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I have a Linux host and couple of routerboadrs. I created a GRE tunnel, but Linux does not answer keepalive packages. Then router mark gre connection as unreachable, so I cant send to Linux host from router subnet. If linux sends something into tunnel (ping, etc.) - RouterOS mark connection as reacheble. Second and next packages routed nicely until one minute idle (no traffic).

Tunnel in linux a make in this way:

remote=x.x.x.x
dev=gre21
network=10.21.0.0/16

ip tunnel add ${dev} mode gre remote ${remote} ttl 255
ip addr add 172.16.1.1/24 peer 172.16.1.21 dev ${dev}
ip link set ${dev} up
ip route add ${network} dev ${dev}

And ip l:

14: gre21: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1476 qdisc noqueue state UNKNOWN 
    link/gre 0.0.0.0 peer 109.60.170.15

How to set state "running"?

How to keep alive tunnel? Ping in cron?

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1 Answer 1

This is not exactly a direct answer to the GRE tunnel keepalive, however you may find it easier to use the MikroTik EoIP option to a linux server as this has been ported and allows tunnel ID and keepalive in a similar fashion (also handles fragmentation for any size link).

https://code.google.com/p/linux-eoip/

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"1 core load 70%, bandwidth 54+58(TX/RX) Mbps" - is bad performance result. –  eri Nov 14 '13 at 12:42
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