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Asymmetrical speed of GRE tunnel

Hi folks

I'm trying to understand a problem I have with a GRE setup and I've reached the end of my own ideas. I need som help.

It's a router to router setup using Cisco 1921 connected using a 4G aggergation device. On the link created by the aggregator I'm running a GRE tunnel between the routers and then OSPF in the tunnel to set up the routing between the routers.

The tunnel is up and OSPF is FULL so that's all good. The 4G aggregation has an MTU of 1440 and unless I set the ip tcp adjust-mss value to something near MTU 1350 on the client side of one of the routers, no traffic is sent to the clients. That's an oddity in it self but what I cannot understand is why I get a 3mbit/s download to the clients and 10 mbit/s upload. It's almost like there is something in my setup causing problems with the download.

Here's some of my config if that shares any light

Client side router

interface FastEthernet0.999

desc Interface_connecting_to_4G

encapsulation dot1Q 999

ip address 192.168.40.1 255.255.255.0

ip nat inside

ip virtual-reassembly

ip tcp adjust-mss 1300

ip ospf 1 area 2

no snmp trap link-status

end

interface Tunnel3

desc Tunnel_to_HQ

bandwidth 10000

bandwidth inherit

ip unnumbered Loopback1

ip ospf network point-to-point

ip ospf cost 1

ip ospf hello-interval 3

ip ospf dead-interval 8

ip ospf 1 area 0

tunnel source FastEthernet0.810

tunnel destination 194.112.9.204

tunnel path-mtu-discovery

end

HQ side router

interface Tunnel6

description Tunnel_to_remote_site

bandwidth 10000

ip unnumbered Loopback1

ip ospf network point-to-point

ip ospf dead-interval 8

ip ospf hello-interval 3

ip ospf 1 area 0

ip ospf cost 1

tunnel source 194.112.9.204

tunnel destination 172.16.10.5

tunnel path-mtu-discovery

Any ideas, and I'm happy to fill in any details as needed?

/Fredrik

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