10-09-2006 08:39 PM - edited 03-05-2019 12:09 PM
Dear all,
on one of my router(MPLS Service) the BGP datagram size shows as
Datagrams (max data segment is 516 bytes)
and on another router(ISP Service) it shows
Datagrams (max data segment is 536 bytes):
Can anybody tell me the reason of such difference
Regards
Mahesh
Solved! Go to Solution.
10-11-2006 04:45 AM
The mtu of 516 is most likely due to the fact that you use MD5 authentication on this session. MD5 authentication adds 20 bytes of overhead in the TCP header, hence the MSS being reduced by 20 bytes.
Hope this helps,
10-10-2006 06:02 AM
536 is the default MSS (max segment size) for a TCP connection which is Very small considering the amount of data we transfer.
This can cause delays in BGP convergence.
Enable path MTU discovery and clear the BGP session
ip tcp path-mtu-discovery
clear ip BGP *
check the size now by
show ip bgp neighbor | include max data segment
http://www.cisco.com/en/US/products/ps6922/products_feature_guide09186a0080666002.html
HTH
Narayan
10-11-2006 01:57 AM
I accept ,
But my basic question is on one of my router it shows 516 and another router it shows 536. why it is so?
i will enable mtu discovery once i take approval from customers..
so please provide me details of why it is 516 if document tells that default is 536
regards!!
10-11-2006 02:25 AM
Mahesh,
Have you specified any MTU vlaue on any interface?
Narayan
10-11-2006 03:01 AM
Dear Narayan,
I have not specified any MTU on interface
Regards!!
10-11-2006 04:45 AM
The mtu of 516 is most likely due to the fact that you use MD5 authentication on this session. MD5 authentication adds 20 bytes of overhead in the TCP header, hence the MSS being reduced by 20 bytes.
Hope this helps,
10-11-2006 04:58 AM
Thanks hritter and narayan for your extended support.
Regards!!
Mahesh
10-11-2006 08:18 PM
Harold
Thanks for the information. Never thought this could be the reason
Narayan
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