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A Generic Routing Encapsulation (GRE) interface enables direct routing to a peer that does not need to be directly connected, similar to a VPN tunnel, but without encryption. GRE is frequently combined with an encrypted transport to enable routing or other features not possible with the encrypted transport on its own. GRE interfaces can be combined with dynamic routing protocols such as BGP, or use static routing.
To create a GRE object, TNSR requires an object name, positive integer instance
ID, source IP address, and destination IP address. The first step is to run the
gre <object-name> command, which enters
config-gre mode. Inside
config-gre mode, the following commands are available:
- instance <id>
Required instance identifier. This value is used to generate the GRE interface name in TNSR in the form of
gre<id>. For example, with an
1, the GRE interface name is
- source <ip-address>
Required IP address on TNSR to use as a source for GRE traffic associated with this instance. Can be an IPv4 or IPv6 address.
- destination <ip-address>
Required IP address of the remote GRE peer, which is the destination for GRE traffic associated with this instance. Can be an IPv4 or IPv6 address, but the address family must match that of the
- encapsulation route-table <route-table>
This option controls which route table is used by the GRE object, for traffic utilizing the GRE interface. The default behavior is to use the default routing table.
- tunnel-type <type>
TNSR supports multiple GRE tunnel types, where
<type>is one of the following:
Layer 3 encapsulation, the default type of GRE tunnel, which can carry layer 3 IP traffic and above.
- erspan session-id <id>
Encapsulated Remote Switched Port Analyzer (ERSPAN). This requires a session ID number, which is an integer in the range
0..1023. When combined with Switch Port Analyzer (SPAN) Interfaces, ERSPAN can deliver copies of local packets to a remote host for inspection. Explained in detail in GRE ERSPAN Example Use Case.
Transparent Ethernet Bridging (TEB)
This example creates a new GRE object named
test1, with an instance id
1, and the source and destination addresses shown:
tnsr(config)# gre test1 tnsr(config-gre)# instance 1 tnsr(config-gre)# source 203.0.113.2 tnsr(config-gre)# destination 203.0.113.25 tnsr(config-gre)# exit
Upon commit, the new GRE interface will be available for use by TNSR. The name
of the GRE interface is
gre<instance id>, which in this case results in
gre1. The GRE interface can then be configured similar to other interfaces
tnsr(config)# interface gre1 tnsr(config-interface)# ip address 10.2.123.1/30 tnsr(config-interface)# enable tnsr(config-interface)# exit tnsr(config)# exit
For an example ERSPAN configuration, see GRE ERSPAN Example Use Case
To view a list of current GRE objects, use
tnsr# show gre Name Instance Type Source IP Dest IP Encap Rt Session Id ----- -------- ---- ----------- ------------ ---------- ---------- test1 1 L3 203.0.113.2 203.0.113.25 ipv4-VRF:0 0
This command prints a list of all GRE objects and a summary of their configuration.