09-25-2004 09:08 AM - edited 03-02-2019 06:46 PM
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
09-25-2004 09:20 AM
Here is the diagram
09-25-2004 09:35 AM
09-25-2004 10:48 AM
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
09-25-2004 11:01 AM
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,
09-25-2004 12:48 PM
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
09-25-2004 06:11 PM
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,
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