General Networking/Lan/Wan/TCP window Size for E1 & E3


If router is having multiple WAN interface operets at different data rates (like E1 2Mbps, E3 32Mbps) how to choose the TCP window size?

We configured router E3 as primary link and E1 as backup link and both links are having 300ms RTT.

If I allotted Receive window size 12,00,000 based on E3, if will it work for E2 ???

What's the purpose of having E1 as backup for an E3? In case of an outage you can not play around much with window size or for that matter tweaking any other parameter. In TCP header, Window size is defined by 16 bits so you can have minimum 2 bytes to 64KB and default in most of the systems being 16KB. So you may want to decide accordingly and make sure all OS and hardware support the same else you won;t get benefitted out of it. And lastly...E1 working as backup of E3 is not a good idea :).

Hope this helps.

General Networking/Lan/Wan

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Sudhanshu Gupta


Any question related to IP routing protocols - BGP/OSPF/IGRP/EIGRP/RIP, HSRP. Bridging/DLSW, Cisco routers and Switches, LAN/WAN installation and monitoring.


I have about 14 yeras of experience in networking. I am an MCSE and CCIE (7334).

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