Use ERSPAN to Send Mirrored Traffic through GRE Tunnels

Unless device traffic is visible to a firewall, the firewall cannot include it in the logs it forwards to IoT Security. When you need to collect data for devices whose traffic doesn't pass through a firewall, mirror their traffic on network switches and use Encapsulated Remote Switched Port Analyzer (ERSPAN) to send it to the firewall through a Generic Routing Encapsulation (GRE) tunnel. After the firewall decapsulates the traffic, it inspects it similar to traffic received on a TAP port. The firewall then creates enhanced application logs (EALs) and traffic, threat, WildFire, URL, data, GTP (when GTP is enabled), SCTP (when SCTP is enabled), tunnel, auth, and decryption logs. It forwards them to the logging service where IoT Security can access and analyze the IoT device data.

You can use this feature for any deployments where traffic from remote switches needs to be inspected. IoT Security is just one use case.

This feature requires switches that support ERSPAN such as Catalyst 6500, 7600, Nexus, and ASR 1000 platforms.

Configure a switch that supports ERSPAN to mirror traffic on one or more source ports or VLANs, and forward it through a GRE tunnel to a destination port on a next-generation firewall.
For configuration instructions, see the Cisco documentation for your switch.
Enable ERSPAN support on the firewall.
By default, ERSPAN support is disabled.
Log in to the firewall and select

Device

Session

.

Click the

Edit

icon for Session Settings, select

Enable ERSPAN Support

, and then click

OK

.

The ERSPAN Support check box in the Session Settings section is now selected.
Commit
your change.
Create a Layer 3 security zone specifically to terminate the GRE tunnel and receive mirrored IoT device traffic from the source port on the network switch.
Select
Network
Zones
and then
Add
a zone.
Enter the following and leave the other settings at their default values:
Name
: Enter a meaningful name for the zone such as
ERSPAN-IoT-data
.
Log Setting
: Select
IoT Security Default Profile
or another log forwarding profile that sends the required types of logs to the logging service for IoT Security.
You must already have logging services enabled on the firewall.
Type
:
Layer3
Click
OK
.
Create a Layer 3 interface and bind it to the zone you just created.
Select
Network
Interfaces
Ethernet
and then click the Ethernet interface on which you want to terminate the GRE tunnel from the switch. Optionally, use a subinterface.
Enter the following and leave the other settings at their default values:
Comment
: Enter a meaningful note about the interface for later reference.
Interface Type
:
Layer3
Virtual Router
: Choose the virtual router you want to route to the interface. Consider using a separate virtual router exclusively for ERSPAN traffic.
Security Zone
: Choose the zone you just created.
Click
IPv4
, select
Static
for the address type, and
Add
an IP address for the interface.
The switch uses this in its GRE tunnel configuration as the IP address of its peer.
Click
Advanced
and either add a
New Management Profile
or select a previously defined profile that allows the Ethernet interface to accept different types of administrative traffic.
Click
OK
to save the new interface management profile and then click
OK
again to save the Ethernet interface configuration.
Create a tunnel interface with an IP address in the same subnet as that of the corresponding tunnel interface on the switch and bind it to the zone you just created.
Select
Network
Interfaces
Tunnel
and then
Add
the logical tunnel interface for the GRE tunnel from the switch.
Enter the following and leave the other settings at their default values:
Interface Name
: The field on the left is read-only and contains the text “tunnel”. Enter a number in the field on the right to complete the name. For example, enter
8
to make the name
tunnel.8
.
Virtual Router
: Choose the same router you used for the Layer 3 interface.
Security Zone
: Choose the same zone to which you bound the Layer 3 interface.
Click
IPv4
and
Add
an IP address that’s in the same subnet as the IP address of the logical tunnel interface on the switch.
Click
Advanced
and either add a
New Management Profile
, or select a previously defined profile, to allow the tunnel interface to accept different types of administrative traffic.
Click
OK
.
Configure static routes for the virtual router (VR) for ERSPAN.
Select
Network
Virtual Routers
and then click the virtual router for ERSPAN.
Click
Static Routes
and then click
+ Add
.
Enter the following and leave the other settings at their default values:
Name
: Enter a name for the static route.
Destination
:
0.0.0.0/0
If you know the subnets beyond the switch, create individual static routes for each of them. Otherwise, use a separate VR for ERSPAN and set a default route.
Interface
:
ethernet1/3
(the interface you previously configured)
Next Hop
:
None
Click
OK
.
Configure a GRE tunnel with ERSPAN enabled.
Select

Network

GRE Tunnels

and then click

+ Add

.

Enter the following and leave the other settings at their default values:

Name

: Enter a name for the GRE tunnel; for example,

GRE-ESPAN-for-IoT-data

Interface

: Choose the Layer 3 interface you configured for GRE tunnel termination.

Local Address

: Choose

IP

and the IP address of the Layer 3 interface where the GRE tunnel terminates.

Peer Address

: Enter the IP address of the switch egress interface from which it initiates the GRE tunnel.

Tunnel Interface

: Choose the logical tunnel interface you configured for the GRE tunnel.

ERSPAN

: (select)

Click

OK

.

The IP addresses of the Ethernet and tunnel interfaces in relation to each other and the rest of the network look like this.
Commit
your changes.