Subject: RE: Last call on LSP Ping

From: "Gray, Eric" <[email-masked]>
Date: Fri, 6 Dec 2002 15:40:28 -0500

George,

	Some routers may be hard coded to discard these packets
(which raises another issue, see below).  Most will route them
(by default) to the bit bucket.  Some (probably a very few) may
have to consume filtering resources (as implied by the spirit
of the RFC) in order to accomplish this.  All of which is fine,
unless and until you get such a packet being stripped and sent
on a network containing hosts.  What would a host do with the
packet - crash?

	Which brings us to the second problem: what happens if a
box is hard coded to push "localhost" packets right back at ya? 

Eric W. Gray
Systems Architect
Celox Networks, Inc.
[email-masked]
508 305 7214

> -----Original Message-----
> From: George Swallow [mailto:[email-masked]]
> Sent: Friday, December 06, 2002 3:02 PM
> To: Shahram Davari
> Cc: 'Thomas D. Nadeau'; [email-masked]; [email-masked]
> Subject: Re: Last call on LSP Ping
> 
> > More proof:
> >
> > RFC 1812 (Requirements for IP Version 4 Routers):
> >
> >
> >    A router SHOULD NOT forward any packet that has an invalid IP
> >    destination address or a destination address on network 0.  A router
> >    SHOULD NOT forward, except over a loopback interface, any packet that
> >    has a destination address on network 127.  A router MAY have a switch
> >    that allows the network manager to disable these checks.  If such a
> >    switch is provided, it MUST default to performing the checks...
> >
> >    A router SHOULD provide a mechanism to filter out obviously invalid
> >    routes (such as those for net 127).
> 
> Which is exactly what we want the router that get this to do.
> 
> ...George
> 
> ==================================================================
> George Swallow       Cisco Systems                  (978) 497-8143
>                      250 Apollo Drive
>                      Chelmsford, Ma 01824

---

From: Curtis Villamizar <[email-masked]>
Date: Fri, 06 Dec 2002 16:14:00 -0500

In message <[email-masked]
> on a network containing hosts.  What would a host do with the

Why would it crash.  A UDP/IP packet to 127.0.0.1 with an unsupported
port number is simply discarded and an ICMP packet is sent.  Maybe the
event is logged.  This is IP 101 stuff.

Send one to your local BSD box and see what happens.

  4.1. Sending an MPLS Echo Request

   An MPLS echo request is a (possibly) labelled UDP packet.  The IP
   header is set as follows: the source IP address is a routable address
   of the sender; the destination IP address is a (randomly chosen)
   address from 127/8; the IP TTL is set to 1.  The source UDP port is
   chosen by the sender; the destination UDP port is set to 3503
   (assigned by IANA for MPLS echo requests).  If the echo request is
   labelled, the MPLS TTL on all the labels except the outermost should
   be set to 1.

Note that if port 3503 is supported, the box supports MPLS-Ping.  If
there is nothing on port 3503, then the normal way to handle this is
send an ICMP packet to the source (which according to the above must
be routeable).

Also why would IANA, the author of RFC1700, assign the UDP port for
this usage if this usage violated RFC1700.  Maybe a clarification from
an AD could end this thread.

> box is hard coded to push "localhost" packets right back at ya? 

That's an imagionary box.  Such a box doesn't conform to specs
(forwards a packet to 127/8 to other than the loopback) and such a box
doesn't exist, so why would we need to consider it.

Curtis