Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
New Member

Unequal load balance and OSPF

Hi

Eigrp, ospf, BGP all are support equal load balance.

But if I have HO and 3 branches . Ho connected all branches 3 ISP line.

If 3 ISP is unequal metric and if I run OSPF then data is transfer only one path.

that means no load balancing among the path.I know with the EIGRP can be done Unequal load balance. so with OSPF its not possible.

pls easily explain .

Thanks

Biplob

17 REPLIES
Bronze

Re: Unequal load balance and OSPF

Not possible with ospf.

As far as I know you can only do unequal loadbalance with EIGRP, and with a combination of e-BGP and static routes.

Re: Unequal load balance and OSPF

OSPF uses COST of an interface as metric, which is calculated based on BW on interface by default.

But you can directly manipulate the cost of an interface without directly varying BW of interface which hampers QOS & other tools. Please note, lower cost interface is preferred over hisger cost.

So you may want to change the cost on interface over which you need to load-balance.

New Member

Re: Unequal load balance and OSPF

Hi

My question was if IF ISP line with 64, 128,256 connected branch then when OSPF ruuning among the three path data provide or only one path data pass.

thanks

Biplob

Re: Unequal load balance and OSPF

You will only get multiple routes if the total path costs to the destination are equal. Practically, in your situation you will only get multiple paths if you can persuade them they have the same cost. Then the load balancing will be even, not unevan as you are looking for.

Kevin Dorrell

Luxembourg

New Member

Re: Unequal load balance and OSPF

HI

so In this case eigrp use will be best ?

Biplob

Re: Unequal load balance and OSPF

I would say so, as long as all the routers are Cisco.

Kevin Dorrell

Luxembourg

Re: Unequal load balance and OSPF

Hall of Fame Super Gold

Re: Unequal load balance and OSPF

Kevin,

keep in in mind, uneven load balancing with EIGRP requires process switching. In most cases, that is not a viable option.

So generally speaking EIGRP unequal load balancing must be avoided and one has to find other ways to balance traffic.

Re: Unequal load balance and OSPF

Sorry Paolo, but I beg to differ. I think the load balancing is handled by CEF. The algorithm is based on a weighted 16-slot hash profile. Here are some documents about it:

http://www.cisco.com/en/US/tech/tk827/tk831/technologies_tech_note09186a0080094806.shtml

http://www.cisco.com/en/US/products/hw/modules/ps2033/prod_technical_reference09186a00800afeb7.html

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

Kevin Dorrell

Luxembourg

Hall of Fame Super Gold

Re: Unequal load balance and OSPF

Hi Kevin,

this has been discussed many times in the past already.

I've challenged anybody to produce either:

a) One production example of EIGRP unequal load balacing - no matter whta the switching path used.

or

b) A lab example of EIGRP unequal load balance with CEF switching.

So far, nobody has responded. If you can be the one to prove that A and/or B are real, I'll be glad to declare myself wrong.

Re: Unequal load balance and OSPF

OK, I'll try it out in the lab and see what happens. It may not be this week though.

Could you give me some links to the previous discussions so that I can read "the story so far".?

Thanks.

Kevin Dorrell

Luxembourg

Hall of Fame Super Gold

Re: Unequal load balance and OSPF

In this forum, but I've not a ready link.

However the only thing that came out was that nobody at cisco could demosntrate the fact that you can have unequal and CEF (or orvef fast) switching at the same time.

Cisco Employee

Re: Unequal load balance and OSPF

Paolo,

The eigrp variance feature will work in conjunction with cef switching to load-balance the traffic unequally among outbound interfaces.

routerD#sh ip ro 192.168.13.0

Routing entry for 192.168.13.0/24

Known via "eigrp 1", distance 90, metric 307200, type internal

Redistributing via eigrp 1

Last update from 192.168.23.3 on Ethernet1/0, 00:00:55 ago

Routing Descriptor Blocks:

* 192.168.12.1, from 192.168.12.1, 00:00:55 ago, via Ethernet0/0

Route metric is 307200, traffic share count is 2

Total delay is 2000 microseconds, minimum bandwidth is 10000 Kbit

Reliability 255/255, minimum MTU 1500 bytes

Loading 1/255, Hops 1

192.168.23.3, from 192.168.23.3, 00:00:55 ago, via Ethernet1/0

Route metric is 614400, traffic share count is 1

Total delay is 4000 microseconds, minimum bandwidth is 5000 Kbit

Reliability 255/255, minimum MTU 1500 bytes

Loading 1/255, Hops 1

routerD#sh ip cef 192.168.13.0 internal

192.168.13.0/24, version 25, epoch 0, per-destination sharing

0 packets, 0 bytes

tag information set, all rewrites owned

local tag: 32

via 192.168.12.1, Ethernet0/0, 0 dependencies

traffic share 2

next hop 192.168.12.1, Ethernet0/0

valid adjacency (0x0150DE98)

tag rewrite with Et0/0, 192.168.12.1, tags imposed {}

via 192.168.23.3, Ethernet1/0, 0 dependencies

traffic share 1

next hop 192.168.23.3, Ethernet1/0

valid adjacency (0x0150DBC8)

tag rewrite with Et1/0, 192.168.23.3, tags imposed {}

0 packets, 0 bytes switched through the prefix

tmstats: external 0 packets, 0 bytes

internal 0 packets, 0 bytes

Load distribution: 0 1 0 1 0 1 0 1 0 1 0 0 0 0 0 (refcount 1)

Tags distribution: 0 1 0 1 0 1 0 1 0 1 0 0 0 0 0 (addr 1C135F8)

Hash OK Interface Address Packets Tags imposed

1 Y Ethernet0/0 192.168.12.1 0 none

2 Y Ethernet1/0 192.168.23.3 0 none

3 Y Ethernet0/0 192.168.12.1 0 none

4 Y Ethernet1/0 192.168.23.3 0 none

5 Y Ethernet0/0 192.168.12.1 0 none

6 Y Ethernet1/0 192.168.23.3 0 none

7 Y Ethernet0/0 192.168.12.1 0 none

8 Y Ethernet1/0 192.168.23.3 0 none

9 Y Ethernet0/0 192.168.12.1 0 none

10 Y Ethernet1/0 192.168.23.3 0 none

11 Y Ethernet0/0 192.168.12.1 0 none

12 Y Ethernet0/0 192.168.12.1 0 none

13 Y Ethernet0/0 192.168.12.1 0 none

14 Y Ethernet0/0 192.168.12.1 0 none

15 Y Ethernet0/0 192.168.12.1 0 none

refcount 6

routerD#

Regards,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Hall of Fame Super Gold

Re: Unequal load balance and OSPF

Harold,

great. What i'd also like to see, is a snapshot with populated statistics:

0 packets, 0 bytes switched through the prefix

tmstats: external 0 packets, 0 bytes

internal 0 packets, 0 bytes

I mean, good so far, now what happens when you pass traffic ?

Any report of customers having this in production ?

Cisco Employee

Re: Unequal load balance and OSPF

Paolo,

I do not currently have test equipment to inject traffic but the show command I provided is the actual FIB, so unless CEF is disabled on a specific interface, the FIB is used to forward packets and these packets will be forwarded based on the hashing buckets seen in the show command as can be seen with the following command:

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.3

192.168.24.4 -> 192.168.13.3 : Ethernet0/0 (next hop 192.168.12.1)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.1

192.168.24.4 -> 192.168.13.1 : Ethernet0/0 (next hop 192.168.12.1)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.2

192.168.24.4 -> 192.168.13.2 : Ethernet0/0 (next hop 192.168.12.1)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.4

192.168.24.4 -> 192.168.13.4 : Ethernet1/0 (next hop 192.168.23.3)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.5

192.168.24.4 -> 192.168.13.5 : Ethernet0/0 (next hop 192.168.12.1)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.6

192.168.24.4 -> 192.168.13.6 : Ethernet1/0 (next hop 192.168.23.3)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.7

192.168.24.4 -> 192.168.13.7 : Ethernet1/0 (next hop 192.168.23.3)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.8

192.168.24.4 -> 192.168.13.8 : Ethernet1/0 (next hop 192.168.23.3)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.9

192.168.24.4 -> 192.168.13.9 : Ethernet0/0 (next hop 192.168.12.1)

routerD#sh ip cef exact-route 192.168.24.4 192.168.13.10

192.168.24.4 -> 192.168.13.10 : Ethernet0/0 (next hop 192.168.12.1)

As far as your second question, yes there are customers using unequal cost load balancing in their production networks.

Regards,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Hall of Fame Super Gold

Re: Unequal load balance and OSPF

Very good, you provided the exact type of information that has been missing in previous discussion on the subject, and I've rate your post, thanks!

Bronze

Re: Unequal load balance and OSPF

I hope you are finding some of this useful.

And just to let you know, you might be able to use staic routes for unequal loadbalancing, it depends on your setup.

Are you using MPLS, Frame relay or something totaly different?

297
Views
10
Helpful
17
Replies
CreatePlease to create content