RB5009 - invalid mtu 8000 on ether1 any idea why?

RouterOS Beginner Basics
1

Hi,

I have a fiber box in my house and RB5009 is connected to that fiberbox via ether1 port for internet connection

I’m getting this error every 2-3 second in the log
15:06:42 radvd,warning invalid mtu 8000 on ether1 from fe80::8e94:1fff:fef9:ac26
15:06:44 radvd,warning invalid mtu 8000 on ether1 from fe80::676:b0ff:fe65:970e

I expect this has something to do with my ISP
What can I do to make it stop?

This is what I get on reboot:
16:33:26 system,info router rebooted
16:33:26 interface,info VLAN_20 link up
16:33:36 bridge,info hardware offloading activated on bridge “LAN_BRIDGE” ports: ether2,ether5,ether4,ether3,ether6,sfp-sfpplus1,ether7,ether8
16:33:37 poe-out,info ether7 detected poe-out status: on
16:33:37 poe-out,info ether8 detected poe-out status: on
16:33:38 interface,info ether1 link up (speed 1G, full duplex)
16:33:38 dhcp,info dhcp-client on ether1 got IP address XXX.XXX.XXX.XXX
16:33:38 radvd,warning invalid mtu 8000 on ether1 from fe80::676:b0ff:fe65:970e
16:33:39 interface,info ether7 link up (speed 1G, full duplex)
16:33:39 interface,info ether8 link up (speed 1G, full duplex)
16:33:40 radvd,warning invalid mtu 8000 on ether1 from fe80::8e94:1fff:fef9:ac26
16:33:43 system,info,account user XXXXXX logged in from XXX.XXX.XXX.XXX via winbox
16:33:44 system,info,account user XXXXXX logged in from XXX.XXX.XXX.XXX via winbox
16:33:44 radvd,warning invalid mtu 8000 on ether1 from fe80::676:b0ff:fe65:970e
16:33:44 radvd,warning invalid mtu 8000 on ether1 from fe80::8e94:1fff:fef9:ac26
16:33:49 radvd,warning invalid mtu 8000 on ether1 from fe80::8e94:1fff:fef9:ac26
16:33:50 radvd,warning invalid mtu 8000 on ether1 from fe80::676:b0ff:fe65:970e
16:33:53 radvd,warning invalid mtu 8000 on ether1 from fe80::8e94:1fff:fef9:ac26
16:33:54 radvd,warning invalid mtu 8000 on ether1 from fe80::676:b0ff:fe65:970e
16:33:58 radvd,warning invalid mtu 8000 on ether1 from fe80::676:b0ff:fe65:970e
16:33:58 radvd,warning invalid mtu 8000 on ether1 from fe80::8e94:1fff:fef9:ac26

2

Anyone?

3

Have you checked this: https://forum.mikrotik.com/search.php?keywords=radvd

4

Check this thread:
http://forum.mikrotik.com/t/radvd-invalid-mtu-log-spam/169939/5
particularly the article linked to by Darknate

Addresses starting with fe80:: are link-local addresses, your fe80::676:b0ff:fe65:970e and fe80::8e94:1fff:fef9:ac26 “resolve” in converters like:
http://www.sput.nl/internet/ipv6/ll-mac.html
to Cisco equipment.

5

https://en.wikipedia.org/wiki/Radvd

6

Upstream IPv6 router is improperly configured. IIRC RouterOS handles it gracefully but it will be in the logs.

7

You could perhaps set ether1 mtu to 8000 and see if it stops.
And see if anything breaks.

8

This is of the most annoying things to debug :slight_smile: