[syslinux] [tftp-hpa] [Patch] Bad src address on replies from aliased interfaces

H. Peter Anvin hpa at zytor.com
Thu Feb 16 08:11:37 PST 2006

Simon Vallet wrote:
> On Wed, 15 Feb 2006 17:42:32 -0800
> "H. Peter Anvin" <hpa at zytor.com> wrote:
>>tftp-hpa *is* supposed to report back using the same IP number that it 
>>received, so something is screwed up.
> I had some time to dig a bit into the problem, and it appears that
> there is a typo in recvfrom.c -- this prevented myrecvfrom() to retrieve
> the correct IP from the initial request, and it therefore returned a
> zeroed myaddr back to main.
> The patch fixes this, and the child does get the correct address when
> replying to the initial request. But the client still gets a timeout
> *on the first connection to the alias* -- subsequent ones are fine.
> This is very weird.

Are you using inetd mode?  If so, it's likely inetd doesn't provide the 
right magic to deliver IP_RECVDSTADDR; running in standalone mode should 
take care of that.

> Attached is the minimal patch to correct the typo, and a tcpdump output
> showing the first tftp request to the alias -- only the alias (.132) is
> replying (no more replies from the .129 address), however all it sends
> out are ICMP unreachables. Any ideas ?

This implies nothing is bound on port 69 on that address, or that you 
have a filter that's blocking that port having the same effect.


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