Non-zero DPDK port won't get default gateway possibly after F-Stack 1.24

[whatmatrix]

Could you help me understand why it happens and how to make it work without calling ff_route manually?

Symptom

My test app was only able to connect() to a TCP host when using DPDK port0. connect() call with a non-zero DPDK port will return errno 113 "No Route to Host".

Debug Steps

The packet capture showed that the F-Stack won't send an ARP request for a gateway IP address. It is possible that the TCP stack does not know a MAC address for the default gateway.

ff_netstat -rn showed that there is no default gateway.

Workaround

connect() works after manually adding the default gateway using ff_route.

Comments

It worked fine in F-Stack 1.23.

Each DPDK port has an IP address within the same subnet and the same gateway.

[whatmatrix]

I found the cause.

f95b80e#r155453758

In this commit, file ff_veth.c line number 880, it adds fib_num = cfg->port_id. Without this line (fib_num == RT_DEFAULT_FIB), this issue does not happen.

@jfb8856606 as author of the commit, can you help me understand what was the intended change and why it is happening?

[whatmatrix]

I think now I understand why it is happening.

If cfg->port_id == 0 (DPDK port 0), then fib_num == RT_DEFAULT_FIB == 0. Only the port0 gateway is added to the default routing table. If there is no port 0 in a process under multi-process application, the default gateway will not be set.

I am curious what was the intention.