[6.8.3] Network traffic hitting incorrect L3 interface.

https://forums.unraid.net/bug-reports/stable-releases/report-guidelines-r68/

 

This is a new Unraid install.

After reviewing the routing table, it looks like the default route that was added during initial install/setup - dhcp IP on eth0 (native vlan20)- was created with a metric=260.

The newly added vlan30 interface with static IP was automatically added as a new default route with a metric=1.

 

Why does the first (presumably management/main) interface receive a metric of 200+ and new interface(s) receive the highest priority metric=1?

 

I believe the first interface configured out of the box should have the lowest metric (metric=1)?

Setting metrics using DHCP is a dynamic interaction. There is no such thing as first come, first served.

In other words there are no guarantees that the first interface, which comes up, will get the lowest metrics.

 

Also the system itself can not know which priority is needed, it treats all interfaces equal. Only the user can determine what is really desired.

 

Usually, it is not needed to have additional default gateways. E.g. a VLAN interface is a local network without internet access. And in such a case a static entry without default gateway can be configured.

 

The correct way to set priority, is to set the metric for each interface and VLAN specifically in case multiple default gateways are defined (using DHCP).

 

In your case specify a higher metric for each VLAN that you have created.

Hi @bonienl

Thank you for your response.

If you are utilizing the other vlan(s) such as 30 in this case for deploying dockers, wouldn't the additional default gateway(s) be needed?

Additional default gateways are usually not needed, but if they exist and with the correct metrics set, they will be used only when the more preferred choice is not available. I.e. an interface goes down and a second interface exists as backup.

 

When DHCP is used to obtain an IP address, your router will automatically add a default gateway to each interface/VLAN, which results in having multiple default gateways.

In the next release of Unraid, it is possible to set metric=0 for additional interfaces/VLANs, which let the system ignore the default gateway announced by the router.

With this approach you can let your main interface (br0) get a default gateway, while all other interfaces/VLANs just get an IP address by DHCP and avoid all kinds of routing problems.