Protocol 17 floods from Vietnam & Mexico?

Wed Sep 13 15:59:20 UTC 2017

The port info is in the first  fragmented packet as was mentioned elsewhere.  My guess is someone fragmenting large packets ( the mtu is set to  1464 or so). and  the host is receiving those fragment, but it not  reconstructing the packets.  If  it is possible to do a tcpdump/wireshark etc , then the content of the packets can be very easily observed .  
18:04:32.391082 IP 138-122-97-251.internet.static.ientc.mx > 
umbrellix.net: ip-proto-17
18:04:32.391088 IP 138-122-97-251.internet.static.ientc.mx > 
umbrellix.net: ip-proto-17
18:04:32.391110 IP 115.75.50.106.35180 > umbrellix.net.10454: UDP, bad 
length 65500 > 1464
18:04:32.391145 IP 115.75.50.106 > umbrellix.net: ip-proto-17
18:04:32.391152 IP 115.75.50.106 > umbrellix.net: ip-proto-17
18:04:32.391158 IP 115.75.50.106 > umbrellix.net: ip-proto-17

      From: Christopher Morrow <morrowc.lists at gmail.com>
 To: Krunal Shah <KShah at primustel.ca> 
Cc: "nanog at nanog.org" <nanog at nanog.org>
 Sent: Wednesday, September 13, 2017 7:59 AM
 Subject: Re: Protocol 17 floods from Vietnam & Mexico?

On Wed, Sep 13, 2017 at 9:59 AM, Krunal Shah <KShah at primustel.ca> wrote:

> It might be spoofed source IPs
>
>
if you are seeing large fragmented udp packets.. it's almost always not
spoofed.
or historically speaking anyway it's not been spoofed.

There are cases with dns reflection that include spoofing, but by the time
you see the large packet .. that's not spoofed it's coming from the dns
server talking to you, why it's talking to you is due to spoofing, but
that's outside (most times) your span of control.

>
> Krunal Shah
>
>
>
>
>
>
> -----Original Message-----
> From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of Mark Andrews
> Sent: Tuesday, September 12, 2017 10:45 PM
> To: Large Hadron Collider
> Cc: nanog at nanog.org
> Subject: Re: Protocol 17 floods from Vietnam & Mexico?
>
>
> In message <08ed2903-c81c-aa2e-cd04-4fa117840d14 at gmx.com>, Large Hadron
> Collider writes:
> > Yes, I'm being UDP flooded. I worked that out by grepping /etc/protocols.
> >
> >
> > On 12/09/2017 18:24, Matt Harris wrote:
> > > Protocol 17 is UDP.  UDP is pretty common on the internet. Not sure
> > > why source and destination ports aren't being shown by your tool
> > > there, might be malformed UDP packets designed to obscure themselves
> > > from or otherwise evade some intrusion detection or firewall systems.
>
> No ports are listed because they are not the initial fragment of the UDP
> packet.  Only the initial fragment that contains the UDP header has the
> ports reported.
>
> Mark
> --
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                INTERNET: marka at isc.org
>
>
>
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