We have a3640 router with two 100 fastethernet connections. Currently the usage on fe 0/0 is very high average is 95mbit/s. We have a server that is running backups, what I'd like to know is why doesn't the server soak up the remaining bandwidth? Is there something inherent with ethernet that prevents usage up 100mbit/s or is there something I need to do on the router?
You should best replace the router. To my best knowledge, the 3640 does not route 100Mb/s at wire speed. To confirm this, check the cpu load on the router (sh proc). If this is approaching the 100% mark you know how things are.
To make sure that you are getting the maximum out of your router, make sure that fast switching is ON. This can be verified by looking at the interface config:
sh ip int e1/0
Ethernet1/0 is up, line protocol is up
Internet address is 18.104.22.168/24
Broadcast address is 255.255.255.255
Address determined by non-volatile memory
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Look for the following line:
IP fast switching is enabled <<< This one!!
Use the interface command: ip route-cache to activate Fast Switching if it is disabled.
Your processor is 61% busy on average over the last 5 mins. Relate this to the actual througput. Then (for simplicity) assume a linear increase of througput and CPU-load. This will result in an estimate of your router's ultimate performance. Keep in mind that the 3600 platform originally dates from the times when 10Mb was the standard for a WAN interface. The performance was simply not designed for a 10-fold increase of that figure. This is one of the reasons why it was replaced some 8-10 years ago.
Kindly let us know from where you are referring that the bandwidth utilisation is touching 95mbps.
Are you referring to any bandwidth utilisation graphs or from the show interface statistics.
If it was from "show interface statistics", what is the load interval configured on the interface. Can kindly paste the output here to examine. 300 seconds is the default load interval. Hence with this configuration, the statistics that you are observing by the show interface output, is the average data for the past 300 seconds. As you are seeing only the average figure here, it will not reflect the exact current utilisation.
You can reduce the load-interval down to 30 seconds to get much better statistics.
However we should keep in mind that again this will just be a moving average for the 30 second window. We can never estimate the actual utilisation exact down to the second. Thats how bandwidth monitoring works.
What is the protocol nature of the traffic generated by your server. If it is for backup purpose, then i assume it would be based on TCP.
One point to consider here is that for a given TCP data transfer window, we can never see a link getting utilised full. It is due to the sliding window nature of TCP.
Hence with just one data transfer we cannot witness the intermediate link getting fully utilised.
Probably you can generate more traffic to pass through that link to witness the near/full utilisation of that fastethernet link.
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