Cisco 7200 Series - Bandwidth clarification

dubbakor 17 years ago

Hello All, we have a gigabit MAN connection to an outside network provided by At&T. I wanted a usage report from them and they said the report servers were down etc., I asked them to open up SNMP so that I can setup MRTG to monitor the usage and they did.

When mrtg created the first mrtg.cfg file, the GigabitEthernet0/0 interface (coming form the outside network to the router) showed a Max Speed of 125.0 kBytes and GigabitEthernet1/0 interface (from router to my LAN) showed a Max Speed of 125.0 MBytes.

I called and asked them about this and the technician said, the bandwidth is showing 1000 kbits for interface GigabitEthernet0/0 and

1000000 kbits for GigabitEthernet1/0. Whereas, both should have been at 1000000 kbits. He said he will change the bandwidth to 1000000 kbits for interface GigabitEthernet0/0 also using the bandwidth command. Does this mean that we were getting only 100Mbps until now as against 1Gbps on that interface?

I asked him if I should reboot the router for the changes to be effective and he said no and that the bandwidth now is showing 1000000 kbits. I created a fresh mrtg.cfg and it now shows 125.0 MBytes for both the interfaces.

Again, does this mean that we were not getting gigabit bandwidth until the new configuration on the router?

Please clarify.

Thanks, DK

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Doug McIntyre 17 years ago

They were correct, MRTG uses the 'bandwidth' parameter as its Max Speed bytes.

No, you can't tell anything about the speed you were getting via what the 'bandwidth' was set for on the interface. The bandwidth parameter does not affect the actual speed. Some SP's use it as a place keeper for marking things.

The main thing IOS uses it for is to keep track of different sized links in both STP and EIGRP and other dynamic routing protocols.

Ie. you can setup load-balanced EIGRP, and give more "weight" to one link vs. the other, even if they are identical, by changinging the bandwidth parameter. That doesn't mean that the router would use more bandwidth on the other, but in the load balancer calculations, more weight would be given to the one with more bandwidth, and potentially it would be used more.

In single link setups, you can change it whatever you want, and it'll do nothing. As I mentioned above, some use it as a placeholder to document stuff..

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Mulbagal 17 years ago

Doug, thanks for the clarification.

DK.

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