linux-kernel - Re: [PATCH] net:ipv4: Packet is not forwarded if bc_forwarding not configured on ingress interface

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Message-ID: <32dc320d-abb0-475d-ca94-bac3bd26f825@gmail.com>
Date:   Sun, 28 Feb 2021 20:20:38 -0700
From:   David Ahern <dsahern@...il.com>
To:     Henry Shen <henry.shen@...iedtelesis.co.nz>, davem@...emloft.net
Cc:     yoshfuji@...ux-ipv6.org, dsahern@...nel.org, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        chris.packham@...iedtelesis.co.nz
Subject: Re: [PATCH] net:ipv4: Packet is not forwarded if bc_forwarding not
 configured on ingress interface

On 2/28/21 5:53 PM, Henry Shen wrote:
> When an IPv4 packet with a destination address of broadcast is received
> on an ingress interface, it will not be forwarded out of the egress
> interface if the ingress interface is not configured with bc_forwarding 
> but the egress interface is. If both the ingress and egress interfaces
> are configured with bc_forwarding, the packet can be forwarded
> successfully.
> 
> This patch is to be inline with Cisco's implementation that packet can be 
> forwarded if ingress interface is NOT configured with bc_forwarding, 
> but egress interface is.
> 

In Linux, forwarding decisions are made based on the ingress device, not
the egress device.