Support for IP Jumbo Packets (~9K) in the Zephyr IP stack and on Virtual POSIX Ethernet Interfaces

[bob2oneil]

I have had some success in getting up 2 virtual Ethernet interfaces in Zephyr for the native POSIX board target. One interface will represent a common bridge between multiple running instances of a Zephyr application simulating a radio with a wired and wireless interface. The wireless interface for each instance will have a single IP assigned to each instance, and each wireless iface will have the MTU set to 9K, and will be promiscuous representing a radio being able to sense all over the air packets.

I was able to set the MTU to the 9K range on the iface that will be the common OTA bridge for each running Zephyr instance.

However, by inspection of the source code eth_native_posix.c, there is a suggestion that the threads are operating on tx and rx buffers that are of the typical 1500 byte size.

Is IP fragmenting required to support IP Jumboframes?

struct eth_context {
	uint8_t recv[NET_ETH_MTU + ETH_HDR_LEN];
	uint8_t send[NET_ETH_MTU + ETH_HDR_LEN];
	uint8_t mac_addr[6];
	struct net_linkaddr ll_addr;

Does anyone has experience attempting to use IP Jumboframes with the Zephyr network stack and particularly native POSIX emulation?

The dump of my net ifaces is as follows suggesting support for the IP jumbo frames:

Interface 0x555555601f88 (Ethernet) [1]
===================================
Link addr : 02:00:5E:00:53:3B
MTU       : 1500
Flags     : AUTO_START,IPv4
Promiscuous mode : disabled
Ethernet capabilities supported:
	TXTIME
	Promiscuous mode
IPv4 unicast addresses (max 258):
	192.0.1.1 manual preferred infinite
	192.0.1.255 manual preferred infinite
	200.168.1.1 manual preferred infinite
	200.168.1.2 manual preferred infinite
	200.168.1.3 manual preferred infinite
	200.168.1.4 manual preferred infinite
	200.168.1.5 manual preferred infinite
IPv4 multicast addresses (max 0):
	<none>
IPv4 gateway : 0.0.0.0
IPv4 netmask : 255.255.255.0

Interface 0x555555602028 (Ethernet) [2]
===================================
Link addr : 02:00:5E:00:53:CC
MTU       : 9014
Flags     : PROMISC,AUTO_START,IPv4
Promiscuous mode : enabled
Ethernet capabilities supported:
	TXTIME
	Promiscuous mode
IPv4 unicast addresses (max 258):
	138.0.0.1 manual preferred infinite
IPv4 multicast addresses (max 0):
	<none>
IPv4 gateway : 0.0.0.0
IPv4 netmask : 255.255.255.0

[bob2oneil]

There is currently no support for Jumboframes in the Zephyr stack, the MTU seems fixed to 1514 and below. This issue has been addressed as well as a potential bug listed as low priority.

[bob2oneil]

There is a source code mod that can be made to a Native POSIX source file that will enabled this feature, but will not be incorporated into the mainline Zephyr code base, which does not support IP jumboframes.

Refer to the following:

#36745