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New Member

MTU and MSS setting on DMVPN tunnel int with MLPPP

Hi All,

My 3821 DMVPN hub router has this configuration and the MTU may be higher than it should be.

interface Tunnel0

description Tunnel for DMVPN

bandwidth 4500

ip address 10.x.x.x

no ip redirects

ip mtu 1416

no ip next-hop-self eigrp 170

ip nhrp authentication ots

ip nhrp map multicast dynamic

ip nhrp network-id 100

ip nhrp holdtime 360

ip nhrp cache non-authoritative

ip tcp adjust-mss 1360

no ip split-horizon eigrp 170

delay 1000

qos pre-classify

tunnel source Multilink1

tunnel mode gre multipoint

tunnel key 100000

tunnel protection ipsec profile otsvpn


I have 3 three questions:

What do you recommend for the MTU and MSS size for a DMVPN tunnel interface which use a multilink PPP interface as a tunnel source?

what's the overhead bytes of

GRE = 24 ??

IPsec = 52 ??

outside IP header = 20 bytes

MLPPP = ??

Should I enable fragmentation on the MLPPP interface? will these commands reduce latency and jitter?

ppp multilink fragment delay 10

ppp multilink interleave

Thank you in advance for any info.


New Member

Re: MTU and MSS setting on DMVPN tunnel int with MLPPP

I think you pretty much got it down. I'm using a similar setup with GRE tunnel except without the IPSec header.

My calculation was 1476 MTU and MSS_Window size is 1460 for my particular setup, GRE tunnel only.