Description
This article describes how to configure and troubleshoot a GRE tunnel between two FortiGates.
Additional information about GRE is available in the related articles at the end of this document or in the FortiGate CLI Reference or Administration guide at https://docs.fortinet.com
Scope
FortiGate or VDOM in NAT mode.
Support for GRE tunneling was added in FortiOS 3.0.
Diagram
The following topology is used:
Expectations, Requirements
- Establish a GRE tunnel between both FortiGates to be able to reach each remote LAN 10.x.x.x.
- The GRE interface will remain unnumbered and remote subnets reachable with static routes.
Configuration
| CLI configuration of FortiGate 1 # config system interface
edit "port1"
set ip 198.51.100.1 255.255.255.0
set alias Internet
next
edit "port2"
set ip 10.1.1.254 255.255.255.0
set alias LAN
next
end
# config system gre-tunnel
edit "toFG2" set interface "port1" set local-gw 198.51.100.1 set remote-gw 203.0.113.2 next end # config firewall policy
edit 0 set srcintf "port2" set dstintf "toFG2" set srcaddr "all" set dstaddr "all" set action accept set schedule "always" set service "ALL" next edit 0 set srcintf "toFG2" set dstintf "port2" set srcaddr "all" set dstaddr "all" set action accept set schedule "always" set service "ALL" next end # config router static edit 0 set device "port1" set gateway 198.51.100.254 set comment "default-route to Internet ISP"
next edit 0 set device "toFG2" set dst 10.2.2.0 255.255.255.0 next end |
CLI configuration of FortiGate 2
# config system interface
edit "port1"
set ip 203.0.113.2 255.255.255.0
set alias Internet
next
edit "port2"
set ip 10.2.2.254 255.255.255.0
set alias LAN
next
end
# config system gre-tunnel
edit "toFG1"
set interface "port1"set local-gw 203.0.113.2 set remote-gw 198.51.100.1 next end # config firewall policy edit 0 set srcintf "port2" set dstintf "toFG1" set srcaddr "all" set dstaddr "all" set action accept set schedule "always" set service "ALL" next edit 0 set srcintf "toFG1" set dstintf "port2" set srcaddr "all" set dstaddr "all" set action accept set schedule "always" set service "ALL" next end # config router static edit 0
set device "port1" set gateway 203.0.113.254 set comment "default-route to Internet ISP"
edit 0next set device "toFG1" set dst 10.1.1.0 255.255.255.0 next end |
Verification
Routing table of FortiGate 1:
|
# get router info routing-table all Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
|
Routing table of FortiGate 2:
|
# get router info routing-table all Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
|
Note: Both routing tables show that the remote subnets 10.x.x.x appear as pseudo-connected (a static route appearing as directly connected and pointing to a local interface instead of a next-hop).
Verify the GRE tunnels:
|
# diag sys gre list vd=0 devname=toFG1 devindex=3 ifindex=22
|
|
# diag netlink interface list | grep -A1 "toFG1"
if=toFG1 family=00 type=778 index=22 mtu=1476 link=0 master=0
ref=12 state=off start fw_flags=0 flags=up p2p run noarp multicast
|
|
# get system interface [...]
|
Troubleshooting
While starting a ping from PC1 to PC2, take a sniffer trace on either FortiGate to see if the traffic reaches and is forwarded on all interfaces (see also the related article about using the sniffer on GRE interfaces).
|
# diagnose sniffer packet any "icmp" 4 interfaces=[any]
|
|
# diagnose sniffer packet any "icmp" 4 interfaces=[any] |
Additional info on GRE offloading:
Use the # diagnose npu np6 npu-feature command to see the NP6 features that are enabled on the FortiGate and those that are not.
# diagnose npu np6 npu-feature
np_0 np_1
------------------- --------- ---------
Fastpath Enabled Enabled
HPE-type-shaping Disabled Disabled
Standalone No No
IPv4 firewall Yes Yes
IPv6 firewall Yes Yes
IPv4 IPSec Yes Yes
IPv6 IPSec Yes Yes
IPv4 tunnel Yes Yes
IPv6 tunnel Yes Yes
GRE tunnel No No
GRE passthrough Yes Yes
IPv4 Multicast Yes Yes
IPv6 Multicast Yes Yes
CAPWAP Yes Yes
RDP Offload Yes Yes
Some of these parameters are configurable, however, GRE is not one of them. (GRE tunnel cannot be enabled using a CLI command.)
- GRE tunnel means, FortiGate offloading the GRE tunnel that is terminated on FortiGate.
- GRE passthrough means, FortiGate offloading GRE traffic 'flowing' through FortiGate.
Sample GRE tunnel session output:
# diagnose sys session list
session info: proto=47 proto_state=00 duration=54 expire=5 timeout=0 flags=00000000 sockflag=00000000 sockport=0 av_idx=0 use=4
origin-shaper=
reply-shaper=
per_ip_shaper=
class_id=0 ha_id=0 policy_dir=0 tunnel=/ vlan_cos=0/255
state=may_dirty
statistic(bytes/packets/allow_err): org=704/11/1 reply=0/0/0 tuples=2
tx speed(Bps/kbps): 12/0 rx speed(Bps/kbps): 0/0
orgin->sink: org pre->post, reply pre->post dev=31->10/10->31 gwy=10.5.50.36/0.0.0.0
hook=pre dir=org act=noop 10.5.51.89:0->10.5.50.36:0(0.0.0.0:0)
hook=post dir=reply act=noop 10.5.50.36:0->10.5.51.89:0(0.0.0.0:0)
misc=0 policy_id=8 auth_info=0 chk_client_info=0 vd=0
serial=005c9b23 tos=ff/ff app_list=0 app=0 url_cat=0
rpdb_link_id = 00000000
dd_type=0 dd_mode=0
npu_state=00000000
no_ofld_reason: npu-flag-off
total session 1
Sample GRE passthrough session output:
session info: proto=47 proto_state=00 duration=103 expire=8 timeout=0 flags=00000000 sockflag=00000000 sockport=0 av_idx=0 use=4
origin-shaper=
reply-shaper=
per_ip_shaper=
class_id=0 ha_id=0 policy_dir=0 tunnel=/ vlan_cos=0/255
state=log may_dirty npu f00
statistic(bytes/packets/allow_err): org=4488/51/1 reply=0/0/0 tuples=2
tx speed(Bps/kbps): 43/0 rx speed(Bps/kbps): 0/0
orgin->sink: org pre->post, reply pre->post dev=23->10/10->23 gwy=10.5.50.36/0.0.0.0
hook=post dir=org act=snat 3.3.3.3:0->4.4.4.4:0(10.5.51.89:0)
hook=pre dir=reply act=dnat 4.4.4.4:0->10.5.51.89:0(3.3.3.3:0)
misc=0 policy_id=10 auth_info=0 chk_client_info=0 vd=0
serial=005d9f3b tos=ff/ff app_list=0 app=0 url_cat=0
rpdb_link_id = 00000000
dd_type=0 dd_mode=0
npu_state=0x000400
npu info: flag=0x81/0x00, offload=8/0, ips_offload=0/0, epid=131/0, ipid=144/0, vlan=0x0000/0x0000
vlifid=144/0, vtag_in=0x0000/0x0000 in_npu=1/0, out_npu=1/0, fwd_en=0/0, qid=2/0
no_ofld_reason:
Looking at the outputs, it can be seen that the second session is offloaded.
Related Articles:
Technical Note: Restricting the built-in Sniffer to a GRE interface
Technical Note: Configuring OSPF on a GRE tunnel between two FortiGates
Technical Note: Configuring and verifying a GRE over IPsec tunnel
Technical Note: Configuring and verifying a GRE over IPsec tunnel using 'encapsulation gre'
