Re: some trouble when using vrf

[David Ahern <dsa@cumulusnetworks.com>]

On 4/16/19 5:26 AM, linmiaohe wrote:
> Hi all:
>     I meet some trouble when using vrf, it's very nice of you if you
> can help me fix it.
> 
>     1.If I bind a vrf address before I set SO_BINDTODEVICE opts to bind an
> enslaved device, "Cannot assign requested address" will occurs. It's
> because only after we set SO_BINDTODEVICE opts to bind an enslaved device,
> then we can lookup the route in the specified l3mdev domain.
>     I think we couldn't limit the order of bind ip addr and SO_BINDTODEVICE opts
> otherwise many vrf unaware apps many need to change their code.
>     I can't find a convenient way to fix it.Here is an example:
> 
>     ...
>     bind(sock_fd, (struct sockaddr *)&addr_serv, sizeof(addr_serv));
>     ...
>     ret = setsockopt(sock_fd, SOL_SOCKET, SO_BINDTODEVICE, bind_dev, strlen(bind_dev)+1);
>     ...
>     This code snipet doesn't work if the ip address of addr_serv is not in default vrf. And
> "Cannot assign requested address" will occurs.

Applications must bind to the device first and then bind to the local
address. As I recall this applies regardless of whether it is a VRF or
other.


> 
>     2.When I run a udp server in default vrf and set net.ipv4.udp_l3mdev_accept=1,
> it's supposed to work accorss VRFs.
>     But it occurs when udp server received a packet, it sends back with the source
> ip address from default vrf which is supposed to from the specified l3mdev domain.
> And the connection between server and client is broken. It's because udp server
> run in default vrf and doesn't bind the enslaved device, so only the route table in
> default vrf is avaliable.

UDP applications can use cmsg with IP_PKTINFO to send the reply out the
same device as the request was received. An app can also track the
relationship of the enslaved device to a VRF to use a VRF based lookup
to send a response. Choices.


> 
>     For example,I run a udp server in default vrf and set net.ipv4.udp_l3mdev_accept=1:
>     [root@localhost vrf]# sysctl -a | grep l3mdev
>     net.ipv4.raw_l3mdev_accept = 1
>     net.ipv4.tcp_l3mdev_accept = 1
>     net.ipv4.udp_l3mdev_accept = 1
> 
>     Then connect the server and send a udp packet to the specified vrf. Here is tcpdump output:
>     17:28:54.925417 IP 10.0.0.2.43003 > 10.0.0.1.irdmi: UDP, length 17
>     17:28:54.925953 IP 9.85.153.236.irdmi > 10.0.0.2.43003: UDP, length 17
>     ps. 10.0.0.2 is client ip, 10.0.0.1 is specified vrf ip, and 9.85.153.236 is default vrf ip.
>     10.0.0.1 and 9.85.153.236 are in the same host.
> 
> Thanks a lot if you can help me fix these. Have a nice day.
> 
> 
>