Packet Drops - GRE Tunnels

Answered Question
Nov 20th, 2009
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Hi

Got this scenario and see Packet drops.

Physical link is ok

Bandwidth is less than 40% used on both ends


IPSEC Over GRE with Two Tunnels from Site_A to Site_B with different service provider.

EIGRP is running between the Tunnels


From Site_A if I try to reach a host in Site_B it prefers Tunnel 10 most of the time

From Site_B if I try to reach a host in Site_A it prefers Tunnel 20 most of the time


On Site_A

Tunnel 10 is termined with ISP 1 having 8MB ( recently upgraded)

Tunnel 20 is termined with ISP 2 having 1.5MB


On Site_B

Tunnel 10 is termined with ISP 1 having 4MB

Tunnel 20 is termined with ISP 2 having 1.5MB


Both Internet link is terminated on the same router at both ends and connects to Core for LAN Users


Site_A_Core................VPN_RTR---------------8MB--------------INTERNET--------------4MB------------------VPN_RTR-----------------------Core_Site_B  [ ISP1]

Site_A_Core................VPN_RTR------------1.5MB---------------INTERNET-----------1.5MB------------------VPN_RTR-----------------------Core_Site_B  [ ISP 2]


Is it also possible to control traffic share count on both links

Correct Answer by Giuseppe Larosa about 7 years 7 months ago

Hello tadlab707,

forgive me I don't remember your name and currently it is not visible.


>> how did you get variance 6 for above BW,  ( 8/1.5 = 5.3 )


that is what I did a ratio of BWs on the two tunnels.


I don't understand how you can have 8 Mbps on HQ side and 4 Mbps on BB8 side, if you refer to link speed provided by provider.

all these tunnels are point-to-point GRE tunnels.


However, you have got the idea behind EIGRP load balancing over unequal cost links.


to provide complete information EIGRP metric with default k -values  is given by:


256 * (sum of delays on path in tens of microseconds) + 256 * 10^7 / ( min BW on path in kbps)


Hope to help

Giuseppe

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Giuseppe Larosa Fri, 11/20/2009 - 06:53
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Hello tadlabs707,


you should give more information about how the two GRE tunnels are used


Are you using a dynamic routing protocol over the two GRE tunnels or you are using simple static routes?


With a dynamic routing, more specifically with EIGRP you may be able to handle two unequal links



Hope to help

Giuseppe

Amin Shaikh Fri, 11/20/2009 - 08:09
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Hi Giuseppe

Initial plan was to use one link for Application using PBR but it doesnt work. Time to time it get into issues.


GRE Tunnels are used in load sharing mode, EIGRP is running over the tunnel. I have attached the config.

Earlier I had taken your advice and moved to EIGRP for unequal Bandwidth.


Traffic from HQ passes to B8 using 8MB Link

but Traffic from B8 passes to HQ using 1.5MB Link ???


Packet drops are for few seconds and then reachability is ok, it happens time to time.

Physical link is ok.  I suspect config issues. Can u help by checking the config.


Is it possible I dont lose packets since two links are under EIGRP from HQ to B8


B8 = Branch8

Attachment: 
Giuseppe Larosa Fri, 11/20/2009 - 09:37
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Hello,

I now remember that we had discussed about this scenario in some previous thread.


However, in the configuration files that you have attached for HQ router and for Branch router 8 I don't see an attempt to modify EIGRP metrics.


these commands like increasing delay and/or modifying bandwidth needs to be set under tunnel interfaces.


example:


on both sides tunnel 55 is primary


interface tunnel 55

delay 10000

bandwidth 8000


interface tunnel 56

delay 10000

bandwidth 1500


if you do so on both sides and then you add the variance command in router eigrp mode


the value to be used should be integer ( BW1/BW2 ) in our case is 6


router eigrp 3

variance 6


all this has to be done on both sides


Hope to help

Giuseppe

Amin Shaikh Fri, 11/20/2009 - 10:27
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Thanks Giuseppe

I have 15 Tunnels in total on the router.

Total BW link 1 = 8MB

Total BW link 2 = 1.5MB


what I understood from your email variance is nothing to do with number of tunnels but with BW

how did you get variance 6 for above BW,  ( 8/1.5 = 5.3 ) 


Do variance needs to be applied on both ends



On Branch8 there is BW=4 and BW=1.5   ( 4/1.5 = 2.6 ) = 3

Correct Answer
Giuseppe Larosa Fri, 11/20/2009 - 12:41
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Hello tadlab707,

forgive me I don't remember your name and currently it is not visible.


>> how did you get variance 6 for above BW,  ( 8/1.5 = 5.3 )


that is what I did a ratio of BWs on the two tunnels.


I don't understand how you can have 8 Mbps on HQ side and 4 Mbps on BB8 side, if you refer to link speed provided by provider.

all these tunnels are point-to-point GRE tunnels.


However, you have got the idea behind EIGRP load balancing over unequal cost links.


to provide complete information EIGRP metric with default k -values  is given by:


256 * (sum of delays on path in tens of microseconds) + 256 * 10^7 / ( min BW on path in kbps)


Hope to help

Giuseppe

Amin Shaikh Fri, 11/20/2009 - 21:43
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Hi Giuseppe

Its not a point to point link, its 8MB Internet.

Thanks alot I got the unequal loadbalancing working Ok.


Help me on PBR, I will post it again. I had hardtime getting it work, after getting great help from you and Rick.

Mohamed Sobair Sat, 11/21/2009 - 02:02
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Hello Tadlabs,


I recommend if you look at Eigrp documentation (How the variance works in Eigrp) for more information.


The Variance is multiplier and is used in Eigrp for un equal cost loadbalancing, look at the example bellow:


If you have a router with 3 possible paths to specific destination network, lets assume you have the following metric for each path:


1- 2

2- 4

3-6


Eigrp shall use path 1 by default as it has the lowest metric to that destination, as its Feasible distance. To place path 2 in the routing table with a metric of 4, you have to use variance 2, 2 * 2 = 4 .  If you want to place path 3 in the routing table, you should configure the variance to be 3 , as 3*2 = 6. and so on and so forth.



What exactly you need from PBR so we can help you further?



Mohamed

Richard Burts Sat, 11/21/2009 - 03:00
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To add a bit to the response from Mohamed, for EIGRP variance to work the route must qualify as a feasible successor. So even if you configure variance of 3 the more expensive route with metric of 6 will not be placed into the routing table unless it satisfies the feasibility condition.


HTH


Rick

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