On Wed, Mar 08, 2017 at 12:43 PM GMT, Nikolay Aleksandrov wrote: > On 08/03/17 14:05, Jakub Sitnicki wrote: >> On Tue, Mar 07, 2017 at 11:01 AM GMT, Nikolay Aleksandrov wrote: >>> This patch adds support for ECMP hash policy choice via a new sysctl >>> called fib_multipath_hash_policy and also adds support for L4 hashes. >>> The current values for fib_multipath_hash_policy are: >>> 0 - layer 3 (default) >>> 1 - layer 4 >>> If there's an skb hash already set and it matches the chosen policy then it >>> will be used instead of being calculated. The ICMP inner IP addresses use >>> is removed. >>> >>> Signed-off-by: Nikolay Aleksandrov <niko...@cumulusnetworks.com> >>> --- >>> v2: >>> - removed the output_key_hash as it's not needed anymore >>> - reverted to my original/internal patch with L3 as default hash >> >> What about ICMP PTB (Fragmentation Needed) forwarding that makes PMTUD >> work with ECMP in setups like described in RFC7690 [1]? >> >> ptb -> router ecmp -> next hop L4/L7 load balancer -> destination >> >> router --> load balancer 1 ---> >> \\--> load balancer 2 ---> load-balanced service >> \--> load balancer N ---> >> >> Removing special treatment of ICMP errors will break it, won't it? >> > > Yes, I am aware and this decision was made with that in mind. > We'd like to use the HW hash when available and IIRC that doesn't play well > with > special-casing ICMP errors for anycast as it may not match also. Another > thing, > again if I remember correctly, was that this behaviour is closer to how > hardware > handles ECMP.
OK, I wanted to make sure that is not an oversight that ECMP routing in ipv4 stack is to be dumbed down to match the hardware behavior. I thought that it was an advantage that we want to have over hardware routers. (To be fair, I should mention that we don't have it in ipv6 stack ATM.) > > One thing we can do is leave the current L3 behaviour with ICMP error handling > and add a new L3 mode that tries to use the skb hash when available and > doesn't > care about the packet type. > > What do you think ? Sounds good to me. Would be good to hear other opinions also. Thanks, Jakub
