rfc 1812 third party address on traceroute

Mikael Abrahamsson swmike at swm.pp.se
Tue May 31 05:30:42 UTC 2016

On Mon, 30 May 2016, Randy Bush wrote:

> of course, simpletons such as i would desire the source of the time
> exceeded message to be A.  after all, this is the interface to which i
> sent the icmp with the TTL to expire.

I agree 100%, and I'd venture to guess that most of the people running 
networks expect it to work like you describe.

> cursory research and talking with C & J seem to indicate that they do 
> what i want not what some folk have interpreted 1812 to mean.  at least 
> on some models.
> is anyone seeing the dreaded rfc1812 behavior in a citable fashion?  how
> common is it?

I have been told that there were versions of IOS XR that stopped doing 
what people wanted, people screamed, and then it's now back to the 
behaviour that you describe.

In RFC1812 2.2.7 there is talk about router-id. When reading that I think 
it is generic enough to work for IPv6 as well?

Another thing I've seen: People number their links with ULAs. ICMP error 
messages (including PTBs) are then sent from the router using the ULA 
address. This is obviously a disaster since that PTB sourced from ULA 
address is going to be BCP38:ed (hopefully). What's the interaction here 
with choosing a source address for the ICMP error message from something 
with the same RFC6724 label as the ICMP error message is being sent to?

Mikael Abrahamsson    email: swmike at swm.pp.se

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