[c-nsp] Cisco CRS, ASR9K & 7600 MPLS hashing/load-balance: are EXP bits included?

Irina Arsenieva ecralar at hotmail.com
Thu May 18 12:33:30 EDT 2017

Hi Adam,

In this particular case I have > 1 EXP codepoint in BE class and I plan to remark to these codepoints.

And congestion on single link between 2 LSRs is the reason for my question.



From: adamv0025 at netconsultings.com <adamv0025 at netconsultings.com>
Sent: 18 May 2017 14:58
Subject: RE: [c-nsp] Cisco CRS, ASR9K & 7600 MPLS hashing/load-balance: are EXP bits included?

> Hello all,
> A quick question - are EXP bits included in ECMP hashing algo on Cisco
> ASR9K and 7600 acting as LSR (_NOT_ headend/tailend/LER)?
> I have a particular case where FAT PWE with static flow labels are not
> balanced well, so looking to fix that with EXP bit rewrite.
> Many thanks
Very good question I actually don't know answer to.
It looks like in Junos it can be enabled/disabled, but IOS and XR are
different, different hash inputs in different situations, can't see any
config option to enable/disable EXP/TOS/802.1p.
Although personally I would not want the hashing to change depending on the
QOS markings on the packet.
See, if you look at all the usual hash inputs they are time invariant (well
u can argue the ingress interface -but that's not usually on by default).
In case you allow for down/up marking in the core, then introducing QOS
markings into the hash algo may result in a case where if you down mark some
packets due to congestion it changes hashing resulting in even more


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