Operator LB entropy hash changes without a stable address
Gyan Mishra <hayabusagsm@gmail.com> Sun, 02 February 2020 12:42 UTC
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From: Gyan Mishra <hayabusagsm@gmail.com>
Date: Sun, 02 Feb 2020 07:41:48 -0500
Message-ID: <CABNhwV2TD6Tt_K-0LgEOuJhZqTzQ6J83bRWoBGr8RMJizfDxag@mail.gmail.com>
Subject: Operator LB entropy hash changes without a stable address
To: 6MAN <6man@ietf.org>, Fernando Gont <fgont@si6networks.com>
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Fernando Can we add txt related to this topic of L2 Ethernet bundle hash or L3 multi parallel links ECMP hash changes when temporary address is employed. This is commonly used by all operators: L2 hash load balancing hash entropy: 802.1ad is a QinQ technology used by providers for backbone bridges Ethernet relay services instances. Inner tag is provider label and outer tag is customer label. The flow hash entropy is based on source/destination hash, however if the address is not stable and changing, that changes the hash entropy for load balancing flows. That throws off the lb entropy and now you don’t get close to 50/50 lb entropy with 2 links in an Ethernet bundle. There are many instances when bundled ethernet aggregation or MLAG is employed where a Src/dest hash is used to create entropy for load balancing of flows ; as well as in MPLS L2 vpn and NG L2 VPN ethernet service instance e-line, e-lan, e-tree where a fat pseudo wire” is deployed requiring stable IP for lb entropy to work properly. L3 ECMP hash load balancing entropy: Another instance where stable IP is necessary is related along those same lines of thought to BGP IGP ISIS or OSPF ECMP flow based load balancing hash hash where flows lb entropy is created to get the even load balancing over multiple parallel L3 links in a enterprise or provider operators network. When the address keeps changing that changes the load balancing entropy for the hash. So now instead of the flow going over L3 link A it is now going over link B. So this is an operational impact consequence on a operators network enterprise or service provider from address changing. Thinking about this further if let’s say all addresses change based on current valid 9 days / preferred 1 day you have a new preferred address daily. So let’s say their are thousands of flows on a particular L2 or L3 path the hash is constantly changing. It’s possible with the randomness off all the addresses constantly changing some may or may not rehash to a different path so load balancing may or may not be impacted. However the larger impact is now troubleshooting an operators network to trace a flow and determine which link is carrying a particular flow which is now ever changing. So added MTTR (mean time to recovery) during an outage for operations to debug and troubleshooting tracing a flow. -- Gyan Mishra Network Engineering & Technology Verizon Silver Spring, MD 20904 Phone: 301 502-1347 Email: gyan.s.mishra@verizon.com