auto load balance.  Now assuming OSPF is running over the tunnels, the device @ location A that is behind the two routers will recevie 2 routes from RT1 & RT2 - as they are of equal cost - that device will LB.

**** WARNING ****

If you run EIGRP over the tunnels and you have OSPF on the LAN @ both locations - you will have to perform mutual redistribution @ location A on RT1 & RT2 - be VERY careful, you will quite easily introduce a routing loop.

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