Arista EOS Tunneling (2) - GRE

Supported and Release:
The GRE Tunneling in EOS is supported from 4.15.0F (Apr 2015)

Not like the interface tunnel configuration in Cisco OS's, Arista uses nexthop-group and decap-group as the encap and decap endpoints. (EOS also has tunnel interfaces, but it is performed by software and ONLY for control plane purpose).

GRE Header Info:

• Protocol #: 47 (0x2F)
• Between Outer IP Header and Payload packet:
• GRE Flags (2B)
• Protocol Type (2B) = 0x0800 (ipv4)
• Key (4B) if enabled tunnel-key shown as below

Diagram and configuration:

Configuration details:

• nexthop-group <tunnel_intf_name> type gre
• on Arad platform: there is 4 encap - gre, ip-in-ip, mpls and mpls-over-gre
• size 1:
• # of ecmp path
• tunnel-source intf <intf, loopback most of time>
• Source ip of outer GRE/IP header
• entry 0 tunnel-destination <ip>
• Dest ip of GRE/IP header
• match above size #, starting from 0
• tunnel-key ingress-interface
• if enabled, will add 4B of GRE key value after 4B GRE header(flag + protocol#). This key is calculated from ingress interface + vlan id. 

Show output:

R1.yo412#sh ip decap-group

NOTE: "D" column indicates dynamic entries

D | Name               | Type       | Info              | Version | Address Type

--|--------------------|------------|-------------------|---------|-------------

  | gre-tunnel-1       | GRE        | 100.1.255.1       |         |

R1.yo412#sh platform arad decap-group

        DecapIp         |   LIF

------------------------+-------

100.1.255.1             |      1

R1.yo412#show nexthop-group

gre-tunnel-1

  Id         2

  Type       gre  (key: ingress-interface)

  Size       1

  TTL        64

  Source IP  100.1.255.1 (Loopback1)

  Counters   shared

  Entries (left most label is the top of the stack)

    0  100.1.255.2

         Via 100.1.12.2, Ethernet7/36/1  (100.1.255.2/32)

         00:1c:73:44:58:d0, Ethernet7/36/1

R1.yo412#sh platform arad ip nexthop-group

gre-tunnel-1

Type: GRE (key: ingress-interface)

Ecmp Fec Id: -

 ---------------------------------------------------------------------------------------------------------

|Pos|  Tunnel DIP   |Tunnel SIP [idx]    |TTL[idx]| FEC |OLIF |Cmd |     Intf      |VID | MAC / CPU Code  |

 ---------------------------------------------------------------------------------------------------------

|0  |100.1.255.2    |100.1.255.1    [0  ]|64 [0  ]|1047 |6144 |GRE |Et7/36/1       |3983|00:1c:73:44:58:d0|

R1.yo412#sh platform arad ip route | egrep '222|VRF|ID'

|VRF|   Destination    |     |                    |     |       |                   | ECMP|  FEC | Tunnel

| ID|      Subnet      | Cmd |     Destination    | VID |Outlif |   MAC / CPU Code  |Index| Index|T Value

|0  |222.100.0.0/16    |ROUTE| Et5/1/1            |3984 |4094   | 00:1c:73:3b:ce:c9 |  -  |1046  |   -

|0  |222.200.0.0/16    |ROUTE| Et7/36/1           |3983 |  -    | 00:1c:73:44:58:d0 |  -  |1047  |G 100.1.255.2