Disclaimer

The content of this material are challenges faced onsite and how I personally resolved them. Please be noted that solutions posted here

1> should not be considered as ultimate. The material may be considered for reference only.

2> should not be considered as guarantee that solutions may work. Contact Cyberoam support before making any changes.

3> blog does NOT belong to the Cyberoam. It's a blog...a personal blog.

Changes done after referring this site may seriously damage the network. So...

........DO CHANGES AT YOUR OWN RISK

(please contact cyberoamsupport before implementing any changes)

Friday, 17 February 2012

MSS and MTU

Some times my users complain that the internet is slow or the website being access is not possible. The issue turns out to be the MSS/MTU issue.

what is the difference between MSS and MTU?

DP= Data packet
PL=Packet length=MTU= Maximum Transmission Unit
IPHL= IP header length

DP=PL  -  IPHL
DP= MTU-IPHL-----------------------> equation 1

Also, DP=TCPHL + MSS  -------------------->equation 2

where TCPHL= TCP header length
          MSS= Maximum Segment Size

Combining eq 1 and eq2 we have

MSS+TCPHL=MTU- IPHL

MSS= MTU-IPHL-TCPHL

But the minimum header size of the ip header and the tcp header if 40 Bytes.
 Therefore,

MSS=MTU-20-20

Finally we go

MSS=MTU-40

To check the MSS value of a segment in the Cyberoam check step 1 from below link:
http://cyberoamexpert.blogspot.in/2012/02/traffic-for-virtual-host-explained.html

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