Re: Protocol 17 floods from Vietnam & Mexico?

[i mawsog via NANOG <nanog () nanog org>]

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 () gmail com>
 To: Krunal Shah <KShah () primustel ca> 
Cc: "nanog () nanog org" <nanog () 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 () 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 () nanog org] On Behalf Of Mark Andrews
> Sent: Tuesday, September 12, 2017 10:45 PM
> To: Large Hadron Collider
> Cc: nanog () nanog org
> Subject: Re: Protocol 17 floods from Vietnam & Mexico?
>
>
> In message <08ed2903-c81c-aa2e-cd04-4fa117840d14 () 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 () isc org
>
>
>
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