CentOS - Mar 2018 - tftpd server S not responding

On Wed, Mar 28, 2018 at 6:25 PM, Steven Tardy <sjt5atra at gmail.com>
wrote:
> On Wed, Mar 28, 2018 at 3:16 PM Asif Iqbal <vadud3 at gmail.com>
wrote:
>
> > It is not respoding to A server which is sending the tftp read request
> RRQ.
> >
> > I do see the RRQ packets coming from A to S, but S never responds back
> from
> > a different port Y to A
> >
> > So this part is working fine
> >
> >
> >
> > https://en.wikipedia.org/wiki/Trivial_File_Transfer_
> Protocol#/media/File:Tftp-rrq.svg
> >
> > But I do not see any attempts to even send a data packet back in my
> packet
> > capture running on S
>
>
> Are A and S on different IP subnets?
>
Yes

> Does S have a second IP on the SAME subnet as A?
>
No

> Any ASA or other firewalls between the two?
>

Firewall is set to any any between the two. Also internal firewall is down
Firewall is not seeing any return pkts


> If so this is expected behavior.
>
>
I was hoping S will at least try to reply to the RRQ pkt with a DATA pkt
I do not see S is even bothering to try.

A(x) ---- RRQ ---> S(69)   and then I am expecting this S(y) --- DAT 1 -->
A(x)

>
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> https://lists.centos.org/mailman/listinfo/centos
>


-- 
Asif Iqbal
PGP Key: 0xE62693C5 KeyServer: pgp.mit.edu
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

On Wed, Mar 28, 2018 at 9:15 PM, Asif Iqbal <vadud3 at gmail.com> wrote:
>
>
> On Wed, Mar 28, 2018 at 6:25 PM, Steven Tardy <sjt5atra at gmail.com>
wrote:
>
>> On Wed, Mar 28, 2018 at 3:16 PM Asif Iqbal <vadud3 at gmail.com>
wrote:
>>
>> > It is not respoding to A server which is sending the tftp read
request
>> RRQ.
>> >
>> > I do see the RRQ packets coming from A to S, but S never responds
back
>> from
>> > a different port Y to A
>> >
>> > So this part is working fine
>> >
>> >
>> >
>> > https://en.wikipedia.org/wiki/Trivial_File_Transfer_Protocol
>> #/media/File:Tftp-rrq.svg
>> >
>> > But I do not see any attempts to even send a data packet back in
my
>> packet
>> > capture running on S
>>
>>
>> Are A and S on different IP subnets?
>>
>
> Yes
>
>
>> Does S have a second IP on the SAME subnet as A?
>>
>
> No
>
>
>> Any ASA or other firewalls between the two?
>>
>
>
> Firewall is set to any any between the two. Also internal firewall is down
> Firewall is not seeing any return pkts
>
>
>
>> If so this is expected behavior.
>>
>>
> I was hoping S will at least try to reply to the RRQ pkt with a DATA pkt
> I do not see S is even bothering to try.
>
> A(x) ---- RRQ ---> S(69)   and then I am expecting this S(y) --- DAT 1
-->
> A(x)
>

BTW, If I reverse the role and have S try to send a tftp read request, A
reply back right away
and I do the see the file.


>
> >
>> _______________________________________________
>> CentOS mailing list
>> CentOS at centos.org
>> https://lists.centos.org/mailman/listinfo/centos
>>
>
>
>
> --
> Asif Iqbal
> PGP Key: 0xE62693C5 KeyServer: pgp.mit.edu
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
>
>

-- 
Asif Iqbal
PGP Key: 0xE62693C5 KeyServer: pgp.mit.edu
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

A STATEFUL firewall with ?ip any any? can and will still block asymmetric
communications due to the firewall keeping track of state (hence tha name
stateful firewall).

Tcpdump on your servers /other/ NICs and you?ll see the tftp traffic
leaving your server on some other NIC (probably on with the default route).

The upstream firewall will then block the tftp response if it never saw the
tftp request (due to asymmetry).