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Webcast-Catalyst9k
New Member

dmvpn fragmentation / reassembly - what's too many

In our DMVPN configuration I am seeing fragmentation / reassembly counters increasing, but I don't know what would be considered too many or too high a rate.

Background;

DMVPN with GODI over MPLS

Router Tunnel Interfaces configured similarily

Tunnel xxx

ip mtu 1400

ip tcp adjust-mss 1360

Physical interfaces associated with Tunnel have 1500 MTU

Issuing Show IP Traffic, IP counters are;

Frags: 27262619 reassembled, 22261 timeouts, 0 couldn't reassemble

3577061 fragmented, 7155711 fragments, 293 couldn't fragment

Command issued a few minutes later shows;

Frags: 27263830 reassembled, 22261 timeouts, 0 couldn't reassemble

3578119 fragmented, 7157827 fragments, 293 couldn't fragment

Router has been up for 1 week.

To me these numbers seem high, but I believe I have accounted for the proper over head in my Tunnel MTU and MSS values.

Are these counters too high?

How can I lower these frags and reassemblies?

I have been referring to Cisco document ID 25885 are there other sources?

thanks in advance

1 REPLY
New Member

Re: dmvpn fragmentation / reassembly - what's too many

appologies - 1 clarification

The ip tcp adjust-mss is on the LAN side interface of the router and not on the Tunnel interface

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