Variance - EIGRP

feliperodero · ‎06-09-2005

Hi,

I have 2 routers in site A and 2 paths to get site B. EIGRP is running between them. Here is output of the command:

show ip eigrp topology 172.30.0.0/23:

show ip eigrp topology 172.30.0.0/23

IP-EIGRP (AS 1): Topology entry for 172.30.0.0/23

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1162496

Routing Descriptor Blocks:

172.31.8.4 (Serial4/2), from 172.31.8.4, Send flag is 0x0

Composite metric is (1162496/281600), Route is External

Vector metric:

Minimum bandwidth is 4096 Kbit

Total delay is 21000 microseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 1

External data:

Originating router is 1.1.1.1

AS number of route is 100

External protocol is OSPF, external metric is 4

Administrator tag is 0 (0x00000000)

172.28.7.253 (GigabitEthernet0/3), from 172.28.7.253, Send flag is 0x0

Composite metric is (1165056/1162496), Route is External

Vector metric:

Minimum bandwidth is 4096 Kbit

Total delay is 21100 microseconds

Reliability is 255/255

Load is 4/255

Minimum MTU is 1500

Hop count is 2

External data:

Originating router is 1.1.1.1

AS number of route is 100

External protocol is OSPF, external metric is 4

Administrator tag is 0 (0x00000000)

So I have 2 paths to get site B with different metrics.

I've configure VARIANCE 10 in the router 1 (in site A) in order to have 2 true routes and balance traffic, but output of command show ip route 172.30.0.160 is:

show ip route 172.30.0.160

Routing entry for 172.30.0.0/23

Known via "eigrp 1", distance 170, metric 1162496, type external

Redistributing via eigrp 1

Last update from 172.31.8.4 on Serial4/2, 00:11:21 ago

Routing Descriptor Blocks:

* 172.31.8.4, from 172.31.8.4, 00:11:21 ago, via Serial4/2

Route metric is 1162496, traffic share count is 1

Total delay is 21000 microseconds, minimum bandwidth is 4096 Kbit

Reliability 255/255, minimum MTU 1500 bytes

Loading 1/255, Hops 1

So, only 1 route to destination.

May I configure any additional command to get these 2 paths to site B ?

Thansk a lot,

Kevin Dorrell · ‎06-09-2005

Your problem is due to the other condition for a feasible successor: that its advertised distance must be less than the feasible distance of your best route.

With the best route, you are 1162496 from the destination, and the next hop is 281600 from the destination. With your second best route, you would be 1165056 from the destination, and the next hop would be 1162496 from the destination. So he is no closer to the destination than you are now. So he cannot be a feasible successor.

We actually have a borderline case here - the next hop on your backup route is the same distance from the destination as you are. If he were one metric closer, 1162495, then he would be a feasible successor and you could load balance on him.

What you could do is to increase your metric very slightly. Find out what the default delay is on S4/2 - I suspect it is 20000 microseconds. Then configure a very slightly greater value, say 21000 microseconds, using the command delay 2100. That should raise your FD above 1162496, and will make the other next-hop seem attractive enough to use.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_command_reference_chapter09186a00800874a8.html#wp1031165

Hope this makes sense.

Kevin Dorrell

Luxembourg

feliperodero · ‎06-09-2005

Thanks a lot. Now it's running well.