What your describing is fairly common and you can "fix" this by adjusting the delay metric of router interfaces in your path. In your example, you could adjust the delay between the routers so that the path metrics are equal. This is, as you note, the preferred approach with IGRP/EIGRP to manipulate metrics.
One thing to note though is that by making the paths appear equal, you are, in fact, "lying" to the router R1. Since the real bw and delay are not equal, the router is doing what it should do, pick the path with the most preferred route based on these factors. If you have multiple routes with unequal cost, you can use the "variance" command in IGRP/EIGRP so that you can send a fraction of packets over the lesser preferred path. In your case, if you used the command "variance 2" under the EIGRP statement for R1, it would consider alternative, less preferred paths as long as they were less than or equal to (2*preferred path metric). The router would then send half as many packets along the less preferred path as the most preferred path. If you used "variance 3" it would use (3*preferred path metric) and send 1/3 as many packets, etc. etc. for any n value "variance n". In your scenario, using the variance command may be preferred since you may not want a less preferred path getting the same amount of packets as the most preferred path. Then again, since the delay values are so close, the paths may, for all practical purposes, be roughly equal in performance, so equal sharing of the paths may be better. That's something you would have to determine in practice, based on your particular network traffics characteristics. HTH, Kent -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Tuesday, March 12, 2002 6:30 PM To: [EMAIL PROTECTED] Subject: EIGRP Metric and Route inconcistence [7:38043] Hi, By default EIGRP uses 2 metric: Bandwidth and Delay to calculate routes. It is recomended that we should not change the Actual Bandwith, but we can change the interface delay for the traffic enginering purposes. The metric is : Min Bandwidth + Cumulative Delay. This can end up with a problem of "route non-consiste1nce". Here is my counter example: R2 / \ / \ R1 R4-----R5 \ / \ / R3 Link 1-2 : Bandwidth = 10M, delay = 10ms 2-4 : Bandwidth = 20M, delay = 5ms 1-3 : Bandwidth = 20M, delay = 15ms 3-4 : Bandwidth = 20M, delay = 5ms 4-5 : Bandwidth = 10M, delay = 10ms The traffic from R1 to a network directly connected to R4 will be load balance between routes R1-R2-R4 and R1-R3-R4. because the Metric of the two routes are the same: R1-R2-R4 = Bandwidth (i.e. 10^7 / 10000) + Delay (i.e 1000 + 500) = = 1000 + 1000 + 500 = 2500 R1-R3-R4 = 500 + 1500 + 500 = 2500 However, traffic from R1 heading for R5 is not load-balanced because the Metric R1-R2-R4-R5 is 3500 while the metric R1-R3-R4-R5 = 4000 that means all traffic from R1 -> R5 will go via R2 That's is a kind of inconcistence, which may lead to bottleneck, and cause difficulty for traffic engineering. Could you please tell me if I am wrong or right ? If I am right, how we can overcome this problem. Thanks a lot. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38118&t=38043 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
