netlink

Use these commands to display detailed statistics about network input and output, and to configure some advanced network settings. This can be useful when optimizing performance or troubleshooting many aspects at the link, IPv4 or IPv6, and TCP or UDP layers, such as:

• transmission (TX) queue length

• received (RX) bytes

• dropped packets

• collisions

• transmission errors

• oversized frame MTU

• ARP link neighbors

• bridge loops

• stale route cache

• current IP sessions

Syntax

diagnose netlink backlog get

diagnose netlink backlog <backlog_int>

diagnose netlink bridge list-member

diagnose netlink device

diagnose netlink interface list [<interface_name>]

diagnose netlink ip list [<interface_name>]

diagnose netlink ip add <interface_name> <address_ipv4> <subnet_v4mask>

diagnose netlink ip delete <interface_name> <address_ipv4>

diagnose netlink ip flush [<interface_name>]

diagnose netlink ipv6 list [<interface_name>]

diagnose netlink ipv6 add <interface_name> <address_ipv6> <subnet_v6mask>

diagnose netlink ipv6 delete <interface_name> <address_ipv6>

diagnose netlink ipv6 flush [<interface_name>]

diagnose netlink neighbor list

diagnose netlink neighbor add <interface_name> <address_ipv4> <neighbor_mac>

diagnose netlink neighbor delete <interface_name> <address_ipv4>

diagnose netlink neighbor flush

diagnose netlink neighbor6 list

diagnose netlink neighbor6 add <interface_name> <address_ipv4> <neighbor_mac>

diagnose netlink neighbor6 delete <interface_name> <address_ipv4>

diagnose netlink neighbor6 flush

diagnose netlink queue-len <interface_name> <queue-length_int>

diagnose netlink redundant list [<interface_name>]

diagnose netlink route list

diagnose netlink route flush

diagnose netlink route6 list

diagnose netlink route6 flush

diagnose netlink rtcache

diagnose netlink session

diagnose netlink tcp

Variable	Description	Default
<address_ipv4>	Enter an IPv4 IP address.
<address_ipv6>	Enter an IPv6 IP address.
<interface_name>	Enter the name of the network interface, such as port1. If the interface name is optional, then the command applies to all network interfaces in the scope of the command.
<neighbor_mac>	Enter a physical media access control (MAC) address that defines the network interface card (NIC) of an ARP neighbor.
<queue-length_int>	Enter the maximum number of messages in the transmission (TX) queue. Note: If the queue is too small for the volume of network traffic, delays and dropped packets may occur.
<subnet_v4mask>	Enter an IPv4 IP subnet mask.
<subnet_v6mask>	Enter an IPv6 IP subnet mask.
backlog <backlog_int>	Enter the backlog limit.

Example

FortiMail # diagnose netlink session

System Time:  2025-05-23 12:08:40 EDT (Uptime: 15d 1h 5m)

Protocol              Remote IP Remote Port               Local IP  Local Port Expire(s)

tcp               172.20.212.15      50551          172.20.140.29         443   255

...

FortiMail # diagnose netlink neighbor list

System Time:  2025-05-23 13:47:03 EDT (Uptime: 15d 2h 44m)

ifindex=4 ifname=port1 172.20.140.2 d4:76:a0:03:14:e6 state=00000002 use=113126 confirm=17 update=113126 ref=1

ifindex=4 ifname=port1 172.20.140.223 00:0c:29:51:88:f4 state=00000004 use=35481 confirm=35481 update=32050 ref=0

ifindex=4 ifname=port1 172.20.140.89 1c:1b:0d:98:4a:e8 state=00000004 use=130439454 confirm=130445454 update=130439454 ref=0

ifindex=1 ifname=loopback 0.0.0.0 00:00:00:00:00:00 state=00000040 use=130581896 confirm=137 update=130581896 ref=0

FortiMail # diagnose netlink route6 list

System Time:  2025-05-23 15:28:10 EDT (Uptime: 15d 4h 25m)

tab=100 type=local protocol=netd flag=00000000 oif=1(loopback) prio=5

tab=254 type=unicast protocol=kernel flag=00000000 oif=4(port1) dst:2607:f0b0:f:640::/64 prio=100

...

FortiMail # diagnose netlink interface list

System Time:  2025-05-23 15:38:29 EDT (Uptime: 15d 4h 35m)

if=loopback family=00 type=772 index=1 mtu=65536 link=0 master=0

flags=up loopback run

if=bond0 family=00 type=1 index=2 mtu=1500 link=0 master=0

flags=broadcast master multicast

if=dummy0 family=00 type=1 index=3 mtu=1500 link=0 master=0

flags=broadcast noarp

...

FortiMail # diagnose netlink device

System Time:  2025-05-23 15:39:14 EDT (Uptime: 15d 4h 36m)

Inter-|   Receive                                                |  Transmit

face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed

loopback: 18930057   97298    0    0    0     0          0         0 18930057   97298    0    0    0     0       0          0

bond0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0

dummy0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0

port1: 1878497783 6277327    0 568825    0     0          0      3268 304878720  998264    0    0    0     0       0          0

gre0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0

...

FortiMail # diagnose netlink tcp

System Time:  2025-05-23 15:39:36 EDT (Uptime: 15d 4h 36m)

sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode

0: 0100007F:0FA0 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 1974 1 00000000dfc8c3c5 100 0 0 10 0

1: 00000000:03E1 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 3058 1 000000003be029fa 100 0 0 10 0

...

Related topics

sniffer

hardware

system interface

system route