1812 internet router

[foxbatreco]

Hii,

My n/w has 25 clients and is supported by 1 Mbps 1:1 internet link by our isp.the query for these are:

1)during daytime when my off is fullfledged, the internet response is very slow and as the day comes to a close it becomes quicker.I have checked the utilisation of b/w which shows only around 600 Kbps during these hours and i fail to understand why the internet gets so dull.pls help me out how do i troubleshoot the problem arena, i am using a cisco 1812 router.sometimes when i chek the ip nat table it shows 40% of users on outside local connecting to port 53 and still remaining the same, wht does tht imply?? can i have any good nms for monitoring the same and how do i pinpoint the problem arena??

2) When i call my isp to chk the same , they disconnect the local n/w and check the connection as a standalone user which gives them 1 Mbps of b/w on numerous downloads collectively.they say the entire b/w availability can only be chked on numerous downloads.. is it true, why cant we chk it on single tranfer??cant i get the full 1 Mbps on a single transfer??

[gpulos]

A1:

the users connected to the outside port 53 are those that are most likely surfing. port 53 is DNS and is used when a user browses the web or needs any name resolution.

a nice NMS that is available to you for FREE is the Cisco Network Assistant.

please see this link for more CNA info:

http://www.cisco.com/en/US/products/ps5931/products_data_sheet0900aecd8034fbf1.html

A2:

you could get the full 1 Mpbs on a single transfer, but this will require quite a large file/transfer.

you have to understand how TCP works with window sizing to know what to expect in using available bandwidth.

long story short, TCP uses window sizing to determine how much of an increase in data size that can be sent in the next transmission;

likewise it uses window sizing to decrease how much data can be sent in the next transmission. as the TCP session length increases, so will the window size.

if there are no mitigating factors, those that keep the tcp window from increasing, then tcp will continue to increase the window throughout the tcp session. this has the benefit of being able to utilize more bandwidth with every transmission of the session.

in order for a single host to utilize the entire 1 Mbps of bandwidth, the session has to last long enough, and no other impacting factors abound, for TCP to increase the window size to the point where an entire 1 Mbps is utilized.

the way i do this for testing is to transfer HUGE files, 1 GB or more. depending on the link size, i can usually get a maximum utilization. it is tricky sometimes to reach because TCP has many factors that can keep the window size from increasing such as network delay, traffic, errors, timeouts, etc.