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New Member

Load balancing using eigrp

I need to do load balancing for two links headed for the same destination. One link is a 64K radio link direct to the destination. The other link has a 64K link to another router, that is then connected to the final destination via a 128K radio link. What should the load balancing configuration look like? Should it be on all the three routers involved? I have tried the following script on the source router:

router eigrp 100

variance 3

But traffic keeps on going through the directly connected link and the one with two hops is not being used.

Please help

15 REPLIES

Re: Load balancing using eigrp

Hi Friend,

Can you please update the metric values which eigrp must have calculated for both the path?

Config look to be ok please paste the metric value and will take it further.

Regards,

Ankur

New Member

Re: Load balancing using eigrp

I will need to go and check what the metric values are. I actually just assumed that since all the links involved were radio links, then the cost of the longer link was double than that of the directly connected link.

I will get back to you. Let me go the clients site again.

New Member

Re: Load balancing using eigrp

Please find the output from the following scenario when i issue the command

sh ip eigrp topology 0.0.0.0 0.0.0.0

IP-EIGRP topology entry for 0.0.0.0/0

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 40514560

Routing Descriptor Blocks:

182.31.167.137 (Serial1/0), from 182.31.167.137, Send flag is 0x0

Composite metric is (40514560/28160), Route is External

Vector metric:

Minimum bandwidth is 64 Kbit

Total delay is 20100 microseconds

Reliability is 255/255

Load is 7/255

Minimum MTU is 1500

Hop count is 1

External data:

Originating router is 182.31.192.1

AS number of route is 0

External protocol is Static, external metric is 0

Administrator tag is 0 (0x00000000)

Exterior flag is set

182.31.167.81 (Serial1/1), from 182.31.167.81, Send flag is 0x0

Composite metric is (41026560/10514432), Route is External

Vector metric:

Minimum bandwidth is 64 Kbit

Total delay is 40100 microseconds

Reliability is 250/255

Load is 8/255

Minimum MTU is 1500

Hop count is 2

External data:

Originating router is 182.31.192.1

AS number of route is 0

External protocol is Static, external metric is 0

Administrator tag is 0 (0x00000000)

Exterior flag is set

New Member

Re: Load balancing using eigrp

The reported distance for the secondary link (feasible successor) seems to be higer than the feasible distance for primary link (successor).

If the feasible condition is not satisfied, the variance command is not considering the route for load balancing.

You can play with the "delay" interface command to adjust this.

Also remember (when verifying the balancing) that by default EIGRP load balances per-destination and not per-packet.

You may want to change this using the command

(config-if)#ip load-sharing per-packet

HTH

Pls. rate the post if it helped.

Re: Load balancing using eigrp

Hi bellocarico,

I agreee with your point but can you throw some light as how come reported distance be more on the backup link.

As updated by the poster in his first initial post he has a backup path in which the next hop is a router on which bandwidth is 128K. So if we calculate the reported distance of the backup path it will be less than the feasible distance.

(10000000/128+total delay)*256 should give less value than the feasible distance which is 40514560.

Esilavwe can you please confirm if you have changed the bandwidth value on second router which is there on the backup route.

Regards,

Ankur

New Member

Re: Load balancing using eigrp

It could be for different reason.

The most common is usually to forget the bandwidth command or intentionally set a bandwidth value different from the interface speed.

Re: Load balancing using eigrp

Hi Friend,

Yes that could be the reason and that is the reason I have asked the original poster (Esilavwe) in my previous post to update if he had changed or configured any bandwidth command on backup link.

Regards,

Ankur

New Member

Re: Load balancing using eigrp

I've forgotten to add: even if with the above values doesn't work, going down to numbers the variance is not correct either (as it should be min 4 in this case)

Variance should be = (FD primary / RD seconday) ~ rounded up to the next higher integer number

New Member

Re: Load balancing using eigrp

Thank you guys for the replies.

However, i don't think the reported distance on the back up link is greater than the FD(Feasible Distance), please correct me if i am wrong. If you check form the command output i posted it is 10514432 while the FD is 40514560.

So what can be the reason why load balancing is failing?

New Member

Re: Load balancing using eigrp

I would increase the variance to 4 in any case as mentioned.

Could you please post the EIGRP relevant config?

Also, can I ask you how you are checking the load balancing?

Regards

Re: Load balancing using eigrp

Hi,

You are right..your RD is less than FD it should work.

What is the detsination IP/Subnet that you want to reach.

Please paste :

show ip route

show ip eigrp topology

Looking for ur reply.

-amit singh

Re: Load balancing using eigrp

To the original poster:

Variance 3 is good. Actually, variance 2 should work as well in your case.

If you do a show ip route 0.0.0.0 then you should be seeing 2 routes in the routing table. The router should be doing unequal cost load balancing. Can you confirm whether you are seeing this happening?

If the above holds true, how did you find out the traffic is always taking one path. If you were tracing the path from a host on the LAN to a destination through the router then the packet is switched (forwarded) depending on the switching type of ingress interface. However, if you traced to an unknown (0.0.0.0) destination from the router itself then the traffic is process switched and it will give you a better picture of whether unequal cost load balancing is working or not.

On the other hand, if you don't see the 2nd route with a lower metric show up in the routing table then can you add the command 'maximum-paths 4' under the EIGRP process. The default is 4 but it is good to make sure that's not an issue here.

Hope that helps!

HTH,

Sundar

*Please rate all helpful posts.

Re: Load balancing using eigrp

I do agree with Sundar, its not the varience factor which will do the trick. Even varience 2 should work.

Sundar, the original poster has posted the outptut for 0.0.0.0 from the eigrp topology but I am sure that will be some EIGRP routes as well.We need to look more into it by the config perspective.

To the original poster:

I think the better here would be if see the full router configs from both the routers, the source and the destination. Please paste both the router configs.

Regards,

-amit singh

New Member

Re: Load balancing using eigrp

thank you all for your input. From all the responses it helped me understand load balancing better than before.

I realised like Sundar has written that i only needed a variance of 2. I have configured this and now the load is being balanced.However i have noticed that the secondary link is only carrying outbound traffic while all the inbound traffic is coming in through the primary link.

To check for load balancing i am using the sh int. See the out put below from the two interfaces. The input and output rates tell me if a link is carrying traffic or not:

FOR S1/0:

sh int s1/0

Serial1/0 is up, line protocol is up

Hardware is PowerQUICC Serial

Description: Connected to Head-Office 0/4

Internet address is 182.31.167.138/30

MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 107/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

LCP Open

Open: IPCP

Last input 00:00:02, output 00:00:00, output hang never

Last clearing of "show interface" counters 23:15:55

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/9/32 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 48 kilobits/sec

5 minute input rate 27000 bits/sec, 3 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

114659 packets input, 25194133 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

131 input errors, 70 CRC, 41 frame, 0 overrun, 0 ignored, 20 abort

59513 packets output, 4867461 bytes, 0 underruns

0 output errors, 0 collisions, 1 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

DCD=up DSR=up DTR=up RTS=up CTS=up

AND FOR S1/1

sh int s1/1

Serial1/1 is up, line protocol is up

Hardware is PowerQUICC Serial

Description: Connected to Lamya House 1/1

Internet address is 182.31.167.82/30

MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,

reliability 255/255, txload 79/255, rxload 1/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

LCP Open

Open: IPCP

Last input 00:00:01, output 00:00:00, output hang never

Last clearing of "show interface" counters 23:14:58

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: weighted fair

Output queue: 2/1000/64/0 (size/max total/threshold/drops)

Conversations 1/7/32 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 48 kilobits/sec

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 20000 bits/sec, 3 packets/sec

39537 packets input, 2480536 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

53208 packets output, 4507906 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

DCD=up DSR=up DTR=up RTS=up CTS=up

I DON'T KNOW IF I NEED TO LOAD BALANCE AT THE DESTINATION AS WELL. IF THAT IS THE CASE THEN I AM IN TROUBLE BECAUSE THAT IS THE MAIN ROUTER WITH SO MANY LINKS TO MANY OTHER DESTINATIONS.

Re: Load balancing using eigrp

Unfortunately, that's true that you would have to configure the far end device (main router) to perform load balancing for the return traffic. One option you have is if you are using p-t-p (sub-int) interfaces on the far end device then you can tweak the bw&delay to make the routes show up with even metric across both links back to the remote. Though this mayn't be an optimal solution as it mayn't reflect the actual bw of the link but it's an option especailly if you can't modify anything globally under the EIGRP process.

HTH,

Sundar

*Please rate all helpful posts.

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