On 12/6/22 1:36 PM, team lnx wrote:
> On Tue, Dec 6, 2022 at 12:10 PM David Ahern <dsahern@xxxxxxxxx> wrote:
>>
>> On 12/6/22 9:43 AM, team lnx wrote:
>>> Hello,
>>>
>>> I am a beginner for xdp and following is the setup
>>>
>>> 3rd party Board - (64 bit arch): This has 2 ethernet interfaces
>>> supporting XDP (v0 and v1)
>>> Host machine: Ubuntu
>>>
>>> step 1: 3rd party Board <-----connected over ethernet (v0) ------> Host - Ubuntu
>>> step 2: echo "1" > /proc/sys/net/ipv4/ip_forward
>>> step 3: Assign static ip address for v0 and v1
>>> step 4: run: xdp_fwd -D v0 v1 on 3rd party Board
>>> step 5: start ping from host to v0 of 3rd party Board with expectation
>>> of forwarding from v0 to v1
>>>
>>> Observation : In the above experiment I see xdp_fwd has a return code
>>> always set to XDP_PASS and when I traced it found that below
>>> conditions is the reason
>>> in net/core/filter.c
>>> if (res.type != RTN_UNICAST) {
>>> return BPF_FIB_LKUP_RET_NOT_FWDED;
>>> }
>>>
>>> 1. Could you please help in understanding the reason behind this ?
>>
>> RTN_LOCAL means delivery to a local process -- ie., nothing to forward
>> to another device / host.
>>
>> RTN_MULTICAST and RTN_BROADCAST: broadcast is not supported. Multicast
>> ... I forget how to use that. The fib lookup and xdp_fwd test predates
>> multicast support
>>
>>
>>> 2. Once #1 is resolved, do we need to add manually arp table/neighbor
>>> information as well ?
>>>
>>
>> the xdp_fwd app is a demo. In a production deployment, you will need to
>> have something manage the neighbor entries for hosts. e.g., look at `ip
>> neigh ... managed` if you have a new enough kernel.
>>
>
> Thanks for the response,
> Understood #2, but for #1
> I have initiated ping from Host (ubuntu) -> V0 (ethernet) of 3rd party
> board with intention of forwarding/redirecting to V1 on the same board
>
> But I see XDP_PASS being returned instead of XDP_REDIRECT, anything
> missing/wrong in steps ?
>
look at the return code from the fib_lookup. It indicates why the lookup
failed if it does not return BPF_FIB_LKUP_RET_SUCCESS:
enum {
BPF_FIB_LKUP_RET_SUCCESS, /* lookup successful */
BPF_FIB_LKUP_RET_BLACKHOLE, /* dest is blackholed; can be
dropped */
BPF_FIB_LKUP_RET_UNREACHABLE, /* dest is unreachable; can be
dropped */
BPF_FIB_LKUP_RET_PROHIBIT, /* dest not allowed; can be
dropped */
BPF_FIB_LKUP_RET_NOT_FWDED, /* packet is not forwarded */
BPF_FIB_LKUP_RET_FWD_DISABLED, /* fwding is not enabled on
ingress */
BPF_FIB_LKUP_RET_UNSUPP_LWT, /* fwd requires encapsulation */
BPF_FIB_LKUP_RET_NO_NEIGH, /* no neighbor entry for nh */
BPF_FIB_LKUP_RET_FRAG_NEEDED, /* fragmentation required to fwd */
};
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