Re: Death by extension header

[Fernando Gont <[e-mail]>]

Hello, Tom,

On 13/7/20 15:53, Tom Herbert wrote:
[....]
> 
> Fernando,
> 
> draft-ietf-6man-icmp-limits-08 defines the ICMP errors for limits of
> number of options, length of extension headers, length of extension
> header chain, etc. However, I don't believe any default limits are
> suggested other than the RFC8504 limits.

Yep, that's what I meant.



> Wrt byte length, the most interesting limit with regards to routers is
> when the aggregate length of the header chain exceeds the size of the
> parsing buffer in the device. 

Indeed.


> As I understand it common lengths of
> parsing buffers are 128, 256, or 512 bytes. That might suggest the
> default minimum should be 128 bytes or maybe 256 bytes. That is, we
> would expect that routers should be able to process IP header,
> extension headers, and first four bytes of transport header (e.g. to
> get ports for ECMP) fit in the parsing buffer in the first N bytes of
> the packet. We can narrow this down if the standard is followed such
> that routers only process the IPv6 and HBH headers, intermediate
> destinations in a routing header only process headers through the
> routing header, and end hosts process all options.

Please see: 
https://tools.ietf.org/html/draft-gont-v6ops-ipv6-ehs-packet-drops-03 . 
Folks need to look deeper. SO unless the entire length of the EH chain 
is limited, this problem will be faced.

Indeed, the longer the EH-chain length, the higher the chances of 
packets being dropped -- as per RFC7872 and others.

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: [e-mail]
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