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bej Beginner
Beginner

Problems with load balancing, EIGRP

I have 4 2501 routers and 2 computers. PC 1 is using Win XP and PC 2 Win 98. All routers are running IOS 2500-I-L, ver 12.1(2)T. When i send data from PC 2 to PC 1, traffic will not load balance across the 2 available paths. See diagram and configuration.

Show outputs on LabD

LabD#sh ip route

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

C 192.168.30.0/24 is directly connected, Loopback0

C 192.168.60.0/24 is directly connected, Loopback3

C 192.168.10.0/24 is directly connected, Serial1

C 192.168.40.0/24 is directly connected, Loopback1

172.16.0.0/24 is subnetted, 3 subnets

D 172.16.205.0 [90/4096000] via 192.168.10.15, 01:05:12, Serial1

[90/4224000] via 172.16.56.44, 01:05:12, Serial0

C 172.16.56.0 is directly connected, Serial0

D 172.16.31.0 [90/3584000] via 192.168.10.15, 01:05:12, Serial1

C 192.168.20.0/24 is directly connected, Ethernet0

10.0.0.0/24 is subnetted, 1 subnets

D 10.10.10.0 [90/3609600] via 192.168.10.15, 01:05:13, Serial1

[90/4249600] via 172.16.56.44, 01:05:13, Serial0

C 192.168.50.0/24 is directly connected, Loopback2

D 192.168.0.0/18 is a summary, 01:05:16, Null0

LabD#sh ip eigrp topo 10.10.10.0 255.255.255.0

IP-EIGRP topology entry for 10.10.10.0/24

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 3609600

Routing Descriptor Blocks:

192.168.10.15 (Serial1), from 192.168.10.15, Send flag is 0x0

Composite metric is (3609600/3097600), Route is Internal

Vector metric:

Minimum bandwidth is 1000 Kbit

Total delay is 41000 microseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 2

172.16.56.44 (Serial0), from 172.16.56.44, Send flag is 0x0

Composite metric is (4249600/1817600), Route is Internal

Vector metric:

Minimum bandwidth is 800 Kbit

Total delay is 41000 microseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 2

LabD#trace 10.10.10.1

Type escape sequence to abort.

Tracing the route to 10.10.10.1

1 192.168.10.15 4 msec

172.16.56.44 4 msec

192.168.10.15 4 msec

2 172.16.205.1 8 msec

172.16.31.1 8 msec

172.16.205.1 8 msec

3 10.10.10.1 8 msec 4 msec 4 msec

Traceroute from PC 2:

tracert 10.10.10.1

1 3ms 3ms 3ms 192.168.20.179

2 4ms 4ms 5ms 172.16.56.44

3 6ms 6ms 6ms 172.16.205.1

4 5ms 5ms 5ms 10.10.10.1

6 REPLIES 6
Highlighted
bej Beginner
Beginner

Re: Problems with load balancing, EIGRP

Here is the diagram

bej Beginner
Beginner

Re: Problems with load balancing, EIGRP

Here is the diagram

Highlighted
VIP Mentor

Re: Problems with load balancing, EIGRP

Hello,

from your trace, you can see that the topology with the two paths is configured correctly. Possibly, you load-balancing scheme is per-destination. By default, on most Cisco routers, fast switching is enabled under interfaces. This is a demand caching scheme that does per-destination load-balancing. To set per-packet load-balancing, enable process switching (or disable fast switching) using the following commands:

Router# config t

Router(config)# interface Ethernet 0

Router(config-if)# no ip route-cache

Router(config-if)# ^Z

With per-packet load-balancing, packets are evenly distributed among the available links.

Can you try this on your router and see if it makes a difference ?

Regards,

Georg

www.solutionfinders.nl

Highlighted
Cisco Employee

Re: Problems with load balancing, EIGRP

Take most be taken when using per-packet loadsharing. I have seen more issues caused by it than performance improvement. This is mostly related with TCP retransmissions that could be caused by out of sequence packets.

Hope this helps,

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
Highlighted
bej Beginner
Beginner

Re: Problems with load balancing, EIGRP

Thanks for your replies. I tried to use per-packet loadsharing, it did not make a difference. I am using Pcattcp to measure throughput from PC 2 to PC 1. With both interfaces on LabD up i get about 116KBytes/s, with interface serial 1 shutdown i get approx. 90 KBytes/s throughput. With load balancing i would expect approx. 1800kbits throughput to PC 1

Highlighted
Cisco Employee

Re: Problems with load balancing, EIGRP

This is exactly what I was referring to in my previous posting. When using TCP with per-packet loadsharing, you can't expect the throughput to double just because you have twice the bandwidth. If you use a sniffer trace, you will probably see alot of TCP retransmissions, which is not too good performancewise.

Hope this helps,

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