Dell Networking OS10 Introduction to GRE Configuration
Summary: Generic Routing Encapsulation (GRE) is an IP encapsulation protocol used to establish a virtual point-to-point connection between two routers across a network. It is commonly used to tunnel routing protocols like RIP and OSPF between different sites. GRE is described in Request for Comments (RFC 2784. ...
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Instructions
Key Topics Covered
Configuration of GRE Tunnels:
- GRE tunnels are configured between two routers to send and receive GRE packets directly.
- Configuration involves setting up tunnel interfaces, specifying tunnel mode, source, and destination.
Restrictions and Limitations:
- A maximum of 100 tunnels supported
- IPv6 is not supported on underlay and overlay paths.
- Certain interfaces and IP addresses have restrictions when used with GRE tunnels.
Tunnel Keepalive Settings:
- Configuring keepalive settings to monitor tunnel endpoint reachability using Internet Control Message Protocol (ICMP) echo and reply packets.
Equal-Cost MultiPath (ECMP) Overlay and Underlay:
- ECMP load sharing for distributing traffic among available routes
- Supported combinations for overlay and underlay ECMP routes.
Commands and Examples:
- Detailed command syntax and examples for configuring GRE tunnels, keepalive settings, and ECMP routes
Possible Issues with Misconfiguration
Tunnel Flapping:
- Incorrect keepalive settings can cause the tunnel to frequently go up and down, leading to instability.
MTU Mismatch:
- GRE tunnels over paths with different MTU settings can cause packet fragmentation or loss.
Routing Loops:
- Misconfigured routing can lead to loops, causing excessive traffic and potential network outages.
Best Practices
Consistent MTU Settings:
- Ensure that MTU settings are consistent across the GRE tunnel to avoid fragmentation.
Proper Keepalive Configuration:
- Configure keepalive settings to monitor tunnel health and avoid unnecessary flapping.
Clear Documentation:
- Maintain clear documentation of tunnel configurations and associated routes to prevent misconfigurations.
Use Cases for GRE Tunnels.
Connecting Remote Sites:
- GRE tunnels can connect remote sites over the Internet, allowing for secure and efficient communication.
Tunneling Non-IP Traffic:
- GRE can encapsulate non-IP traffic, making it versatile for various network protocols.
Load Balancing:
- Using ECMP with GRE tunnels can distribute traffic load across multiple paths, enhancing network performance.
Network Topology Example
Imagine a network with two remote sites, Site A and Site B, connected over the Internet. Each site has a router with a GRE tunnel configured between them.
The topology would look like this:
Site A (10.10.10.0/24) ---- OS10-1 ---- Internet ---- OS10-2 ---- Site B (10.20.10.0/24)
OS10(config)# interface tunnel 10 OS10(conf-if-tunnel-10)# <165>1 2022-11-11T17:55:16.614662+00:00 OS10 dn_alm 731 - - Node.1-Unit.1:PRI [event], Dell (OS10) %IFM_ASTATE_UP: Interface admin state up :tunnel10 OS10(conf-if-tunnel-10)# ip vrf forwarding red % Error: Interface tunnel10, Tunnel mode is mandatory config and must exist for other tunnel configs. OS10(conf-if-tunnel-10)# mode gre-ipv4 OS10(conf-if-tunnel-10)# ip vrf forwarding red OS10(conf-if-tunnel-10)# ip address 120.1.1.1/24 OS10(conf-if-tunnel-10)# <165>1 2022-11-11T17:55:31.454972+00:00 OS10 dn_alm 731 - - Node.1-Unit.1:PRI [event], Dell (OS10) %IP_ADDRESS_ADD: IP Address add is successful. IP 120.1.1.1/24 in VRF:red added successfully OS10(conf-if-tunnel-10)# tunnel destination 16.16.16.16 OS10(conf-if-tunnel-10)# tunnel source loopback10 OS10(conf-if-tunnel-10)# <165>1 2022-11-11T17:56:17.197783+00:00 OS10 dn_alm 731 - - Node.1-Unit.1:PRI [event], Dell (OS10) %IFM_OSTATE_UP: Interface operational state is up :tunnel10
OS10(conf-if-tunnel-10)# show configuration ! interface tunnel10 mode gre-ipv4 no shutdown ip vrf forwarding red ip address 120.1.1.1/24 tunnel destination 10.10.10.10 tunnel source loopback10 keepalive down-timer 10 keepalive enable keepalive probe-interval 6 keepalive up-timer 12
| Underlay ECMP routes | Overlay ECMP routes | Supported |
|---|---|---|
| Static | Static | Yes |
| Static | OSPF | Yes |
| Static | BGP | Yes |
| OSPF | Static | Yes |
| OSPF | OSPF | No |
| OSPF | BGP | Yes |
| BGP | Static | Yes |
| BGP | OSPF | Yes |
| BGP | BGP | No |
OS10(config)# hardware overlay-ecmp-profile mode balanced-overlay-ecmp OS10(config)# <165>1 2022-10-11T10:25:26.474891+00:00 AG1-9978 dn_alm 717 - - Node.1- Unit.1:PRI [event], Dell (OS10) %VXLAN_OVERLAY_ECMP_PROFILE_MODIFIED: VxLAN Overlay ECMP: Configuration is modified, Save and Reload the device for the profile to be effect
OS10# show running-configuration interface tunnel 21 ! interface tunnel21 mode gre-ipv4 no shutdown ip address 10.10.10.2/24 tunnel destination 5.5.5.5 tunnel source loopback3 OS10# show running-configuration interface tunnel 22 ! interface tunnel22 mode gre-ipv4 no shutdown ip address 10.10.10.3/24 tunnel destination 6.6.6.6 tunnel source loopback4 OS10# show running-configuration interface tunnel 23 ! interface tunnel23 mode gre-ipv4 no shutdown ip address 10.10.10.4/24 tunnel destination 7.7.7.7 tunnel source loopback5 OS10# show running-configuration interface tunnel 24 ! interface tunnel24 mode gre-ipv4 no shutdown ip address 10.10.10.5/24 tunnel destination 8.8.8.8 tunnel source loopback6 OS10# show running-configuration route ! ip route 77.1.1.0/24 100.1.1.2 ip route 77.1.1.0/24 10.10.10.2 ip route 77.1.1.0/24 10.10.10.3 ip route 77.1.1.0/24 10.10.10.4 ip route 77.1.1.0/24 10.10.10.5 OS10# show ip route 10.1.1.0/24 Routing entry for 77.1.1.0/24 Known via static Distance 1, Metric 0 Last update 08:57:53 Routing descriptors Blocks: via 100.1.1.2 tunnel10 via 10.10.10.2 tunnel21 via 10.10.10.3 tunnel22 via 10.10.10.4 tunnel23 via 10.10.10.5 tunnel24
OS10# show ip route 67.67.67.0/24 Routing entry for 67.67.67.0/24 Known via ospf, type Distance 110, Metric 21 Last update 09:35:46 Routing descriptors Blocks: via 10.1.1.2 ethernet1/1/25:1 via 12.1.1.2 ethernet1/1/25:2 via 23.2.2.2 vlan2 via 23.2.3.2 vlan3 via 23.2.4.2 vlan4 via 23.2.5.2 vlan5 via 23.2.6.2 vlan6 via 23.2.7.2 vlan7 via 23.2.8.2 vlan8 via 23.2.9.2 vlan9 OS10# show ip route 68.68.68.0/24 Routing entry for 68.68.68.0/24 Known via ospf, type Distance 110, Metric 21 Last update 09:36:35 Routing descriptors Blocks: via 10.1.1.2 ethernet1/1/25:1 via 12.1.1.2 ethernet1/1/25:2 via 23.2.2.2 vlan2 via 23.2.3.2 vlan3 via 23.2.4.2 vlan4 via 23.2.5.2 vlan5 via 23.2.6.2 vlan6 OS10# show running-configuration interface vlan 2 ! interface vlan2 no shutdown ip address 23.2.2.1/24 ip ospf 1 area 0.0.0.0 OS10# show running-configuration interface vlan 3 ! interface vlan3 no shutdown ip address 23.2.3.1/24 ip ospf 1 area 0.0.0.0 OS10# show running-configuration interface vlan 4 ! interface vlan4 no shutdown ip address 23.2.4.1/24 ip ospf 1 area 0.0.0.0 OS10# show running-configuration interface tunnel 21 ! interface tunnel21 mode gre-ipv4 no shutdown ip address 131.131.131.1/24 tunnel destination 67.67.67.67 tunnel source loopback3 OS10# show running-configuration interface tunnel 22 ! interface tunnel22 mode gre-ipv4 no shutdown ip address 132.132.132.1/24 tunnel destination 68.68.68.68 tunnel source loopback4
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Example
OS10# clear counters interface tunnel 10
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Example
OS10(config)# interface tunnel 10
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Example
OS10(conf-if-tunnel-40)# ip address 10.1.1.1/24
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Example
OS10(conf)# ip route 1.1.1.0/24 interface tunnel 10 OS10(conf)# ip route 2.2.2.0/24 3.3.3.3 interface tunnel 10
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Example
OS10(conf-if-tunnel-4)# ip vrf forwarding Vrf_red
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Example
OS10(conf-if-tunnel-1)# keepalive down-timer 10
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Example
OS10(conf-if-tunnel-1)# keepalive enable
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Example
OS10(conf-if-tunnel-1)# keepalive probe-interval 10
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Example
OS10(conf-if-tunnel-1)# keepalive up-timer 10
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Example
OS10(conf-if-tunnel-1)# mode gre-ipv4
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Example
OS10(conf-if-tunnel-40)# tunnel destination 10.10.10.10
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Example
OS10(conf-if-tunnel-4)# tunnel source vlan 10
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Example
OS10(conf-if-tunnel-1)# tunnel ttl 220
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Example
OS10# show interface tunnel 10 Tunnel 10 is up, line protocol is up Hardware is Tunnel Tunnel mode GREv4 Tunnel source IP 2.2.2.2, Tunnel source Intf loopback1 Tunnel destination 7.7.7.7 Tunnel TTL 255 Tunnel keepalive enabled Keepalive probe interval 10, Up timer 5, Down timer 5 Interface index is 45 Internet address is 10.1.1.1/24 Mode of IPv4 Address Assignment: MANUAL Interface IPv6 oper status: Enabled ARP type: ARPA, ARP Timeout: 60 Last clearing of "show interface" counters: 00:11:22 Queuing strategy: fifo Input statistics: 0 packets, octets Output statistics: 0 packets, octets Time since last interface status change: 00:27:11
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Example
OS10# show running-configuration interface tunnel ! interface tunnel10 no shutdown mode gre-ipv4 ip address 100.1.1.1/24 tunnel destination 3.3.3.3 tunnel source 1.1.1.1 ! interface tunnel20 no shutdown mode gre-ipv4 ip address 101.1.1.1/24 tunnel destination 5.5.5.5 tunnel source 6.6.6.6 OS10# show running-configuration interface tunnel 10 ! interface tunnel10 no shutdown mode gre-ipv4 ip address 100.1.1.1/24 tunnel destination 3.3.3.3 tunnel source 1.1.1.1
Example
OS10# show tunnel Name Mode Source-IP Destination-IP SrcIntf TTL VRF Status Protocol ================================================================================================= Tunnel 1 GREv4 1.1.1.1 6.6.6.6 Loopback 2 255 default up up Tunnel 2 GREv4 2.2.2.2 7.7.7.7 Loopback 123 255 default up up Tunnel 3 GREv4 3.3.3.3 8.8.8.8 Loopback 100 255 default up up OS10# show tunnel 10 Name Mode Source-IP Destination-IP SrcIntf TTL VRF Status Protocol ================================================================================================= Tunnel 10 GREv4 1.1.1.1 7.6.6.6 Loopback 2 255 default up up
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Example
OS10# show ip int gig 1/3 GigabitEthernet 1/3 is up, line protocol is down Internet address is 10.11.0.1/24 Broadcast address is 10.11.0.255 Address determined by user input IP MTU is 1500 bytes Helper address is 192.168.0.1 192.168.0.2 Directed broadcast forwarding is disabled
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Example
OS10# show ip route Codes: C - connected S - static B - BGP, IN - internal BGP, EX - external BGP, EV - EVPN BGP O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2, E1 - OSPF external type 1, E2 - OSPF external type 2, * - candidate default, + - summary route, > - non-active route Gateway of last resort is not set Destination Gateway Dist/Metric Last Change -------------------------------------------------------------------- C 1.1.1.0/24 via 1.1.1.1 ethernet1/1/1:1 0/0 01:32:53 C 10.1.1.0/24 via 100.1.1.1 loopback1 0/0 00:00:06 C 2.2.2.0/24 via 2.1.1.1.1 Tunnel 1 0/0 00:00:15 OS10# show ip route static Codes: C - connected S - static B - BGP, IN - internal BGP, EX - external BGP, EV - EVPN BGP O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2, E1 - OSPF external type 1, E2 - OSPF external type 2, * - candidate default, + - summary route, > - non-active route Gateway of last resort is not set Destination Gateway Dist/Metric Last Change ---------------------------------------------------------------------- C 1.1.1.0/24 via 1.1.1.1 ethernet1/1/1:1 0/0 01:32:53 C 10.1.1.0/24 via 100.1.1.1 loopback1 0/0 00:00:06 S 80.1.10.0/24 via 100.1.1.1 tunnel10 1/0 00:02:33
OS10# show ip ospf interface tunnel 10 tunnel10 is up, line protocol is up Internet Address 100.1.1.1/24, Area 0.0.0.0 Process ID 1, Router ID 1.1.1.1, Network Type broadcast, Cost: 1 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 1.1.1.1 (local), Interface address 100.1.1.1 Backup Designated router (ID) , Interface address 0.0.0.0 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Neighbor Count is 0, Adjacent neighbor count is 0 OS10# show ip ospf 1 interface tunnel 10 tunnel10 is up, line protocol is up Internet Address 100.1.1.1/24, Area 0.0.0.0 Process ID 1, Router ID 1.1.1.1, Network Type broadcast, Cost: 1 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 1.1.1.1 (local), Interface address 100.1.1.1 Backup Designated router (ID) , Interface address 0.0.0.0 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Neighbor Count is 0, Adjacent neighbor count is 0
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Example
OS10# show ip ospf 1 statistics interface tunnel 10 Interface tunnel10 Receive Statistics rx-invalid 0 rx-invalid-bytes 0 rx-hello 0 rx-hello-bytes 0 rx-db-des 0 rx-db-des-bytes 0 rx-ls-req 0 rx-ls-req-bytes 0 rx-ls-upd 0 rx-ls-upd-bytes 0 rx-ls-ack 0 rx-ls-ack-bytes 0 Transmit Statistics tx-failed 0 tx-failed-bytes 0 tx-hello 52 tx-hello-bytes 3328 tx-db-des 0 tx-db-des-bytes 0 tx-ls-req 0 tx-ls-req-bytes 0 tx-ls-upd 0 tx-ls-upd-bytes 0 tx-ls-ack 0 tx-ls-ack-bytes 0 Error packets (Receive statistics) bad-src 0 dupe-id 0 hello-err 0 mtu-mismatch 0 nbr-ignored 0 wrong-proto 0 resource-err 0 bad-lsa-len 0 lsa-bad-type 0 lsa-bad-len 0 lsa-bad-cksum 0 auth-fail 0 netmask-mismatch 0 hello-tmr-mismatch 0 dead-ivlmismatch 0 options-mismatch 0 nbr-admin-down 0 own-hellodrop 0 self-orig 0 wrong-length 0 checksumerror 0 version-mismatch 0 area-mismatch 0
Additional Information
Affected Products
SmartFabric OS10 SoftwareArticle Properties
Article Number: 000228691
Article Type: How To
Last Modified: 03 Oct 2025
Version: 2
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