OSPF load balancing not working

[hanwucisco]

it must be something to do with CEF.

I've set up a simple scenario, please see the attached picture. R1 (two loop addreses) as source, R4 (3 loop addresses) as destination. I did ping from R1 to R4. every time, the traffic goes through R3. As shown in "show interface s0/0 and s0/1" on R4.

I have hunch it is something to do with CEF, but can't figure it out.

any idea would be great,

thanks,

====R1===

hostname R1

!

no aaa new-model

ip subnet-zero

!

!

ip cef

no ip domain lookup

interface Loopback0

ip address 1.1.1.1 255.255.255.0

!

interface Loopback1

ip address 1.1.2.1 255.255.255.0

!

interface Serial0/0

ip address 1.1.12.1 255.255.255.0

serial restart-delay 0

!

interface Serial0/1

ip address 1.1.13.1 255.255.255.0

serial restart-delay 0

!

router ospf 1

log-adjacency-changes

network 0.0.0.0 255.255.255.255 area 0

!

====R2====

R2#sh run

Building configuration...

!

hostname R2

!

no aaa new-model

ip subnet-zero

!

!

ip cef

no ip domain lookup

!

ip audit po max-events 100

!

!

!

interface Serial0/0

ip address 1.1.12.2 255.255.255.0

serial restart-delay 0

!

interface Serial0/1

ip address 1.1.24.2 255.255.255.0

serial restart-delay 0

router ospf 1

log-adjacency-changes

network 0.0.0.0 255.255.255.255 area 0

!

end

R2#

======R3======

R3#sh run

Building configuration...

Current configuration : 845 bytes

!

version 12.3

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname R3

!

boot-start-marker

boot-end-marker

!

!

no aaa new-model

ip subnet-zero

!

!

ip cef

no ip domain lookup

!

!

interface Serial0/0

ip address 1.1.13.3 255.255.255.0

serial restart-delay 0

!

interface Serial0/1

ip address 1.1.34.3 255.255.255.0

serial restart-delay 0

!

!

router ospf 1

log-adjacency-changes

network 0.0.0.0 255.255.255.255 area 0

!

no ip http server

no ip http secure-server

ip classless

!

!

end

R3#

====R4====

hostname R4

!

boot-start-marker

boot-end-marker

!

!

no aaa new-model

ip subnet-zero

!

!

ip cef

no ip domain lookup

!

ip audit po max-events 100

!

interface Loopback0

ip address 4.4.4.4 255.255.255.0

!

interface Loopback1

ip address 4.4.5.4 255.255.255.0

!

interface Loopback2

ip address 4.4.6.4 255.255.255.0

!

interface Serial0/0

ip address 1.1.24.4 255.255.255.0

serial restart-delay 0

!

interface Serial0/1

ip address 1.1.34.4 255.255.255.0

serial restart-delay 0

router ospf 1

log-adjacency-changes

network 0.0.0.0 255.255.255.255 area 0

!

!

end

R4#

[Marwan ALshawi]

ok here there are couple of points you need to check

first is the two interfaces have the same cost

do simply show ip route and make sure that your routing table shows two possible routes to the destination you want to reach

if the above is not valid then make sure both interface have the same cost

once you have the interfaces installed in te routing table for the required destination route

by default the cef load balancing is oer session you could change it per pack to get more even load balancing ( on the exit interfaces of R1 use the command load-shapre then chose the per packet option )

but i am assuming this is for testing as per packet load balancing cause some out of synic packets ..etc need to be careful with it in a production environment

good luck

HTH

if helpful Rate

[milan.kulik]

Hi,

AFAIK, CEF should be always using per-packet load sharing for packets originated by the router itself.

It would be worth checking the existence of multiple routing paths by

show ip cef 4.4.4.4 internal

and some other checkes listed in

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

It's also possible the per-packet load sharing is working fine in your case, just the hash function is using R3 as the first hop in all cases you used for your tests.

Do you always see 1.1.34.4 in the traceroute outputs as the folllowing hop?

Or is there 1.1.24.4 sometimes (depending on source/destination pair)?

HTH,

Milan

[paul driver]

HI

You can manipulate the preffered path by distance/cost/bandwdth or maxing out the lsa for one path.

Also  the next hop is defined by the ospf network type, on  point-to-point its not the orignating router its advertising the router

can you post ospf route table.

show ip route ospf

show ip route x.x.x.x

res

Paul