Technical Tip: How To Use Cisco Security Group Tag as policy matching criteria

[oarslan]

Description
This article describes how to Use Cisco Security Group Tag as policy matching criteria.

The FortiGate can read the Cisco Security Group Tag (SGT) in Ethernet frames, and use them as matching criteria in firewall policies.
A policy can match based on the presence of a SGT, or the detection of a specific ID or IDs.

Solution
When a packet with a SGT passes through and a session is established, the ext_header_type=0xc5:0xc5 flag is included in the session table.
This feature is available in flow mode policies for virtual wire pair policies or policies in transparent mode VDOMs.

To configure a firewall policy to detect SGTs in Ethernet frames.

# config firewall policy
    edit 1
        set sgt-check {enable | disable}
        set sgt <ID numbers>
    next
end

Examples.

In these examples, PORT2 and PORT5 are in a virtual wire pair.
Firewall policies are created that pass traffic with SGTs with a specific ID number, any ID number, or either of two specific ID numbers.

To configure the virtual wire pair.

# config system virtual-wire-pair
    edit "test-vwp-1"
        set member "port5" "port2"
        set wildcard-vlan enable
    next
end

To configure a firewall policy to match frames that have a SGT with ID 20 and allow them through.

# config firewall policy
    edit 1
        set srcintf "port2"
        set dstintf "port5"
        set action accept
        set srcaddr "all"
        set dstaddr "all"
        set schedule "always"
        set service "ALL"
        set sgt-check enable
        set sgt 20
    next
end

To configure a firewall policy to match frames that have a SGT with any ID.

# config firewall policy
    edit 1
        set srcintf "port2"
        set dstintf "port5"
        set action accept
        set srcaddr "all"
        set dstaddr "all"
        set schedule "always"
        set service "ALL"
        set sgt-check enable
    next
end

To configure a firewall policy to match frames that have the SGT with IDs 20 or 21.

# config firewall policy
    edit 1
        set srcintf "port2"
        set dstintf "port5"
        set action accept
        set srcaddr "all"
        set dstaddr "all"
        set schedule "always"
        set service "ALL"
        set sgt-check enable
        set sgt 20 21
    next
end

To check the session list.

# diagnose sys session list

session info: proto=6 proto_state=01 duration=10 expire=3593 timeout=3600 flags=00000000 socktype=0 sockport=0 av_idx=0 use=3
origin-shaper=
reply-shaper=
per_ip_shaper=
class_id=0 ha_id=0 policy_dir=0 tunnel=/ vlan_cos=0/0
state=log may_dirty br dst-vis f00
statistic(bytes/packets/allow_err): org=112/2/1 reply=60/1/1 tuples=2
tx speed(Bps/kbps): 10/0 rx speed(Bps/kbps): 5/0
orgin->sink: org pre->post, reply pre->post dev=13->10/10->13 gwy=0.0.0.0/0.0.0.0
hook=pre dir=org act=noop 10.1.1.11:36970->10.1.2.11:80(0.0.0.0:0)
hook=post dir=reply act=noop 10.1.2.11:80->10.1.1.11:36970(0.0.0.0:0)
pos/(before,after) 0/(0,0), 0/(0,0)
dst_mac=00:b0:e1:22:cf:e4
misc=0 policy_id=1 auth_info=0 chk_client_info=0 vd=1
serial=0000183c tos=ff/ff app_list=0 app=0 url_cat=0
sdwan_mbr_seq=0 sdwan_service_id=0
rpdb_link_id=00000000 rpdb_svc_id=0 ngfwid=n/a
npu_state=0x000001 no_offload
no_ofld_reason:  disabled-by-policy
ext_header_type=0xc5:0xc5
total session 1