David,

Juniper networks is motivated to promote RFC 5837 now, as opposed to eleven years ago, because the deployment of parallel links between routers is becoming more common

Large network operators frequently require more than 400 Gbps connectivity between their backbone routers. However, the largest interfaces available can only handle 400 Gbps. So, parallel links are required. Moreover, it is frequently cheaper to deploy 4 100 Gbps interfaces than a single 400 Gbps interface. So, it is not uncommon to see two routers connected by many, parallel 100 Gbps links. RFC 5837 allows a network operator to trace a packet interface to interface, as opposed to node to node.

I think that you are correct in saying that:

- LINUX is more likely to be implemented on a host than a router
- Therefore, LINUX hosts will  not send RFC 5837 ICMP extensions often

However, LINUX hosts are frequently used in network management stations. Therefore, it would be very useful if LINUX hosts could parse and display incoming RFC 5837 extensions, just as they display RFC 4950 ICMP extensions.

Juniper networks plans to support RFC 5837 on one platform in an upcoming release and on other platforms soon after that.

                                                                                 Ron




Juniper Business Use Only

-----Original Message-----
From: David Ahern <redacted> 
Sent: Wednesday, March 24, 2021 11:19 PM
To: Ron Bonica <redacted>; Zachary Dodds <redacted>; Ishaan Gandhi <redacted>
Cc: Andreas Roeseler <redacted>; David Miller <davem@davemloft.net>; Network Development <redacted>; Stephen Hemminger <stephen@networkplumber.org>; Willem de Bruijn <willemdebruijn.kernel@gmail.com>; junipeross20@cs.hmc.edu
Subject: Re: rfc5837 and rfc8335

[External Email. Be cautious of content]


On 3/23/21 10:39 AM, Ron Bonica wrote:

Hi Folks,



The rationale for RFC 8335 can be found in Section 5.0 of that document.
Currently, ICMP ECHO and ECHO RESPONSE messages can be used to 
determine the liveness of some interfaces. However, they cannot 
determine the liveness of:



  * An unnumbered IPv4 interface
  * An IPv6 interface that has only a link-local address



A router can have hundreds, or even thousands of interfaces that fall 
into these categories.



The rational for RFC 5837 can be found in the Introduction to that 
document. When a node sends an ICMP TTL Expired message, the node 
reports that a packet has expired on it. However, the source address 
of the ICMP TTL Expired message doesn't necessarily identify the 
interface upon which the packet arrived. So, TRACEROUTE can be relied 
upon to identify the nodes that a packet traverses along its delivery 
path. But it cannot be relied upon to identify the interfaces that a 
packet traversed along its deliver path.

It's not a question of the rationale; the question is why add this support to Linux now? RFC 5837 is 11 years old. Why has no one cared to add support before now? What tooling supports it? What other NOS'es support it to really make the feature meaningful? e.g., Do you know what Juniper products support RFC 5837 today?

More than likely Linux is the end node of the traceroute chain, not the transit or path nodes. With Linux, the ingress interface can lost in the layers (NIC port, vlan, bond, bridge, vrf, macvlan), and to properly support either you need to return information about the right one.
Unnumbered interfaces can make that more of a challenge.